Marcus Gunn pupil
Encyclopedia
Marcus Gunn pupil 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 most common cause of Marcus Gunn pupil is a lesion
of the optic nerve
(proximal to the optic chiasm
) or severe retina
l disease. It is named after Scottish
ophthalmologist Robert Marcus Gunn
.
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.
Medical sign
A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....
observed during the swinging-flashlight test
Swinging-flashlight test
The swinging-flashlight test is used to help a practitioner decide whether reduced vision is due to ocular disease.-Process:For an adequate test, vision must not be entirely lost. In dim room light, the examiner notes the size of the pupils...
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 most common cause of Marcus Gunn pupil is a lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
of the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
(proximal to the optic chiasm
Optic chiasm
The optic chiasm or optic chiasma is the part of the brain where the optic nerves partially cross...
) or severe retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
l disease. It is named after Scottish
Scottish people
The Scottish people , or Scots, are a nation and ethnic group native to Scotland. Historically they emerged from an amalgamation of the Picts and Gaels, incorporating neighbouring Britons to the south as well as invading Germanic peoples such as the Anglo-Saxons and the Norse.In modern use,...
ophthalmologist Robert Marcus Gunn
Robert Marcus Gunn
Robert Marcus Gunn was a Scottish ophthalmologist remembered for Gunn's sign and the Marcus Gunn pupil.- Biography :...
.
Examination
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
Anisocoria
-Causes:In the absence of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve or the sympathetic pathways...
is absent. A Marcus Gunn pupil is seen, among other conditions, in optic neuritis
Optic neuritis
Optic neuritis is the inflammation of the optic nerve that may cause a complete or partial loss of vision.-Causes:The optic nerve comprises axons that emerge from the retina of the eye and carry visual information to the primary visual nuclei, most of which is relayed to the occipital cortex of the...
. It is also common in retrobulbar optic neuritis due to multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
but only for 3-4 weeks, until the visual acuity begins to improve in 1–2weeks and may return to normal.
See also
- Adie syndromeAdie syndromeAdie syndrome, sometimes known as Holmes-Adie's syndrome or Adie's Tonic Pupil, is a neurological disorder characterized by a tonically dilated pupil. It is named after the British neurologist William John Adie...
- AnisocoriaAnisocoria-Causes:In the absence of the iris or eyeball proper, anisocoria is usually the result of a defect in efferent nervous pathways controlling the pupil traveling in the oculomotor nerve or the sympathetic pathways...
- CycloplegiaCycloplegiaCycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation.-Anatomy:The iris is the heavily pigmented colored part of the eye. It has a contractile diaphragm in front of the lens with a central opening called the pupil...
- MiosisMiosisMiosis is the constriction of the pupil of the eye to two millimeters or less...
- Parinaud's syndromeParinaud's syndromeParinaud's Syndrome, also known as dorsal midbrain syndrome is a group of abnormalities of eye movement and pupil dysfunction. It is caused by lesions of the upper brain stem and is named for Henri Parinaud , considered to be the father of French ophthalmology...
- SyphilisSyphilisSyphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...