Marcus Gunn pupil
Marcus Gunn pupil Classification and external resources
The left optic nerve and the optic tracts. A Marcus Gunn pupil indicates an afferent defect, usually at the level of the retina or optic nerve. Moving a bright light from the unaffected eye to the affected eye would cause both eyes to dilate, because the ability to perceive the bright light is diminished.
Marcus Gunn pupil (relative afferent pupillary defect) is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less (therefore appearing to dilate) when a bright light is swung from the unaffected eye to the affected eye. The affected eye still senses the light and produces pupillary sphincter constriction to some degree, albeit reduced.
The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye.
In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at. This indicates an intact direct and consensual pupillary light reflex. When the test is performed in an eye with an afferent pupillary defect, light directed in the affected eye will cause only mild constriction of both pupils (due to decreased response to light from the afferent defect), while light in the unaffected eye will cause a normal constriction of both pupils (due to an intact afferent path, and an intact consensual pupillary reflex). Thus, light shone in the affected eye will produce less pupillary constriction than light shone in the unaffected eye.
A Marcus Gunn Pupil is distinguished from a total CN II lesion, in which the affected eye perceives no light. In that case, shining the light in the affected eye produces no effect.
Anisocoria is absent. A Marcus Gunn pupil is seen, among other conditions, in optic neuritis. It is also common in retrobulbar optic neuritis due to multiple sclerosis but only for 3-4 weeks, until the visual acuity begins to improve in 1–2weeks and may return to normal. 
LensRetinaRetinitis (Chorioretinitis, Cytomegalovirus retinitis) · Retinal detachment · Retinoschisis · Ocular ischemic syndrome/Central retinal vein occlusion · Retinopathy (Bietti's crystalline dystrophy, Coats disease, Diabetic retinopathy, Hypertensive retinopathy, Retinopathy of prematurity) · Macular degeneration · Retinitis pigmentosa · Retinal haemorrhage · Central serous retinopathy · Macular edema · Epiretinal membrane · Macular pucker · Vitelliform macular dystrophy · Leber's congenital amaurosis · Birdshot chorioretinopathyOther
- ^ "utah.edu". http://umed.med.utah.edu/neuronet/lectures/2002/Basics%20in%20Neuro-Ophthalmology.htm. Retrieved 2009-05-27.
- ^ doctor/2687 at Who Named It?
- ^ Pearce J (November 1996). "The Marcus Gunn pupil". J. Neurol. Neurosurg. Psychiatr. 61 (5): 520. doi:10.1136/jnnp.61.5.520. PMC 1074053. PMID 8937350. http://jnnp.bmj.com/cgi/pmidlookup?view=long&pmid=8937350.
- ^ Mumenthaler Neurology 4ed, Thieme 2004, page 486 Demyelinating diseases
accommodationOther binocularVisual disturbances
and blindnessAmblyopia · Leber's congenital amaurosis · Subjective (Asthenopia, Hemeralopia, Photophobia, Scintillating scotoma) · Diplopia · Scotoma · Anopsia (Binasal hemianopsia, Bitemporal hemianopsia, Homonymous hemianopsia, Quadrantanopia) · Color blindness (Achromatopsia, Dichromacy, Monochromacy) · Nyctalopia (Oguchi disease) · Blindness/Low visionOther
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Marcus Gunn pupil — the defect of pupillary movement seen in the Marcus Gunn pupillary phenomenon … Medical dictionary
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