Atrophy of the optic nerve may be the result of preceding neuritis, when it is called "consecutive atrophy;" or the atrophy may have commenced as such, and slowly progressed without inflammatory change, "simple atrophy." It may also come on after injury to the head, the history being that after a blow the sight of one eye was lost. At first the ophthalmoscope shows no change, but in about two or three months complete atrophy of the disc sets in. The cause is damage to the optic nerve behind the eyeball.

With the ophthalmoscope the atrophic optic disc is seen to be white or bluish-white in colour, frequently its margin appears irregular, and it may be cupped. The atrophic cup varies from the glaucomatous in not having steep sides, so that the vessels do not appear broken in their course as in the latter affection; it does not take in the whole nerve, but only its central part, which slopes gradually backwards; the vessels appear curved on the surface of the disc, but are not altered in calibre as in glaucoma. Atrophy of the retina frequently accompanies atrophy of the optic disc.

In cases of atrophy of the optic nerves vision is always much impaired; some patients with extremely white discs can count fingers, distinguish large letters, or even read ordinary print, but in the majority of cases vision is reduced to bare perception of light.

Treatment.—The treatment of atrophy of the optic nerves, especially if associated with a similar condition of the retina, is most unsatisfactory, and, indeed, almost hopeless. Should a certain amount of vision still remain, and no change have taken place for many months, we may safely assure our patient that he will retain what sight he has. The drugs which have been principally used are iron, either alone or in combination with nux vomica, strychnia taken by the mouth or injected

hypodermically, phosphorus, quinine, or other tonics, and opium in gradually increasing doses. Galvanism has also been employed.

CHAPTER XII.

AMBLYOPIA, AMAUROSIS, AND FUNCTIONAL FAILURES OF SIGHT.

Blunt sight or amblyopia in one eye occurs in cases of squint. A squinting person in order to avoid the inconvenience of double vision suppresses the image in the squinting eye. After a time the perception becomes so dulled that objects are seen indistinctly or not at all with this eye, even when it is properly directed by exclusion of its fellow. Some improvement of sight may be brought about by systematic practice of the squinting eye by itself, the sound eye being closed.

Amblyopia in one eye may also occur from defective retinal image. Corneal nebulæ, congenital cataract, high degrees of hypermetropia and astigmatism are the chief causes. In the majority of cases the retina is not properly educated, but in some it is probably imperfectly developed. Practice of the defective eye in hypermetropia and astigmatism, aided by suitable convex, spherical, or cylindrical lenses, will, if commenced early in life and persevered with, cause some improvement; no improvement is to be expected if the defect be not treated till late in life.

A rapid or almost sudden loss of sight in one eye, accompanied by neuralgia on the same side of the head and face, and without change visible by the ophthalmoscope, is sometimes met with. The sufferers are generally young adults, the failure of sight is often attributed to exposure to cold, it may be due to reflex from carious teeth, or possibly to inflammation extend

ing from the latter along the periosteum, and affecting the optic nerve at its entrance into the orbit. Mr. Nettleship suggests a "retrobulbar neuritis" as the

cause.

Blistering over the mastoid or temple, with iodide of potassium internally, will usually effect a cure. But some cases end in atrophy of the optic nerve and blindness of the affected eye. Carious teeth must be stopped or removed.

Amblyopia from hæmorrhage.—In some cases of frequently recurring hæmorrhage extending over a long period as the bleeding from piles, or menorrhagia, serious impairment of vision may take place. The ophthalmoscope shows no change, or at most some pallor of the discs. Arrest of the hæmorrhage will cure the amblyopia.

Hemiopia or Hæmianopsia signifies loss of one half of the visual field; both eyes are usually affected, and as a rule the lateral halves of the field suffer. In the majority of cases the right or left lateral half of each field is lost, in some cases the temporal half of each field is lost, and in one case which I have seen the upper half of each field was wanting.

Loss of the right half of each field indicates loss of function of the left half of each retina, and is probably caused by disease of the left optic tract. Loss of the two temporal halves indicates loss of function of the nasal half of each retina, and may depend on disease of the anterior part of the chyasma. Hemiopia may be transient or permanent, some persons appear to suffer from it as a kind of migraine; the attack coming on rather rapidly, arriving at its height and then gradually disappearing, the whole lasting about half an hour and leaving behind it a general feeling of discomfort. Sometimes the edges of the dark portion of the field

are bounded by a bright zigzag line. Transient hemiopia is probably purely functional and is often associated with gastric disturbance.

Closely allied to the foregoing is a transient loss of sight of one eye; the symptoms are identical with those of transient hemiopia, with the difference that the whole field is lost, there being no perception of light for some minutes. In one case, which I have examined ophthalmoscopically during an attack, I found the retinal vessels, both arteries and veins, gorged with blood, and watched them return to the normal condition as vision was restored. In all these cases any anomaly of refraction should be carefully neutralised.

Permanent hemiopia may last for any time without change visible to the ophthalmoscope, in some cases, however, atrophy of the disc is present.

Hysterical amblyopia and amaurosis.-In some cases of hemi-anæsthesia, partial loss of sight or complete blindness (amaurosis) with dilatation and immobility of the pupil of the eye on the affected side occurs. Complete or partial loss of sight, in some cases associated with colour blindness in one eye, may also be met with in cases where no hemi-anesthesia exists. In both classes of cases ophthalmoscopic examination shows all the ocular structures to be healthy, but often some anomaly of refraction is revealed. With the rare exception of some cases of hemi-anesthesia the reflex action of the pupil both direct and indirect is normal.

In another class of cases irritative symptoms occur; there is photophobia with spasmodic closure of the lids; lachrymation and spasm of accommodation. Exmination reveals no corneal or other disease; one or both eyes may be affected, and the symptoms often follow some slight injury to the eye. The sufferers are usually young females (not children), but occasionally