The impact of presbyopic spectacles and contact lenses on driving performance … · 2010-06-09 · vision correction for driving (n = 50), bifocal spectacles (BIF, n = 54), progressive

The impact of presbyopic spectacles and

contact lenses on driving performance

Byoung Sun Chu

Dip (Optom), BEng, MOptom, FIACLE

Thesis submitted to fulfill the requirements of

Doctor of Philosophy

School of Optometry & Institute of Health and Biomedical Innovation

Queensland University of Technology

Brisbane, Australia

2010

Vision & Driving Research, School of Optometry, QUT

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Statement of original authorship

The work contained in this thesis has not been previously submitted to meet

requirements for an award at this or any other higher education institution. To the

best of my knowledge and belief, the thesis contains no material previously

published or written by another person except where due reference is made.

Signed ………………………………….………………………. Date ………………………………….……………………….

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Abstract

Presbyopia affects individuals from the age of 45 years onwards, resulting in difficulty in

accurately focusing on near objects. There are many optical corrections available

including spectacles or contact lenses that are designed to enable presbyopes to see

clearly at both far and near distances. However, presbyopic vision corrections also

disturb aspects of visual function under certain circumstances. The impact of these

changes on activities of daily living such as driving are, however, poorly understood.

Therefore, the aim of this study was to determine which aspects of driving performance

might be affected by wearing different types of presbyopic vision corrections. In order

to achieve this aim, three experiments were undertaken.

The first experiment involved administration of a questionnaire to compare the

subjective driving difficulties experienced when wearing a range of common presbyopic

contact lens and spectacle corrections. The questionnaire was developed and piloted,

and included a series of items regarding difficulties experienced while driving under day

and night-time conditions. Two hundred and fifty five presbyopic patients responded to

the questionnaire and were categorised into five groups, including those wearing no

vision correction for driving (n = 50), bifocal spectacles (BIF, n = 54), progressive

addition lenses spectacles (PAL, n = 50), monovision (MV, n = 53) and multifocal contact

lenses (MTF CL, n = 48). Overall, ratings of satisfaction during daytime driving were

relatively high for all correction types. However, MV and MTF CL wearers were

significantly less satisfied with aspects of their vision during night-time than daytime

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driving, particularly with regard to disturbances from glare and haloes. Progressive

addition lens wearers noticed more distortion of peripheral vision, while BIF wearers

reported more difficulties with tasks requiring changes in focus and those who wore no

vision correction for driving reported problems with intermediate and near tasks.

Overall, the mean level of satisfaction for daytime driving was quite high for all of

the groups (over 80%), with the BIF wearers being the least satisfied with their

vision for driving. Conversely, at night, MTF CL wearers expressed the least

satisfaction.

Research into eye and head movements has become increasingly of interest in

driving research as it provides a means of understanding how the driver responds to

visual stimuli in traffic. Previous studies have found that wearing PAL can affect eye

and head movement performance resulting in slower eye movement velocities and

longer times to stabilize the gaze for fixation. These changes in eye and head

movement patterns may have implications for driving safety, given that the visual tasks

for driving include a range of dynamic search tasks. Therefore, the second study was

designed to investigate the influence of different presbyopic corrections on driving-

related eye and head movements under standardized laboratory-based conditions.

Twenty presbyopes (mean age: 56.1 ± 5.7 years) who had no experience of wearing

presbyopic vision corrections, apart from single vision reading spectacles, were

recruited. Each participant wore five different types of vision correction: single

vision distance lenses (SV), PAL, BIF, MV and MTF CL. For each visual condition,

participants were required to view videotape recordings of traffic scenes, track a

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reference vehicle and identify a series of peripherally presented targets while their

eye and head movements were recorded using the faceLAB® eye and head tracking

system. Digital numerical display panels were also included as near visual stimuli

(simulating the visual displays of a vehicle speedometer and radio). The results

demonstrated that the path length of eye movements while viewing and

responding to driving-related traffic scenes was significantly longer when wearing

BIF and PAL than MV and MTF CL. The path length of head movements was greater

with SV, BIF and PAL than MV and MTF CL. Target recognition was less accurate

when the near stimulus was located at eccentricities inferiorly and to the left, rather

than directly below the primary position of gaze, regardless of vision correction

type.

The third experiment aimed to investigate the real world driving performance of

presbyopes while wearing different vision corrections measured on a closed-road

circuit at night-time. Eye movements were recorded using the ASL Mobile Eye, eye

tracking system (as the faceLAB® system proved to be impractical for use outside of

the laboratory). Eleven participants (mean age: 57.25 ± 5.78 years) were fitted with

four types of prescribed vision corrections (SV, PAL, MV and MTF CL). The measures

of driving performance on the closed-road circuit included distance to sign

recognition, near target recognition, peripheral light-emitting-diode (LED)

recognition, low contrast road hazards recognition and avoidance, recognition of all

the road signs, time to complete the course, and driving behaviours such as braking,

accelerating, and cornering. The results demonstrated that driving performance at

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night was most affected by MTF CL compared to PAL, resulting in shorter distances

to read signs, slower driving speeds, and longer times spent fixating road signs.

Monovision resulted in worse performance in the task of distance to read a signs

compared to SV and PAL. The SV condition resulted in significantly more errors

made in interpreting information from in-vehicle devices, despite spending longer

time fixating on these devices. Progressive addition lenses were ranked as the most

preferred vision correction, while MTF CL were the least preferred vision correction

for night-time driving.

This thesis addressed the research question of how presbyopic vision corrections

affect driving performance and the results of the three experiments demonstrated

that the different types of presbyopic vision corrections (e.g. BIF, PAL, MV and MTF

CL) can affect driving performance in different ways. Distance-related driving tasks

showed reduced performance with MV and MTF CL, while tasks which involved

viewing in-vehicle devices were significantly hampered by wearing SV corrections.

Wearing spectacles such as SV, BIF and PAL induced greater eye and head

movements in the simulated driving condition, however this did not directly

translate to impaired performance on the closed- road circuit tasks.

These findings are important for understanding the influence of presbyopic vision

corrections on vision under real world driving conditions. They will also assist the

eye care practitioner to understand and convey to patients the potential driving

difficulties associated with wearing certain types of presbyopic vision corrections

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and accordingly to support them in the process of matching patients to optical

corrections which meet their visual needs.

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Key words

Vision and driving

Presbyopia

Presbyopic vision correction

Progressive addition lenses

Bifocal spectacle lenses

Monovision

Multifocal contact lenses

Eye and head movements

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Acknowledgments

“Are you ready?” ………. “Are you ready?” ……….

There was one person saying “Are you ready?” using a walki-talki on every

single night of our experiments. It was simply to confirm whether our team

was ready to go, but it means much more for me as from it I can feel the

passion and dedication of Professor Joanne Wood towards the research.

Passion, dedication, encouragement and generosity!

These are the words which describe my supervisors, Professor Joanne Wood and

Professor Michael Collins. My tentative ideas for a research project in the beginning

of this journey would never have been brought to fruition without their support and

wisdom and it has been a privilege to work with them. Thanks again to Joanne for

your dedication, helping me collect data until very late at night and guiding me to

think and write in scholarly ways. I am very sure Laura might not like me as you

have put too much time for me during day and night-time. Thanks to Michael for

your generous guidance and being a subject even at night-time. Thanks also to Dr

Peter Hendicott for being supportive and for your constructive comments on the

draft of this thesis.

Thanks must go to the vision and driving research team, Trent Carberry and Ralph

Marszalek, who have been with me throughout my journey, even till very late at

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night. It was very enjoyable to work with you and I thank you for your support,

positive energy and sharing memory.

I would like to thank the optometrists who helped with recruiting participants for

Experiment 1: Phillip Hong, Sonia Shin, Lucy Hsieh, Damien Fisher, Celia Bloxsom,

Kate Johnson, Luke Arundel, Mark Hinds, Jonathan Shaw, Oliver Woo, and Malinda

Halley. Importantly, I would like to thank my participants for their time and effort. I

also thank Dr. Philippe Lacherez for his valuable advice on data analysis. I also would

like to thank the contact lens & visual optics laboratory team, with special thanks to

Brett Davis who always provided the right tools whenever I needed them, and Dr

Scott Read who always answered my simple and sophisticated questions. You are

great people to be with. Also, thanks to John Stephens who made all the electric

devices (near display panels) despite the many modifications. Thanks to Cliff

McCarty for making all the spectacles and ordering contact lenses. I am also grateful

to the friendly administration staff, Catherine Foster, Fiona Lauder and Yvonne

Kenwrick who always welcome me at the School office. It was the most pleasant

place for me to be.

I would like to especially thank Associate Professor Barbara Junghans (UNSW), who

has witnessed my journey from the beginning to this moment and always gives me

a huge hug and encouragement.

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This thesis is also dedicated to my family; especially my parents, wife Mei Ying and a

little adorable distractor, Seung Woo (Harry) who came out into the world at the

most busiest moment of Dad’s PhD journey causing lack of sleep and a twilight

state, but you are still the biggest bonus in my life.

I will miss the moments lying on the driving circuit waiting for the research vehicle

to come, changing bio-motion clothes, walking like a Robot, running and loading

stuff to the fleet vehicle, watching the sparkling stars in the dark sky, the sweat of

hard work and the sound of “Are you ready?”. Thanks again for everyone for

giving me this invaluable memory which I loved and will love forever.

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Publications Arising from this Research

Journal articles

1. Chu, B. S., Wood, J. M. and Collins, M. J. (2009) Effect of presbyopic vision

corrections on perceptions of driving difficulty. Eye and Contact Lens, 35(3),

133-143.

2. Chu, B. S., Wood, J. M. and Collins, M. J. (2009) Influence of presbyopic

corrections on driving-related eye and head movements. Optometry and Vision

Science, 86 (11), 1267-1275

Published abstract

1. Chu, B. S., Wood, J. M. and Collins, M. J. (2009) Effect of presbyopic vision

corrections on eye and head movements. Clinical Experimental and

Optometry, 92(1), 61.

2. Chu, B. S., Wood, J. M. and Collins, M. J. (2009) Driving-Related Eye and

Head Movements Are Changed by the Type of Presbyopic Correction.

Invest. Ophthalmol. Vis. Sci. 2009 50: E-Abstract 3982.

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Table of Contents

Chapter 1. Introduction ...................................................................................... 31

1.1 Background .................................................................................................. 31

1.2 Aims of the study ......................................................................................... 32

1.3 Significance .................................................................................................. 35

Chapter 2. Literature review............................................................................... 37

2.1 Ageing population and driving ..................................................................... 37

2.2 Presbyopia and implications for driving ...................................................... 40

2.3 Visual function change with age and driving ............................................... 42

2.3.1 Visual acuity ........................................................................................ 43

2.3.2 Contrast sensitivity ............................................................................. 45

2.3.3 Visual field ........................................................................................... 47

2.3.4 Stereopsis ............................................................................................ 49

2.3.5 Glare disability .................................................................................... 50

2.3.6 Summary of visual functions and driving ............................................ 51

2.4 Presbyopic vision corrections ...................................................................... 52

2.4.1 Bifocal spectacle lenses .................................................................... 53

2.4.2 Progressive addition spectacle lenses .............................................. 54

2.4.3 Monovision contact lenses ............................................................... 56

2.4.4 Multifocal contact lenses .................................................................. 60

2.4.5 Summary of presbyopic vision corrections ......................................... 62

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2.5 Presbyopic vision corrections and driving ................................................... 63

2.6 Day and night-time driving........................................................................... 64

2.7 Eye and head movements for driving .......................................................... 65

2.8 The effect of in-vehicle devices for driving .................................................. 67

2.9 Different approaches for assessing driving performance ............................ 69

2.9.1 Simulator driving research .................................................................. 69

2.9.2 Open-road driving research ................................................................ 71

2.9.3 Closed-road circuit driving research ................................................... 71

2.10 Summary of literature review ...................................................................... 72

Chapter 3. Rationale and research design ........................................................... 75

Chapter 4. Experiment 1: Questionnaire - perceptions of driving difficulty when

wearing presbyopic vision corrections ................................................................. 79

4.1 Introduction ................................................................................................. 79

4.2 Methods ....................................................................................................... 81

4.2.1 Design and development of questionnaire ........................................ 81

4.2.2 Participants ......................................................................................... 84

4.2.3 Scoring of questionnaires ................................................................... 85

4.2.4 Analysis ................................................................................................ 86

4.3 Results ......................................................................................................... 87

4.4 Discussion ..................................................................................................... 98

4.5 Conclusion .................................................................................................. 105

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Chapter 5. Experiment 2: Influence of presbyopic corrections on driving-related

eye and head movement .................................................................................. 107

5.1 Introduction ............................................................................................... 107

5.2 Methods ..................................................................................................... 109

5.2.1 Participants ....................................................................................... 109

5.2.2 Presbyopic vision corrections ........................................................... 111

5.2.3 Distance targets ................................................................................ 113

5.2.4 Near targets ...................................................................................... 116

5.2.5 Laboratory set-up and procedures ................................................... 117

5.2.6 Recording of eye and head movements ........................................... 119

5.2.6 Analysis ............................................................................................. 120

5.3 Results ....................................................................................................... 122

5.4 Discussion................................................................................................... 125

5.5 Conclusion .................................................................................................. 131

Chapter 6. Experiment 3: Night-time driving performance while wearing

different presbyopic vision corrections ............................................................. 133

6.1 Introduction ............................................................................................... 133

6.2 Methods ..................................................................................................... 135

6.2.1 Participants ....................................................................................... 135

6.2.2 Vision corrections and fitting methods ............................................ 138

6.2.3 Visual performance measures .......................................................... 140

6.2.4 Night-time driving performance and fixations ................................. 144

6.2.5 Analysis ............................................................................................. 162

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6.3 Results ....................................................................................................... 163

6.3.1 Visual performance measures .......................................................... 163

6.3.2 Night-time driving performance and fixations measures ................. 166

6.3.3 Correlations between visual performance, driving performance and

fixation measures ............................................................................. 176

6.4 Discussion ................................................................................................... 179

6.5 Conclusion .................................................................................................. 188

Chapter 7. Conclusions ..................................................................................... 191

7.1 Implications for driving safety ................................................................... 193

7.1.1 Visbility of traffic-related objects at distance ................................... 193

7.1.2 Day and night-time driving................................................................ 194

7.1.3 In-vehicle devices and dashboard ..................................................... 195

7.1.4 Eye and head movements and fixation duration .............................. 196

7.2 Subjective perceptions of driving difficulty and objective driving

performance ....................................................................................................... 197

7.3 Clinical implications .................................................................................... 199

7.3.1 Visual function of presbyopic vision correction ................................ 199

7.3.2 Fitting approach of presbyopic contact lenses ................................. 201

7.3.3 The effect of adaptation ................................................................... 202

7.4 Summary .................................................................................................... 203

References ................................................................................................... 205

Appendices ................................................................................................... 221

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List of Figures

Figure 2.1. Projected increase in drivers aged 60 years and above. ......................... 38

Figure 2.2.Effect of age and relative accident involvement ratio .............................. 40

Figure 2.3. The predicted number of people worldwide with presbyopia, and the

number of people with uncorrected presbyopia. ............................................... 41

Figure 2.4. Diagram of zones in a typical progressive addition lens .......................... 55

Figure 2.5. Pupil size and relative coverage of optic zone of MTF CL. ....................... 61

Figure 2.6. Average severity rates at day and night-time by different road type ..... 64

Figure 4.1. Mean (SE) score of each group on clarity of street directory. ................. 92

Figure 4.2. Mean (SE) score of each group on peripheral distortion. ....................... 93

Figure 4.3. Mean (SE) score of each group on disturbance of glare. ......................... 96

Figure 4.4. Mean (SE) score of each group on disturbance of halo. .......................... 96

Figure 4.5. Mean (SE) score of each group on overall satisfaction. ........................... 97

Figure 5.1. Example of a captured scene from the video recording. ....................... 114

Figure 5.2. Digital numeric display panels for near targets. .................................... 117

Figure 5.3. Experimental set-up and relative location of screen and near targets. 118

Figure 5.4. Photograph of faceLAB® system. ........................................................... 120

Figure 5.5. Captured eye and head movement path lengths .................................. 121

Figure 5.6. Mean (SE) of path lengths of eye and head movements. ...................... 123

Figure 5.7. Mean (SE) of accuracy of identification of near targets. ....................... 125

Figure 6.1. Photograph of spectacle frame used for SV and PAL. ........................... 138

Figure 6.2. Photographs of the Berkeley Glare Tester. ............................................ 144

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Figure 6.3. Schematic diagram of the closed-road circuit. ...................................... 145

Figure 6.4. Stationary vehicle with headlight beam to create glare from on-coming

vehicle ................................................................................................................ 145

Figure 6.5. Low contrast road hazard on the closed-road circuit during night-time. ....

................................................................................................................. 146

Figure 6.6. Photograph of the research vehicle used in the study. ......................... 146

Figure 6.7. Screenshot of the VigilVanguard™ system output. ............................... 147

Figure 6.8. Eye tracking system – ASL Mobile Eye. .................................................. 149

Figure 6.9. Road signs along the driving circuit ....................................................... 151

Figure 6.10. Location of near targets (radio and speedometer) and LEDs .............. 152

Figure 6.11. Electronic circuit of LED display ........................................................... 153

Figure 6.12. Captured video footage from VigilVanguard™ system for assessment of

lane crossing time. ............................................................................................. 155

Figure 6.13. Captured video footage when the vehicle crossed the right lane. ...... 155

Figure 6.14. Captured video footage when the vehicle crossed the left lane. ........ 155

Figure 6.15. The task of measuring the distance to recognize a standard street sign. .

................................................................................................................. 156

Figure 6.16. Photograph of the four standard street signs used in the study. ........ 157

Figure 6.17. Procedure for measuring distance VA on the closed-road circuit. ...... 158

Figure 6.18. The types of distance signs used. ......................................................... 160

Figure 6.19. Distance VA under different viewing conditions. ................................ 165

Figure 6.20. Mean (SE) of percentage of near targets correctly identified. ............ 170

Figure 6.21. Mean (SE) of distance to recognize standard street signs. .................. 172

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Figure 6.22. Mean (SE) of the total fixation duration when observing near targets. ....

................................................................................................................. 173

Figure 6.23 Mean (SE) of the total fixation duration when observing distance targets

................................................................................................................. 175

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List of Tables

Table 4.1. Characteristics of each group. ....................................................................88

Table 4.2. Mean scores for each question ..................................................................89

Table 5.1. Mean unaided distance VA of participant under photopic condition .... 110

Table 6.1. Inclusion criteria for participants. ........................................................... 136

Table 6.2. Characteristics of participants. ................................................................ 137

Table 6.3. Details of monovision and multifocal contact lenses. ............................. 140

Table 6.4. Types of road signs on the closed-road circuit. ....................................... 151

Table 6.5. Mean (SD) of visual performance measures. .......................................... 164

Table 6.6. Mean (SD) of driving performance measures. ........................................ 167

Table 6.7. Mean (SD) of eye movement fixations. ................................................... 168

Table 6.8. Correlation coefficients (r) between visual performance measures and

driving performance measures. ........................................................................ 178

Table 7.1. Summary of results from experimental Chapters 4, 5 and 6. ................. 192

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List of Abbreviations

BIF: Bifocal spectacle lenses

D: Dioptre

HVID: Horizontal Visible Iris Diameter

LE: Left eye

LED: Light-Emitting-Diode

MTF CL: Multifocal contact lenses

MV: Monovision

PAL: Progressive addition lenses

RE: Right eye

SD: Standard Deviation

SE: Standard Error

Sec: Second

Sec of arc: Seconds of arc

SV: Single vision distance lenses

VA: Visual acuity

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Chapter 1

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Chapter 1. Introduction

This chapter provides an overview of the research involved in this thesis, including the

background, aims, and significance.

1.1 Background

Interest in research on the driving safety of older drivers has increased over recent

years as a result of the increasing age of the general population. The decline in

visual function with age is likely to have a significant negative effect on driving

performance, as 90% of the driving task is believed to be dependent on vision (Hills,

1980). One of the physiological changes in visual function that occurs with ageing is

difficulty with focusing on near objects, known as presbyopia, which usually

becomes apparent when people are in their mid forties. Therefore, persons aged

over 45 years typically need corrective lenses to be able to focus at near distances.

Many studies have investigated the impact of presbyopic corrections on tasks such as

reading, visual performance and head movements (Gupta, Naroo, & Wolffsohn, 2009;

Han, Ciuffreda, Selenow, Bauer et al., 2003; Proudlock, Shekhar, & Gottlob, 2004).

However, the effect of presbyopic vision corrections on driving has received only

limited attention in previous studies. Even though previous surveys have reported the

subjective problems of glare and haloes experienced when wearing monovision (MV)

or multifocal contact lenses (MTF CL) for night-time driving (Back, Grant, & Hine, 1992;

Chapter 1

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Papas, Young, & Hearn, 1990), it is not clear to what degree different presbyopic

corrections impair driving performance.

The only study that has investigated the impact of presbyopic vision corrections was

reported by Wood et al., (1998). This involved a comparison of objective measures

of driving performance for adapted monovision wearers when wearing their

monovision correction compared to their habitual correction (spectacles or

unaided). They reported that sign recognition, mirror checks, lane deviation, driving

time, parking angle and speed estimation were not adversely affected when wearing

MV during the daytime under real world in-traffic driving conditions.

Currently, there are increasing numbers of presbyopic vision corrections available, with

new materials and designs of spectacles and contact lenses. Therefore, it is important

to determine the effect of different types of the latest presbyopic vision correction

designs on driving. The assessment of unadapted wearers of presbyopic vision

corrections is also useful, given that the initial performance of presbyopic corrections

may be problematic and is a key factor in estimating the success of presbyopic

corrections.

1.2 Aims of the study

The overall aim of this study was to investigate the effects of various forms of

commonly used presbyopic corrections (e.g. bifocal spectacle lenses (BIF),

progressive addition lenses (PAL), MV and MTF CL) on day and night-time driving

Chapter 1

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performance. In order to achieve the aim of the study, three studies were

conducted. These studies, along with their specific aims are described below.

Experiment 1. Questionnaire study on perceptions of driving difficulties

when wearing presbyopic vision corrections

The aim of Experiment 1 was to determine the subjective driving difficulties

experienced by adapted wearers of five different vision correction types (no vision

correction, BIF, PAL, MV and MTF CL) by mail-out questionnaire. A questionnaire

was developed to establish the level of satisfaction with aspects of each correction

type for driving and to identify any problems experienced when wearing these

vision corrections while driving. Based on the aims of this study, the following

hypotheses were developed.

1) The PAL group will notice more peripheral blur while driving.

2) The BIF group will have difficulty changing gaze from the forwards driving

scene to in-vehicle devices.

3) The MV group will have difficulty judging distances while driving.

4) The MTF CL group will have less clear vision which could reduce visibility of

the road environment and traffic.

5) The visibility of all vision corrections will be poorer at night-time and the

effect of glare will be greater with MV and MTF CL.

Experiment 2. Influence of presbyopic corrections on driving-related eye

and head movements

Chapter 1

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The aim of Experiment 2 was to investigate the eye and head movement patterns

adopted when wearing presbyopic vision corrections (single vision distance lenses

(SV), BIF, PAL, MV and MTF CL) while viewing dynamic visual stimuli (videos of

traffic scenes) in a laboratory situation. These traffic scene videos included day and

night-time driving and freeway and suburban roads.

The following hypotheses were developed based on the aims of this study.

1) Wearing PAL will produce greater eye and head movement than any other

type of vision correction due to peripheral blur.

2) Wearing SV will result in experiences of difficulty viewing near in-vehicle

devices.

3) Eye and head movements will differ between day and night-time conditions.

Experiment 3. Effect of different types of presbyopic vision corrections on

real world driving performance under night-time conditions

The aim of Experiment 3 was to determine whether driving performance is affected

by wearing presbyopic vision corrections. The results of Experiment 1 and 2 were

considered in the design of Experiment 3 so that issues such as night-time glare,

reduced clarity of distance targets, and difficulty in focusing on near targets were

specifically tested. In addition, another type of eye tracking system was used to

record fixation patterns while driving, given that the tracking system used in

Experiment 2 was not found to be practical for use when driving in the field. In

order to investigate which visual measures predicted any differences in driving

Chapter 1

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performance, a range of visual performance measures were assessed with these

presbyopic corrections prior to assessment of driving performance.

Based on the aims of the study, the following hypotheses were developed.

1) Driving performance tasks which are dependent on distance visual acuity

(VA) will be affected by wearing MV and MTF CL due to reduced VA.

2) Recognition of targets viewed in the side mirrors will be affected by wearing

PAL due to peripheral blur.

3) The clarity of viewing in-vehicle devices will be affected by wearing SV.

4) Efficiency viewing in-vehicle devices will be modulated by the limited near

segments of PAL lenses

1.3 Significance

The onset of presbyopia at around 45 years of age inevitably means that all drivers will

face the question of whether to wear a presbyopic vision correction, which provides

the convenience of clear distance and near vision, when driving and which type should

be worn. Extensive research on the effect of vision on driving has confirmed that vision

provides the major sensory input for driving, however, the effect of presbyopic vision

corrections, which modify visual experience, has not been investigated. This is an

important gap in the literature as currently available presbyopic vision corrections do

not provide completely natural vision and may disturb aspects of visual function which

could be detrimental to safe driving. Therefore, this research is important to determine

whether wearing presbyopic vision corrections affect driving performance and in what

Chapter 1

36

way. The results of this research will help quantify differences in driving performance

when wearing different presbyopic corrections and provide valuable information for

understanding the benefits and limitations of wearing different presbyopic vision

corrections when driving. In addition, the information gained from this study can be

used to advise presbyopic drivers about what they can realistically expect with regards

to visual performance while driving with different kinds of presbyopic corrections, and

to assist in the design of optimum presbyopic corrections. The presbyopic vision

corrections investigated in this study were those that are commonly used, therefore

the results are relevant to optometry practitioners and their presbyopic patients.

Chapter 2

37

Chapter 2. Literature review

2.1 Ageing population and driving

Over the past half-century, there has been rapid growth in the aged population

worldwide. It has been reported that the current growth rate of the population

aged 60 years or over is significantly higher than that of the total population, with

predictions that the growth rate will be 3.5 times as rapid as that of the total

population by 2030 (UN, 2001). While almost one in five persons in developed

countries was aged 60 years or over in 2000, one in every three persons will be 60

years or over by 2050 (UN, 2001).

This demographic transition into an ageing society will have a profound effect on a

range of community issues, such as economic, health and social activities (Restrepo

& Rozental, 1994). Of these, driving safety has become an important focus of

research because of the projected increase in the number of older drivers on our

road systems.

Driving a private vehicle can enable drivers to fulfil many essential needs including

driving to the shops, accessing medical services, participating in social activities and

visiting friends (Rosenbloom, 1993). Thus driving is a means of maintaining

independence and quality of life for the elderly population (Banister & Bowling,

2004; Cvitkovich & Wister, 2001). Given the importance of driving to everyday living,

Chapter 2

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driving cessation has potential detrimental effects on the mobility of older people

and may result in a reduction in well-being, limited community access and increased

depressive symptoms (Davey, 2007; Fonda, Wallace, & Herzog, 2001). Thus older

drivers wish to continue to drive as long as possible into old age in order to

maintain their quality of life (Jette & Branch, 1992).

With the convenience and importance of driving for the aged population, it is

anticipated that there will be a greater number of older drivers on our roads in the

future (Eberhard, 1996). It has been reported that the licensure rate for those aged

65 years and older has increased steadily from 63% in 1983 to 75% in 1995 in the

United States (Lyman, Ferguson, Braver, & Williams, 2002). Another report

estimated that 73% of persons aged 60 years and above had a driver’s licence in

2001, and predicted that this will increase to 96% by 2031 in the state of Victoria in

Australia (Figure 2.1) ("Older drivers," 2008)

Figure 2.1. Projected increase in drivers aged 60 years and above

(Based on the data “Traffic Accident Commission, Victoria, 2008”).

Chapter 2

39

This increase in the number of older drivers on our road systems poses a potential

risk for road safety, as the abilities required for safe driving, including cognitive,

motor and sensory function, can be affected by normal ageing processes. Studies

indicate that older drivers adjust their driving behaviour through self-regulation to

reduce the risk of accidents such as avoiding peak hour traffic, night-time driving,

unfamiliar routes, poor weather conditions and also driving fewer miles than other

age groups (Lyman, McGwin, & Sims, 2001; McGwin, Chapman, & Owsley, 2000).

While these driving patterns should reduce the rate of crash involvement per driver

in this age group (Lyman et al., 2002), crash statistics indicate that older drivers

have higher crash rates per distance travelled than either young or middle-aged

drivers (Alvarez & Inmaculada, 2008; Langford & Koppel, 2006). Increasing age has

also been shown to be significantly associated with increased crash involvement

resulting in severe injuries (Hanrahan, Layde, Zhu, Guse, & Hargarten, 2009; Skyving,

Berg, & Laflamme, 2009) (Figure 2.2). Accordingly, the issue of safe and efficient

mobility for older drivers has become an important social problem. The high crash

rate of older drivers may arise from a range of factors including restriction of

physical movement, impaired cognitive functions, and the visual deterioration that

occurs with age (Owsley, 1994; Wood, 1998, 2002b). Among the factors affecting

driving safety, vision is considered to be a key factor as it makes up approximately

90% of the sensory input required to drive (Hills, 1980).

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Figure 2.2. Effect of age and relative accident involvement ratio.

(Reprinted from Accid Anal and Prev., 27(4), Stamatiadis, N., and Deacon, J. “Trends in

highway safety: Effects of an aging population on accident propensity”, 443-459., 1995

with permission from Elsevier)

2.2 Presbyopia and implications for driving

Presbyopia is an age-related change in the function of the eye which results in an

inability to see near objects clearly. Presbyopia is the most common physiological

change occurring in adults after about 45 years of age, with the exact onset

depending on a range of factors such as individual refractive error, climate or

geographic location (Holden et al., 2008; Miranda, 1979), and importantly, it is

irreversible. The most widely accepted explanation of how presbyopia develops is

Helmholtz’s theory, which suggests that presbyopia is due to a loss of elasticity of

the crystalline lens and capsule combined with changes in the ciliary muscle and

choroid which become less efficient with ageing. This decrease in the flexibility and

elasticity of the lens means that the lens cannot change shape to focus on near

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41

objects when the ciliary muscle contracts (Marmer, 2001; Strenk, Strenk, & Koretz,

2005).

With the demographic transition toward an ageing population, the number of

people with presbyopia is increasing worldwide, and they need adequate near

vision for the many tasks they perform, including reading or viewing computers.

However, it has been reported that approximately half of people with presbyopia

are either uncorrected or undercorrected (Holden et al., 2008) (Figure 2.3). A lack of

adequate optical correction in presbyopes has been found to have negative effects

on health-related quality of life when measured by a self-administered

questionnaire, the National Eye Institute Refractive Error Quality of Life (NEI-RQL)

Instrument (McDonnell, Lee, Spritzer, Lindblad, & Hays, 2003).

Figure 2.3. The predicted number of people worldwide with presbyopia, and the number of

people with uncorrected presbyopia from 2005 to 2050

(Based on the data from Holden et al., 2008).

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Another survey study using a different questionnaire by Patel et al. (2006) also

found that near vision-related quality of life such as reading, writing, cooking and

threading a needle were significantly affected by uncorrected presbyopia.

Considering the in-vehicle environment, it is possible that uncorrected presbyopia

may also disturb viewing the dashboard and in-vehicle devices such as navigation

and entertainment systems. However, the effect of presbyopia on driving, which

involves both near and distance vision, has not been investigated. In addition, the

effect of wearing vision corrections for presbyopia while driving is also unknown.

Therefore, investigation of the impact of corrected and uncorrected presbyopia on

driving is an important research area, particularly with the increasing use of in-

vehicle devices.

2.3 Visual function change with age and driving

In addition to presbyopia, a number of other changes in the eye and visual system

accompany normal ageing in healthy older adults. The declines in VA, contrast

sensitivity, and increased susceptibility to disability glare are thought to be due to

the combined effects of several factors including loss of media transparency,

changes in pupil size (senile miosis), and neuronal and receptor loss in the visual

pathways (Owsley, Sekuler, & Siemsen, 1983; Spear, 1993; Weale, 1975). However,

senile miosis also increases depth of field by occluding peripheral rays which are the

most affected by refractive blur, which can be advantageous, resulting in less

reliance on spectacle and contact lens corrective power (Schwartz, 2002).

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The relationship between driving and vision has been widely researched in

recognition of the importance of vision for driving. In particular, the decline in visual

function with age has been considered in relation to the role of visual capability and

driving performance in older drivers (Cole, 2002; Wood, 2002b). In this section, the

literature on the relationship between the changes in visual function with age and

driving will be discussed.

2.3.1 Visual acuity

Visual acuity is the most commonly measured visual function and is a measure of

the finest detail that can be seen (spatial resolution). A decrease in VA with age has

been found in several large population-based studies (Foran, Mitchell, & Wang,

2003; Klein, Klein, Lee, Cruickshanks, & Gangnon, 2006; Rubin et al., 1997), and this

decline has been shown to accelerate with increased age. However, in early

presbyopia, distance VA is relatively normal (Foran et al., 2003; Haegerstrom-

Portnoy, 2005).

To obtain a driver’s license in the Australia, private drivers must obtain a minimum

corrected VA of 6/12 in the better eye or binocularly, whereas a commercial driver

must obtain a minimum 6/9 in the better eye and a minimum of 6/18 in the other

eye (Horton & Joseph, 2002). Despite the fact that VA is the most commonly

adopted visual standard for licensing in most developed countries, the relevance of

VA to road safety remains unclear, as only a limited number of studies have shown

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an association between VA and crash rates, whereas others have failed to find any

association.

Burg (1967) examined the crash records of 17,500 drivers in the United States

America (USA), and found no significant correlations between VA and crash rates

for drivers below 54 years of age, and only weak correlations for those drivers over

54 years of age. Other studies have similarly failed to report a significant association

between VA and crash involvement (Ball, Owsley, Sloane, Roenker, & Bruni, 1993;

Decina & Staplin, 1993; McCloskey, Koepsell, Wolf, & Buchner, 1994). These studies

suggested that reductions in VA may have little effect on the risk of injurious

crashes for drivers in this age group. While Owsley et al. (1998) did find a slight

trend, suggesting that drivers with a VA of less than 6/12 might have more crashes

than those with VA better than 6/12, the relationship was not statistically significant.

Hunt et al. (1993) also failed to find an association between VA and performance on

an on-road driving assessment.

Conversely, Davison (1985) analysed 1,000 drivers’ accident history and visual

functions and found that monocular and binocular VA were significantly correlated

with crash rates, with the effect being stronger for older drivers. Hofstetter (1976)

also found that those drivers with poor VA (defined as VA below the lower quartile)

reported a significantly higher number of accidents (three or more) compared with

those with good VA. Similarly, Ivers, Mitchell and Cumming (1999) showed that a

reduction in two lines of VA (0.20 logMAR) was associated with an increased risk of

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accidents. In an experimental study, Higgins, Wood and Tait (1998) examined the

effect of artificially blurring vision to VA levels of 6/6 to 6/12, 6/30 and 6/60 on

driving performance measured on a closed-road. They showed that the percent of

road signs detected and the number of road hazards hit deteriorated significantly

with reductions in VA, however, measures such as lane keeping were not affected

by reductions in VA.

2.3.2 Contrast sensitivity

Contrast sensitivity is considered to be a more comprehensive measure

representing visual function in real world conditions than VA (Elliott, 1987), as

contrast thresholds are measured for different spatial frequencies. This better

represents vision in a natural environment which consists of a diversity of contrasts,

textures, borders and spatial frequencies. Therefore, measurement of the human

contrast sensitivity function provides a more complete assessment of visual

capability, by assessing both spatial resolution and contrast sensitivity (Woods &

Wood, 1995).

Many studies have used the Pelli-Robson chart to measure contrast sensitivity,

showing that there is little change in contrast sensitivity throughout adulthood until

approximately 60 to 65 years of age (Haegerstrom-Portnoy, Schneck, & Brabyn,

1999), thereafter declining 0.1 log contrast sensitivity per decade (Rubin et al.,

1997). Mean log contrast sensitivity was approximately 1.8 to 1.9 log contrast

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sensitivity in the 20’s age group and around 1.8 log contrast sensitivity in the 60’s

age group (Elliott & Bullimore, 1993; Elliott, Sanderson, & Conkey, 1990).

Given that the driving environment includes a range of objects of different sizes and

contrasts, the relationship between contrast sensitivity and driving safety has been

considered as a more relevant factor to safe driving (Schmidt, 1961), and many studies

have demonstrated an association between contrast sensitivity and crashes and

driving-related tasks.

Evans and Ginsburg (1985) compared road sign discrimination ability between younger

and older drivers. In their study, both groups had VA better than 6/6, however, the

older drivers showed significantly poorer contrast sensitivity and performed worse on

the road sign discrimination task. A similar relationship between contrast sensitivity

and sign legibility distance was found by Kline et al. (1990). Contrast sensitivity has also

been shown to predict drivers’ recognition performance (signs, hazards and

pedestrians) under day and night conditions in closed road studies (Wood & Owens,

2005). Reduced contrast sensitivity has been associated with difficulty driving under

night-time conditions, in the accuracy of distance judgements (Rubin, Roche, Prasada-

Rao, & Fried, 1994), and under high-risk driving situations such as rush hour or heavy

traffic (McGwin et al., 2000).

Decina and Staplin (1993) reported that a combined visual screening battery that

included contrast sensitivity, VA and visual fields was significantly related to increasing

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47

crash involvement in older drivers. More recently, a study by Owsley, Stalvey, Wells,

Sloane and McGwin (2001) found that cataract patients with a history of crash

involvement were eight times more likely to have reduced contrast sensitivity than

controls. Their finding was supported by closed-road studies which showed that poor

contrast sensitivity was associated with poor driving performance measures in drivers

with simulated (Wood, Dique, & Troutbeck, 1993) and real cataracts (Wood, 2002a)

and that driving performance improved following cataract surgery (Wood & Carberry,

2006).

2.3.3 Visual field

Visual fields are a measure of visual sensitivity across the field of view and are

known to decline with age (Johnson & Keltner, 1983; Klein, 1991). Visual fields are

commonly tested with short duration stimuli presented across a person’s central

and peripheral vision while the person is fixating straight centrally. The reduction in

visual fields with age have been reported in people over 64 years (Haegerstrom-

Portnoy et al., (1999). Similarly, Spry and Johnson (2001) reported that reductions in

the visual field with age increased among those aged 70 years and over.

The evidence from studies relating visual field loss to either crash risk or indices of

driving performance has been inconclusive. In a study involving 10,000 drivers with

automated visual field testing, Johnson and Keltner (1983) found that drivers with

binocular vision field loss had crash and conviction rates twice as high as those of

drivers with normal visual fields, while those with monocular field loss and

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monocular drivers with normal visual fields, had similar crash rates to the control

drivers.

Early studies showed a weak relationship between visual field and crash

involvement (Burg, 1967; Council & Allen, 1974). More recent studies also failed to

find a relationship between the extent of visual field and crashes (Ball et al., 1993;

Decina & Staplin, 1993). McGwin et al. (2004) found that there was no difference

between drivers with glaucoma and drivers without glaucoma on collision and at-

fault crash rates, however, when the extent of the visual field loss was further

classified, those with moderate or severe visual field defects were found to have an

increased crash risk even though the association was not significant (McGwin et al.,

2005). Similarly, a study of on road driving performance showed that drivers with

glaucoma had one or more at-fault critical interventions due to failure to see and

yield to a pedestrian, while the level of satisfactory manoeuvres and skills were

equivalent to the controls (Haymes, LeBlanc, Nicolela, Chiasson, & Chauhan, 2008).

A closed-road study which simulated binocular visual field restrictions showed that

driving performance was impaired only when extensive visual field loss was

simulated (Wood & Troutbeck, 1992). On road driving assessment of drivers with

visual field defects also demonstrated that driving skills were adversely affected

with drivers who had severe binocular visual field defects (Bowers, Peli, Elgin,

McGwin, & Owsley, 2005). In another on-road driving assessment study, Racette

and Casson (2005) showed that extent of visual field defects is related to driving

performance, but there were large individual differences in the driving safety rating

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49

of those with visual field defects. Together, these findings suggest that while minor

or moderate visual field loss may not pose a significant risk factor for driving safety,

a fact supported by both closed and open road studies of driving performance and

crash data, severe visual field loss appears to be an important risk factor for unsafe

driving.

2.3.4 Stereopsis

Stereopsis represents the ability to detect the relative depth of objects using

binocular disparity and is important in undertaking many activities of daily living

(Norman et al., 2008). Haegerstrom-Portnoy et al. (1999) found a decrement in

stereoacuity with increasing age using a Frisby stereotest. Similarly, Garnham and

Sloper (2006) showed that while there is some decline in stereoacuity with age, the

magnitude of the stereoacuity reduction was dependent upon the stereoscopic

tests used. However, considering the driving environment, the role of stereopsis in

safe driving is unclear, as there are many other cues for judging depth or distance,

such as the road narrowing in the distance (an example of a perspective cue),

overlapping of objects and relative size.

A large study of 1,801 drivers by Rubin et al. (2007) found no correlation between

stereoacuity and self-reported crash involvement. In a study of 10 drivers with

convergent strabismus and reduced stereopsis, only driving through the slalom

course was significantly worse than that for the control drivers, while the ability to

stop in front of obstacles, reverse into a parking space and estimate the relative

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positions of two cars was not affected (Bauer, Dietz, Kolling, Hart, & Schiefer, 2001).

Bauer et al. (2001) concluded that stereopsis may be most important under

dynamic situations at intermediate distances. The role of stereoacuity on braking

responses was also explored using a custom-built go-cart on a linear track by Tijtgat,

Mazyn, De Laey and Lenoir (2008). The group with poorer stereoacuity (400 sec of

arc or worse) actually exhibited more cautious braking behaviour, including earlier

onset of braking, longer stopping distances and an earlier time of peak deceleration

compared to the control group (stereoacuity better than 40 sec of arc), suggesting

that reduced stereoacuity may not be related to an increase in rear-end collisions.

2.3.5 Glare disability

Glare disability describes the impairment of visual function resulting from the

presence of a bright light source in the field of vision (Babizhayev, 2003). Disability

glare is commonly assessed by determining the extent of VA loss that occurs with

the introduction of a bright light source. The difference in the number of letters

read between the no glare condition and glare conditions is known as the disability

glare index (Bailey & Bullimore, 1991). Previous studies have reported that there is

a linear increase in the reduction in VA in the presence of glare with increasing age

(Bailey & Bullimore, 1991; Haegerstrom-Portnoy et al., 1999; Rubin et al., 1997).

Elderly drivers more commonly report problems with glare and driving compared to

young drivers, possibly because of their higher prevalence of cataracts, which

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51

increases their glare sensitivity (Babizhayev, 2003) and results in difficulty in

detecting low contrast objects (Van der Berg, 1991).

A study by Theeuwes, Alferdinck and Perel (2002) found that glare has a

detrimental effect on real world driving performance, such that drivers found it

more difficult to detect simulated pedestrians along the roadside in the presence of

glare and also reduced their speed on winding roads. Similarly, a study by Gray

(2007) using a driving simulator, found that the presence of simulated glare reduced

the safety margin for making a safe turn across traffic at an intersection, thus

increasing the risk for a collision, and that the older drivers exhibited a reduction

in the safety margin compared to younger drivers.

2.3.6 Summary of visual functions and driving

The importance of vision for driving has been emphasised for decades and many

studies have demonstrated that poorer visual functions are associated with reductions

in driving safety for a range of driving measures. Retrospective crash studies have

shown limited evidence between specific visual function measures and crash

involvement, while more recent studies involving a combination of visual function

measures have found them to be associated with crash involvement and unsafe driving.

One of the difficulties in establishing the extent of the relationship between visual

function and crash involvement may be because drivers with degraded visual function

may compensate for their visual loss by driving more defensively and reducing their

driving exposure.

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2.4 Presbyopic vision corrections

Correcting presbyopia can be achieved by several methods including surgical and

non-surgical options which allow near objects to be seen clearly. Options for

presbyopic surgical correction include laser surgery to produce monovision and

multifocal effects, anterior ciliary sclerostomy, scleral expansion bands, corneal

inlays and implantation of artificial intraocular lenses (IOLs) (Hamilton, Davidorf, &

Maloney, 2002; Jacobi, Dietlein, Lüke, & Jacobi, 2002; Jain, Ou, & Azar, 2001;

Malecaze, Gazagne, Tarroux, & Gorrand, 2001; Yilmaz et al., 2008). Non-surgical

options include spectacles and contact lenses. These options have different optical

characteristics which aim to provide functional near vision while also providing clear

distance vision. As the aim of this research was to investigate the effects of non-

surgical optical correction (contact lenses and spectacle lenses) on driving

performance, surgical options will not be included in this literature review. The non-

surgical options for the correction of presbyopia include several spectacle and

contact lens designs such as BIF and PAL, and MV and MTF CL.

The use of presbyopic vision corrections will increase as the number of people aged

45 years and above in the population increases. It has been reported that the

majority of presbyopes are prescribed PAL (37% of presbyopes) and bifocal/trifocal

spectacles (16% of presbyopes) (Nichols, 2009). Another study by Sheedy, Hardy and

Hayes (2006) estimated that approximately 50% of spectacles dispensed for

presbyopes are PAL. The prescription of MTF CL has increased steadily over the 10-

year period between 1996 to 2005 in the United Kingdom (UK), from approximately

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53

3% to 6% (Morgan & Efron, 2006). In a seven year survey of contact lens prescribing

patterns in Canada, 9.7% of all soft contact lens fitted were MTF CL (Woods, Jones,

Jones, & Morgan, 2007), which is in accord with another recent study reporting that

soft MTF CL represented 10% of fitting or refitting of all types of contact lenses

(Nichols, 2009). A recent report showed that the use of MV and MTF CL soft lenses

increased by 7% during 2008 worldwide. In particular, the use of MV and MTF CL in

Australia has increased in the last three years from, 7% in 2006 to 12% in 2007 and

14% in 2008 (Morgan et al., 2007, 2008; 2009). It has also been suggested that the

use of contact lenses for correcting presbyopia will further increase as the next

generation of presbyopes, who currently prefer to wear contact lenses to spectacles

in daily work or sport, wish to continue wearing contact lenses once they become

presbyopic (Bennett, 2006).

2.4.1 Bifocal spectacle lenses

The invention of the BIF is attributed to Benjamin Franklin in the mid 1700s, and is

the most basic method for correcting presbyopia to provide near and distance

vision within the same lens (Callina & Reynolds, 2006). The main advantage of BIF is

that they provide clear vision with two distinctive correction zones which have

different optical characteristics within the same lens.

An important disadvantage of BIF is the presence of a visible line which divides the

lens into the distance and near portions. When wearing BIFs, reflections from the

top of flat top bifocal segment designs can result in vertical streak reflections which

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54

have been reported to be “disconcerting” during night driving (Jalie, 2003). In

addition, due to prismatic effects at the top of the reading segment and the

absence of an intermediate viewing range, wearers may experience apparent

displacement of objects known as “prism jump” when their gaze switches between

the distance and near zones (Alonso & Alda, 2003). Additionally, although clear

vision is obtained through both the distance and near portions, there are

intermediate distances at which objects cannot be focused clearly, known as the

intermediate viewing zone. Another disadvantage of wearing BIF is that

psychologically, the visible line is commonly associated with the appearance of

ageing and imperfection (Glass, 2001).

2.4.2 Progressive addition spectacle lenses

Progressive addition lenses are characterised by a gradual increase in power along

the lens surface from the upper to the lower portion, enabling continuous clear

vision at all distances: distance vision, intermediate (which is not offered by BIF) and

near vision (Callina & Reynolds, 2006; Sheedy, 2004a). Additionally, unlike BIF, PAL

have a seamless appearance which is similar to that of SV. With these advantages,

PAL have been shown to be the preferred presbyopic correction with high success

rates in the range of 80% to 97% (Boroyan et al., 1995; Cho, Barnette, Aiken, &

Shipp, 1991; Sullivan & Fowler, 1989). One study demonstrated that up to 92% of

previous BIF wearers preferred PAL when given a choice between PAL and BIF

following a trial of PAL (Boroyan et al., 1995).

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Progressive addition lenses consist of four main zones (Figure 2.4): a distance zone

that provides the distance viewing power, a near zone that provides the near power,

an intermediate power progression for viewing objects at intermediate distances

and the peripheral zone (Atchison, 1987). The area of the lens where optimum and

unaberrated vision can be obtained through the progressive change in power is

called the “corridor” (Callina & Reynolds, 2006). The corridor varies in shape, width,

and length depending on the manufacturer’s design (Sheedy et al., 2006). However,

image quality through the corridor can be slightly blurry, as the light rays pass

through a range of different dioptric powers resulting in a less sharp image (Burns,

1995). In addition, in order to provide clear vision for all distances, the dioptric

power of PAL needs to be varied across the lens surfaces, which induces unwanted

aberrations, resulting in distorted vision through the peripheral zones of the lenses

(Sheedy, 2004a). These unwanted aberrations are affected by the power of the

addition, such that a higher addition results in increased astigmatism in the

peripheral zone due to greater change in lens curvature (Sheedy et al., 2006).

Figure 2.4. Diagram of zones in a typical progressive addition lens.

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Selenow, Bauer, Ali, Spencer and Ciuffreda (2002) compared the visual performance

of PAL with that of SV in a computer-based reading task at an intermediate distance

(64 cm). They found that PAL presented only a limited intermediate zone resulting

in reduced visual performance compared to SV. In addition, PAL have been found to

induce longer durations of eye and head movements compared to SV in reading

tasks, due to the smaller zone of clear vision of PAL (Han, Ciuffreda, Selenow, Bauer

et al., 2003). Thus PAL wearers need to learn to indentify where the clear zone of

the lens is and how to coordinate eye and head movements to ensure that they are

viewing through the required lens power at a given working distance (Pedrono,

Obrecht, & Stark, 1987). If the eyes are not directed through the correct portion of

the PAL, the wearer will experience a sensation of distortion, or apparent motion of

the visual field (“swim effect”) which is either due to changes in the amount of

astigmatism, or to variations in the axis of the astigmatism in the infero-lateral

zones of the lens (Pedrono et al., 1987; Simonet, Papineau, & Lapointe, 1986).

2.4.3 Monovision contact lenses

Monovision refers to an optical technique, where one eye is corrected for distance

vision while the other eye is corrected for near vision. This approach has been

widely adopted as a presbyopic vision correction, with advantages including the use

of conventional single vision contact lenses, ease of fitting and immediate

judgement of success by the wearer (Bennett, 2008).

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57

Studies have also reported high success rates for MV wear. Back, Holden and Hine

(1989) indicated that MV was the most successful contact lens option compared to

bifocal contact lenses, showing a 67% success rate. Another study by Harris, Sheedy

and Gan (1992) found that 90% of subjects chose to wear MV after a 6-week period

of wear while only 10% of subjects preferred to wear diffractive bifocal contact

lenses. Collins, Bruce and Thompson (1994) reported that 78% of subjects were

satisfied with MV at the completion of 8 weeks wear. In a review of a number of MV

studies, Jain, Arora and Azar (1996) found that the mean success rate for wearing

MV was 76% and rose to 81% after the exclusion of contact lens related intolerant

individuals.

Even though wearing MV is a highly successful option to correct presbyopia, there

have been concerns regarding the adverse consequences of wearing MV which

include reduced stereopsis, VA and contrast sensitivity, while peripheral VA is

unaffected (Collins, Brown, Verney, Makras, & Bowman, 1989). These reductions in

visual function resulting from MV wear have been found to affect near performance

on tasks such as card filing and letter editing compared to controls (distance contact

lenses with reading glasses) (Sheedy, Harris, Busby, Chan, & Koga, 1988). In the

incident of Delta Airline Flight 554’s collision with the ground while landing at

LaGuardia Airport in 1996, the pilot wore MV and this was considered by the

Federal Aviation Administration (FAA) to be one of the contributing factors to the

crash because of resulting misperceptions and visual illusions while flying

(Nakagawara, Montgomery, & Wood, 2001).

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Reduced stereopsis is a well known disadvantage of MV. Papas et al. (1990)

reported that stereoacuity was reduced with MV compared to diffractive bifocal

contact lenses and other studies have reported decreased stereoacuity with MV

compared to MTF CL (Back et al., 1992; Kirschen, Hung, & Nakano, 1999; Richdale,

Mitchell, & Zadnik, 2006). Similarly, a study by Situ, Du Toit, Fonn and Simpson

(2003) found that near stereoacuity with MV was 109 sec of arc while it was 43 sec

of arc with bifocal contact lenses. This reduction in stereoacuity has been shown to

be positively correlated with increasing magnitude of the power of the addition

(Gutkowski & Cassin, 1991).

Due to monocular blur, wearing MV also affects visual functions such as distance VA

and contrast sensitivity. Binocular VA with MV has also been shown to be slightly

reduced compared to that with a spectacle correction. A study by Back et al. (1992)

found that there was a 0.10 logMAR reduction with MV compared to spectacles in

low illumination, and an 0.04 logMAR reduction under high illumination conditions.

However, a recent study showed that distance VA with MV is actually better than

MTF CL, given that the distance VA with MV was -0.01 logMAR compared with 0.05

logMAR for MTF CL (Gupta et al., 2009).

A study by Collins, Brown and Bowman (1989) found binocular contrast sensitivity

with MV was decreased compared to that with a spectacle correction. Rajagopalan,

Bennett and Lakshminarayanan (2006) also found contrast sensitivity at higher

spatial frequencies with MV to be worse compared to PAL. The decrease in contrast

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sensitivity is related to the magnitude of defocus. If monocular defocus is more than

+2.50D, binocular contrast sensitivity becomes equivalent to monocular contrast

sensitivity due to the effect of suppression of the defocused eye (Pradhan &

Gilchrist, 1990).

For MV wearers, it is unclear if a period of adaptation is required. Sheedy, Harris

and Gan (1993) found that there was no significant improvement in VA and

stereoacuity after commencing MV wear over a period of eight weeks. Similarly,

Collins et al. (1994) reported no significant changes in VA, near stereoacuity and

blur suppression over eight weeks of MV wear. However MV wearers do report

subjective improvements in visual satisfaction over this period (Collins et al., 1994).

In prescribing MV, the practitioner needs to determine which eye should be

corrected for distance and which corrected for near. The most commonly used

method is to prescribe the distance correction for the “dominant” or “sighting” eye

and the non-dominant eye for near vision (Evans, 2007). In determining the

“dominant” or “sighting” eye, the participant is asked to extend their arms, forming

a small hole with both hands and binocularly centre a given distance target in that

hole. When the examiner occludes either eye, the eye aligned with the target is

defined as the dominant eye (Bennett, 2008). Despite many practitioners using tests

of sighting ocular dominance to prescribe the distance lens in monovision,

controversy still exists over whether such tests should be used, particularly as there

are so many possible tests for ocular dominance (Evans, 2007; McMonnies, 1974).

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2.4.4 Multifocal contact lenses

The concept of MTF CL is to combine two or more different dioptric powers within

the optical zone of a contact lens to provide clear vision across a range of focal

distances. Generally, MTF CL are classified as either simultaneous or alternating

vision designs. Simultaneous designs are based upon several different design

concepts such as multi-zone concentric, diffractive design, or aspheric designs.

Aspheric designs are commonly available and utilise an aspheric curvature within

the optical zone on the front or back surface providing a progressive power change

from the centre to the periphery of the optical zone. The centre-distance aspheric

design consists of a centre positive power that is less than the peripheral area,

whereas centre near type have more positive power in the centre of the lens

(Guillon, Maissa, Cooper, Girard-Claudon, & Poling, 2002).

The principle of simultaneous vision is to use near and distance optic zones which

are located within the entrance pupil, enabling partial focus of near and distant

objects at the same time. Consequently, the visual system is able to use the clear

image of the object at the desired viewing distance while ignoring the out-of-focus

image (Bennett, 2006). However, the in-focus image is present simultaneously with

the out-of-focus image, resulting in a reduction in the contrast of the focused image

(Koffler, 2002). Gupta et al. (2009) found that wearing MTF CL resulted in

significantly poorer distance and near VA compared to MV when the prescription

power was equivalent to the best spectacle prescription and no modification of the

prescription was made. Other studies have found that distance VA with MTF CL was

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approximately 1 line worse (0.10 logMAR) than with spectacles (Fisher, Bauman, &

Schwallie, 2000; Kirschen et al., 1999; Richdale et al., 2006). Contrast sensitivity was

also poorer when wearing MTF CL than with spectacles (Rajagopalan et al., 2006)

for medium and high spatial frequencies (Collins, Brown, & Bowman, 1989). The

extent of contrast loss is dependant on the relative amounts of in-focus to out-of-

focus image on the retina and is closely related to pupil size (Borish, 1988) (Figure

2.5). For instance, when wearing a centre-near design and when the pupil is small,

distance vision will be less clear than near vision. On the other hand, when the pupil

is large, proportionally more light will pass through the distance viewing portion

than the near viewing portion), resulting in compromised near vision.

Figure 2.5. Pupil size and relative coverage of optic zone of MTF CL.

(A; small pupil with centre-near (CN) design, distance vision is compromised

B; large pupil with centre-near design, near vision is compromised).

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2.4.5 Summary of presbyopic vision corrections

Presbyopia is an inevitable physiological change that occurs with age, resulting in a

reduction in the clarity of near vision. While there are many interventions available

to address the problems of presbyopia, wearing spectacles and contact lenses are

easy and effective interventions for individuals who require clear distance and near

vision within one optical correction. However, as there are many presbyopic vision

corrections with different optical characteristics that affect visual function in

different ways, individuals need to prioritise their visual tasks, including outdoor

activities, reading, working with a computer and driving, and select the vision

correction which works best for their visual requirements.

When distance tasks are a priority, spectacles options such as BIF and PAL may be

good options as their distance VA is usually better than with MV and MTF CL (Back

et al., 1992; Collins, Brown, & Bowman, 1989; Papas et al., 1990). However, motion

sickness with PAL needs to be considered and the appearance with the visible line is

a limitation of BIF. If depth perception is important, MV may not be a good option

as MV induces anisometropia which reduces stereopsis and affects near vision-

related tasks. With its advantage of no adverse effects on binocular visual function,

the use of MTF CL is steadily increasing. However, degraded VA is a limitation unless

modifications to the MTF CL power is prescribed (e.g. one lens is prescribed with

over plus or less plus). In addition, increased haloes and glare are common

complaints of MV and MTF CL wearers regarding night-time driving.

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2.5 Presbyopic vision corrections and driving

Most studies that have investigated the association between wearing presbyopic

vision corrections and driving difficulties have been based on self-report using

questionnaires that provide data about participants’ previous driving experience. A

study by Josephson and Caffery (1987) found that 80% of presbyopic contact lenses

wearers reported driving difficulties at night-time with MV and MTF CL (aspheric

bifocal) and Back et al. (1992) also found that patients wearing bifocal contact

lenses experienced more haloes than wearers of MV. Schor, Landsman and Erickson

(1987) found that haloes were reported by MV wearers at lower levels of

illumination and that the haloes reduced with increasing illumination. In addition, as

the size of the light source increased, blur suppression was enhanced compared to

that with smaller light sources. In addition, 17% of MV wearers were not satisfied

with MV for driving and this level of dissatisfaction was greater at night-time due to

distance vision blur and ghosting around lights (Collins, Goode, Tait, & Shuley, 1994).

The only objective measurement of driving performance with MV was conducted by

Wood et al. (1998) with thirteen MV wearers on the open road under daytime

conditions. No adverse effects on sign recognition, mirror checks, lane-keeping

deviations, driving time and speed estimation were found with MV.

However, little is known about how other presbyopic vision corrections affect real

world measures of driving performance, nor the effect on driving performance

when patients are unadapted to their presbyopic vision correction.

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2.6 Day and night-time driving

Environmental lighting conditions have significant implications for driving as visual

performance varies under different levels of illumination. Several studies have

provided evidence that drivers’ ability to avoid collisions is impaired under dim

lighting conditions (Owens and Sivak, 1996; Elvik, 1995). In addition, the injury crash

rate for drivers increases during night-time hours (Rice et al,. 2003). According to

Plainis, Murray and Pallikaris (2006), the severity of fatal collisions almost doubled

at night between 1996 and 2005 for different types of roads in the UK (Figure 2.6).

In addition, they indicated that the average injury severity rates at night-time were

almost three times higher for situations where there was no street lighting

compared to those where street lighting was present.

Figure 2.6. Average severity rates at day and night-time by different road type (1995 to

2004). (Reproduced from “Road traffic casualties: understanding the night-time death toll,

Plainis, Murray and Pallikaris., 12(125-128), 2006 with permission from BMJ Publishing

Group Ltd.”)

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Target detection was shown to become poorer with decreasing background

luminance at night (0.01cd/m2) (Alferdinck, 2006), and it became even worse in the

presence of oncoming headlight beams (Anderson & Holliday, 1995). In addition, in

closed road driving studies, driving speeds and road sign recognition were reduced

under conditions of decreased illumination and for older drivers (Owens, Wood, &

Owens, 2007). The decrease in visual function under low illumination conditions

(e.g. night-time) and increased glare sensitivity with increasing age are likely

contributing factors to the increased risk of crashes at night-time. Increased pupil

size at night also causes more haloes around lights due to refraction of light into

peripheral parts of pupil which may not be the optical portion of the lens (Stone,

1970) and problems with haloes at night is a common complaint from MV and MTF

CL wearers compared to spectacles wearers.

2.7 Eye and head movements for driving

Research into head and eye movements has become of increasing interest in driving

research as it provides insight into how the driver responds to visual stimuli in

traffic. During driving, eye and head movements are important to monitor the

forward traffic scene to avoid potential hazards, allowing the driver to obtain

information from their visual field that is useful for driving (Land, 2006).

However, eye and head movements are potentially affected by wearing presbyopic

vision corrections. In particular, PAL are known to affect head movements due to

restriction of the intermediate viewing zone. For example, Han et al. (2003)

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investigated eye and head movements in a simulated computer-based environment

and found that reading tasks, as well as eye and head movements, were adversely

affected by the use of PAL compared to SV. PAL resulted in slower eye movement

velocities and stabilization of gaze occurred later than for SV. A study by Jones,

Phillips, Kenyon, Kors and Stark (1982) found that head movements increased when

reading with PAL compared to BIF, and that this difference persisted after months

of adaptation to the PAL. However, a study by Proudlock et al. (2004) found no

significant difference in head movements between a group of SV wearers and a

group of BIF or PAL wearers. This failure to find between gr