Desktop publishing and validation of custom near visual acuity charts

Customized visual acuity (VA) assessment is an important part of basic and clinical vision research. Desktop computer based distance VA measurements have been utilized, and shown to be accurate and reliable, but computer based near VA measurements have not been attempted, mainly due to the limited spatial resolution of computer monitors. In this paper, we demonstrate how to use desktop publishing to create printed custom near VA charts.

We created a set of six near VA charts in a logarithmic progression, 20/20 through 20/63, with multiple lines of the same acuity level, different letter arrangements in each line and a random noise background. This design allowed repeated measures of subjective accommodative amplitude without the potential artifact of familiarity of the optotypes. The background maintained a constant and spatial frequency rich peripheral stimulus for accommodation across the six different acuity levels. The paper describes in detail how pixel-wise accurate black and white bitmaps of Sloan optotypes were used to create the printed custom VA charts.

At all acuity levels, the physical sizes of the printed custom optotypes deviated no more than 0.034 log units from that of the standard, satisfying the 0.05 log unit ISO criterion we used to demonstrate physical equivalence. Also, at all acuity levels, log unit differences in the mean target distance for which reliable recognition of letters first occurred for the printed custom optotypes compared to the standard were found to be below 0.05, satisfying the 0.05 log unit ISO criterion we used to demonstrate functional equivalence.

It is possible to use desktop publishing to create custom near VA charts that are physically and functionally equivalent to standard VA charts produced by a commercial printing process.