An in-depth examination of recent studies on visual acuity and refractive error variability

Accurately measuring visual acuity (VA)—how clearly a person sees—and refractive error (RE), the focusing power of the eyes, is crucial in many areas. These measurements help guide clinical decisions, support research studies, inform screening programs, and are used for legal or administrative purposes, like getting a driver’s license or qualifying for military service. Because of their importance, these measurements are often treated as very precise and unchanging.

However, research shows that VA and RE measurements can vary quite a bit.

A better understanding of the variability of VA and RE is essential for enhancing clinical decision-making, developing guidelines and regulations, improving screening practices, and advancing research in the field of vision research. To better understand this variability, researchers closely associated with easee conducted a systematic review of 18 carefully selected studies in the field. Their findings were well-received in the scientific community.

The review found that both distance VA and RE measurements show a high degree of variability, often greater than the commonly accepted thresholds (±0.15 LogMAR for VA and ±0.5 diopters for RE). In many cases, the evidence supporting these thresholds was either weak or based on studies with significant limitations, leading to low confidence in their accuracy.

As a result, the authors suggest more rigorous studies are needed to establish reliable limits for how much VA and RE measurements can vary. In the meantime, they recommend using more flexible thresholds—±0.20 LogMAR for VA and ±0.70 diopters for RE—and emphasize that some variability in these measurements is normal and expected.