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Pupil assessment and abnormalities

Pupillary light reflex pathway

Relative afferent pupillary defect (RAPD)

Pupil Evaluation

The pupil’s function is to control the amount of light entering the eyes, providing the best visual function under varying degrees of light intensity. The normal diameter of a pupil is 3 to 4 mm under average lighting conditions. In dim lighting the pupil size is larger and in bright light it is smaller.

Pupils are usually larger in children and smaller in the elderly.

Twenty percent of fibers in the optic tract are for pupillary function.

Changes of the pupil in accomodation:

The pupil changes when focusing on near objects. With accommodative effort, a “near synkinesis” is evoked, including increased accommodation of the lens, convergence of the visual axes of the eyes and pupillary constriction or miosis.

How to accurately assess the pupils

Tonic pupil or Adie's pupil

Lesions of the sympathetic system cause a small pupil Horner's Syndrome Horner's Syndrome, consists of pupillary miosis which is more accentuated in darkness. Light and near reactions are intact. There is ipsilateral ptosis due to paresis of Muller's muscle (not the levator muscle of the eyelid) There is an pseudo enophthalmos because of the associated ptosis. Occasionally anhydrosis of the face will also be seen.

Pharmacologic testing, to confirm the diagnosis of a Horner's syndrome:

Parinaud syndrome: