Download - AC/A
Vergence Response
Tonic
Proximal
Accommodative
Fusional
AC/A Ratio
Accommodation response produces a convergence response
Accommodative convergenceAC/A expressed in ∆/D
CA/C Ratio
Less commonly measured in practice
Convergence response produces an accommodation response
Convergence accommodationCA/C expressed in D/∆
Near Response (Near Triad)
Accommodation
Vergence
Pupil
Accommodation
Blur driven responseOther optical cues such as chromatic
aberration contributeNon-optical cues such as size, rate of
change, time to contactVergence
Vergence
Disparity driven responseEye movements usually complex
with version and vergence interactions
Non-optical cues contributeAccommodation
Pupil Response
Miosis observed for near viewingNo drive from accommodationNo drive from vergenceNon-optical cues such as perceived
distance are main drivers
Accommodation & Vergence
AC/A
Response 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
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7
Unit ratioResponse
AC/A Distribution
Measurement of AC/A
Difficult to measure response AC/A
Stimulus AC/A used in practiceNot appropriate to measure in
older age groups Useful in younger patients with
BV problems
Heterophoria Method
Comparison of phoria at D & NAC/A = PD +((∆N - ∆D)/D)
Example
PD 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 Methods
Synoptophore Method: Similar to gradient but using synoptophore
Fixation Disparity Method: Indirect method and not appropriate clinically
Significance of AC/A
Has 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/A
AC/A similar in mon and binocularStudies of twins show similar AC/AAC/A unchanged by vision training
Effect of Drugs
Miotics
Cycloplegics
Effect of local drugs
Effect of Age
No value in presbyopiaRemains constant up to presbyopia
Summary
A useful measure in practiceVery easy to measureConsult Primary Care text for clinical
variations in techniqueHelps understand BV problemHelps management of BV problem