Reference: Griffin, Ch. 3, pg. 64-73, 87-92

Scheiman, pg. 34-57; 225-232; 239-246

Richman and Cron, pg 16-17

I. Introduction: A convergence insufficiency is a group of fusional dysfunctions that are characterized by:

- increased exophoria at near with distant normal heterophorias

- decreased BO vergence (positive) at near

- reduced NPC

- intermittent suppression at near

It is the most common vergence anomaly, as 25- 30% of general pop. have complained of some form of this dysfunction

A. These dysfunctions fall along a continuum:

1. At one end, a "true" convergence insufficiency (a convergence dysfunction at near).

2. At the other end, a "pseudo-convergence insufficiency (an accommodative dysfunction which has, as its most prominent feature, reduced convergence at near.

3. Along the line is a range of "mixed bag" dysfunctions, either led by a fusional convergence problem at near or accommodative dysfunction.

B. Demographics: Convergence dysfunctions strike at any age, but in general, it doesn't rear its ugly head until the age of 9 or 10. "True" C.I. cases are a bit easier to remediate than the "pseudo" type, but it is best to catch these dysfunctions early (less mal-adaptations)

II. "True" Convergence Insufficiency:

A. Signs found during (normal P.C. exam)

*1. Increased exophoria at near with distant normal heterophorias

*2. Decreased BO vergence (positive) at near

*3. Reduced NPC

*4. Intermittent suppression at near

*5. Plus is difficult on accom. facility  (most prominent under binoc. testing)

*6. NRA may be reduced, but also may be close to normal; PRA is normal - high

B. Additional tests reveal:

*7. AC/A (calculated or gradient) is below expected values

*8. (-) Plus acceptance (MEM, Binoc. X-Cyl.)

*9. Normal lag results (sometimes a lead of accom.)

*10. Reduced jump vergence at near (8 BI/BO flippers): more difficulty with BO

*11. Reduced performance in convergence at near through + 1.00

C. Rationale for test results:

1. Low AC/A ratio and poor proximal/fusional convergence skills are the root of this dysfunction

2. They may tend to over accommodate at near to compensate (ie gain accom. conv.)

3. A "true" convergence dysfunction will not be to eager to let go of accommodation

III. "Pseudo" Convergence Insufficiency: primarily an accommodative dysfunction

A. Signs found during (normal P.C. exam)

*1. Increased exophoria at near with distant normal heterophorias

*2. Decreased BO vergence (positive) at near

*3. Reduced NPC

*4. Intermittent suppression at near

*5. Minus is difficult on accom. facility (monoc. or binoc.)

*6. PRA is reduced

*7. NRA may be reduced, but is usually normal

B. Additional tests reveal:

*8. AC/A (calculated) is low; AC/A (gradient) is normal- high

*9. (+) Plus acceptance (MEM, Binoc. X-Cyl.)

*10. Rather large lag of accommodation

*11. Reduced jump vergence at near (8 BI/BO flippers)

*12. Same or improved performance in convergence at near through + 1.00 (ie. vergence ranges)

C. Rationale for test results:

1. Accommodative dysfunction is the root of pseudo C.I.

2. They tend to "give up the ship" on convergence at near (even if fusional vergence is normal) because of accommodative dysfunction

3. A "pseudo" convergence dysfunction will be to eager to let go of accommodation; plus is indicated at early stages here.

IV. Basic Exophoria: IS NOT CONSIDERED TO BE A CONVERGENCE INSUFFICIENCY TYPE, but most of its characteristics do fit in the conversation today.

A. This dysfunction involves a high exophoria at distance and near

B. Exophoria at near is due to low fusional convergence skills

C. Exophoria at distance is due to low tonic convergence

D. AC/A is normal.

V. Graphical Appearance of the Convergence Insufficiencies

A. "True" C.I.:

*1. Increased exophoria at near with distant normal heterophorias

*2. Decreased BO vergence (positive) at near

*3. Low AC/A; steep slope

*4. Reduced NRA (in some cases)

B. Pseudo C.I.:

*1. Increased exophoria at near with distant normal heterophorias

*2. Decreased BO vergence (positive) at near

*3. Normal AC/A ratio

*4. Low PRA

*5. Possibly low NRA

C. Basic Exophoria

1. Increased exophoria at distance and near

2. Decreased BO vergence (positive) at distance and near

3. Normal AC/A ratio

4. Low PRA

VI. System Control Analysis (Stereophonic Model) Approach to Convergence Insufficiencies:

A. Theoretical/experimental considerations:

1. It has been suggested (and experimentally validated) that when the response AC/A ratio is low, the corresponding CA/C ratio tends to be high.

2. It has been suggested (and experimentally validated) that in most non-strabismic binocular vision anomalies, vergence adaptation is weak.

3. Above all else, remember; I'D RATHER BE BLURRED THAN BE DOUBLE

B. Keeping these tidbits in mind, let us now examine our two diagnoses.

1. It is assumed:

a. our patient orthophoric at distance

b. our patient has 10 XP'

c. numbers represent relative vergence demand (orthophoria @ near is 0)

2. True convergence insufficiency: AC/A = 1/1; CA/C = 1.0D/6D; PRC = 7D BO; poor vergence adaptation.

a. initial vergence response barely is able to fuse target .

b. this gives rise to ________ of convergence accommodation.

i. is this output possible?

ii. what element within the control unit would limit the maximum amount of convergence accommodation?

c. to keep the target clear, only _____ of blur driven accommodation is necessary.

d. unfortunately, with the (high/low) AC/A ratio, there is ______ D of accommodative convergence to help out!

e. decay of this fast vergence system begins and vergence adaptation doesn't help a lick!

f. to avoid diplopia, we must crank the accommodation upward to gain some accommodative convergence.

g. the results:

i. a tendency to over-accommodate (under binocular conditions)

ii. a fused, but blurry optical image

iii. an inability to succeed in long term near point tasks

iv. a cranky patient

2. Pseudo-convergence insufficiency: AC/A = 4/1; CA/C = 0.6D/6D; PRC = 12D BO; poor vergence adaptation.

a. initial vergence response is able to fuse target.

b. this gives rise to ________ of convergence accommodation.

c. to keep the target clear, _____ of blur driven accommodation is necessary.

d. unfortunately, with accommodative abilities, it is a struggle to meet the accommodative demand; it delivers 0.75 D of accommodation. This results in _____ D of accommodative vergence

e. decay of the accommodative system begins and accommodative adaptation doesn't help a lick!

f. vergence adaptation isn't too helpful on the vergence side, either.

g. to avoid diplopia, we must crank the vergence upward to gain some vergence accommodation.

h. unfortunately, the vergence system "gives up" as the accommodative system fails.

i. the results:

i. a tendency to under-accommodate (under binocular conditions)

ii. a tendency to react to this by under-converging

iii. an inability to succeed in long term near point tasks

iv. a cranky patient