This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Forced duction test is to find out? 
Select and explain. 
A. Ocular muscle palsy, B. Ocular muscle spasm, C. Angle of detion, D. Refractive error
A: Ocular muscle palsy
Answer: A: Ocular muscle palsy 
Explanation: Ans. is 'a' i.e., Ocular muscle palsy Forced duction test It is performed to differentiate between the incomitant squint due to paralysis of extraocular muscle and that due to mechanical restriction of the ocular movements. FDT is positive (resistance encountered during passive rotation) in cases of incomitant squint due to mechanical restriction and negative in cases of extraocular muscle palsy.