QS Study

Visual acuity is the degree to which the details and contours of objects are perceived. A visual acuity test is an eye exam that checks how well you see the details of a letter or symbol from a specific distance. VA is the most common clinical measurement of visual function.

Visual acuity is usually defined in terms of the minimum separable- e.g., the shortest distance by which two lines can be separated and still be perceived as two lines. Clinically visual acuity is often determined by the use of the familiar Snellen letters charts viewed at a distance of 20 ft (6m). The individual being tested reads aloud the smallest line distinguishable. It refers to your ability to discern the shapes and details of the things you see.

The result is expressed as a fraction. The numerator of the fraction is 20, the distance at which the subject reads the chart. Dominator is the greatest distance from the chart at which a normal individual can read the smallest line, the subject can read.

Fig: Visual Acuity

Normal visual acuity is 20/20. A subject with 20/15 VA has better than normal vision (Not farsightedness) and one with 20/100 VA has subnormal vision. If your visual acuity is not 20/20, you may need corrective eyeglasses, contact lenses, or surgery. It is reliant on optical and neural factors, i.e.,

(i) the sharpness of the retinal focus within the eye,

(ii) the health and functioning of the retina, and

(iii) the sensitivity of the interpretative faculty of the brain.