Evaluating the Pupil

Examination of the pupil is best performed in a dimly lit room.

Size and symmetry of pupils is assessed by asking the patient to fixate on a distant object, such as a letter on the Snellen chart. A dim light is then directed on to the face from below so that both pupils can be seen simultaneously in the diffuse illumination. Normally, the two pupils in any individual are of equal size, although slight differences in size might be observed in up to 20% of the population. Usually, physiological unequal pupils (anisocoria) remain unaltered by changing the background illumination.

In order to assess the pupil light reflex, a strong focal light is shone on the pupils, one after the other. The direct reaction and the consensual reaction (other pupil) are observed. If the afferent arc of the pupil pathway were normal, the direct and consensual reactions would be equal.

To assess the near response of the pupil, ask the patient to gaze at a distant object (e.g., Snellen chart), then at a near object (e.g., his own finger tip just in front of his nose). Observe the pupil as the patient changes gaze from distant to near fixation and vice versa. Generally, if the pupil light reflex is intact, the near reflex is normal.

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