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
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: Forced duction test (FDT) is performed to differentiate between the incomitant squint due to paralysis of extraocular muscle and due to mechanical restriction of the ocular movements. FDT is positive in case of incomitant squint and negative in extraocular muscle palsy Ref ; A.K.Khurana ; 6 th edition; page no: 357