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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
Marcus Gunn phenomenon is an autosomal dominant condition with incomplete penetrance, in which nursing infants will have rhythmic upward jerking of their upper eyelid. This condition is characterized as a synkinesis : when two or more muscles that are independently innervated have either simultaneous or coordinated movements.
However, papillitis may be unilateral, whereas papilledema is almost always bilateral. Papillitis can be differentiated from papilledema by an afferent pupillary defect (Marcus Gunn pupil), by its greater effect in decreasing visual acuity and color vision, and by the presence of a central scotoma. Papilledema that is not yet chronic will not ...
When the optic nerve is damaged, the sensory (afferent) stimulus sent to the midbrain is reduced. The pupil, responding less vigorously, dilates from its prior constricted state when the light is moved away from the unaffected eye and towards the affected eye. This response is a relative afferent pupillary defect (or Marcus Gunn pupil). [1]
This test detects the afferent pupil defect, also referred to as the Marcus Gunn pupil. It is conducted in a semidarkened room. In a normal reaction to the swinging-flashlight test, both pupils constrict when one is exposed to light. As the light is being moved from one eye to another, both eyes begin to dilate, but constrict again when light ...
For example, in a person with abnormal left direct reflex and abnormal right consensual reflex (with normal left consensual and normal right direct reflexes), which would produce a left Marcus Gunn pupil, or what is called left afferent pupillary defect, by physical examination. Location of the lesion can be deduced as follows:
Robert Marcus Gunn (1850, Dunnet – 29 November 1909, Hindhead) was a Scottish ophthalmologist remembered for Gunn's sign and the Marcus Gunn pupil. Early life and education [ edit ]
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