====== Marcus Gunn pupil ======

AKA (relative) [[afferent pupillary defect]] (APD or RAPD), AKA amaurotic pupil. Finding: [[consensual response]] to light is stronger than the direct (normal responses are equal). Contrary to some textbooks, the amaurotic pupil is not larger than the other
((Walsh FB, Hoyt WF. Clinical Neuro-Ophthalmology. Baltimore 1969)).

The presence of the consensual reflex is evidence of a preserved [[third cranial nerve]] (with parasympathetics) on the side of the impaired direct reflex. Best detected with the swinging flashlight test.

===== Etiologies =====

Lesion anterior to the chiasm ipsilateral to the side of the impaired direct reflex:

1. either in the retina (e.g. retinal detachment, retinal infarct e.g. from embolus)

2. oropticnerve,asmayoccurin:

a) optic or retrobulbar neuritis: commonly seen in MS, but may also occur after vaccinations or viral infections, and usually improves gradually

b) trauma to the optic nerve: indirect 

or direct c) compression by tumor anterior to the chiasm
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Relative Afferent Pupillary Defect (RAPD) is a condition in which [[pupil]]s respond differently to light stimuli shone in one [[eye]] at a time due to unilateral or asymmetrical disease of the [[retina]] or [[optic nerve]]. 

[[Swinging flashlight test]] or Marcus Gunn test is one of the most basic eye exams that neurologists, ophthalmologists, optometrists and primary care doctor perform when visiting most of their patients. The doctor asks her patient to look ahead then shines a penlight first toward one eye, then the other, alternating quickly to observe patient’s pupils’ response to the light. In case if both pupils do not show a similar response to the light stimuli, shone in one eye at a time, the patient will be diagnosed with RAPD or [[Marcus Gunn pupil]]s. The results of this simple yet very important test help doctors in early diagnosis of many important eye related diseases such as optic neuropathy and multiple sclerosis.