Abstract
Purpose::
We describe the use of Sweep Visual Evoked Potential recordings in assessment of the visual acuity in preverbal children. We validate the SVEP resolution acuity as it relates to optotype recognition acuity in these patients.
Methods::
Sweep Visual Evoked Potential (SVEP) recordings were used to follow visual acuity development in amblyopic children secondary to congenital cataract until children became literate. Children included consisted of 11 patients with dense unilateral congenital cataract that underwent lensectomy between 4days and 8 months of age (average 10 weeks), and 7 patients with partial unilateral cataract who were diagnosed between 8 weeks and 27 months of age (average 27 weeks) who were initially followed without surgical intervention. All patients were enrolled in SVEP testing protocol, and began testing upon presentation or within two months of cataract surgery. On average testing was performed every two months in the preliterate age range.
Results::
We found a significant correlation between final VEP acuity (average final 6months of testing) and final visual acuity on linear Snellen or HOTV testing optotypes. The average of the last 6 months of SVEP test results for each child was compared to the initial optotype test results for the treated eyes. This includes both the unilateral aphakic eyes and partial cataract eyes. The results of the SVEP and optotype acuity were converted to logmar vision and are shown in figure 1. Final VEP vs initial optotype acuity is plotted and linear regression of the results show a high correlation (R2=0.8701) for the data set, the slope of the linear regression shows that the SVEP resolution vision testing does tend to over estimate optotype recognition acuity. It also must be kept in mind that the test values of SVEP and Snellen acuity were not necessarily acquired at the same point in time. In general, once the child began to cooperate with subjective vision testing the SVEP testing was phased out, and therefore the optotype acuity occurred several months after the SVEP testing was discontinued in many of the patients.
Conclusions::
Present knowledge of the development of vision in the preliterate age is primarily based on Teller grating acuity studies. While this test is practical and provides a standard for visual assessment in preliterate children, its main limitation is that it relies on a psychophysical response. We have found that the SVEP cycles/degree values for visual acuity correlated more closely to actual optotype recognition acuity in our group of amblyopes. Final visual outcome by Snellen optotype recognition acuity correlated highly with SVEP resolution acuity.
Keywords: visual acuity • amblyopia • clinical research methodology