DISEASES OF THE OPTIC NERVE.

Anatomy. The fibers of the optic nerves arise in two bands, called the optic tracts, from the corpora geniculata, corpora quadrigemina, and ophthalmic ganglion, which in turn are connected by radiating fibers with the center in the occipitoangular region of the cortex. (Fig. 100.) Each optic tract winds obliquely across the corresponding crus cerebra, and converges forward to meet its fellow, forming at their intersection the optic commissure or chiasm, which is composed of six sets of fibers, viz.: a set crossing from the right side of the brain to the left eye; a second set pursuing the same course from the opposite side-decussating fibers ;

a third set, anterior, connecting the two retinæ—interretinal fibers; a fourth and a fifth set, lateral, connecting the hemisphere of one side with the retina of the same side-cerebroretinal; and a sixth set, posterior, connecting one optic tract with the other-intercerebral. The optic nerves diverge from the chiasm to pass through the optic foramen in each sphenoid bone. The nerve is covered by prolongations of membranes of the brain as far as the lamina cribrosa, at which point the dura mater fuses with the sclera, the other membranes are disconnected, the medullary covering of the nerve-fibers ceases, and the axis-cylinders pass through to form the nerve-fiber layer of the retina. The ophthalmic artery and vein pierce the nerve obliquely about 18 mm. posterior to the lamina cribrosa,

and are continued forward in the center of the nerve, passing through the porus opticus to be distributed to the retina. (See Frontispiece.)

INFLAMMATION OF THE OPTIC NERVE.

Synonyms.-Choked disc, optic neuritis, papillitis, neuroretinitis. Choked disc is so called on account of the interference of return of blood through retinal veins, by pressure from swelling at this point. Papillitis generally describes an inflammation limited to the intraocular head of the optic nerve, although in all probability, in the majority of cases, the nerve is affected throughout its entire length. There is less swelling than in choked disc, the visual disturbance appears earlier, and the disease leads to atrophy and blindness oftener than does choked disc. Neuroretinitis or papilloretinitis are terms used to describe an inflammation which involves the retina as well as the optic nerve. It is characterized by hemorrhages, patches of fatty degeneration that appear as white spots, deposition of pigment, etc., similar to the changes in albuminuric retinitis. Causes. The condition often called choked disc is usually the result of a brain tumor, and is almost invariably bilateral. If unilateral, it is probably caused by a tumor in the orbit. Other intracranial diseases causing inflammation of the optic nerve are: tubercular basilar meningitis of children, epidemic cerebrospinal meningitis, in fact, meningitis from other infectious diseases or from any suppurative origin. Infectious diseases, syphilis, lead-poisoning, and other systemic affections may cause an optic neuritis directly. Tumors or diseases of the orbit may have the same effect.

The line of distinction between retinitis and neuroretinitis is so slight that we can probably associate closely the causes of the former with those of the latter; however, in albuminuric retinitis, the greatest changes are in the retina rather than in the nerve head, and the urinary tests are quite indicative. Cases of inflammation of the optic nerve in which the cause is unknown are sometimes seen. Occasionally, several members of a family, the males particularly, and of apparently healthy parents, are attacked between the eighteenth and twenty-fourth years by a bilateral optic neuritis. In other cases,“catching cold,” suppression of the menses, lactation, etc., are given as causes. In such cases, there must be a suspicion that there was latent inflammation which became prominent under the conditions mentioned, and was not directly due to them.

Symptoms and Diagnosis.-The systemic condition is often simultaneously affected. The principal ocular sign is impairment of vision,

gradually passing into total blindness. Particularly typical are diminution of central visual acuity, unsymmetric contraction of the visual field, and impaired color-sense. The ophthalmoscopic appearance of choked disc is a swelling and opacity in the disc and its immediate neighborhood. (Fig. 101.) That the papilla is larger than normal and projects into the vitreous, may be proved by the parallax test. The papilla, while undergoing inflammation, has what has been called a woolly appearance, united with swelling and congestion. The small vessels of the disc are dilated, so that many of them are visible, unless masked by excessive edema. The retinal arteries are diminished in size, and veins are swollen and tortuous. The edges of the

disc are lost, and a striated flame-like or grayish haziness spreads over the disc into the adjoining retina, nearly equal upon all sides. In severe forms there are macular changes resembling albuminuric retinitis.

Prognosis. The course is usually chronic, sometimes lasting years, finally ending in optic nerve atrophy. Of course, the prognosis is affected by the cause. Cerebral tumors are usually fatal in a short time. The various forms of meningitis are always serious. Restoration of vision is doubtful; there is little hope of regaining lost visual power. However, cures with restoration of normal visual acuity, and cures of amblyopia of every degree, have been reported.

Treatment is naturally directed to the cause. If the cerebral tumor can be located, surgical interference may be of great value. A syphilitic gumma will yield to mercury and potassium iodid. If no cause is discernible, diaphoresis, the mercurials and iodids, and tonics may be tried. Blood-letting from the temporal region has been reported of value. Possibly mild cases get well of themselves. If there is reason to suspect that the neuritis is orbital in origin, systemic treatment will prove of little value; and in well-defined malignant orbital disease immediate enucleation is imperative.

RETROBULBAR OPTIC NEURITIS.

Definition.-Inflammation of the optic nerve beyond the eyeball, in which the disc is not involved at first, papillitis arising in the advanced stage. Causes. Acute retrobulbar neuritis is caused by exposure to cold, acute infectious diseases, sudden cessation of the menses, and any condition which leads to a sudden exudation into the sheath of the optic nerve. The most common cause of the chronic form is excessive use of tobacco and alcohol; although lead-poisoning, syphilis, quinin, and other toxic agents may produce it. As a rule, both tobacco and alcohol are simultaneously used to excess, and act conjointly. The disease is often called tobacco- or alcohol-amblyopia, or toxic- and intoxication-amblyopia, although many authors distinguish between intoxication-amblyopia and retrobulbar neuritis from other causes.

Symptoms.—In the acute disease, total blindness results in a few days, and there is often pain in the eye, increased by movement or pressure. The ophthalmoscope reveals a papillitis of moderate severity. In the more common chronic disease, the chief symptom is slowly diminishing central vision. The patient complains that he sees poorly, especially in bright light, and his vision improves at sundown (nyctalopia). Examination with the perimeter shows a central scotoma, at first for color, and finally for light. At the onset, the field of vision remains nearly normal, and only begins to be obliterated when fixation becomes impossible, and nystagmus results. With the ophthalmoscope there is first seen slight hyperemia of the disc, and later a grayish-white discoloration of the temporal halves of the papillæ. The outlines are obscured, the veins are enlarged, and the arteries diminished in size.

Prognosis may be considered favorable if the disease has not progressed to atrophy, and if the patient can be made to stop drinking and smoking; but relapses are likely to occur whenever the abstinence is suspended. Treatment.—In the acute form, general blood-letting, salivation, active

diaphoresis, and other antiphlogistic measures are indicated. In chronic cases, abstinence from tobacco and alcohol must be enforced, and strychnia administered in increasing doses. If syphilitic, the disease yields to the mercurials and the iodids. Any other discoverable cause should be treated according to the indications.

ATROPHY OF THE OPTIC NERVE.

Causes. The vast majority of cases are secondary to some retinal or cerebral lesion, or from pressure along the course of the nerve, in

which cases it follows some variety of neuritis. Most cases are due to some disease of the brain or spinal cord, especially of syphilitic origin. Of the cerebral diseases might be mentioned: disseminated sclerosis, progressive paralysis, and general paralysis; of the diseases of the spinal cord, locomotor ataxia is a prominent cause. Mechanical pressure from tumors, traumatism, embolus in the central artery, cutting off the blood supply, and the toxic agents, causing retrobulbar neuritis, lead to optic atrophy. Blindness, or amblyopia following severe hemorrhages, is supposed to be due to atrophy of the optic nerve. Sexual abuse, catching cold, physical and mental excesses, have all been set down as causes.

Symptoms and Diagnosis.-The patient notices an early disturbance