anatomy of the pupillary reflexes
Last reviewed 01/2018
The size of the pupils depends on the balance of sympathetic and parasympathetic activity supplying the iris:
- sympathetic activity tends to dilate the pupil
- parasympathetic activity tends to constrict the pupil
The pathway of the pupillary light reflex consists of:
- retinal receptor cells
- bipolar cells
- ganglion cells
- optic nerve and tract
- pretectal nucleus of the high midbrain
- Edinger-Westphal nucleus
- efferent two neurone pathway via the oculomotor nerve
- constrictor muscle of the iris
It should be noted that the lateral geniculate nucleus of the thalamus and the cerebral cortex are not involved in the pupillary reflexes. Hence a patient who is cortically blind will have intact light reflexes.