Baseline Pupil Size
Resting pupil size is influenced by several factors, including ambient light, state of retinal adaptation, level of arousal, and patient age. The frequency and amplitude of both pupils oscillate rhythmically and in synchrony; this phenomenon is called hippus. Hippus is independent of variations in illumination or in fixation of the eyes. Pupils typically become smaller as a result of aging. Sleepiness results in loss of cortical inputs that inhibit the Edinger-Westphal nucleus, thus causing small pupils. Severely elevated intraocular pressure may result in enlargement of the pupil, possibly due to iris ischemia. Pupils are often dilated after generalized tonic-clonic seizures. Extremely small pupils suggest pontine hemorrhage, narcotic intoxication, or pilocarpine use. Extremely large pupils may be normal (especially in young patients) or may suggest parasympathetic pharmacologic blockade from use of topical or systemic drugs, use of stimulants, or a state of high anxiety.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.