Most isolated trochlear nerve palsies are due to

The most common cause of congenital trochlear nerve palsies is congenital cranial dysinnervation syndrome, followed by an abnormal superior oblique tendon. The most common cause of acquired isolatedfouh nerve palsy, after idiopathic, is head trauma. ... Fouh nerve palsymay become manifest after cataract surgery Ref ganong's review of medical physiology 25e 542