The evaluation of a web‐based tool for measuring the uncorrected visual acuity and refractive error in keratoconus eyes: a prospective open‐label method comparison study

Purpose To evaluate the outcome of a web‐based digital assessment of visual acuity and refractive error, compared to a manifest refraction assessment, in keratoconus patients with complex refractive errors. Material and methods Keratoconus patients, aged 18 to 40, with a refractive error between ‐6 and +4 diopters were eligible. Each participant subsequently underwent an uncorrected visual acuity and a refractive assessment. Refractive error was assessed with the web‐based tool (index test), an autorefractor, and a manifest refraction (reference test) by an optometrist. Corrected visual acuity was assessed with the web‐based and manifest refractive prescription. Non‐inferiority was defined as the 95% limits‐of‐agreement (95%LoA) of the differences in spherical equivalent between the index and reference test not exceeding +/‐ 0.5 diopters. Agreement was assessed by an intraclass correlation coefficient and Bland‐Altman analyses. Results A total of 100 eyes of 50 patients were examined. The overall mean difference of the uncorrected visual acuity measured ‐0.01 LogMAR (95%LoA:‐0.63–0.60). The variability decreased in the high uncorrected visual acuity subgroup (mean difference: 0.15 LogMAR, 95%LoA:‐0.25–0.55). The intraclass correlation coefficient of the three refractive assessments was 0.32. The overall mean difference in spherical equivalent between the index and reference test measured ‐0.58 diopters (95%LoA:‐4.49 – 3.33, P=0.008). The mean differences for myopic and hyperopic subjects were 0.09 diopters (P=0.675) and ‐2.06 diopters (P<0.001), respectively. Conclusions Our results show promising results in the ability of the web‐based tool to remotely assess visual acuity in keratoconus patients. The agreement is better in higher visual acuity ranges and could provide physicians with an objective measurement to enhance teleconsultations, especially relevant when access to health care is limited. The assessment of the refractive error using the web‐based tool was found to be inferior to the manifest refraction and deserves further training of the tools algorithm.