What is visual acuity? What are its limitations?
Visual acuity describes the acuteness or “sharpness” of vision; that is the ability to perceive small details. The primary measurement tool is the letter chart introduced in 1862 by Donders and Snellen at the Eye Infirmary at Utrecht in the Netherlands. Visual acuity measurement is so common that visual acuity measurement is often mistaken as a unique indicator for vision in general. This is a misconception. Visual acuity loss can detect many disorders, but not all. A primary example is glaucoma, which can do extensive and irreversible visual field damage before visual acuity is affected. Letter chart acuity tells us something about the very small retinal area onto which the letter seen is projected. When the image of that letter is blurred due to optical factors (opacities, refractive error) the surrounding image will be equally blurred. But when visual acuity loss is due to retinal factors, letter chart acuity tells us nothing about how the surrounding retina functions. Visual acuity
