<prompt> Forced duction test is to find outOcular muscle palsyOcular muscle spasmAngle of detionRefractive error  <response>: Refer: AK Khurana Comprehensive Ophthalmology, 6th edition, pg no. 353 - 354 Forced duction testIt is performed to differentiate between the incomitant squint due to paralysis of extraocular muscle and that due to the 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. 