develop CI usually do so as a result of a loss in accommodative convergence and may be successfully treated with vision training.² Induced BO prism effect as a result of bifocal lenses, may be another cause of CI in presbyopes. This is especially true in aphakics wearing high plus prescriptions.

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 gynecological, obstetric and/or menstrual 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 include: frontal headaches^;8 eye aches, pulling sensations, heavy eyelids,^6,8,11 sleepiness, diplopia^;2,6,8,13,16 loss of concentration,4 blurred vision,^2,813,16 tearing,’4 and dull orbital pain. Less common complaints include nausea, motion sickness, dizziness;” panoramic headaches;”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, burning and/or tearing of the eyes. In another study, Kent and Steeve6 found that 60% of their population of CIs had headaches, 49% experienced blurring of print, 34% had ocular fatigue, and 21% had intermittent diplopia. Eighteen percent of patients with CI are asymptomatic.’⁷ This absence 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 psychological 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 neuroses and anxiety reactions cause CI. Furthermore, it is reasonable to suspect that sustained near point discomfort might produce nervousness, tenseness and anxiety. 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 imbalance, then one would not expect to find a high success rate with visual therapy alone. (See treatment results.) Therefore, the authors feel that the psychological component may be a manifestation of CI rather than a cause.

Findings

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 fusional convergence demanded for

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single bmocular vision. Passmoré and MacLean’ found that 79% of their CI population demonstrated exophoria at near, 18% orthophoria, and 3% esophoria. In another study, Cushman and Burri21 found 63% of CIs exhibited 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.

Fusional convergence or positive fusional reserve is the amount of convergence available to overcome temporal disparity in order to obtain fusion. Various authors^{9, 13, 22} have reported low positive fusional reserves in CI. Mould¹⁵ and Passmore & MacLean consider ^8-10 pd. low, Mayou” reports 10-20 p.d. to be low; Hirsch¹⁷ defines low as 12 p.d.; and Mould⁷ uses 15 p.d. Reduced positive fusional reserves correlate highly with symptomatology. It should be noted that convergence findings vary with

stimula used, illumination. speed of measurement and instructional set. These factors may ac count for the differences reported by various authors.

Another criterion for the assessment of fusional ability is the recovery point. This is defined as the point at which fusion, after being broken, is reestablished. Fusional recovery consists of voluntary convergence, and convergence in response to temporal disparity. Hirsch^’7 reported that recoveries will be low in CIs. Davies²³ stated 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 recovery 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 sensory information.

C. Near Point of Convergence (NPC)

A receded near point of convergence has been described by Duane’ as the most consistent finding in CI. These findings have been reported to beyond 13.1 cm17, 9.5 cm^2, and 3 inches. Davies²⁴ recommended that the NPC be performed 12 times to evaluate ocular fatigue.” According to Davies, asymptomatic patients show only slight decrements of the NPC over time while patients presenting symptoms show a significant recession of the NPC over time. Capobianco²⁵ has noted that NPC will recede in the presence of a red lens over one eye. She thought that the degradation was a result of loss of voluntary convergence. However, this is incorrect since voluntary convergence is not stimulus bound. Furthermore, the red lens alters the fusible details by reducing the contrast of the target and by a!tering its color. Therefore, the recession of the NPC is most likely due to a loss in fusional convergence.

It is common to see head retraction, sweating, facila grimaces, and wrinkling of the fore

674 Journal of the American Optometric Association