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.

Measuring the heterophoria: Agreement between two methods in non-presbyopic and presbyopic patients

“…Once evaluated the cover–uncover test to rule out the existence of strabismus at distance or near vision, the alternate cover test (ACT) protocol was then performed to evaluate the heterophoria status, alternately occluding eyes and observing eye movement when uncovered, 3 , 7 , 19 , 28 , 29 , 30 while using a trial frame. We employed a minimum occlusion time of 5 s to minimize the effect of vergence adaptation.…”

Synchronization of a Removable Optical Element with an Eye Tracker: Test Case for Heterophoria Measurement

“…Duration of dissociation has been reported to affect subjective heterophoria measurements in nearly seven of 16 participants, whose heterophoria was more than 3 PD more exophoric with prolonged dissociation. 16 Barnard 36 reported clinically insignificant heterophoria measurements for two-second versus ten-second cover durations, although the heterophoria measurement for longer cover durations tended to be higher values. Similarly, also the current study did not find statistical or clinical differences between the three seconds’ and ten seconds’ cover duration heterophoria measurements and found higher heterophoria values for the longer cover durations.…”