Marcus Gunn pupil is due to ?
Ans. is 'b' i.e., Relative afferent papillary defect Marcus Gunn pupil Marcus Gunn pupil is seen in relative afferent pathway defect (RAPD) An incomplete optic nerve lesion or retinal disease cause it (in contrast to amaurotic light reflex, where there is total afferent pathway defect). It is best tested by swinging flash light test. To perform this test, a bright flash light is shone to one pupil and constriction of that pupil is noted. Then the flashlight is quickly moved to the contralateral pupil and the response in that pupil is noted. This swinging to and fro of the flashlight is repeated several times while the pupillary response is observed. Normally, both pupils constrict equally and the pupil to whom light is transferred remains tightly constricted. In the presence of relative afferent pupillary defect in one eye, both the pupil will dilate when the flash light is moved from the normal to the abnormal eye. This is a paradoxical resposne. This is called Marcus Gunn pupil and is the earliest indicator of optic nerve disease even in the presence of a normal visual acuity. Relative afferent papillary defect (RAPD) or Marcus Gunn pupil is a reliable and objectve sign of unilateral or assymmetric disease or any lesion in afferent papillary pathway, i.e., retina, optic nerve, optic chiasma, optic tract or midbrain (pretectal nucleus). However, RAPD is most characteristic of lesions in the optic nerve.
Total afferent pupillary defect
Relative afferent pupillary defect
Efferent pathway defect
Cerebral lesion