Abstract
Purpose :
In a clinical setting, visual acuity (VA) testing is self-paced with no standardised time restriction. Studies have shown reducing optotype presentation duration results in reduced VA, but this has predominantly been investigated in normal vision and less is understood for those with visual impairment (VI). For VI, limiting duration of VA presentation may more accurately reflect their visual capacity and real-world tasks. This experimental study investigated the effect of time-restricted VA measurement in people with reduced vision.
Methods :
We evaluated time-restricted VA in two groups of participants aged 18-72 years: uncorrected myopes to simulate VI (n=20)(0.3-1.3logMAR,Group 1), and those with VI (n=8)(0.2-1.3logMAR,Group 2). A customised VA test was designed. Single optotypes with crowding bars were presented on a screen positioned at 4m under unrestricted, 2s, 1s and 0.5s time durations. Optotypes were initially presented three lines above threshold (determined using conventional VA chart). Five optotypes of same size were presented, and if three or more correct, optotype size was reduced by 0.1logMAR. Threshold determined when less than three letters were correctly guessed, and VA was scored by letter. Testing was repeated 3 times and averaged. Measurements were taken monocularly with preferred eye, and presentation order randomised.
Results :
Table 1 presents mean VA and difference between unrestricted and time-limited testing. Mean (+/-SD) difference in VA between unrestricted and 0.5s was Group 1=0.05LogMAR+/0.04 and Group 2=0.05LogMAR+/-0.05. VA was significantly reduced with shortest time duration (0.5s) for both groups compared to unrestricted (Group 1 t(19)=-5.20,p<0.00001: Group 2 t(7)=-2.64,p<0.034), but not for 2s durations (p>0.07). For 1s, results mixed. Comparing across groups, there was a similar degradation in VA measures with time-limited presentation (p>0.40).
Conclusions :
Reducing optotype presentation time results in reduced VA when time restricted to 0.5s. However, those with VI did not have a greater reduction in VA but were similarly affected by reduced presentation time. Although statistically significant, the modest VA reduction with time-limited optotype presentation demonstrates that VA measured under typical conditions is not an overestimate of vision achievable in real world conditions.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.