Etiology.—Glaucoma may possibly be caused by excessive secretion of fluid within the eyeball; or by alterations in such fluid which hinder its escape. But the causes that most commonly produce it, and are best understood, act by caus ing obstruction of the channels of out flow.
The chief channels for the escape of fluid from the eye pass from the periph ery or "angle" of the anterior chamber through "Fontana's space" to a circle of lymphatic and venous channels in the adjoining sclera, called the canal of Schlemm. Adhesion of the periphery of the iris to the cornea Or pressure of the iris against the cornea closes these chan nels.
The liability to glaucoma increases with age; and Priestley Smith has pointed out that the crystalline lens, like other epithelial structures, continues to grow until old age, diminishing the space between it and the ciliary processes, and increasing the liability of these proc esses to be pressed against the iris and close the outflow channels.
The use of a mydriatic is liable to cause glaucoma through thickening of the iris at its periphery during dilatation of the pupil. Exclusion of the pupil by iritic adhesions is likely to lead to pushing for ward of the iris by fluid from the deeper parts of the eye, and blocking of the out flow channels. Dislocation or swelling of the crystalline lens is likely to do the same thing. Causes of swelling of the ciliary processes and iris, as overweari ness, and physical or mental shock may cause outbreaks of glaucoma; and consti tutional conditions, particularly gout, have been accused of causing it. Pain, insensitiveness of the cornea, and cup ping of the optic disk are due to the ex cessive intra-ocular pressure.
Varieties. — Glaucoma in its typical form is marked with exacerbations, dur ing which the tension of the eyeball is increased, with pericorneal redness, in creased pain, diminished acuteness of vision, and generally increased severity of all the symptoms. This has been called inflammatory glaucoma. It is either acute or chronic. Sometimes the exacerbation is so severe as to destroy light-perception in a few days, or even a few hours: glau coma fulminans. When the increase of tension is preceded or accompanied by retinal hemorrhages it is called hemor rhagic glaucoma. Glaucoma quickly re turning after iridectomy and compelling the removal of the eye is malignant.
When no noticeable exacerbations oc cur, but the increase of tension and im pairment of vision are gradually pro gressive, the condition is called one of simple glaucoma. When glaucoma arises in an eye not previously diseased it is called primary. When it follows other ocular disease or injury, as wounds caus ing swelling of the crystalline lens, in flammation of the iris, or intra-ocular tumor, it is called secondary glaucoma. When all sight has been lost, and the tension is continuously elevated, the case is said to be one of absolute glaucoma.
Prognosis.—Glaucoma not efficiently treated ultimately causes complete and hopeless blindness, usually with a period of great pain. This end may be reached in a few days or only after many years. Treatment may save what sight remains,, or some that has been very recently lost may be restored. But vision that has been lost more than a few days or weeks cannot be regained. The prognosis for hmmorrhagic glaucoma is extremely bad_ Simple glaucoma often pursues its course unchecked by any treatment. Inflam matory glaucoma is quite amenable to the usual remedial measures if applied early. Secondary glaucoma can be cured by re moval of its cause, as by the extraction of a swelled or dislocated crystalline lens. The prognosis must always be guarded, for eases mild in the beginning may be come fulminating or malignant.
Treatment. — Iridectomy is the chief remedy 'for glaucoma. It is best done by making with a narrow knife an incision a little back from the corneal margin close to the periphery of the iris. One fifth of the iris should be removed, quite up to its ciliary attachment. The after treatment resembles that of cataract ex traction, except that the patient may be allowed more freedom.
Sclerotomy may be anterior or poste rior. The former consists in making a scleral incision parallel to the corneal margin much as for iridectomy, but longer and not completed, a bridge of sclera being left standing at the middle of it. Posterior sclerotomy consists in making an incision in the direction of an antero-posterior meridian of the eyeball, usually below the tendon of the external rectus, allowing a little of the vitreous to escape.