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
Illuminated frenzel glasses are used in detecting- 
Select and explain. 
A. Nystagmus, B. Heterophoria, C. Esotropia, D. Astigmatism
A: Nystagmus
Answer: A: Nystagmus 
Explanation: Frenzel goggles are a diagnostic tool used in ophthalmology, otolaryngology and audiovestibular medicine for the medical evaluation of involuntary eye movement (nystagmus). They are named after Frenzel, a German physician Ref AK khurana 6/e p515