Effective Snellen Fraction as The Standard Visual Acuity Score: “One-to-All” Algorithm

Title Effective Snellen Fraction as The Standard Visual Acuity Score: “One-to-All” Algorithm
Author, Co-Author Naganathan Muthuramalingam, William Monaco
Topic Functional Vision/Pediatrics
Program Number
Ballroom A-B
Qassim University

Purpose: Eye care providers are transitioning from the use of traditional Snellen charts and purchasing expensive computerized charts to avoid confusion created by the interpretation of visual acuity (VA) results. However, current computerized and ETDRS charts do not eliminate the clinician’s propensity for any other connotation than Snellen notation. This study is designed to measure the reliability of an algorithm that takes into consideration flaws in the VA testing with Snellen or ETDRS charts.

Methods: Sixty participants with best-corrected visual acuity of 20/20 took part in the study. Cataract simulator goggles were used to consistently degrade distance VA to 20/80 in these normal participants. The VA of the right eye was tested in every participant. VA was tested using the Snellen and ETDRS chart. The testing was done twice within a 1-week interval. Participant responses were recorded by hand on a scoring sheet. Later those data were scored by traditional methods and with the algorithm.

Results: VA obtained with ETDRS chart by ETDRS scoring method was statistically significant (p<0.001) from the scores obtained by using algorithm. VA scores were not statistically significant (p=0.61) when the proposed algorithm was used to determine acuity with the traditional Snellen and ETDRS charts. When a one-week test, re-test, scoring interval was used, the VA scores obtained with algorithm, for Snellen and ETDRS chart was p=0.02 and p=0.80 with mean difference of 0.017, 95% CI (0.09, -0.13) and 0.0009, 95% CI (0.1, -0.1) respectively.

Conclusion: The proposed algorithm provides a simple means to effectively measure VA in Snellen and LogMAR connotation for Snellen charts as well as LogMAR charts. Based on the data of this study, we recommend that the focus for facilitating clinician’s use of LogMAR be shifted to help them understand and use LogMAR connotation by means of this simple translational tool.

Affiliation of Co-Authors Pennsylvania College of Optometry at Salus University