Sharpness of central vision. Refractive errors, such as myopia, hypermetropia and astigmatism, are the most common causes of poor visual acuity. Poor visual acuity for near objects occurs in presbyopia.
sharpness of vision: the degree to which a person is able to distinguish and resolve fine detail. The essential requirements are a healthy retina and the ability of the eye to focus incoming light to form a sharp image on the retina. Acuity of distant vision is often expressed as a Snellen score (see Snellen chart) or a LogMAR score (see LogMAR chart); acuity of near vision as a Jaeger score (see Jaeger test types).
Stimulation of the retina of the EYE with light causes changes in the electrical activity of the cerebral cortex (see BRAIN). These changes can be measured from outside the skull and can give valuable information about the state of the visual pathway from the retinal ganglion cells to the occipital cortex. Not only can it determine that function is normal, it can also help to diagnose some causes of poor VISION.... visual evoked response
(visual reinforced audiometry, VRA) a behavioural test of hearing for children aged approximately 6 to 30 months in which the subject sits between two calibrated loudspeakers. A sound is generated from one loudspeaker. Children who turn towards the sound are rewarded by brief illumination of a toy adjacent to the loudspeaker. Older children can be tested with headphones, rather than using the loudspeakers, to enable each ear to be tested separately. The test can be adapted for use with older subjects who have learning disabilities.... visual reinforcement audiometry
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