Text-book of ophthalmology . ll diameter are always large enough to occupy the whole pupillary areaof the lens, so that the transparent peripheral zone is always entirely con-cealed behind the iris when the pupil is not dilated. Hence, as far as visionis concerned, the denseness of the opacity is the only thing that has to beconsidered. As this latter varies greatly, all gradations are found betweenalmost normal sight and considerable impairment of vision. Treatment is required for lamellar cataract only when the interferencewith vision is considerable. In these cases there are two ways to cho
Text-book of ophthalmology . ll diameter are always large enough to occupy the whole pupillary areaof the lens, so that the transparent peripheral zone is always entirely con-cealed behind the iris when the pupil is not dilated. Hence, as far as visionis concerned, the denseness of the opacity is the only thing that has to beconsidered. As this latter varies greatly, all gradations are found betweenalmost normal sight and considerable impairment of vision. Treatment is required for lamellar cataract only when the interferencewith vision is considerable. In these cases there are two ways to choosefrom for improving the sight by operative means. The transparent periph-ery may be exposed and rendered available for vision by means of an iridec-tomy, or the lens may be removed altogether. The latter is accomplished inyoung people by discission; in older ones, in whom a hard nucleus is alreadypresent in the lens, by extraction. Each of these procedures has its definiteindications, its advantages, and its Fia. 229.—Teeth with Hypoplasia of the Enamel from a Man with Lamellar Cataract. The teeth are yellow with rough surface. In most of them two furrows, separated by a protuber-ance, run around the crown. The protuberance represents an enamel of normal thickness, while inthe course of the furrow the enamel is very thin. So too, the little pits which are to be seen most dis-tinctly on the right upper canine tooth, indicate spots where the enamel is thinned. Iridectomy is proper only when the peripheral, transparent zone of thelens is pretty broad. It retains for the patients the possibility of seeing ata distance and near by without glasses, but the visual acuity is never par-ticularly good, since in fact the central opacity remains, and the iridectomycauses disfigurement by depriving the pupil of its round shape, and alsogives rise to dazzling. On the other hand, removal of the lens produces aradical cure, and, in favorable cases, may raise the visual acui
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