—If the cause of the optic neuritis is one that can be removed, partial or complete recovery is likely to follow. Otherwise the neuritis passes into the optic atrophy, and blindness results.
— Besides the efficient treatment of its cause and especially the treatment for syphilis in all doubtful cases, the standard treatment for optic neuritis of intracranial origin is by potassium iodide in doses rapidly in creased up to the limit of tolerance. Tapping the sheath of the optic nerve has been tried with the idea of relieving pressure, but it is of doubtful benefit.
Retrobulbar optic neuritis is marked by pain in the orbit and soreness or tenderness on moving the eye or press ing it backward. Vision is impaired in some part of the field of the affected eye. At first the disk may appear nor mal, or slightly swelled and hazy. Later it may show signs of atrophy. Recovery usually occurs, and vision may be com pletely restored. The causes are cold, rheumatism, syphilis, acute fevers, and alcoholic or other poisoning. (See Toxic AMBLYOPIA.) It may attend de generative disease of the brain and spinal cord. It is to be treated through its cause, and by local blood-letting, potas sium iodide, and later strychnine.
Optic Atrophy.—Atrophy of the optic nerve consists essentially in atrophy of some or all of its nerve-fibres. It is always attended with impairment of vis ion, and is a common cause of perma nent blindness. It is also important as a sign of disease in the central nervous system.
—The impairment of vision generally affects central vision, and al ways includes some limitation of the visual field. It is at first progressive. The fields for colors are usually con tracted earlier and to a greater extent than the field for form; and they may be obliterated, producing acquired color blindness. When the blindness is com plete, especially if it has come on rapidly, the pupils may be widely dilated. More commonly the pupils are not greatly en larged. With the ophthalmoscope the optic disk is found less vascular than normal. It may be a dead white, or gray, bluish, or greenish hue. It presents few small vessels. The large branches of the retinal vessels may be of normal size, or they may be greatly contracted.
Atrophy, not due to preceding disease of the optic nerve or retina or to injury or to press ure on the nerve or chiasm, is called primary atrophy. It may be congenital or hereditary or may follow acute dis ease or syphilis. It sometimes accom panies or precedes spinal sclerosis, or is caused by poisoning by lead, alcohol, etc. Atrophy following injury to, or
pressure upon, the optic nerve is called secondary. Consecutive atrophy is atro phy following optic neuritis or neuro retinitis, or disease of the retina or cho roid, as embolism of the central retinal artery or syphilitic chorioretinitis. Its causes are those of the conditions it fol lows.
— The ophthalmoscopical picture of advanced atrophy is usually quite striking. But commencing atro phy cannot be certainly recognized with the ophthalmoscope; and even the ap pearance of pronounced atrophy may be simulated in disease, like quinine blind ness or iscluemia of the retina from se vere haemorrhage, which admits of par tial or complete recovery. The diagnosis is most safely based on narrowing of the field of vision, particularly for colors, with ophthalmoscopical appearances that point toward atrophy.
In primary atrophy the disk is usually gray and its details, with the lamina cribrosa, very distinct. The retinal ves sels are not greatly narrowed. The field of vision is contracted regularly. In secondary atrophy the disk is more likely to be white. The retinal vessels may or may not be contracted. In consecutive atrophy the nerve-head is usually opaque, the neighboring choroid disturbed, and the retinal vessels somewhat contracted and often irregular in calibre. The vis ual field is irregularly contracted. After chorioretinal disease the disk shows dirty-yellowish color, and the lamina is hidden.
— The most effective measures are those di rected to the causes of the atrophy, and they must be as varied as those causes. In addition, mercury and potassium io dide may be tried in the early stages, even in cases not of syphilitic origin. Later strychnine should be tried in doses ris ing gradually to the physiological limit. This is sometimes as high as V, grain, three times daily by the mouth, or once daily hypodermically. General meas ures, including change of occupation and climate, may be beneficial. Inhalations of nitrite of amyl and applications of galvanic electricity have been tried with reported benefit in some cases. Primary atrophy generally goes on to blindness. The prognosis for secondary and con secutive atrophies depends on early treatment and the possibility of control ling the cause.
Tumors of the optic nerve cause pro trusion of the eye and loss of sight. They begin in childhood and develop slowly, without pain or much interfer ence with the movements of the eyeball. They are usually myxomas or fibromas which do not recur after removal.