A 68-year-old woman presents to the resident clinic for decreased vision. Visual acuity is hand motion OD and 20/25 OS. On exam you see a mature, white cataract in her right eye (see below) and only a mild cataract in the left eye. As part of your exam, you perform a swinging flashlight test, and you detect a positive relative afferent pupillary defect (RAPD) in the right eye.
What should you conclude based on this test?
A. The patient has a neurological defect in the anterior visual pathway of the right eye
B. The patient has a neurological defect in the anterior visual pathway of the left eye
C. Removal of the cataract will resolve the RAPD
D. You cannot make a conclusion until the cataract is removed.
The correct answer is A.
Explanation:
The correct answer is A. In this case, you detect a positive RAPD in the same eye as a dense, white cataract. A relative afferent pupillary defect occurs when there is a defect in the afferent visual pathway (from the retina, to the optic nerve, through the optic tracts, to the lateral geniculate body of the thalamus) that leads to decreased pupillary constriction to the same light source relative to the fellow eye. The key fact to answer this question correctly is that pathologies such as a dense cataract or cornea pathology that are anterior to the retina are not known to cause an RAPD. Therefore, we could conclude here that the patient has a neurologic defect in the anterior visual pathway of the right eye (A), and removal of the cataract will not resolve the RAPD (Thus answer choice C is incorrect). A neurologic defect in the anterior pathway of the left eye would lead to a left-sided RAPD (B). Interestingly, some reports have suggested that a dense cataract may cause a CONTRALATERAL RAPD (in this case a RAPD of the left eye) because it increases scattering of light, increasing the neural signal that reaches the midbrain (A Unilateral Cataract Produces a Relative Afferent Pupillary Defect in the Contralateral Eye - ScienceDirect. Accessed November 15, 2025. https://www.sciencedirect.com/science/article/pii/S0161642090325848). Therefore, the test is still reliable, and if there were no neurologic pathology, we would expect either no RAPD or potentially a contralateral RAPD (in the eye WITHOUT the cataract).
Photo source: https://eyewiki.org/White_Cataract