Abstract
Purpose: :
To examine the relationship between myopia and visual acuity (VA) at a 5 and 10 foot test distance using both the Lea symbols and HOTV chart. Common barriers in pediatric vision screening include lack of space in the pediatrician's office and limited attention of the young patient. Reducing the test distance to 5 feet from 10 feet is thought to decrease space requirements and increase childrens’ attention. Theoretically, reducing the test distance by half increases accommodative demand of the task two-fold. Such an increase in accommodative demand may suggest an overestimation of VA in low uncorrected myopes. This study investigated the relationship between low amounts of myopic blur, test distance, and chart type in an adult cohort with optimum attention to the task. The goal was to determine if moving from 10 feet to 5 feet still enables reliable detection of VA in subjects with low amounts of myopia.
Methods: :
VA was measured in 10 visually normal adults at 5 foot and 10 foot test distances with both the Lea Symbols and HOTV chart. Test distance and chart type were presented in a randomized order. Four myopic conditions were simulated at each test distance with defocusing lenses of +0.75D, +1.50D, +2.00D, and +2.50D. The order of lens testing was from most to least blur. VA results were compared (2-way repeated measure ANOVA) for each blur level, chart type, and test distance.
Results: :
The amount of induced myopia affected VA under all test conditions. However, the only statistically significant pair-wise comparison between the 5 and 10 foot distance was with +0.75D induced myopia for the Lea chart. No statistically significant differences in VA as a function of distance were found in any of the other conditions. Chart type covariate analysis was performed to determine if there was an effect on VA for each condition. Overall, subjects read more letters on the HOTV chart than the Lea chart in each simulated condition.
Conclusions: :
Integrity of the screening was maintained under myopic defocus of +0.75 to +2.50D regardless of test distance or chart type. Chart type comparison showed HOTV gave consistently better VA with induced myopia, perhaps owing to spatially distinct optotypes over equally blurring Lea symbols. Further research needs to be conducted to determine if a 5 foot test distance would enhance attentiveness and VA testing in a pediatric population.
Keywords: visual acuity • screening for ambylopia and strabismus • myopia