Studies on the Experimental Induction of Ptosis in Horses

The precise appearance of ptosis due to lesions at different sites was investigated in experimental ponies. The angles of the eyelashes to the head was used as an objective measurement of ptosis after local anaesthesia of the sympathetic trunk or the palpebral nerve and the administration of an ocular alpha agonist or antagonist. It was shown that ptosis is not an inevitable consequence of palpebral nerve pathology, that ocular α antagonists can induce ptosis, and that α agonist eyedrops have an inconsistent effect on the equine pupil, but are consistent at reversing ptosis induced by sympathetic denervation in unsedated horses.