Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/847

OPHTHALMOLOGY 783 than half the corneal circumference. A portion of iris is drawn through the corneal incision and cut off (iridectomy). Then the lens -capsule is lacerated by a needle. The lens is forced out of the eye by gentle pressure on the sclerotic below. All fragments of lens -substance are carefully removed, the edges of the incision are brought together, the eyes bandaged, and the patient kept in bed for a few days. Ninety-five per cent, of the cases do well, the others going wrong from haemorrhage into the eye, iritis, or sup puration of the eye. In lamellar cataract two courses are open. If dilatation of the pupil by atropine enables the patient to see clearly, the removal of a portion of iris (artificial pupil) will be sufficient ; if not, the solution of the lens must be effected by the needle operation. In traumatic cataract the pupil is kept dilated by atropine to prevent iritis. If severe iritic or glaucomatous symptoms arise an incision must be made in the cornea, and the softened lens removed along a grooved scoop or by suction. After the cataract is removed strong convex glasses must be worn for near vision and a somewhat weaker pair for distant vision. Their use must not be allowed till at least two months after the operation. Dislocation of the Lens may arise from a blow or spon taneously. The lens may pass into the anterior or posterior chamber. If in the posterior chamber it may be invisible, but the iris will be tremulous and the refraction very hyper- metropic. If the dislocation be partial the edge of the lens may be seen with the ophthalmoscope as a dark curved line. The lens generally becomes opaque. It may, and often does, cause glaucoma. Glaucoma is a most serious disease, characterized in all its forms by increased tension of the eyeball, impairment of sight, and ultimate irremediable blindness. Its course is usually chronic, lasting sometimes many years ; sometimes absolute blindness comes on in a few hours or days. In the chronic form the earliest symptoms are rapid onset of presbyopia, making it necessary to change the spectacles frequently, and attacks of mistiness of sight, during which artificial lights appear surrounded by coloured rings. Gradually sight is impaired and the field of vision contracted. The pupil is dilated and sluggish ; the cornea may be " steamy " and insensitive, the anterior chamber shallow. Large veins pierce the sclerotic a little way from the corneal margin. The lens may have a greenish hue (hence the name), or may become opaque. The optic disk, if visible ophthalmoscopically, is " cupped " or hollowed, and in advanced cases also atrophied. The retinal vessels bend abruptly in rising over its edge, or in deep cupping seem to have their course interrupted for a short distance. The arteries pulsate either spontaneously or on slight press ure on the eyeball. The tension (ascertained by pressing the eyeball against the floor of the orbit) is variously increased. This form may be painless throughout, and the gradual impairment of vision may lead to the fatal error of a diagnosis of cataract. More usually there are occa sional acute attacks. Acute glaucoma comes on suddenly ; there is much pain in the eye and temple and congestion of the globe ; increase of tension and loss of sight are extremely rapid. All the symptoms depend on the increased tension of the intraocular fluids. The loss of sight and contraction of the visual field result from compression of the retina and its vessels. Pressure on the ciliary nerve paralyses the iris and the accommodation (hence the presbyopia), and renders the cornea insensitive. The anterior chamber is shallowed by the lens being driven forwards, and the disk is cupped by being driven backwards through the lamina cribrosa, the least resistent part of the sclerotic. The veins of the sclerotic are enlarged in order to relieve the ob- clioroid. structed vasa vorticosa. The explanation of the increase of tension is not yet complete. In most cases it is probably due to deficient removal of fluid. Normally this take.s place through the suspensory ligament of the lens, round the free edge of the iris, leaving the anterior chamber at the angle of junction of the iris and cornea. Block ing of any part of this channel (most often at the above angle) would cause increase in the tension. Increased blood-supply is also in many cases a cause. Glaucoma is most common after forty. It may be either primary or secondary to some disease or injury of the eye. Eserine applied locally has proved useful in some early cases of glaucoma. Iridectomy that is, the removal of a portion of iris through an incision in the cornea is the most successful mode of checking the disease. In secondary glaucoma the treatment must be directed to the cause, if it is removable. Muscse, Volitantes. The floating bodies, specks, <ic., so Diseases often complained of are usually of no importance. They f the occur most frequently in myopic eyes. Pathological muscse, Vltr however, depend on the presence of opacities in the vitre ous, detectable by the ophthalmoscope. They are of very various sizes and shapes, from large masses, as in recent haemorrhage, to strings, specks, knotted bodies, or finely sparkling particles (cholesterin), or as a diffuse cloud or haze obscuring the retina. From the rate at which the bodies move an opinion may be formed of the fluidity of the vitreous. Disease of the vitreous is usually secondary to disease of some of the surrounding parts, as in high de grees of myopia, in hasmorrhagic and syphilitic choroiditis and retinitis, and diseases of the ciliary region. Haemor rhage is frequent after blows on or wounds of the eye. Disseminated Choroiditis is usually a symmetrical dis- Diseases ease, arising from acquired or inherited syphilis. There f the . are no characteristic symptoms, but the ophthalmoscope shows in the early stage (rarely observed) yellowish patches (of exudation), over which, unless obscured by haze, the retinal vessels are seen to pass. Later, when the exuda tion gives place to atrophy, white patches are seen of various sizes with masses of black pigment on or around them, distributed irregularly over the choroid. The re tinal vessels may be seen to pass unaltered over some of the white areas. Sometimes the patches of atrophy in volve merely the superficial layers and expose the deeper larger choroidal vessels. Vision is impaired, especially if the yellow spot is involved. The treatment is that for syphilis, with rest and protection of the eyes from light. This at least helps to prevent fresh accessions of the disease if it cannot restore the atrophied choroid. Similar spots are seen in non-syphilitic subjects, probably as the result of choroidal haemorrhage. In myopia the choroid is frequently atrophied near the disk, especially at its outer edge, forming what is variously known as "posterior staphyloma," "myopic crescent," or " sclerotico-choroiditis posterior." This pos terior staphyloma varies much in shape, sometimes sur rounding the disk, sometimes limited to_the yellow spot, causing then greatly impaired central vision. Tubercles are sometimes deposited in the choroid, appear ing as small yellow spots. Their presence may be of assistance in forming a diagnosis of tubercular disease. Rupture of the Choroid from injury is generally seen as a long curved line of atrophy with the concavity towards the disk. Coloboma of the choroid is a congenital defect, indicated by a large white patch of atrophy at the lower part, often embracing the disk, the surface of the sclerotic often looking uneven. It may exist independently of similar defect in the iris. Sarcoma of the Choroid is a malignant tumour, usually