Assessment of Reading Function in Low Vision Using Traditional and Digital MNRead Charts

Nova Southeastern University, Davie, Florida, USA

Objective: This study was conducted to assess reading function in low vision patient using traditional printed and digital MNREad charts. Additionally, comparability of printed and digital MNRead charts was evaluated. Background: The use of traditional printed MNRead chart for assessment of reading function has been evaluated and validated in multiple studies for normally sighted and low vision patients. More studies are needed to validate the digital iPad version of MNRead chart. Methods: For this study, we used traditional and digital iPad-based MNRead charts to assess reading function in low vision patient using vision assistive device (VAD) for reading. We assessed and analyzed the comparability of plate-based traditional MNRead chart and digital version of MNRead chart for the evaluation of low vision patient’s reading performance. Four parameters of reading performance with and without vision assistive device were measured, including maximum reading speed, critical print size, reading acuity, and reading accessibility index. Results: We found that without VAD, maximum reading speed was higher for larger print size (logMAR 1.3 and 1.2) with conventional chart than with the digital chart, critical print size was about the same, and reading acuity was better with iPad MNREAD. The reason for the increased maximum reading speed with larger size print was that the minimum built-in magnification of VAD made large size print too large to fit into the device screen which caused the patient to take more time to view the text, thus, reducing maximum reading speed. On the other hand, better reading acuity on digital MNREAD could be attributed to higher contrast of iPad chart as compared to the conventional chart. We also found that critical print size measurement with and without VAD were about the same with both types of MNREAD charts which suggests both charts are equally reliable and valid for estimating critical print size. Additionally, our comparative analysis showed that reading acuity with the VAD was better when tested with conventional MNREAD chart (logMAR -0.2) than with the digital MNREAD version (logMAR 0.15). This discrepancy is explained by the resolution limitation and smallest available size on digital MNREAD chart. Specifically, the smallest available print size on conventional chart is-0.5 logMAR (20/6.3 Snellen equivalent) while it is -0.1 logMAR (20/16 Snellen equivalent) on the digital chart. Conclusion: Digital iPad-based MNRead chart is comparable to traditional MNRead chart for assessment of reading function in low vision patients using vision assistive devices. iPad resolution and screen size limitations account for differences in estimating reading acuity and maximum reading speed with the conventional and digital chart versions.