Dong et al1 examine the discrepancybetween visual acuity scores obtained at different test distances. Their presentationand analysis of the data are clear, and the concerns raised in the articleare important to anyone measuring visual acuity at different distances inclinical trials or observational studies.
Dong and colleagues used data from 4 well-conducted studies and demonstratedthat visual acuity measured at a shorter distance is 3 to 8 letters poorerthan that measured at a longer distance. We offer an explanation for thisdiscrepancy and present a mathematical model that addresses concerns thatresearchers might have about current, widely used visual acuity protocols.
Bullimore MA, Zadnik K. Consistency Between Visual Acuity Scores Obtained at Different TestDistances. Arch Ophthalmol. 2004;122(11):1729-1731. doi:10.1001/archopht.122.11.1729