Visual function measurement using a laptop computer: does the screen angle matter?

Abstract

Aim: Computerised vision assessment on a laptop provides increased portability and flexibility. How­ever, when a laptop screen is tilted it can alter the visibility of information on the screen. This study evaluated the effect of changing the laptop screen angle on visual acuity (VA) and contrast sensitivity (CS) measurements and compared the results with those obtained using standard clinical tests. Methods: VA and CS were measured with the screen at five angles (80°-100°) in 5° intervals in a ran­domised order. The F.TDRS chart and Pelli-Robson chart were used as standard clinical tests. Results: VA laptop scores were not affected by tilting the screen and were comparable with the ETDRS scores. CS measurements were directly proportional to the screen angle with a mean increase of 0.11 logCS units for every 5° increase. The laptop CS measure­ment was closest to the Pelli-Robson result at an angle of 100°; but the laptop measurement was still on average 0.44 logCS units lower and analysis showed considerable variability between the two tests. Conclusions: The variability between the CS tests means that they are not interchangeable. VA measurements were not affected by the screen angle and produced measurements within normal limits compared with the standard clinical test.