Influence of the Third Cranial

THE adrenergic sympathetic system has been shown to exert a considerable effect on the intra-ocular pressure (Greaves and Perkins, 1952). We know, however, that cholinergic drugs are often effective in lowering the intraocular pressure in glaucoma so that it is possible that the parasympathetic system may also play a part in the control of the tension of the eye. Since the third cranial nerve carries the parasympathetic supply to the intra-ocular musculature, it is logical in the first place to determine whether it is also responsible for the cholinergic control of the intra-ocular circulation. The literature on this subject is small. Henderson and Starling (1904), after some careful exThey used a blind approach to periments, concluded the ganglion, passing a curved that the third cranial electrode round the globe and nerve had no effect on recording the changes in the the intra-ocular presintra-ocular pressure with a sure. Schmerl and SteinSchibtz tonometer. In view of berg (1950) however, the technique employed and the reported that electrical absence of simultaneous recordstimulation of the ciliary ings of the general blood presganglion in the rabbit sure, we feel that their results caused a rise, and caushould be viewed with caution. terization of the gangThe parasympathetic outflow lion caused a fall, in the to the eye, so far as the third intra-ocular pressure. nerve is concerned, originates