8o 



APPLIED ANATOMY. 



as its covering a prolongation of the membranes of the brain. The dura mater 

 when it reaches the foramen splits and gives one layer to form the periosteum lining 

 the orbit and the other to form a fibrous sheath of the nerve. This arrangement 

 prevents pus, forming in the orbit, from passing through the optic foramen into 

 the skull. The arteria centralis retincz enters the nerve on its under side and passes 

 through its centre to the interior of the eye. The nerve itself is covered with a fine 

 pial membrane and an arachnoid separating it from the dura, thus forming subdural 

 and subarachnoid spaces. As these membranes and spaces are continuous with those 

 of the brain, hemorrhage or serous effusions occurring within the brain can thus find 

 their way into the sheath of the nerve. 



As the nerve enters the eye, it is contracted and forms the optic disk or papilla. 



Cornea 



Greater arterial ring 

 Iris 



Lesser arterial ring 

 Ciliary process 



Canal of Schlemm 



^ Cornea 1 loop 



Perforating branch 



Conjunctival vessels 



Anterior ciliary vessels 



Sclera 



Episcleral vessels 



Communication between 



choroidal and optic vessels 

 Central retinal vessels 



\ 



Vena vorticosa 



Supplying choroid 



Short posterior ciliary artery 



Long posterior ciliary artery 

 Communicating twig 

 Inner sheath vessels 

 Outer sheath vessels 



Communication between optic 

 and sheath vessels 



FIG. 94. Diagram illustrating circulation of eyeball. (Leber.) 



It is readily seen with the ophthalmoscope as a round spot somewhat lighter in color 

 than the surrounding eyeground. Coming from a depression or cup in the disk, 

 called the porus opticus, are the retinal arteries and veins. A certain amount of 

 cupping is normal, but if wide and deep, with overhanging edges over which the 

 vessels can be seen to dip, it is indicative of glaucoma. 



Sometimes the papilla or disk is swollen, constituting an optic neuritis. 

 In brain tumor this is frequently the case and is called choked disk, or ' 'stauung 

 papilla" so named because the circulation was thought to be interfered with owing 

 to the intracerebral pressure being transmitted directly to the nerve. On the sub- 

 sidence of a severe neuritis the nerve is left in a state of optic atrophy and blindness 

 is the result. 



