Visual acuity

A measure of the sharpness or clarity of vision, typically expressed as a Snellen fraction (e.g., 20/20, 20/200) or LogMAR value. A person with 20/200 vision must be 20 feet away to see what someone with normal vision sees at 200 feet. Visual acuity of 20/200 or worse in the better eye with best correction is the threshold for legal blindness in many jurisdictions. Low visual acuity affects the ability to read text, recognize faces, perceive fine details, and interact with small interface elements. For digital accessibility, visual acuity is a key factor in determining appropriate text sizes, touch target dimensions, contrast requirements, and magnification levels. It also influences gaze behavior — people with low visual acuity tend to make shorter eye movements and require more cognitive effort to process visual information.