Reliable measurement of reduced visual acuity
Purpose It is essential to make reproducible visual acuity (VA) measurements even in patients with reduced VA. Our mobile vision screening software, EuvisionTab© has not been tested in the low VA ranges yet. Lower VA can be mimicked by using different occluders. The goal of the present study was to test the reliability of the system in wide VA ranges. Methods Two healthy volunteers were included in our study. The Landolt-C optotype was presented in 16 random orientations on a 10.1-inch tablet. Monocular VA measurements were performed according to the current ISO standards with the best refractive correction from 5m viewing distance. Size of the optotypes were adjusted by an adaptive best-Pest algorithm. VA were also determined after the application of eight Bangerter occlusion foils of different strength (<0.1, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0). Each condition was repeated ten times. Results To test the reproducibility of the measurement the 10 data at a given condition were combined into pairs resulting 1620 test-retest differences. The standard deviation of the VA differences remained within 0.14 logMAR for any VA. A weak correlation (p<0.05, r2=0.157) was found between the standard deviations of the test-retest differences and VA values suggesting that in lower visual acuity range the method is even more reproducible.Conclusions Our results demonstrate that the EuvisionTab© system makes reliable measurements even in low VA ranges. Keywords: visual acuity, screening, software, development, Bangerter.