This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ocular motility and squint, Subject name: Ophthalmology
Illuminated Frenzel glasses are used in detecting 
Select and explain. 
A. Nystagmus, B. Heterophoria, C. Esotropia, D. Astigmatism
A: Nystagmus
Answer: A: Nystagmus 
Explanation: (Refer: AK Khurana Comprehensive Ophthalmology, 6th edition, pg no. 358 - 362)Illuminated Frenzel glasses (+20 lenses) are useful for abolishing fixation and thus revealing peripheral vestibular nystagmus