Organic and functional nervous diseases; a text-book of neurology . rognostic importance asindicating a widespread arterial disease. The treatment must alwaysbe directed to a removal of the cause. 630 TEE CBANIAL NEEVES AND THEIR DISEASES. (Edema of the Optic Nerve. Choked Disk. — The optic nerveat its exit from the eyeball receives a double sheath, one layer of whichis continuous with the dura mater and the other with the pia fluid accumulates under pressure within the cranium it thereforefinds its way into the space between these sheaths, distending the duralsheath and compressing
Organic and functional nervous diseases; a text-book of neurology . rognostic importance asindicating a widespread arterial disease. The treatment must alwaysbe directed to a removal of the cause. 630 TEE CBANIAL NEEVES AND THEIR DISEASES. (Edema of the Optic Nerve. Choked Disk. — The optic nerveat its exit from the eyeball receives a double sheath, one layer of whichis continuous with the dura mater and the other with the pia fluid accumulates under pressure within the cranium it thereforefinds its way into the space between these sheaths, distending the duralsheath and compressing the nerve at its exit from the eyeball. Suchcompression is felt earlier by the lymphatics and veins than by theharder nerve fibres, and the consequent result is a dropsical eifusioninto the intraocular portion of the nerve from transudation of fluidfrom the obstructed vessels. This causes a swelling of the optic diskvisible to the ophthalmoscope and causing an appearance shown in Such a swelling may exist for some time without any impairment Fig. Swollen disk in a case of chronic meningitis. (Liebreich.) of vision, hence the importance of ophthalmoscopic examinations in caseswithout ocular symptoms. The experiments of Merz^ have demon-strated that this swelling of the nerve may come and go rapidly andmay vary greatly in degree, according to the varying amount of intra-cranial presisure. The oedema is always attended by venous congestion,but no inflammatory changes may occur, and it is therefore erroneousto identify choked disk with optic neuritis. It is not infrequentlyaccompanied by hemorrhages in the retina. Choked disk will occurunder any condition which obstructs the circulation in the eye or in-creases the intracranial pressure. It is very common in tumors and^ Merz, Arch, of Ophthalmology, July, 1901. DISEASES OF TEE OPTIC NEEVE. 631 abscesses of the brain, occasionally occurs temporarily after largehemorrhaged, and not infrequently accompanies Brights d
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