This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuro-Ophthalmology, Subject name: Ophthalmology
Neutral density filter - 
Select and explain. 
A. Amblyopia, B. Malingering, C. Afferent pupillary defect, D. Efferent pupillary defect
C: Afferent pupillary defect
Answer: C: Afferent pupillary defect 
Explanation: Ans. (c) Afferent pupillary defectRef: Essentials of ophthalmology p. 53"Neutral density filters can be used to grade the severity of afferent pupillary defect"--Essentials of ophthalmology