To the Editor.
—Visual acuity measurement is the most important single test used in ophthalmology. A large variety of visual acuity charts are available, differing in the language, choice of letters, or geometric shapes. With the development of the International Chart in 1909 and the multiple revisions by the International Council of Ophthalmology,1 the luminosity, contrast, distance, and surroundings have been set into what is known as the standard chart (Snellen's chart). Despite all these measures, visual acuity measurement may vary depending on the patient's variables (dry or tearing eyes, diurnal variation in some diabetic patients, previous state of dark adaptation, general alertness and cooperation, and previous memorization of the chart) and on the examiner's variables (patience, interpretation when a patient gives different answers to the same line, and scoring). We noticed a large variation between different examiners' recordings of visual acuity, during the same visit or on follow-up,
Mansour AM, Walsh JB. Measuring Visual Acuity. Arch Ophthalmol. 1985;103(9):1282. doi:10.1001/archopht.1985.01050090034018