Correct! The video shows you a right (relative) afferent pupil defect. The most likely location for the lesion is the RIGHT optic nerve. Of course, the lesion could also be in BOTH optic nerves, so long as the lesion in the RIGHT optic nerve is more damaging than the lesion in the LEFT optic nerve (this test compares afferent visual input in the two optic nerves). Finally, the lesion could also be in the contralateral OPTIC TRACT because the retinal ganglion cell axons that cross in the optic chiasm outnumber those that do not cross. In that case, you would expect to find a homonymous hemianopia on the side of the afferent pupil defect. The lesion could NOT be in the optic radiations, which lie posterior to the pupillary reflex arc and hence do not affect pupil constriction to light. The lesion could also be in the retina (not one of your choices), but only if it severely damages the macular region or causes a widespread retinal detachment. Other outer retinopathies, even if extensive, rarely cause an afferent pupil defect. Does a vitreous hemorrhage cause an afferent pupil defect? Only if extremely dense. Does a cataract cause such a pupil defect? No. In fact, if you find an afferent pupil defect in the eye with a cataract, look for a neural cause. By the way, a dense cataract will rarely cause an afferent pupil defect in the unaffected eye. Why? Think about it.