Use of The Visual System section of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition, requires knowledge and skills in ophthalmology and assessing impairment. Visual acuity usually is measured using symbols (letters, numbers, pictures, or other symbols) presented in a letter chart format. The Visual Acuity Scale (VAS) is a linear scale with fixed increments and provides a reasonable estimate of acuity-related visual abilities; the associated impairment rating is a reasonable estimate of acuity-related performance loss. This article shows how to perform visual acuity calculations and how to assess impairment of visual fields, including visual field test procedures and calculations. Additional factors can lead to a loss of functional vision and can limit the individual's ability to perform activities of daily living and include contrast sensitivity, glare sensitivity, color vision defects, and binocularity, stereopsis, suppression, and diplopia. If functional vision is affected and is not accounted for by visual acuity or visual field loss, the impairment rating of the visual system can be adjusted but should be limited to an increase of the impairment rating of the visual system by, at most, 15 points (ie, less severe than the total loss of one eye). The ability to rate visual impairment requires significant knowledge and education, and therefore a physician trained in ophthalmology should perform the visual examination and visual system impairment rating.