physiology of the pupil Flashcards
What is the normal size of the pupil in bright light and darkness?
The size of the pupil is 3-4 mm in bright light and 4-8 mm in darkness
What is isocoria?
Isocoria refers to pupils of exactly the same size
What is anisocoria?
Anisocoria refers to pupils of different sizes. Physiological anisocoria is when the difference in pupillary sizes is ≤1 mm, and pathological anisocoria is when the difference is more than 1 mm and should be investigated
Which system innervates the pupillary constrictor (sphincter) muscle?
The parasympathetic nervous system innervates the pupillary constrictor (sphincter) muscle
Which system innervates the pupillary dilator muscle?
The sympathetic nervous system innervates the pupillary dilator muscle
What is the direct pupillary reflex?
The direct pupillary reflex is when the pupil in the eye constricts in response to light being shown to that eye
What is the consensual pupillary reflex?
The consensual pupillary reflex is when the pupil in the contralateral eye constricts simultaneously even though the light is not shining directly into that eye
Describe the afferent pathway for the light reflex.
The light reflex is initiated by retinal photoreceptors, transmitted along the optic nerve, undergoes hemidecussation at the optic chiasma, proceeds along the optic tract, synapses at the pretectal nucleus, and ends in both Edinger-Westphal nuclei
Describe the efferent pathway for the light reflex
Efferent fibers travel from the Edinger-Westphal nucleus through the oculomotor nerve (CN-III), synapse and relay at the ciliary ganglion, and postganglionic fibers travel through short ciliary nerves to reach the ciliary muscle and the sphincter pupillae in the iris, which is responsible for pupillary constriction
What diagnostic clues can the evaluation of the pupil provide?
The evaluation of the pupil can provide diagnostic clues to various ocular, neurological, medical, surgical, and pediatric diseases
