# Relative afferent pupillary defect > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Relative_afferent_pupillary_defect > Markdown URL: https://mediated.wiki/source/Relative_afferent_pupillary_defect.md > Source: https://en.wikipedia.org/wiki/Relative_afferent_pupillary_defect > Source revision: 1335974359 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) When one eye's exposure to light creates a muted pupil response in both eyes For the jaw-winking syndrome, see [Marcus Gunn phenomenon](/source/Marcus_Gunn_phenomenon). Medical condition Relative afferent pupillary defect Other names Marcus Gunn pupil 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. Specialty Ophthalmology, Optometry A **relative afferent pupillary defect** (**RAPD**), also known as a **Marcus Gunn pupil** (after [Robert Marcus Gunn](/source/Robert_Marcus_Gunn)), is a [medical sign](/source/Medical_sign) observed during the [swinging-flashlight test](/source/Swinging-flashlight_test)[1] whereupon the patient's [pupils](/source/Pupils) excessively [dilate](/source/Mydriasis) 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. Depending on severity, different symptoms may appear during the swinging flash light test:[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Mild RAPD initially presents as a weak pupil constriction, after which dilation occurs.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] When RAPD is moderate, pupil size initially remains same, after which it dilates.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] When RAPD is severe, the pupil dilates quickly.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] ## Presentation This section is empty. You can help by adding to it. (October 2025) ## Cause Normally, the optic nerve is responsible for sensing light while the oculomotor nerve is responsible for contracting the pupil in response to this light. The most common cause of Marcus Gunn pupil is a [lesion](/source/Lesion) of the [optic nerve](/source/Optic_nerve) (between the retina and the [optic chiasm](/source/Optic_chiasm)) due to [glaucoma](/source/Glaucoma), a severe [retinal](/source/Retina) disease, or due to [multiple sclerosis](/source/Multiple_sclerosis). It is named after [Scottish](/source/Scottish_people) [ophthalmologist](/source/Ophthalmologist) [Robert Marcus Gunn](/source/Robert_Marcus_Gunn).[2] A second common cause of Marcus Gunn pupil is a contralateral [optic tract](/source/Optic_tract) lesion, due to the different contributions of the intact nasal and temporal hemifields.[3] ## Diagnosis The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye.[3] In the [swinging flashlight test](/source/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](/source/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 efferent 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.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] [Anisocoria](/source/Anisocoria) is absent. A Marcus Gunn pupil is seen, among other conditions, in unilateral [optic neuritis](/source/Optic_neuritis).[4] It is also common in retrobulbar optic neuritis due to [multiple sclerosis](/source/Multiple_sclerosis) but unreliable in bilateral optic neuritis.[4][5] A total [optic nerve (CN II)](/source/CN_II) lesion, in which the affected eye perceives *no* light, is very similar to a Marcus Gunn pupil; to distinguish them, in a complete optic nerve lesion shining the light in the affected eye produces zero dilation nor constriction.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] ## See also - [Argyll Robertson pupil](/source/Argyll_Robertson_pupil) - [Adie syndrome](/source/Adie_syndrome) - [Cycloplegia](/source/Cycloplegia) - [Miosis](/source/Miosis) - [Parinaud's syndrome](/source/Parinaud's_syndrome) - [Syphilis](/source/Syphilis) ## References 1. **[^](#cite_ref-1)** ["Pupillary Responses"](http://stanfordmedicine25.stanford.edu/the25/pupillary.html). *Stanford University School of Medicine*. Retrieved 2015-11-04. 1. **[^](#cite_ref-2)** *[doctor/2687](http://www.whonamedit.com/doctor.cfm/2687.html)* at [Whonamedit?](/source/Whonamedit%3F) 1. ^ [***a***](#cite_ref-pmid8937350_3-0) [***b***](#cite_ref-pmid8937350_3-1) Pearce J (November 1996). ["The Marcus Gunn pupil"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1074053). *J. Neurol. Neurosurg. Psychiatry*. **61** (5): 520. [doi](/source/Doi_(identifier)):[10.1136/jnnp.61.5.520](https://doi.org/10.1136%2Fjnnp.61.5.520). [PMC](/source/PMC_(identifier)) [1074053](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1074053). [PMID](/source/PMID_(identifier)) [8937350](https://pubmed.ncbi.nlm.nih.gov/8937350). 1. ^ [***a***](#cite_ref-:0_4-0) [***b***](#cite_ref-:0_4-1) Petzold, Axel; Fraser, Clare L; Abegg, Mathias; Alroughani, Raed; Alshowaeir, Daniah; Alvarenga, Regina; Andris, Cécile; Asgari, Nasrin; Barnett, Yael; Battistella, Roberto; Behbehani, Raed; Berger, Thomas; Bikbov, Mukharram M; Biotti, Damien; Biousse, Valerie (2022). ["Diagnosis and classification of optic neuritis"](https://discovery.ucl.ac.uk/10156457/3/Petzold_on-v7-R3c.pdf) (PDF). *The Lancet Neurology*. **21** (12): 1120–1134. [doi](/source/Doi_(identifier)):[10.1016/s1474-4422(22)00200-9](https://doi.org/10.1016%2Fs1474-4422%2822%2900200-9). [hdl](/source/Hdl_(identifier)):[2078.1/276419](https://hdl.handle.net/2078.1%2F276419). [ISSN](/source/ISSN_(identifier)) [1474-4422](https://search.worldcat.org/issn/1474-4422). [PMID](/source/PMID_(identifier)) [36179757](https://pubmed.ncbi.nlm.nih.gov/36179757). [S2CID](/source/S2CID_(identifier)) [252564095](https://api.semanticscholar.org/CorpusID:252564095).[*[permanent dead link](https://en.wikipedia.org/wiki/Wikipedia:Link_rot)*] 1. **[^](#cite_ref-5)** Mumenthaler Neurology 4ed, Thieme 2004, page 486 Demyelinating diseases ## External links Classification D DiseasesDB: 29599 v t e Diseases of the human eye Adnexa Eyelid Inflammation Stye Chalazion Blepharitis Meibomian gland dysfunction Entropion Ectropion Lagophthalmos Blepharochalasis Ptosis Blepharophimosis Xanthelasma Ankyloblepharon Eyelash Trichiasis Madarosis Distichiasis Trichomegaly Lacrimal apparatus Dacryoadenitis Epiphora Dacryocystitis Xerophthalmia Orbit Exophthalmos Enophthalmos Orbital cellulitis Orbital lymphoma Periorbital cellulitis Conjunctiva Chemosis Conjunctivitis allergic Pterygium Pseudopterygium Pinguecula Subconjunctival hemorrhage Globe Fibrous tunic Sclera Scleritis Episcleritis Cornea Keratitis herpetic acanthamoebic fungal Exposure Photokeratitis Corneal ulcer Thygeson's superficial punctate keratopathy Corneal dystrophy Fuchs' Meesmann Corneal ectasia Keratoconus Pellucid marginal degeneration Keratoglobus Terrien's marginal degeneration Post-LASIK ectasia Keratoconjunctivitis sicca Corneal opacity Corneal neovascularization Kayser–Fleischer ring Haab's striae Arcus senilis Band keratopathy Vascular tunic Iris Ciliary body Uveitis Intermediate uveitis Hyphema Rubeosis iridis Persistent pupillary membrane Iridodialysis Synechia Choroid Choroideremia Choroiditis Chorioretinitis Focal choroidal excavation Polypoidal choroidal vasculopathy Lens Cataract Congenital cataract Childhood cataract Aphakia Ectopia lentis Retina Retinitis Chorioretinitis Cytomegalovirus retinitis Retinal detachment Posterior vitreous detachment Retinoschisis Ocular ischemic syndrome / Central retinal vein occlusion Central retinal artery occlusion Branch retinal artery occlusion Retinopathy diabetic hypertensive Purtscher's of prematurity Bietti's crystalline dystrophy Coats' disease Sickle cell photic Macular degeneration Retinitis pigmentosa Retinal haemorrhage Central serous retinopathy Macular edema Epiretinal membrane (Macular pucker) Vitelliform macular dystrophy Leber's congenital amaurosis Birdshot chorioretinopathy Other Glaucoma / Ocular hypertension / Primary juvenile glaucoma Floater Leber's hereditary optic neuropathy Ocular hypotony Red eye Globe rupture Keratomycosis Phthisis bulbi Persistent fetal vasculature Persistent tunica vasculosa lentis Familial exudative vitreoretinopathy Vogt-Koyanagi-Harada disease Pathways Optic nerve Optic disc Optic neuritis optic papillitis Papilledema Foster Kennedy syndrome Optic atrophy Optic disc drusen Optic neuropathy Ischemic anterior (AION) posterior (PION) arteritic anterior (AAION or arteritic AION) non-arteritic anterior (NAION) Kjer's Leber's hereditary Toxic and nutritional Strabismus Extraocular muscles Binocular vision Accommodation Paralytic strabismus Ophthalmoparesis Chronic progressive external ophthalmoplegia Kearns–Sayre syndrome palsies Oculomotor (III) Fourth-nerve (IV) Sixth-nerve (VI) Other strabismus Esotropia / Exotropia Hypertropia Heterophoria Esophoria Exophoria Cyclotropia Brown's syndrome Duane syndrome Other binocular Conjugate gaze palsy Convergence insufficiency Internuclear ophthalmoplegia One and a half syndrome Refraction Refractive error Hyperopia Myopia Astigmatism Anisometropia / Aniseikonia Presbyopia Vision disorders Blindness Amblyopia Leber's congenital amaurosis Diplopia Scotoma Color blindness Achromatopsia Dichromacy Monochromacy Nyctalopia Oguchi disease Blindness / Vision loss / Visual impairment Anopsia Hemianopsia binasal bitemporal homonymous Quadrantanopia subjective Asthenopia Hemeralopia Photophobia Scintillating scotoma Pupil Anisocoria Argyll Robertson pupil Marcus Gunn pupil Adie syndrome Miosis Mydriasis Cycloplegia Parinaud's syndrome Other Nystagmus Childhood blindness Infections Trachoma Onchocerciasis --- Adapted from the Wikipedia article [Relative afferent pupillary defect](https://en.wikipedia.org/wiki/Relative_afferent_pupillary_defect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Relative_afferent_pupillary_defect?action=history)). 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