An estimate of 100,000 ophthalmic appointments have been cancelled by a single hospital (Moorfields, London, UK) over a 3-month duration due to the COVID-19 pandemic. Innovative ways to support patients unable to attend a formal clinical setting, are extremely important collect the necessary data. In Moorfields hospital research has looked at a number of ways to conduct these assessments allowing the proposal of a home acuity test (HAT) which can be used to measure visual acuity by telephone for a wide range of ophthalmology outpatients with diverse ophthalmic conditions. The researchers found that “test-retest repeatability is relatively high, and agreement in the visual impairment category is good for this sample, supporting the use of printed charts in this context”.
The UK’s Royal College of Ophthalmologists have highlighted that “all face-to-face outpatient activity should be postponed unless patients are at high risk of rapid, significant harm if their appointment is delayed”. To support their patients, there have been several proposals to manage this process using a computer-based assessment for visual acuity (VA). However, VA requires careful calibration, distance, screen size, screen luminance and other factors. Previous studies have shown poor agreement between results of a smartphone or tablet evaluation, compared to a clinical setting. In addition, more than 1 in 8 patients in the UK do not use the internet, including almost 50% of those older 75 years. Further, many paper-based vision charts to be downloaded do not meet the international guidelines for progression of letter size, they do not have crowding bars, and have not been validated to date. To overcome some of these challenges, through an open-sourced tool, a home acuity test (HAT) has been developed. The home acuity test includes a silhouette of a credit card which is in the downloadable test or posted to ensure that the printed size of the image is correct and that no unexpected scaling has taken place. From 150 cm, the largest letters subtend 1.3 logMAR (3/60 or 20/400) and the smallest line measures 0.1 logMAR (6/7.5 or 20/25). According to the research group, there are a total of 58 quadrillion unique charts can be downloaded from https://homeacuitytest.org for home monitoring of vision.
The results of the study were based on 50 control participants (33 [66%] women; mean [SD] age, 36.0 [10.8] years) and 100 ophthalmology patients with a wide range of diseases (65 [65%] women; mean [SD] age, 55.3 [22.2] years). According to the data presented, control participants had a mean (SD) test-retest difference in the HAT line score was −0.012 (0.06) logMAR, with limits of agreement (LOA) between −0.13 and 0.10 logMAR. The mean (SD) difference in visual acuity compared with conventional vision charts was −0.14 (0.14) logMAR (range, −0.4 to 0.18 log MAR) (−7 letters) in controls, with LOA of −0.41 to 0.12 logMAR (−20 to 6 letters). For ophthalmology outpatients, the mean (SD) difference in visual acuity was −0.10 (0.17) logMAR (range, −0.5 to 0.3 logMAR) (1 line on a conventional logMAR sight chart), with the HAT indicating poorer visual acuity than the previous in-clinic test, and LOA of −0.44 to 0.23 logMAR (−22 to 12 letters). In addition, there was good agreement in the visual impairment category for ophthalmology outpatients (Cohen κ = 0.77 [95%CI, 0.74-0.81]) and control participants (Cohen κ = 0.88 [95%CI, 0.88-0.88]). Concluding their study, the researchers stated that “measuring vision at home is unlikely to ever be as accurate as in-clinic assessment by a trained clinician, but these findings show that the HAT can be used to measure vision by telephone for a wide range of ophthalmology outpatients with diverse conditions. Test-retest repeatability is relatively high and agreement in the visual impairment category is good for this sample, supporting the use of printed charts in this context.