Dictionary of terms relating to
eyesight and vision

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Near Acuity

The eye's ability to distinguish an object's shape and details at a near distance such as 16 inches (40 cm).

Near Point of Convergence (NPC)

The closest point at which the two eyes can maintain a single united image.

Near Point of Convergence Test

Measures the patient's ability to point the eyes at an approaching object and to keep them fixed on the object as it reaches the patient's nose. Normal range is 0 to 4 inches away from the nose.

Near Point Streess

Weakness or easy fatigue of the eye due to strain of the ciliary muscle.
See also Asthenopia

Negative Relative Accommodation (NRA)

A measure of the maximum ability to relax accommodation while maintaining clear, single binocular vision.

Normal Retinal Correspondence (NRC)

The foveas of the two eyes are corresponding neural points in the visual cortex and binocular vision can occur.


Rhythmic oscillations or tremors of the eyes which occur independent of the normal eye movements. Generally nystagmus is not curable, but it is manageable. Treatments include prescription glasses or contact lenses, prisms, and vision therapy.