Marcus Gunn pupil is a feature of
OPTIC NEURITIS Signs: 1. Visual acuity is usually reduced markedly. 2. Colour vision is often severely impaired. 3. Pupil shows ill-sustained constriction to light. Marcus Gunn pupil which indicates relative afferent pupillary defect (RAPD) is a diagnostic sign. It is detected by the swinging flash light test. Swinging flash light test: It is performed when relative afferent pathway defect is suspected in one eye (unilateral optic nerve lesion with good vision). To perform this test, a bright flash light is shone on to one pupil and constriction is noted. Then the flash light is quickly moved to the contralateral pupil and response noted. This swinging to-and-fro of flash light is repeated several times while observing the pupillary response. Normally, both pupils constrict equally and the pupil to which light is transferred remains tightly constricted. In the presence of relative afferent pathway defect in one eye, the affected pupil will dilate when the flash light is moved from the normal eye to the abnormal eye. This response is called 'Marcus Gunn pupil' or a relative afferent pupillary defect (RAPD). It is the earliest indication of optic nerve disease even in the presence of normal visual acuity. Ref:- A K KHURANA; pg num:-294,474,475
Ciliary ganglion lesion
Lesion of Edinger-Westphal nucleus
Optic neuritis
Papilloedema
Neuro-ophthalmology