This document discusses measuring and classifying accommodative convergence/accommodation (AC/A) ratios. It defines the AC/A ratio as the change in accommodative convergence per diopter of accommodation. Abnormal AC/A ratios can cause strabismus. There are several methods described for measuring the AC/A ratio clinically, including the heterophoria, gradient, and graphical methods. The document outlines treatments for different AC/A ratio abnormalities like convergence excess, convergence insufficiency, divergence excess, and divergence insufficiency.

2.  Measurement of the convergence induced by
accommodation, per diopter of
accommodation.
 To determine the change in accommodative
convergence that occurs when the patient
accommodates or relaxes accommodates a
given amount.
 Unit = ∆∕D
 Normal range = ( 4 – 6) ∆/D

3.  Abnormalities of the AC/A ratio are very
important causes of strabismus.
 A high AC/A ratio may cause excessive
convergence & produce a convergent
squint during accommodation on a near
object.
 A low AC/A ratio may cause a divergent
squint when the patient looks at a near
object.

4. 1. Stimulus AC/A Ratio
Ratio of accommodative convergence
to stimulus to accommodation.
2. Response AC/A Ratio
Ratio of accommodative convergence
to response to accommodation.
 Usually stimulus AC/A > Response AC/A

5.  Heterophoria method
 Gradient method
 Fixation disparity method
 Graphical method

6.  Simple method, consists of comparing the
measurement of the latent deviation of eyes
 Using prisms & alternate cover test at a point of
distance fixation ( 6m ) with refractive
correction.
 At a point of near fixation ( 33cm ) with
refractive correction.
 IPD should be measured.
 +ve sign for esodeviation, -ve sign for
exodeviation.

7.  AC/A ratio is calculated from this following
formula:-
AC/A = IPD + (∆n - ∆d/D)

8.  The change in the stimulus to
accommodation is produced by means of
ophthalmic lenses not by a change in
viewing distance.
 Concave lenses placed before the eyes
increase the requirement for accommodation
& convex lenses relax accommodation.
 -1D lenses produce an equivalent of 1D of
accommodation, where as +1D lenses relax
accommodation by 1D.

9.  Original deviation is found at near while the
patient wears optical correction & then with
additional lens.
 Ac/A ratio is calculated from this following
formula:-
AC/A = ∆L - ∆O/D

10.  Used by Ogle & co-workers.
 Indirect method, more reliable due to test
under binocular condition.
 Consists of 2 sets of data
 First changes in fixation disparity induced by force
convergence using prism
 Second change in fixation disparity induced by altering
the accommodative stimulus with lens

11.  From these 2 sets of data they determined
stimuli for convergence & accommodation
that gave same fixation disparity.
 Because of its complexity, this test is not
performed in routine clinical practice.

12.  Convergence (in prism diopter) is plotted
along the x- axis.
 Stimulus to accommodation is indicated
along the y-axis.
 Slope of graph represents AC/A ratio.

14.  Diagnosis of convergence excess type of
esodeviation.
 Divergence excess exodeviation
 Divergence insufficiency
 Convergence insufficiency

15.  Apply in those patient who have chance of
obtaining some fusion when eyes are straight
or within 10PD in distance with optical
correction.
 Try to keep eyes straight for distance upto
age of 8 years.

16.  If eso deviation is less then 10PD in distance-
has chance of developing fusion with full
optical correction.
 If eso deviation is greater than 10PD in
distance has no chance of developing fusion
unless the deviation is reduced to under
10PD.

17.  Prescribing Prism
 Prescribing Visual Training
 Alteration of Sph. Portion of Correction
 if AC/A sufficiently large additional plus for
convergence excess

18.  CONVERGENCE EXCESS:
 n>d
 high AC/A ratio
 Treatment
 Near add (overcorrection of plus power
or under correction of minus power
most effective) e.g.
 Base-out prism (alternative method)
 Base-in training(not so effective)

19.  CONVERGENCE INSUFFICIENCY
 n> d
 Low AC/A ratio
 Treatment
 Base-out training (most effective)
 “Pencil push-up” training

20.  DIVERGENCE EXCESS
 n< d
 high AC/A ratio
 Treatment
overcorrection of minus power or
undercorrection of plus power
in mild case base-in prism for full time
wear

21.  DIVERGENCE INSUFFICIENCY
 n>d
 low AC/a ratio
 Treatment
 Base-out prism

22. THANK YOU…….