Marcus Gunn pupil

Revision as of 17:11, 9 August 2012 by WikiBot (talk | contribs) (Robot: Automated text replacement (-{{SIB}} + & -{{EH}} + & -{{EJ}} + & -{{Editor Help}} + & -{{Editor Join}} +))
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search
Marcus Gunn pupil
DiseasesDB 29599

WikiDoc Resources for Marcus Gunn pupil

Articles

Most recent articles on Marcus Gunn pupil

Most cited articles on Marcus Gunn pupil

Review articles on Marcus Gunn pupil

Articles on Marcus Gunn pupil in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Marcus Gunn pupil

Images of Marcus Gunn pupil

Photos of Marcus Gunn pupil

Podcasts & MP3s on Marcus Gunn pupil

Videos on Marcus Gunn pupil

Evidence Based Medicine

Cochrane Collaboration on Marcus Gunn pupil

Bandolier on Marcus Gunn pupil

TRIP on Marcus Gunn pupil

Clinical Trials

Ongoing Trials on Marcus Gunn pupil at Clinical Trials.gov

Trial results on Marcus Gunn pupil

Clinical Trials on Marcus Gunn pupil at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Marcus Gunn pupil

NICE Guidance on Marcus Gunn pupil

NHS PRODIGY Guidance

FDA on Marcus Gunn pupil

CDC on Marcus Gunn pupil

Books

Books on Marcus Gunn pupil

News

Marcus Gunn pupil in the news

Be alerted to news on Marcus Gunn pupil

News trends on Marcus Gunn pupil

Commentary

Blogs on Marcus Gunn pupil

Definitions

Definitions of Marcus Gunn pupil

Patient Resources / Community

Patient resources on Marcus Gunn pupil

Discussion groups on Marcus Gunn pupil

Patient Handouts on Marcus Gunn pupil

Directions to Hospitals Treating Marcus Gunn pupil

Risk calculators and risk factors for Marcus Gunn pupil

Healthcare Provider Resources

Symptoms of Marcus Gunn pupil

Causes & Risk Factors for Marcus Gunn pupil

Diagnostic studies for Marcus Gunn pupil

Treatment of Marcus Gunn pupil

Continuing Medical Education (CME)

CME Programs on Marcus Gunn pupil

International

Marcus Gunn pupil en Espanol

Marcus Gunn pupil en Francais

Business

Marcus Gunn pupil in the Marketplace

Patents on Marcus Gunn pupil

Experimental / Informatics

List of terms related to Marcus Gunn pupil


Overview

Marcus Gunn pupil describes the finding during the swinging-flashlight test whereupon the patient's pupils appear to dilate instead of constrict when the light swings from the unaffected "good" eye to the affected "bad" eye.

It is important to remember that there is no anisocoria in this case. The pupils remain the same size as each other at all times.

Upon shining the light into the "good" eye, both pupils will constrict. However, when the light moves to the "bad" eye, the full strength of the light will not be perceived and both pupils will appear to dilate.

The Marcus Gunn phenomenon is a relative afferent pupillary defect. That is to say, the "bad eye" can still perceive light and respond to it, but not as much as the "good eye"; the bad eye is relatively less responsive than the good eye, but both eyes are still responsive to light. If you shine the light in the bad eye, both pupils will constrict (due to the still-intact consensual light response). However, if you shine the light in the "good eye", the pupils will constrict even more. It is as if you are shining a light of lesser intensity at the bad eye.

In context of the swinging flashlight test, you first shine the light in the good eye, causing full pupillary contraction in both eyes. Then you move the light to the bad eye. The bad eye perceives this same light as if were not as bright, and thus causes the pupils to constrict less. This gives the illusion that both pupils are now dilating as a response to the light. They are actually still constricting in response to the light, but constricting less than when the light was shining at the good eye, because the bad eye perceives a dimmer light. But relative to the previous maximal dilation from shining the light at the good eye, the pupils now dilate. Had you started with the light shining on the bad eye first, you'd see both eyes constrict slightly. This distinguishes the Marcus Gunn Pupil from a total CN II lesion, in which the bad eye perceivs no light. In that case, shining the light at the bad eye produces no effect. In any case the patient themselves should report that they are totally blind in the unreactive eye.

Although the commonest lesion site is the optic nerve, severe retinal disease may also yield a Marcus Gunn pupil and this sign should be taken as indication of a "pre-chiasmatic" visual defect.

Eponym

It is named for Robert Marcus Gunn.[1]

See also

References

  • Bickley L. Bates' Guide to Physical Examination, 9ed. Lippincott Williams & Wilkins
  • Kanski J. Clinical Ophthalmology: A Systematic Approach, 5ed. Butterworth-Heinemann

External links

Template:WikiDoc Sources