Cataract, a disease of the eye in which there is an opacity of the crystalline lens or of its capsular investment. It is most common in old persons, in whom it seems to be the natural consequence of age; but it also occurs in infants, and is even congenital; it appears to be more frequent in cold and damp climates than in warmer regions, and it is certainly hereditary in many instances. Among the exciting causes, especially of the capsular form, are wounds and inflammations of the internal eye; but the ordinary cause is the diminished nutrition of the organ in common with others in advancing age. True cataract may be either lenticular, capsular, or capsulo-lenticular, according as the seat of the opacity is in the lens itself, in its capsule, or in both at the same time. Certain cases of opacity external to the crystalline apparatus have been called false cataracts, and may be caused by the effusion of lymph, blood, or pus, or by false membranes; secondary cataracts are those which follow the surgical operations for the extraction or depression of the lens.

The lenticular cataract may vary in hardness from stony to gelatinous; its opacity is rarely uniform, being generally thickest in the centre and thinnest on the edges; in some cases the opacity begins at the circumference in rays which slowly converge to the centre; the color varies from pearly white to amber yellow. The capsular cataract, which Velpeau considers more common than the lenticular, offers a great variety of colors and streaks, and may occupy either the anterior or posterior surface, or both. In the last form of cataract both the lens and its capsules are involved, with the varieties common to both. The physical sign of cataract is a more or less troubled appearance behind the pupil, of a yellowish color, deepest in the centre, and becoming more distinct as the disease progresses; the rational sign is a gradual diminution of vision, accompanied by the sensation as if a cloud, specks, spiders' webs, or snowflakes were passing before the eyes; objects are seen best in certain positions of the head, as when turned on one side, and during the evening or in the shade when the dilated iris permits more light to enter the pupil; on looking at a candle the flame appears surrounded by a thick bright haze.

The progress of the disease is very slow, generally unaccompanied by fever, pain, or any disturbance of the general health. It is very rare for a person to bo unable to distinguish day from night. M. Sanson has proposed an excellent catoptric test for the detection of cataract by the reflection of light. When a lighted candle is held before the eye of a healthy person, three images of it may be seen: the first erect, moving upward when the candle is moved upward, produced by reflection from the cornea; the second also erect, produced by reflection from the anterior surface of the crystalline capsule, and moving upward with the candle; the third very small and inverted, reflected from the posterior surface of the capsule, moving downward when the light is carried upward. In cataract, the inverted image is from the beginning indistinct, and soon disappears entirely; the deep, erect one is also soon rendered invisible. 13y dilating the pupil with belladonna, this experiment is rendered easy and striking.

Cataract is for the most part remediable only by a surgical operation; certain forms, caused by inllamnia-tion of the capsule, may disappear with the exciting cause without an operation; and cases are on record of the spontaneous cure of lenticular cataract by the rupture of the capsule and the escape of the lens into the anterior chamber of the eye, where it is gradually dissolved. - From the earliest antiquity surgeons have attempted to destroy cataract by means of needles and knives of various forms. Whenever the disease is confined to the lens and its capsule, and the eye in other respects is healthy, and the patient not too young or too old, an operation may be attempted with a prospect of success; in infants, and in persons under 20 years of age, both eyes may be operated on at once; after the age of 80, the chance of a successful issue is generally small. Before submitting persons to this operation, it is well to prepare them a day before by a mild diet and a gentle laxative, and to allay any inflammatory tendency of the organ; and then to smear belladonna ointment around the orbit, or to put a few drops of its fluid extract into the eye, for the purpose of dilating the pupil to its utmost extent. - All operations for cataract reduce themselves to three, which have for their object either to displace the lens, to break it up, or to remove it from the eye. 1. Operation for depression of the lens, or couching.

The description of this may be found even as far back as Celsus; it has undergone many modifications in modern times. The instrument employed is a fine needle, either slightly curved at the end or straight with the point spear-shaped; Scarpa's needle is slightly curved at the end. When the needle is passed through the sclerotic, as ordinarily, the operation is called scleroticonyxis; when it is passed through the cornea, Iceratonyxis. Different needles are preferred by different operators; but, as in the case of the stethoscope, that instrument is the best to which the surgeon is accustomed. In scleroticonyxis the, needle, held like a pen, is passed through the sclerotic perpendicularly to its surface, a line or two from the cornea and a little below its transverse diameter; the concavity of the instrument is turned down, in order to separate rather than to divide the fibres of the membrane; when the needle is fairly in, its concavity is turned backward, so that it may pass under and before the lens without touching the iris or the capsule; when it has reached as far as the pupil, the capsule is lacerated by delicate circular movements of the point; then the needle is applied directly to the lens, which is pushed outward and backward to the bottom of the globe, out of the line of the axis of vision; it is held there a short time, that the cells of the vitreous humor, into which it is pushed, may resume their position around it, and thus prevent its reas-cension in the line of the pupil.

Some surgeons prefer the operation by reclination, which consists in turning the lens backward from an upright to a horizontal position; and some always recline the lens before they depress it. In keratonyxis, the needle is passed through the cornea, about an eighth of an inch from the sclerotic, on its lower and exterior portion, and is directed through the dilated pupil to the lens, whose capsule it is made to lacerate; and, if possible, the lens is depressed, reclined, or broken up. This method is objectionable on account of the danger of wounding the iris, and of the difficulty of reaching the lens, and is applicable only to exceptional cases. After the operation, the eye should be lightly covered, and the patient should remain in bed in a darkened room, with the head raised, and be kept on a low diet for a few days; after four or five days in ordinary cases, a little light may be gradually let into the room, and at the end of three weeks the eye may be generally left uncovered. The accidents most to be feared are inflammation of the iris, choroid coat, and retina, which should be treated by antiphlogistic measures. 2. The operation for breaking up the lens, without depressing it, is very easily performed, and excites very little inflammation; but it requires frequent repetition, is slow in its progress, and is adapted only to soft and especially to congenital cataracts.

The needle is inserted just as in the method for depression, the capsule is divided, and the lens is freely broken up without removing it from its place; the cataract is thus brought into contact with the aqueous humor, and is gradually dissolved by it. 3. In the operation for extraction, the cornea is incised through rather more than half its circumference, the capsule is lacerated, and the lens is extracted from the eye entire; it is performed with a triangular knife, with sharp point, straight and blunt back, the edge slanting obliquely, and the blade growing wider and thicker as it approaches the handle; this kind of knife cuts by the simple motion of pushing, and fills up the incision as it makes it, thereby preventing the escape of the aqueous humor. The cornea may be cut on its inferior or superior half, or obliquely on its external and lower portion, each of which has its special advocates. When the lower half is cut, the knife, with its edge downward and forward, is passed into the external side of the cornea, perpendicular to its axis, a little above its transverse diameter, and about a line from the selerotic; passing in front of the iris, the point is nnule to cut its way out on the inner opposite surface; the cutting of this flap constitutes the first period of the operation, after which the lids are permitted to be closed for a few seconds.

Taking care in the subsequent steps of the operation not to make pressure upon the globe, the surgeon raises the flap, and, by means of a proper needle, lacerates extensively the capsule; if at this time the lens does not of itself come forward into the anterior chamber, gentle and properly directed pressure will cause it to come out; to complete the operation, it is sometimes necessary to remove also the pieces of the divided capsule. When the lower half of the cornea is opaque or in a condition unfavorable to cicatrization, or very small, Wenzel, Richter, and Jager recommend the section of the upper half; the steps of the operation are about the same, though perhaps more difficult to execute; it otters the advantages of presenting less liability of the iris being wounded, of the vitreous humor escaping, and of the lips of the section being separated by the edges of the lids. By the oblique incision, which is the favorite mode in France, the lids could not possibly interfere with the apposition of the edges of the wound.

More care is required after extraction than after depression, to avoid inflammation; after it is certain that the patient can distinguish objects, the eye is lightly covered and the person confined to bed in a dark room, with the head but slightly elevated. - Of these operations, extraction removes with certainty the obstructing lens, is very little painful, does not wound the ciliary vessels or nerves, the choroid, or the retina; but it may cause deformity of the pupil or the escape of the vitreous humor; the edges of the wound may not readily heal, or may ulcerate, with hernia of the iris or opacity of the cornea. Depression leaves a permanent cause of irritation in the eye, and the lens is liable to reas-cend; the needle perforates the choroid and retina, and may cause inflammation of the internal eye; but there is no danger of the escape of the vitreous humor, nor of spots or ulcers of the cornea, nor of hernia of the iris, nor of immediate evacuation of the globe. Depression is best in children and intractable persons, where the eyes are small and deep-seated, the cornea flat, or the conjunctiva irritated.

When the cataract is soft and the pupil small or adherent, extraction is best in old persons, in adults with a large anterior chamber and the eyes sound, and when the cataract is hard or membranous. Convex spectacles are necessary, under proper restrictions, to supply the place of the extracted crystalline lens.