Effect of prolonged dissociation on the subjective measurement of near heterophoria

Abstract

Previous studies have demonstrated that vergence adaptation resulting from the prolonged decay of slow fusional vergence may prevent the accurate assessment of oculomotor deviations. Continuing changes in heterophoria have been reported after 27 days of monocular occlusion. However, since most slow fusional vergence will decay within the first few minutes of dissociation, a clinical assessment of both vergence adaptation and heterophoria could be made more rapidly. This report documents two investigations which examined changes in near horizontal heterophoria during 30 min and 180 min of continuous dissociation, respectively. Seven out of the 16 subjects exhibited significant changes in heterophoria during the 30 min dissociation period, with a mean increase in exophoria of 3.4 delta. The decay of slow fusional vergence took approximately 25 min to reach completion. Thus in the clinical setting, both the degree of vergence adaptation and a more accurate assessment of heterophoria may be obtained by maintaining dissociation for 25 min. Furthermore, the presence of vergence adaptation can be assessed after just 5 min of dissociation.

Comparative Analysis of Strabismus Measurement Using a Video Oculagraphy System and Alternate Prism Cover Test

“…Both methods were conducted based on the maximum plus for the best visual acuity result for distance, and only primary position measurements were considered for comparison. Moreover, to minimize the potential impact of prisms on vergence adaptation, both procedures were performed randomly 53,54 . To eliminate any potential bias during the examination, 2 experienced examiners performed both techniques.…”

“…Moreover, to minimize the potential impact of prisms on vergence adaptation, both procedures were performed randomly. 53,54 To eliminate any potential bias during the examination, 2 experienced examiners performed both techniques. Neither examiner had knowledge of the other's results, and both examiners had extensive experience in measuring strabismus.…”

“…This was accomplished by alternating the occlusion of the eyes and observing the movement of the eyes when uncovered. [53][54][55][56][57][58] Measurements were taken while the participant was fixating on a single optotype from the 6/9-line visual acuity chart, positioned at a distance of 6 m, or the visual acuity of the worst eye for amblyopic subjects.…”