Hutchinson’s pupil – Sequence of changes, mechanism

Hutchinson’s pupil is seen in case of cerebral compression.

There are 3 stages:

Pupil on side of injury Pupil on opposite side
Stage 1 Constricted Normal size
Stage 2 Dilated Constricted
Stage 3 Dilated, fixed Dilated, fixed
Mechanism: The parasympathetic fibers to the pupil are responsible for pupillary constriction. The fibers pass through the periphery of the oculomotor nerve, and hence are the first to be affected in case of compression of the nerve.
  1. In Stage 1, the parasympathetic fibers on the side of injury are irritated, leading to constriction of pupil on that side
  2. In stage 2, the parasympathetic fibers on the side of injury are paralysed, leading to dilatation of pupil. The fibers on the opposite oculomotor nerve are irritated, leading to constriction on the opposite side
  3. In stage 3, the parasympathetic fibers on both sides are paralysed – leading to bilateral pupillary dilatation. Pupils become fixed. This indicates grave prognosis.

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