Introduction: Visual acuity (VA) testing is a critical screening examination for the assessment of visual function. This study describes the development and validation of a smartphone-based VA test: the K-VA test.
Methods: A total of 171 patients with various ocular diseases were examined in our outpatient unit at Aristotle University of Thessaloniki, School of Medicine in Greece. Participants underwent VA examination using the standard Early Treatment Diabetic Retinopathy Study (ETDRS) charts and the K-VA smartphone-based test. The K-VA test was performed by participants themselves. The Bland-Altman method was employed to assess the agreement between the ETDRS charts and the new test for the examination of VA at 1 m and 40 cm. Test-retest reliability was also calculated. A questionnaire regarding the participants' feedback on the K-VA test was completed.
Results: No significant bias was observed between the gold standard ETDRS charts and the K-VA test measurements. The mean difference (95% limits of agreement, LoA) between the K-VA test at 1 m and the ETDRS chart at 4 m was -0.006 (95% LoA -0.129 to 0.117) logarithm of the minimal angle of resolution (logMAR). The agreement of the K-VA test at 40 cm with the near ETDRS chart was also high with a mean difference of -0.007 (95% LoA -0.105 to 0.090) logMAR. Test-retest reliability was found to be high with a mean difference of 0.003 (95% LoA -0.045 to 0.033) logMAR and 0.005 (95% LoA -0.065 to 0.076) logMAR for the K-VA test at 1 m and 40 cm, respectively. A total of 97 participants answered the questionnaire and 71 (73.2%) stated that the test was easy to very easy to use for self-performance.
Conclusions: The study demonstrated that the K-VA application performed well compared with the ETDRS charts and provides reliable and repeatable measurements of VA across a wide range of VA.
Keywords: ETDRS; Mobile applications; Smartphones; Telemedicine; Visual acuity; Visual impairment.
Visual acuity (VA) is the most significant measure of visual function and an accurate examination of VA is of high importance for clinicians. Traditionally, the Snellen and the Early Treatment Diabetic Retinopathy Study (ETDRS) acuity charts are the most commonly used VA tests. However, the examination requires physical presence, which is not always feasible for elderly, mobility-impaired, rural patients, or patients in quarantine due to coronavirus disease 2019 (COVID-19) pandemic. Currently, there are hundreds of vision-testing applications available, with only a few having been validated, especially against the standard ETDRS chart. This study describes the development and investigates the validity of a new smartphone application, the K-VA test, for VA testing in 171 participants with various ocular diseases. Participants performed the K-VA test themselves with the supervision of a healthcare provider. The K-VA test was shown to perform well when compared with the ETDRS charts. We also showed that the test is well accepted by patients familiar with the Android operating system. The test should be performed following the instructions of the attending physician. The K-VA application provides repeatable and reliable measurements of VA across a wide range of VA. This tool offers users a secure system for the tele-transmission of results to physicians for further consultation.
© 2023. The Author(s).