A cataract, (from Cataracta 1804 to mingle together, or put out of order; because the sense of vision is confounded if not destroyed). Dr. Cullen places it as a species of caligo, and names it ca-ligo (lentis) ob maculum opacum pone pupillam; and observes, that he cannot agree with Sauvages, that a cataract should be of a different genus from caligo; and leaves it to the judgment of others to determine whether he has been right in changing the character of caligo, and placing cataract as its species.

A cataract is an opacity of the crystalline humour of the eye, which stops the rays of light from passing to the retina, and preventing vision. Dr. Hunter attributes the disease to an inflammation in the coat of the crystalline humour; but M. de St. Yves seems to intimate that the crystalline humour is itself affected.

Hippocrates called it glaucosis. Galen, hypochysis, and hypochyma; the Arabians, gutta opaca; others, macule oculorum. Celsus, suffusio. It sometimes has the term affusio applied to it; and Cataracta 1805 or which Galen and most of the ancients say is a dryness or concretion of the crystalline humour. AEtius thinks it a change of the crystalline humour to a sky colour, with a dryness and concretion. More modern authors think that the principal difference betwixt a cataract and a glaucoma is, that in the latter the crystalline humour becomes hard, and of a sky colour (glauci coloris); and in the former it is soft. But the idea of cataract is now totally cleared from all that confusion in which it was usually involved; it is universally allowed to be an opacity of the crystalline lens, or its capsule.

M. de St. Yves divides the cataract into the true, doubtful, and false.

The true is when the crystalline humour hath lost its transparency: and the species are, when it is soft; when hard; and when purulent.

The doubtful are those cases in which the success of the operation is as uncertain as the use of topical remedies. Of this there are four sorts: a membranous and a filamentous cataract; cataracts from external injuries; and from a defect of the membrane which covers the bottom of the socket in the vitreous humour. The first and third of these he subdivides again, each into three kinds, as he endeavours to be minute, as well as full, in his description of this disorder.

The false arc those in which the remedies afford no relief further than to palliate pains, or to remove deformity; and these he divides into the glaucoma, and the shaking cataract.

All these minute divisions seem little regarded in present practice; but yet some useful hints will be derived by a perusal of this author.

When a cataract begins, the patient at first complains of a dimness of his sight; and on a careful examination of the eye, a whiteness is perceived very deep in it: on examining the eye at distant periods of time, its opacity becomes more and more manifest to the observer, and the patient very sensibly loses the advantages of seeing. The progress of a cataract is usually very slow.

No medicines are capable of removing this disorder of the eye; but it is sometimes relieved by copious, general, or topical evacuations; sometimes by small doses of muriated mercury, long continued; by drawing electrical sparks, or even by dropping a little of the tincture of opium at night into the eye; in short, by every means of increasing the action of the smaller vessels. The sight, however, can only be restored by an operation.

Sauvages enumerates no less than five species, and of the cataracta vera six varieties. He tells us, that two patients were cured by the internal use of the hyoscyamus: one of the species which he inserts under the title of membranacea is very doubtful. He says, that it was discovered by Lower on horses, and arises from a mucus exuding from the margin of the pupil, or uvea, which concretes sometimes into a membrane that obstructs the pupil; but whether this membranous cataract exists in the human species, he thinks uncertain, notwithstanding it has sometimes been suspected. See Sauvages Nosologia Methodica, vol. ii. p. 723.

Mr. Sharpe gives it as a general rule for proceeding to the operation, when the cataract is entirely opaque; adding, that sometimes they are of a proper consistence for the operation before they become opaque; but forbids the attempt while the patients can perceive any thing. Cataracts are of different colours; the pearl coloured, and those that appear like burnished iron, are thought capable of enduring the needle; the white are supposed to be milky; the green and yellow are horny, and incurable; the black cataract Mr. Sharpe thinks is the gutta serena.

The yellow cataract often adheres to the iris, so as to be incurable. When a gutta serena attends, the operation will not relieve. There is little to be expected from the operation when the size of the diseased eye is either diminished or increased; when, previously to the appearance of any obfuscation, the sight was defective; when in a strong light, of which, from the appearance of the cataract, the patient must be seemingly sensible, no contraction of the iris takes place.

The methods of operating are different. By the first and oldest plan, the thickened crystalline was depressed below the vitreous humour; and it was styled couching, from coucher, to lie down. In the second, the crystalline is extracted.

Before and after the operation, a due regard must be paid to the state of the patient's constitution; and such means are generally advised, as will keep it somewhat below its natural vigour, if otherwise in health.

When no objection to the operation attends, Mr. Sharpe commends the following method for depressing the cataract. "Place the patient in a convenient light, and a suitable height; put a pillow behind his back, that his body may bend forward, and the head approach near to the operator; then inclining the head a little backwards upon the breast of the assistant, and covering the other eye, so as to prevent its rolling, let the assistant lift up the superior eye lid, and the operator depress a little the inferior one: this done, strike the needle through the tunica conjunctiva, somewhat less than one-tenth of an inch from the cornea, even with the middle of the pupil, into the posterior chamber, and gently endeavour to depress the cataract with the flat surface of it. If, after it is dislodged, it rises again, though not with much elasticity, it must again and again be pushed down. If it is membranous, after the discharge of the fluid, the pellicle must be more broken and depressed. If it is uniformly fluid, or exceedingly elastic, we must not continue to endanger a terrible inflammation by a vain attempt to succeed.