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visual acuity Sharpness of vision: the ability of the eye to distinguish between objects that lie close together. This hinges on the ability of the eye to focus incoming light to form a sharp image on the retina. Visual acuity depends on the cone cells, which are most densely packed in the fovea, close to the centre of the retina, and are therefore in the optimum position to receive focused light. In addition, each cone cell synapses with a single bipolar cell in the retina and is thus able to send a separate signal, via the optic nerve fibres, to the brain.
visual acuity (vizh-yoo-ăl) n. sharpness of vision. Acuity of distant vision is often expressed as a Snellen score (see Snellen chart).