Pupillary inequality of less than 0.5 mm (anisocoria) is visible in about 20% of normal people. If pupillary reactions are normal, anisocoria is considered benign.
Test the pupillary reactions to light. Ask the patient to look into the distance, and shine a bright light obliquely into each pupil in turn. (Both the distant gaze and the oblique lighting help to prevent a near reaction.) Look for:
■ The direct reaction (pupillary constriction in the same eye)
■ The consensual reaction (pupillary constriction in the opposite eye)
Always darken the room and use a bright light before deciding that a light reaction is absent.
If the reaction to light is impaired or questionable, test the near reaction in normal room light. Testing one eye at a time makes it easier to concentrate on pupillary responses, without the distraction of extraocular movement. Hold your finger or pencil about 10 cm from the patient's eye. Ask the patient to look alternately at it and into the distance directly behind it. Watch for pupillary constriction with near effort.
Extraocular Muscles. From about 2 feet directly in front of the patient, shine a light onto the patient's eyes and ask the patient to look at it. Inspect the reflections in the corneas. They should be visible slightly nasal to the center of the pupils.
Compare benign anisocoria with Horner's syndrome, oculomotor nerve paralysis, and tonic pupil. See Table 5-9, Pupillary Abnormalities (p. 181).
Testing the near reaction is helpful in diagnosing Argyll Robertson and tonic (Adie's) pupils (see p. 181).
Asymmetry of the corneal reflections indicates a deviation from normal ocular alignment. A temporal light reflection on one cornea, for example, indicates a nasal deviation of that eye. See Table 5-10, Deviations of the Eyes (p. 182).
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