When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be presumed to be the one on the side of the ptosis. Some patients have unequal pupils normally (anisocoria) pupils that react. Alternatively, if the abnormal pupil is the larger one, it will fail to contract in response to light, raising suspicion for a parasympathetic nerve defect, possibly an oculomotor nerve palsy.Ī relative afferent pupillary defect or RAPD also known as a Marcus Gunn pupil does not cause anisocoria. Look at the size, shape, symmetry and reactivity of the pupils.If the smaller of the two pupils is the abnormal one, dimming the ambient light will not cause it to dilate, in which case a defect in sympathetic fibers is suspected, as seen in Horner's syndrome.However, if the difference in the diameter exceeds 1 mm, it may be termed anisocoria (unequal pupil size). Ideally, no two pupils can be of the same length or diameter. It allows light to the cornea and adjusts its size according to the amount of light. Some examples of drugs which may affect the pupils include pilocarpine, cocaine, tropicamide and scopolamine.Īdditionally, dilation of the pupil is termed mydriasis and constriction of the pupil is termed miosis.Ĭomplete Differential Diagnosis of AnisocoriaĬlinically, it is important to establish which of the two pupils is behaving abnormally. The pupil is the black-colored opening in the center of the eye. Physical lesions and drugs causing anisocoria will do so via disruption of these pathways. In the absence of any deformities of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve (parasympathetic fibers) or the sympathetic pathways. This form is termed "simple anisocoria." When pathological, it may be seen in a variety of nervous system pathologies such as Wernicke-Korsakoff syndrome. If you experience the sudden onset of unequal pupil size, seek immediate medical attention. Anisocoria to a mild degree (generally 0.3 to 0.5 mm) can be found in about 20% of people. Our doctors define difficult medical language in easy-to-understand explanations of over 19,000 medical terms. 2 Complete Differential Diagnosis of Anisocoria.
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