AC/A

Vergence ResponseTonic

Proximal

Accommodative

Fusional

AC/A RatioAccommodation response

produces a convergence response

Accommodative convergenceAC/A expressed in ∆/D

CA/C RatioLess commonly measured in

practiceConvergence response produces

an accommodation responseConvergence accommodationCA/C expressed in D/∆

Near Response (Near Triad)Accommodation

Vergence

Pupil

AccommodationBlur driven responseOther optical cues such as chromatic

aberration contributeNon-optical cues such as size, rate of

change, time to contactVergence

VergenceDisparity driven responseEye movements usually complex

with version and vergence interactions

Non-optical cues contributeAccommodation

Pupil ResponseMiosis observed for near viewingNo drive from accommodationNo drive from vergenceNon-optical cues such as perceived

distance are main drivers

Accommodation & Vergence

AC/AResponse AC/A: amount of

accommodative convergence produced by an actual change of 1D of accommodation

Stimulus AC/A: amount of accommodative convergence produced by a change of 1D in the stimulus to accommodation

Accommodation Response

012345678

0 1 2 3 4 5 6 7

Unit ratioResponse

AC/A Distribution

Measurement of AC/ADifficult to measure response

AC/AStimulus AC/A used in practiceNot appropriate to measure in

older age groups Useful in younger patients with

BV problems

Heterophoria MethodComparison of phoria at D & NAC/A = PD +((∆N - ∆D)/D)

ExamplePD 60mm; Distance 3SOP; Near 12SOP

AC/A = 6 + ((12 - 3)/3)AC/A = 6 + (9/3)AC/C = 9:1

Very High AC/A producing anomalous phoria at near

Gradient Test

-15

-10

-5

0

5

10

15

-4 -2 0 2 4

Stimulus to Accommodation (D)

Induced Phoria (∆)

AC/A

Other MethodsSynoptophore Method: Similar to

gradient but using synoptophore

Fixation Disparity Method: Indirect method and not appropriate clinically

Significance of AC/AHas effect on near phoriaLow AC/A leads to large xopHigh AC/A leads to large sopMay be associated with

convergent strabismusHyperopia and high AC/A

associated with convergent squint

Accommodative Strabismus

Innate or Acquired?No relationship between Rx and

AC/AAC/A similar in mon and binocularStudies of twins show similar AC/AAC/A unchanged by vision training

Effect of DrugsMiotics

Cycloplegics

Effect of local drugs

Effect of AgeNo value in presbyopiaRemains constant up to presbyopia

SummaryA useful measure in practiceVery easy to measureConsult Primary Care text for clinical

variations in techniqueHelps understand BV problemHelps management of BV problem