Paralyse third nerve terminations 



DEUGtS ACTING ON THE NERVOUS SYSTEM 45 



(1) Mydriatics. 



(a) ACTING LOCALLY. 



Atropine 



Homatropine 



Hyoscyamine 



Hyoscine 



Scopolamine 



Gelsemine j 



Cocaine Stimulates sympathetic endings. 



(b) ACTING CENTRALLY. 



Ansesthetics (late in their action) 



The dilating centre is stimulated by carbonic dioxide in 

 the blood, and therefore dilatation of the pupil occurs in 

 asphyxia ; also after irritation of sensory nerves, the sexual 

 orgaijs and digestive apparatus. 



Uses. — Mydriatics are useful in dilating the pupil for 

 examination of the eye, and to prevent adhesions of the iris 

 in central corneal ulcers ; in keratitis, to overcome photo- 

 phobia and blepharospasm ; and in iritis, to secure rest of 

 the iris and ciiiary muscles. 



(2) Myotics. 



(a) ACTING LOCALLY (b) ACTING CENTRALLY 



Physostigmine ) Stimulate third Aneesthetics 

 Pilocarpine ) nerve endings Opium 



Uses. — Myotics are employed to prevent prolapse of the 

 iris in wounds and ulcers of the cornea ; to antagonize' the 

 effect of atropine ; to prevent the entrance of light in painful 

 disorders of the eye ; to lessen intra - ocular tension in 

 glaucoma*; and, in alternation with mydriatics, to break ujJ 

 adhesions to the iris.. All the local mydriatics and myotics 

 mentioned above act on the ciliary muscle to destroy the 

 power of accommodation. In tra-ocular tension in glaucoma 

 is usually increased by atropine and other mydriatics, but is 

 diminished by eserine. 



* By opening up the filtration angle at the periohery of the anterioi' chamber 

 and allowing drainage of lymph through the lymph spaces there into the cahal of 

 Schiemm, or to contraction of the intraocular vessels, so lessening secretion 

 (GrOnholm). 



Digitized by Microsoft® 



