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Central part of the retina. Composed uniquely of cone cells and enables precise vision.

Term usually used to indicate vision of less than 20/200. May require additional optical aids, especially for near point tasks.

A device that used to determine degree of red or green color vision deficit. A dial on the anomaloscope is adjusted until the viewer (patient) believes that the green-red balance is appropriate compared with a standard yellow light whose intensity can also be varied. When a person with normal color vision views the “match” made by a patient with abnormal color vision, a deficit in either red or green color vision is readily apparent.