Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/848

784 OPHTHALMOLOGY pigmented, which tends to destroy the eye, to spread along the optic nerve, and to cause metastalic deposits elsewhere in the body. It causes defect of sight, and if the media are clear may be seen by the ophthalmoscope. It often causes glaucoma and cataract. The tumour must be excised with as much of the optic nerve and orbital tissue as can be reached. Diseases Detachment of the Retina is a separation of the retina of the from the choroid by an effusion of serum or of blood, or retina, ^y ^g g row th of a tumour between them. It occurs most frequently in myopia and from blows on the eye (also from dislocation of the lens and in albuminuria). The detachment varies greatly in extent ; it is most usually situated at the lower part of the retina. It causes blind ness on the corresponding opposite part of the visual field. With the ophthalmoscope, instead of the red appearance, a greyish reflexion is seen, generally uneven on the surface, with the retinal vessels, reduced in size and dark in colour, coursing over it. The grey surface may be seen to undulate with movements of the eye. Treatment is generally unsatisfactory. Myopic cases should avoid stooping and strain of the eyes to prevent its extension. Embolism of the Central Artery of the Retina is a plugging of this vessel by a small body, usually detached from one of the valves of a diseased heart. The eye becomes sud denly blind, and on ophthalmoscopic examination the red reflex is found to be replaced by a diffuse white mist, except at the yellow spot where a "cherry-red" spot appears ; and the retinal vessels are often reduced to mere threads. After a time the haze passes off the retina, but an atrophied disk and narrowed blood-vessels are left. Treatment is useless. If the embolism is impacted in one of the branches of the retinal artery these appearances will be localized, and a blind spot will correspond to the affected area. Albuminuric Retinitis occurs in an advanced stage of chronic Blight s disease of the kidneys, usually when the general health has become much impaired. It is especially associated with the granular kidney, and is not seldom the first indication of this serious disease. It causes defective sight, and some of the following characteristic ophthalmo scopic appearances. In the early stage (rarely observed) a greyish haze presents itself at the centre of the retina (from the presence of an albuminous fluid) ; later, pearly- white sharply-defined spots of various sizes appear, often grouped round the yellow spot (due to fatty degeneration of the coagulated albumen and nerve-fibres). With these there may be found many small haemorrhages, or a condi tion of optic neuritis. Vision is seldom completely lost, and may, except in the severest cases, be expected to im prove somewhat, especially in the albuminuria associated with pregnancy. Its treatment is that of its cause. Syphilitic Retinitis is usually a symptom of the second ary stage, affecting both eyes, and producing dimness of vision and night-blindness. Ophthalmoscopically the disk appears hazy, the vessels full and tortuous, the retina also hazy or showing white misty patches, especially near the yellow spot. It is much benefited by a mercurial course. Hsemorrhagic Retinitis is indicated by the appearance all over the retina of small flame-shaped haemorrhages Avith dilated veins. It is perhaps due to gout (Hutchinson). Haemorrhages may result from vascular degeneration. They seriously damage sight if they occur at the yellow spot. Pigmentary Retinitis is a peculiar chronic disease affecting both eyes symmetrically. It is either congenital or begins early in life and advances gradually till it produces com plete blindness. Its cause is not well known. It is strongly hereditary, occurring often in several members of one family ; it has been found also in the descendants of parents nearly related to each other, and it is common among deaf-mutes. In many cases no cause can be assigned. Its earliest symptom is an inability to get about in the dusk (night-blindness). Then follows a gradual contrac tion of the field of vision, the patient feeling as if he looked through a tube, seeing objects clearly within his field in good daylight, but nothing beyond. Eventually this central vision also fails. The ophthalmoscopical ap pearances are symmetrical in both eyes, and are equally characteristic. At the periphery of the retina masses of black pigment are distributed in an irregularly reticulated or lace-like manner over the retina and along the retinal vessels. The disk is pale and " waxlike," and the retinal vessels are much contracted, it may be, reduced to mere threads. As the visual field contracts the retinal pigment approaches the disk. Treatment is of little use. Galvanism has lately been recommended. Glioma of the Retina is a tumour of excessive malignancy, arising in the retina and rapidly filling the eye, and spread ing from the eye along the optic nerve to the brain, or through the sclerotic to the orbit. It occurs in young children. Thorough and early removal of the eye with the optic nerve may prevent its recurrence. The optic nerve may be inflamed in any part of its Disease course, within the skull, in the orbit, and within the eye. f the To the physician the most important of these inflamma- P tic tions is that of the intraocular end of the nerve or papilla, re ti na known as Optic Neuritis or Papillitis (choked disk), on & c . account of its frequent association with tumour of the brain, of which it is one of the most diagnostic symptoms. The signs may be well marked to the ophthalmoscope before there is the slightest impairment of sight. At first the disk is seen swollen, reddened, its edge indistinct, and the veins distended and tortuous. Later, the swelling of the disk increases, obscuring the disk itself, and extending beyond its edge. The surface has a greyish appearance, streaked with reddish lines, which are enlarged blood vessels. The retinal arteries and veins at their commence ment are obscured by the exudation ; at the edge of the swollen disk they bend downwards to reach the retina, over which they pursue a tortuous course, the veins being much distended. Small haemorrhages are often seen on the disk and retina. All traces of the exudation may pass away. More usually the disk becomes atrophied, of a pale-white colour, with an indistinct margin and shrunken retinal vessels. Papillitis of both eyes sometimes also arises from lead- poisoning or anaemia. Papillitis of one eye, with subse quent atrophy, is generally due to local injury to the nerve. Atrophy of the Optic Nerve is sometimes primary, i.e., arises without previous neuritis. In this case the disk becomes gradually of a pale-white or pale-greyish colour, its edge more than usually distinct, and the vessels may not be contracted. Primary atrophy of the optic nerve is one of the most marked symptoms of locomotor ataxia. Many of the cases where no cause is ascertainable are undoubtedly precursory to the usual symptoms of ataxy. Vision always suffers in this form more or less. Atrophy of the disk may be secondary to glaucoma, neuritis, pigmentary retinitis, and some forms of choroid- itis. When unilateral it may be due to embolism, or, if it follow an injury to the head, to fracture of the optic canal, or to a retrobulbar neuritis. Amblyopia, Amaurosis, dr.- Amblyopia means defect ive sight ; amaurosis, blindness without sufficient obvious cause. Such defective sight is not uncommon in a squint ing eye, or one of a different refractive power from its fellow. Tobacco amblyopia occurs in adults from excessive tobacco-smoking, especially when combined with alcoholic excess. There is loss of visual acuteness, as tested by read-