Demonstration of a relative afferent pupil defect (Marcus Gunn pupil) in the left eye, done with the patient fixating upon a distant target. A. With dim background lighting, the pupils are equal and relatively large. B. Shining a flashlight into the right eye evokes equal, strong constriction of both pupils. C. Swinging the flashlight over to the damaged left eye causes dilation of both pupils, although they remain smaller than in A. Swinging the flashlight back over to the healthy right eye would result in symmetric constriction back to the appearance shown in B. Note that the pupils always remain equal; the. | Chapter 029. Disorders of the Eye Part 3 Demonstration of a relative afferent pupil defect Marcus Gunn pupil in the left eye done with the patient fixating upon a distant target. A. With dim background lighting the pupils are equal and relatively large. B. Shining a flashlight into the right eye evokes equal strong constriction of both pupils. C. Swinging the flashlight over to the damaged left eye causes dilation of both pupils although they remain smaller than in A. Swinging the flashlight back over to the healthy right eye would result in symmetric constriction back to the appearance shown in B. Note that the pupils always remain equal the damage to the left retina optic nerve is revealed by weaker bilateral pupil constriction to a flashlight in the left eye compared with the right eye. From P Levatin Arch Ophthalmol 62 768 1959. Subtle inequality in pupil size up to mm is a fairly common finding in normal persons. The diagnosis of essential or physiologic anisocoria is secure as long as the relative pupil asymmetry remains constant as ambient lighting varies. Anisocoria that increases in dim light indicates a sympathetic paresis of the iris dilator muscle. The triad of miosis with ipsilateral ptosis and anhidrosis constitutes Horner s syndrome although anhidrosis is an inconstant feature. Brainstem stroke carotid dissection or neoplasm impinging upon the sympathetic chain are occasionally identified as the cause of Horner s syndrome but most cases are idiopathic. Anisocoria that increases in bright light suggests a parasympathetic palsy. The first concern is an oculomotor nerve paresis. This possibility is excluded if the eye movements are full and the patient has no ptosis or diplopia. Acute pupillary dilation mydriasis can occur from damage to the ciliary ganglion in the orbit. Common mechanisms are infection herpes zoster influenza trauma blunt penetrating surgical or ischemia diabetes temporal arteritis . After denervation of the iris sphincter the .
