This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
Distance of distant direct ophthalmoscopy: 
Select and explain. 
A. 25 cms, B. 50 cms, C. 75 cms, D. 100 cms
A: 25 cms
Answer: A: 25 cms 
Explanation: Distant Direct Ophthalmoscopy Distance at which DDO performed is 25cm done with direct ophthalmoscope. contains light source viewing window. Normally red glow seen Interpretations Red glow= healthy retina Grey glow = Retinal Detachment No glow = vitreous haemorrhage Black spot in centre = cataract or corneal opacity GOLD STANDARD FOR LOCATING SUBLUXATED LENS: DDO