A Method for Quantifying Off Chart Visual Acuities

"Retrospective chart reviews can provide data to test and generate hypotheses, however, they are limited to the data collected, which in some instances is not sufficiently quantitative. Visual acuity for instance would ideally be collected by ETDRS methods for prospective clinical trials. This is often not the case with retrospective studies, where off chart visual acuities (typically <20/400) are recorded as count fingers (CF) at a set distance, hand motion or light perception. The purpose of this study was to determine by geometric optics the Snellen equivalent visual acuities for count fingers at different distances."