SEC. 13. THE NUTRITION OF THE EYE. 



801. The main blood-vessels of the eye are, as we have 

 incidentally seen, the arteria centralis supplying the retina, and 

 the (posterior) ciliary arteries supplying the choroid, ciliary 

 processes and iris, the vessels going to the choroid being called 

 'the short ciliary arteries, and those reaching forward to the 

 ciliary processes and iris, the long ciliary arteries. From the 

 arteria centralis retinae the blood is returned by the vena centralis, 

 while the venae vorticosae of the (posterior) ciliary veins gather up 

 the blood of both the long and the short (posterior) ciliary arteries. 

 These two systems communicate to some extent, with each other 

 by anastomoses at the entrance of the optic nerve, but on the 

 whole are independent. 



In addition to the above, the anterior ciliary arteries pass to 

 the eyeball with each of the four straight ocular muscles, supplying 

 the front part of the sclerotic as well as the edge of the cornea, 

 and sending through the sclerotic 'perforating' arteries to end 

 in the iris, ciliary processes, and front part of the choroid, and 

 so join the system of the posterior ciliary arteries. Corresponding 

 to these anterior ciliary arteries are veins which make their way 

 back to the ocular muscles, and the roots of which are especially 

 connected with the circular canal of Schlemm ( 717). Further, 

 the edge of the cornea is in addition supplied by conjunctival 

 blood-vessels. 



The blood-supply of the various parts of the eye is therefore 

 somewhat as follows. The inner layers of the retina are supplied 

 in a direct manner by the arteria centralis retinse, but the outer 

 layers together with the pigment epithelium in an indirect 

 manner by the close set choroidal network " choriocapillaris " 

 of the posterior ciliary arteries. The choroid proper, that part 

 which serves as an investment to the retina and specialized 

 pigment epithelium, is supplied by the short (posterior) ciliary 

 arteries ; but the front ciliary part of the choroid, together 

 with the ciliary processes and iris, receives blood from the long 

 (posterior) ciliary arteries, and also from the anterior ciliary 

 arteries. The cornea is supplied by the conjunctival as weii 



