Page 1286 - Problem-Based Feline Medicine

62. The cat with abnormal pupil size,

shape or response

Michael E. Bernays

KEY SIGNS
● Slow or absent pupillary light reflex.
● Unequal pupil size or abnormal pupil shape.

MECHANISM
Abnormal pupil sizes or responses are usually due to processes which affect either the:
● Retina: inflammatory, degenerative or hypertensive retinopathies.
● Afferent or efferent nervous pathways involved in the pupillary light reflex or dilation of the
pupil, particularly cranial nerve II and autonomic nerves, i.e. neuropathies.
● Iris: inflammatory or occasionally degenerative diseases.

WHERE?
Pathways involved in the pupillary light reflex.
● Retina, optic nerve, optic chiasm, optic tracts, midbrain, oculomotor nucleus parasympathetic
preganglionic fibers, ciliary ganglion, parasympathetic fibers in long ciliary nerve, iris pupil-
lary sphincter muscle.
Pathways involved in sympathetic dilation of the pupil.
● Thalamus, cervical spinal cord long tracts, T1–T3 spinal nerves, sympathetic preganglionic
fibers, cranial cervical ganglion, sympathetic postganglionic fibers (middle ear**, orbit), iris dila-
tor muscle.

WHAT?
● The most common diseases causing abnormalities of pupil response include hypertensive
retinopathy and infectious diseases of the retina and central nervous system.

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