|Title||Contour interaction reduces visual acuity in children with cerebral visual impairment (CVI)|
|Author, Co-Author||Jasmine Junge, Deborah Orel-Bixler|
Authors: Jasmine Junge, OD and Deborah Orel-Bixler, PhD, OD, FAAO
Purpose: Cerebral visual impairment (CVI) resulting from an early insult to the brain, is the leading cause of vision loss in children in industrialized nations. Visual acuity measured with isolated optotypes or gratings underestimates the visual acuity reduction in persons with amblyopia or CVI. This retrospective study compared the visual acuity obtained with single symbols that had contour bars at 100% and 50% spacing in children with CVI.
Methods: Binocular visual acuity was measured in 36 children aged 7-12 with a diagnosis of CVI during a comprehensive eye examination. Threshold visual acuity was measured using a two-alternative forced choice task using the apple and house Lea optotypes with four flanking bars. The edge-to-edge (between the optotype and bar) spacings were 50% and 100% times the optotype width. The optotypes and flanker bars were both at 100% contrast level.
Results: A Bland-Altman analysis of the difference in visual acuity measures (100% and 50% spacing) versus their mean (in logMAR) was performed. Mean visual acuity ranged from -0.09 to 1.38 logMAR (20/15 to 20/475). Worse acuity with 50% spacing was found in all but one child, and six children showed no difference. For 29 children, the difference ranged from 0.04 to 0.78 logMAR with a trend for an increasing difference between the two acuity measures with worse average acuity.
Conclusions: This pilot study shows a negative effect of contour interaction on visual acuity in children with CVI. Educational materials for children with CVI should take into account the reduction in visibility of central letters or symbols when flanking bars or letters are present. The greater the reduction of visual acuity, the greater the reduction in acuity with increased crowding. For children with CVI, increasing the size of letters may need to be accompanied by an increase in spacing between letters.
|Affiliation of Co-Authors||University of California, Berkeley|