develope CI usually do so as a re-

suit of a loss in accommodative

convergence and may be success-

fully treated with vision train-

ing.2 Induced BO prism effect

as a result of bifocal lenses, may

be another cause of CI in presby-

opes. This is especially true in

aphakics wearing high plus pre-

scriptions.

More females than males

present CI in a ratio of

3:2 6,12,13,14 Manson14 postulated

that this difference may be due

to an anemia secondary to gyne-

cological, obstetric and/or men-

strual problems.

Symptoms

The most frequent symptom

found in CI is discomfort after

reading or near work,’3,8,11,15 and

this usually occurs at the end of

the day.8,11 Other symptoms in-

clude: frontal headaches;8 eye

aches, pulling sensations, heavy

eyelids,6,8,11 sleepiness, diplo-

pia;2,6,8,13,16 loss of concentra-

tion,4 blurred vision,2,813,16 tear-

ing,’4 and dull orbital pain. Less

common complaints include nau-

sea, motion sickness, dizzi-

ness;” panoramic head-

aches;”8” gritty sensations in

the eyes and general fatigue. In

addition, it has been noted that

some CI patients report poor

depth perception, e.g. trouble

parking a car; trouble playing

tennis.

Hirsch’7 reported the incidence

of various symptoms in a CI

population. He found that 38%

of Cl patients had ocular fatigue,

i.e. discomfort or drowsiness;

25% experienced headaches; and

18% had aching, stinging, burn-

ing and/or tearing of the eyes. In

another study, Kent and Steeve6

found that 60% of their popula-

tion of CIs had headaches, 49%

experienced blurring of print,

34% had ocular fatigue, and 21%

had intermittent diplopia. Eigh-

teen percent of patients with CI

are asymptomatic.’7 This ab-

sence of symptomatology may

be due to either suppression,”

avoidance of near visual tasks,’8

high pain threshold or monocular

occlusion.

Various authors have observed

a high percentage of neuroses

and anxiety reactions associated

with symptomatic CI. Mann, 9

and Nawratzki and Avrouskine20

have implicated the psychologi-

cal problem as the cause of the

CI since these patients manifest

symptoms more frequently than

the normal population. However,

these authors have not provided

any direct evidence that neuro-

ses and anxiety reactions cause

CI. Furthermore, it is reasonable

to suspect that sustained near

point discomfort might produce

nervousness, tenseness and anx-

iety. It is the authors’ experience

to see mild degrees of tension

and nervousness disappear after

successful treatment of CI. If CI

were a result of psychological im-

balance, then one would not ex-

pect to find a high success rate

with visual therapy alone. (See

treatment results.) Therefore, the

authors feel that the psychologi-

cal component may be a manifes-

tation of CI rather than a cause.

Findings

A.

Phoria

The near phoria measurement

is the amount of accommodative

and tonic convergence in use at a

given distance. The near phoria

also represents the amount of fu-

sional convergence demanded for

C M

single bmocular vision. Passmoré

and MacLean’ found that 79% of

their CI population demonstra-

ted exophoria at near, 18%

orthophoria, and 3% esophoria.

In another study, Cushman and

Burri21 found 63% of CIs exhibi-

ted an exophoria on a near cover

test. Though most patients with

CI demonstrate an exophoria, it

is neither needed nor necessarily

the cause of symptoms.

B.

Fusional Convergence

Fusional convergence or posi-

tive fusional reserve is the

amount of convergence available

to overcome temporal disparity

in order to obtain fusion. Various

authors9, 13, 22 have reported low

positive fusional reserves in CI.

Mould15 and Passmore & Ma-

cLean consider 8-10 pd. low,

Mayou” reports 10-20 p.d. to be

low; Hirsch17 defines low as 12

p.d.; and Morn7 uses 15 p.d. Re-

duced positive fusional reserves

correlate highly with symptoma-

tology. It should be noted that

convergence findings vary with

stimula used, illumination. speed

of measurement and instruc-

tional set. These factors may ac

count for the differences re-

ported by various authors.

Another criterion for the as-

sessment of fusional ability is

the recovery point. This is de-

fined as the point at which fu-

sion, after being broken, is re-

established. Fusional recovery

consists of voluntary conver-

gence, and convergence in re-

sponse to temporal disparity.

Hirsch’7 reported that recoveries

will be low in CIs. Davies23 sta-

ted that if the adduction value is

high and the recovery is low,

treatment will be of shorter

duration than if the adduction

value itself is low.

The authors feel that the re-

covery point is probably a better

indication of fusional potential

over time since it represents the

patient’s ability to voluntarily

regain fusion on the basis of sen-

sory information.

C. Near Point of Convergence

(NPC)

A receded near point of conver-

gence has been described by

Duane’ as the most consistent

finding in CI. These findings

have been reported to beyond

13.1 cm17, 9.5 cm2, and 3 inches.

Davies24 recommended that the

NPC be performed 12 times to

evaluate ocular fatigue.” Accord-

ing to Davies, asymptomatic pa-

tients show only slight decre-

ments of the NPC over time

while patients presenting symp-

toms show a significant reces-

sion of the NPC over time. Capo-

bianco25 has noted that NPC will

recede in the presence of a red

lens over one eye. She thought

that the degradation was a re-

sult of loss of voluntary conver-

gence. However, this is incorrect

since voluntary convergence is

not stimulus bound. Further-

more, the red lens alters the fusi-

ble details by reducing the con-

trast of the target and by a!-

tering its color. Therefore, the re-

cession of the NPC is most likely

due to a loss in fusional conver-

gence.

It is common to see head re-

traction, sweating, facila grim-

aces, and wrinkling of the fore-

674 Journal of the American Optometric Association