This is a disease of the crystalline lens in which it loses its transparency, becoming opaque, so that the entrance of light to the eye is obstructed. When the disease is fully developed, the patient can barely distinguish light from darkness. The pupil loses its natural blackness, the opaque lens being visible behind it. Cataract is sometimes spoken of as being on the eye, which is a popular error, as it is within the eyeball. In former times many physicians, as well as the common people, often mistook the white spots, already described as opacities of the cornea, for cataract.

The Treatment of Cataract

The only treatment is a surgical operation, which consists in removal of the crystalline lens. This is usually done by making an opening in the eyeball near the edge of the cornea, by means of a cataract knife. Fig. 447. Formerly the lens was punctured by means of a delicate needle passed into the eye, an operation known as "needleing." This plan was adopted particularly in young children. It is now abandoned, however. In the hands of skillful operators, fully four-fifths of those operated upon recover useful sight. It is generally necessary that the patient should wear glasses, two pair being usually required, one for distance, and the other for near objects, as the power of accommodation is of course lost by removal of the lens.

Fig. 447. Cataract Knife.

Fig. 447. Cataract Knife.