TENSION OF THE EYEBALL, DIS ORDERS OF.
To preserve the shape and proper re lations of the refracting surfaces of the eyeball, the sclero-corneal coat is kept distended by its contents, which nor mally press outward with a force equal to the weight of a column of mercury 25 or 30 millimetres in height. To nourish the tissues contained within the outer coat of the eyeball there is a continuous secretion of nutritive fluid; and this fluid, just as constantly, must escape from the eyeball to avoid overdistending it. In pathological conditions the ten sion of the eyeball may be increased or diminished. Increased tension is indi cated by ± T 1, T 2, or + T 3, which indicate different degrees of hardness.; and diminished tension is indicated by — T 1, — T 2, or —T 3, the higher number indicating the greater departure from the normal.
Glaucoma.
Increased tension is generally called glaucoma, from the Greek, sea green. The term was applied on account of the greenish hue of the pupil in elderly people, when dilated, as it commonly is, in glaucoma. But the increased intra ocular tension is now recognized as the essential characteristic of the disease.
Symptoms.—The eyeball is found more resistant to pressure than normal. This is tested by pressing on it above or below the cornea through the partly closed lids. The tips of the two forefingers are com manly used. In the early stages the in creased resistance may not be noticeable or it may only be present a part of the time.
A very early symptom is the appear ance of colored rings around distant lights at night. The colors are arranged as in the solar specturn, with the violet toward the light. These halos may be absent in glaucoma, or present when the tension is not increased. Proximity of the iris to the cornea, shallowness of the anterior chamber, frequently precedes any outbreak of other symptoms; and in the later stages the anterior chamber may be obliterated, the iris coming in contact with the cornea. Dilatation of the pupil usually attends glaucoma. In the early stages the pupil still responds to light and convergence, and varies in size from time to time with the variations of tension. Later it becomes widely dilated and fixed. When the tension of the eyeball is much increased, or has increased rapidly, the cornea is found comparatively insensitive to touch.
Pain occurs, and is severe in most cases. It may be limited to paroxysms, or may be constantly present. It is often referred chiefly to the brow or cheek, or the temple or side of the nose. It may be mistaken for neuralgia or the pain of inflammation. In glaucoma that has lasted some time, the large tortuous veins that emerge from the sclera some dis tance back from the corneal margin are dilated and prominent. During the par oxysms there is generally a marked peri corneal redness. When the tension is very high, or has risen rapidly, the cornea will be found hazy,—"steamy,"—and may hide the deeper parts of the eye.
When the media are clear the ophthal moscopical appearances are characteris tic. In cases not too recent the optic disk is cupped or excavated deeply, the excavation extending to the extreme mar gin of the disk, and having abrupt or overhanging sides over which the retinal vessels appear sharply bent. The retinal veins are often dilated and the arteries rather small. The arteries may be seen to pulsate, especially where they pass over the margins of the cup; and the normal pulsation of the veins may be increased. The optic disk is often surrounded by a ring of choroidal atrophy having all edge that shades rather gradually into the nor mal choroid, called a halo-atrophy.
Diagnosis.—Glaucoma may be distin guished from CATARACT by pain, dilata tion of the pupil, narrowing of the field of vision, cupping of the optic disk, and absence of opacity of the media except during inflammatory exacerbations. From NEURALGIA it must be distinguished by the fundus-changes, and the impairment of visual acuteness or the field of vision, that are present in simple glaucoma, which is most liable to be confounded with that disease. From IRITIS glaucoma is distinguished by the shallow anterior chamber, the dilated pupil, the impair ment of the field of vision, the absence of so-called punctate keratitis, and the marked exacerbations and remissions. From KERATITIS glaucoma may be known by the symptoms just enumerated, and the smoothness of the corneal surface. The discrimination between different varieties has been indicated in describing them.