Marcus Gunn pupil
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Marcus Gunn pupil, also known as a relativeafferent pupillary defect (RAPD), is a non-specific findingsign on physical examination that indicates partial optic nerve dysfunction. It is mainly due to unilateral optic neuropathy (e.g. optic neuritis), or rarely optic chiasm or optic tract lesions.
In response toThis sign is classically elicited on the swinging light input to the affected eye, both eyes do not constrict to a normal extent but the affected pupil shows less constriction than the unaffected pupiltest (or Marcus Gunn test). But ifIf light is shone into the normal eye both eyes constrict normally and equally. It isHowever, in response to light input to the affected eye, both pupils do not constrict to a normal extent, and may be seen to paradoxically dilate as the light moves quickly over it. This occurs because of a decrease in afferent input reaching the pretectal pathway responsible for the pupillary light response in the midbrain via a damaged optic nerve, but efferent fibres to the affected eye are delivered via cranial nerve III.
History and etymology
Robert Marcus Gunn (1850-1909), was a Scottish ophthalmologist 2.
-<p><strong>Marcus Gunn pupil</strong>, also known as <strong>afferent</strong><strong> pupillary defect</strong>, is a non-specific finding that indicates partial <a href="/articles/optic-nerve">optic nerve</a> dysfunction. It is mainly due to unilateral optic neuropathy, or rarely <a href="/articles/optic-chiasm">optic chiasm</a> or <a href="/articles/optic-tract">optic tract</a> lesions.</p><p>In response to light input to the affected eye, both eyes do not constrict to a normal extent but the affected pupil shows less constriction than the unaffected pupil. But if light is shone into the normal eye both eyes constrict normally and equally. It is because of a decrease in afferent input reaching the <a href="/articles/pretectal-pathway">pretectal pathway</a> responsible for the pupillary light response in the midbrain via a damaged optic nerve, but efferent fibres to the affected eye are delivered via <a href="/articles/oculomotor-nerve">cranial nerve III</a>. </p><h4>History and etymology</h4><p><strong>Robert Marcus Gunn </strong>(1850-1909), was a Scottish ophthalmologist <sup>2</sup>.</p>- +<p><strong>Marcus Gunn pupil</strong>, also known as a <strong>relative</strong> <strong>afferent</strong><strong> pupillary defect (RAPD)</strong>, is a non-specific sign on physical examination that indicates partial <a href="/articles/optic-nerve">optic nerve</a> dysfunction. It is mainly due to unilateral optic neuropathy (e.g. <a href="/articles/optic-neuritis">optic neuritis</a>), or rarely <a href="/articles/optic-chiasm">optic chiasm</a> or <a href="/articles/optic-tract">optic tract</a> lesions.</p><p>This sign is classically elicited on the swinging light test (or Marcus Gunn test). If light is shone into the normal eye both eyes constrict normally and equally. However, in response to light input to the affected eye, both pupils do not constrict to a normal extent, and may be seen to paradoxically dilate as the light moves quickly over it. This occurs because of a decrease in afferent input reaching the <a href="/articles/pretectal-pathway">pretectal pathway</a> responsible for the pupillary light response in the midbrain via a damaged optic nerve, but efferent fibres to the affected eye are delivered via <a href="/articles/oculomotor-nerve">cranial nerve III</a>. </p><h4>History and etymology</h4><p><strong>Robert Marcus Gunn </strong>(1850-1909), was a Scottish ophthalmologist <sup>2</sup>.</p>
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