Visual acuity is a measure of form sense and the ability to resolve fine detail. It is defined as the reciprocal of the minimum visual angle that can be resolved, measured in minutes of arc. Visual acuity depends on factors like the size and distance of an object, as well as characteristics of the observer such as accommodation and the optical elements of the eye. There are several methods used to measure visual acuity clinically, including assessing unaided acuity, habitual acuity, and optimal acuity under standardized testing conditions of illumination, testing distance, and letter size. Visual acuity test results can be recorded using decimal notation, percentage acuity, or the traditional Snellen fraction.