AHF 2203 AVIATION HUMAN FACTORS Lecture 8: Vision 1.

AHF 2203AVIATION HUMAN FACTORS

Lecture 8: Vision

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Presentation Outline• Introduction• The importance of VISION• Anatomy of EYE• How Eyes work• Factor affecting vision• Visual Impairment• Types of Vision• Causes of Impaired Vision• How to have better scan of object in the flight?

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Learning Outcomes• At the end of this session, student should be

able to:– identify the parts of the eye and most importantly

the main functions of each part.– understand the limitations of human visions

through given types of vision, dark adaptation, blind spot and etc.

– factors that lead to vision impairments and the steps to overcome it.

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Introduction

• Vision: the most important sense to obtain reference info during flight.

• The eye send image to the brain about aircraft position, velocity and altitude relative to the ground.

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The importance of VISION• Read manuals data & monitoring cockpit

instruments.• Determines visual references for taxiing, take-

offs and approach.• It is the sense that makes you aware of the

position of your aircraft.• Important for identifying terrain features and

obstacles.• You need good depth perception for

determining height and distance5

Eyes anatomy

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Cross Section of the Human Eye

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eyeballeye muscles

• eye muscles: allows eyeball to move in various directions

Rods

Cones

Anatomy of the Eye• Cornea:

– Transparent outer covering of the eye that admits light• Iris:

• Round, pigmented (colored) membrane surrounding the pupil.(colored part of the eye).

• Function: control the dilation of the pupil.• Pupil:

– Adjustable opening in the center of the iris– Function: control the amount of light entered the eye (same with

aperture function of the camera).• Lens:• refracts and focuses light onto the retina

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• Retina:– Thin multi-layered membrane which covers most of the posterior

(backside) compartment of the eye. – Function: to record the image (similar to film function in the camera)– Retina contains TWO types of light-sensitive cells (photosensitive cells)

which are rods and cones.• Rod:

– Nerve cells in the retina. Very sensitive to light & dark (black & white vision)

– 10000 times more sensitive to light than fovea (cones)– Used for low light condition/night vision.– Involve in peripheral vision to detect position references.– Cannot be used to detect detail or to perceive colour.

• Cone:– Nerve cells help to see light/color (color vision)– Area of sharpest vision.

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Internal structures of the eyeball

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transverse section transverse section through the eyeballthrough the eyeball

• special regions:yellow spot(fovea) , blind spot, retina peripheral

a) yellow spot (fovea)— sharpest vision; most concentrated with cones

b) Optic tip (blind spot)— no cones or rods; place where optic nerve leaves the eye

c) Retina peripheral – contains rods

yellow spot

Optic tipoptic nerve

retina

How eyes work?

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Formation of an image in the human eye

•Light from the object is refracted(by cornea and lens) and focused onto the retina.•The image formed is real, inverted and smaller than the object.•The image is detected by rods and cones which cause nerve impulses.•Nerve impulses are transmitted along optic nerve to the brain.•The brain interprets the nerve impulses and ‘sees’ an upright image of the object.

Nerve impulse: The electrical discharge that travels along a nerve fibre

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Formation of an image in the human eye

object

To brain

retina

Optic Nerves

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Factors Affecting Vision

• The better visibility of the object when:– Greater the object size – Greater ambient illumination– Greater Contrast– Greater Viewing Time– Greater Atmospheric Clarity

• During day – object can be identified easier at great distance with good details resolution.

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Cont.• During night– The identification range of deem object is limited

and the details resolution is poor.

• Excess ambient illumination– Especially from light reflected off surface inside

aircraft, cloud, water, snow, and desert terrain can produce GLARE.

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• GLARE may cause– Uncomfortable Squinting• *Squinting: Half Eye is half close in order to see better.

– Eye tearing– Temporary Blindness

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Cont.

Eye Defects

Nearsighted(Myopia)

Farsighted(Hyperopia)

Color Blindness

Impairment of Vision (Eyes Disorder)

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Near Sighted – – Eyeball is too long – Image focuses in front of

the retina.– Eye Lens too convex

• Far Sighted – – Eyeball is too short– Image is focused behind the

retina.– Eye Lens not convex enough

© 2000 Microsoft Clip Gallery

© 2000 Microsoft Clip Gallery19

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Corrective Lenses

• Nearsightedness (Myopia) – – Correction: Use Concave lenses to expand focal lengths.

• Farsightedness (Hyperopia)– – Correction: Use Convex lenses to shortens the focal length.

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Let’s have a test!What numbers do you see?

Color blindness• Due to reduced number of / some defects in one

or more of the cone cells• Inherited

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Others Visual Impairment

• Astigmatism– Impaired focus on object of

different meridians (height level).– Focus disorder of vertical and

horizontal rays– Caused by irregular shape or the

cornea, lens, or both– Can typically be corrected with

glasses with relatively cylindrical lenses.

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AstigmatismNormal Vision

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Types of vision

• Photopic vision (DAY)• Scotopic vision (NIGHT)• Mesopic vision (Dawn/Dusk)

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Photopic vision

• Occurs during day light or bright light

• Central vision• Color sense and sharpness• Best visual acuity 26

• Occurs on dimly nights• Decreases visual acuity• Causes loss of color perception• Causes night blind spot• Involves the rods only

Scotopic Vision

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Mesopic vision

Occurs at dawn, dusk and in full moonlight

Reduces color vision and decreases visual acuity

Involves both rods and cones

Greater emphasis should be placed on off-center vision as

cones become less effective28

Causes of Impaired Vision

• Self-imposed stresses such as self-medication, alcohol consumption, tobacco use, hypoglycemia (low blood sugar), and sleep deprivation (not enough sleep)/ fatigue can seriously impair your vision.

• Inflight exposure to low barometric pressure without the use of supplemental oxygen (above 10,000 ft during the day and above 5,000 ft at night) can result in hypoxia, which impairs visual performance.

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• Fatigue– Cause the eye to overshoot or undershoot the

target.– Effect pilot ability to quickly change focus

between near (e.g. chart), intermediate (e.g. instrument), and distant (e.g. outside) vision.

– We call this as visual fatigue.

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Cont.

• The most common symptom in visual fatigue:– Blurred Vision– Excessive Tearing– “Heavy” Eyelid Sensation– Headaches– Burning, scratchy, or dusty eye sensation.

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Cont.

Other factors that may have an adverse effect on visual performance include:

• windscreen haze, • Improper illumination of the cockpit and/or instruments,• scratched and/or dirty instrumentation, • inadequate cockpit environmental control (temperature and

humidity),• inappropriate sunglasses and/or prescription glasses/ contact

lenses, and

• sustained visual workload during flight.

Cont.

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Reduction night vision in varying altitude (8-10% carbon monoxide blood content)

Altitude Smokers (% reduction)

Non-smokers (% reduction)

4000 20 06000 25 5

10000 40 2014000 55 3516000 60 40

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How to have better scan of object in the flight?

• Focus on the Specific Object• Dark Adaptation• Performing Series of Shot (space eye

movement)• Performing off center viewing (during low and

ambient illumination)

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Focus on the Specific Object• Distant focus without specific object to look at

tends to diminish rather quickly.

• If we fly over water, hazy condition, or between cloud layer at night, our distant focus relax after 60-80 seconds.

• If there are no specific object to focus, our eyes revert to a relax intermediate focal distance of 10-30 ft.

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Cont.• Thats mean we are looking without actually

seeing anything which are DANGEROUS!!

• The solution of this phenomenon is to FOCUS on more distant object that we can see (even it is just a wing tip).

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• Dark adaptation is the process by which the eyes adapt for optimal night visual acuity under conditions of low ambient illumination.

• The lower the starting level of illumination, the more rapidly complete dark adaptation is achieved.

• Visual Purple (Rhodopsin) – Light absorbing protein in membrane of rods– Allows rods to detect images in the dark

• Night flight– 30 minutes required for full adaptation to dark

Dark Adaptation

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• To minimize the time necessary to achieve complete dark adaptation and to maintain it, you should:

avoid inhaling carbon monoxide from smoking or exhaust fumes

get enough Vitamin A in your dietadjust instrument and cockpit lighting to the lowest level

possibleavoid prolonged exposure to bright lightsuse supplemental oxygen when flying at night above

5,000 ft (MSL)

Cont.

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Performing Series of Shot (space eye movement)

• A study of 50 m aircrafts collision reveal that only 8% were head on (opposite direction) collision. However 42 % aircrafts collide when heading in the same direction.

• Therefore, scanning the sky for other aircraft is very important factor to avoid MID-AIR COLLISION.

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• It should cover all area of the sky visible from the cockpit and monitoring cockpit instrumental as well.

• This can be accomplish by performing the series of shot, regularly space eye movement that bring success area of the sky into fovea field.

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Cont.

• Each movement should not exceed 10° for each area and should not be observed at least 1 sec to enable detection.

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Cont.

1 2 4

3

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Performing off center viewing• To see or identify the object under condition

of low and ambient illumination– Avoid looking DIRECTLY to the object for more 2

and 3 seconds because it will disappear.

• Instead, use the off center viewing and that consist 10° ABOVE, BELOW and EITHER SIDE to look at the object

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OBJECT10°

10°

10°

10°

• By switching eyes every 2-3 seconds, we can continue to detect the object.

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OBJECT10°

10°

10°

10°Cont.

Do you know?

• The natural ability to focus your eye is critical to flight safety.

• It is important to know your eyes may required several second to refocus when switching view between near, intermediate, and distance object. For example likes witching view of reading chart/manual, monitoring instrument and looking for traffic or external visual references.

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Conclusion• Of all the sense used for flying by the human

body and mind, vision is far most important.• In aviation, vision supplies data for monitoring

instruments, traffic, written materials, determines visual references for taxiing, takeoffs and approaches to landiong.

• The disruption of vision or impairment increase the unsafe flight level.

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Key Points• Eyes Anatomy and function.• How your eyes work?• Internal Structure of the eye.• Factors affecting vision.• Vision Impairment• Correction of Vision Impairment• Types of Vision• How to have better scan of object?

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End of Presentation #75 Minutes for Q/A session

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