This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and refraction, Subject name: Ophthalmology
Shadow test is used in - 
Select and explain. 
A. Keratometry, B. Ophthalmoscopy, C. Gonioscopy, D. Retinoscopy
D: Retinoscopy
Answer: D: Retinoscopy 
Explanation: Retinoscopy also called skiascopy or shadow test is an objective method of finding out the error of refraction by the method of neutralization Principle Retinoscopy is based on the fact that when light is reflected from a mirror into the eye, the direction in which the light will travel across the pupil will depend upon the refractive state of the eye Reference : A K KHURANA OPHTALMOLOGY,Edition 4,Page-548