Snellen-Lit: An Innovative Miniature Snellen Chart For Space Optimization

Abstract

Space constraint is a major challenge in ophthalmic practice where the standard distance of 6 meters may be unavailable in the triage or consulting room. The objective was to produce a miniature space-saving vision testing chart called Snellen-lit that is not inferior to the standard Snellen’s chart in terms of reliability, ergonomics and reproducibility. Literature search was conducted on the subject related to vision testing specifically using “Snellen’s acuity chart construction” as key words. Snellen-lit was constructed with CorelDRAW tool with data obtained from Pythagoras theorem and trigonometry calculations of tan theta (θ). Theta being 5 minutes of arc, and it is the visual angle subtended at eye’s nodal point. All calculated distances from standard Snellen’s chat were halved such that visual angle of 5 minutes of arc was applicable to Snellen-lit.
The result was that Snellen-lit can be used at 3 meters and still maintains the same vision annotation as standard Snellen’s chat read at 6 meters without compromising accuracy and reliability.

It is concluded that among the vision testing tools, Snellen’s chart remains the commonest in clinic and research settings. Any innovative idea that enhances its applicability without jeopardizing its accuracy, especially innovation that is cost-effective, is a useful addition to vision testing armamentarium. There is a need for real life comparison between standard Snellen’s chart read at 6 meters and Snellen-lit read at 3 meters in clinic setting for concordance or discordance.