Synsskarphet

Synsskarphet, or visual acuity, is the clarity or sharpness of vision, reflecting the eye's ability to resolve fine details at a given distance. It is a basic functional measure of vision used in clinical assessments and is influenced by refractive status and ocular health.

In clinical practice it is typically expressed as a Snellen fraction, such as 20/20 (6/6 in metric). The numerator indicates the testing distance; the denominator indicates the distance at which a person with normal vision can resolve the same detail.

Assessment methods include Snellen charts, ETDRS charts, or LogMAR charts; testing can be monocular or binocular; standard distance is 6 meters or 20 feet. Alternative methods exist for infants and non-verbal individuals.

Significance: visual acuity is used to determine eligibility for driving, monitor disease progression, and guide prescriptions for corrective lenses. However, acuity alone does not capture all aspects of vision, and other measures such as contrast sensitivity can be informative.

Factors affecting acuity include refractive error, media opacities (like cataracts), ocular or retinal disease, neurological conditions, age, lighting, and fatigue. Common conditions affecting acuity include myopia, hyperopia, astigmatism, cataracts, and macular degeneration.

Improvement can be achieved with refractive correction, cataract extraction, or medical management of ocular disease. Historical notes: the Snellen chart popularized distance-based testing in the 19th century and remains widely used, though modern charts like logMAR provide finer gradations.