The lens is held in position by the suspensory ligament, which consists of interlacing fibres attached on the one hand to the ciliary process and on the other to the capsule at the lenticular margins (Fig. 84). Prolapse of the vitreous after cataract extraction is prevented by the integrity of this ligament and the posterior capsule of the lens, together with the hyaloid membrane of the vitreous. The tension on the fibres of the suspensory ligament, in addition to keeping the lens in its place, also exercises traction on the lens capsule. In dislocated lenses there is a gap in the suspensory ligament either as the result of injury or of congenital malformation; when such cases require operation there is some difficulty in producing a sufficient gap in the capsule to promote their absorption, owing to the mobility of the lens and the want of traction on the incision in the capsule.
Fig. 84. Anatomy of the Anterior Segment of the Eye.
| Cil. P. Ciliary process. | S. Ch. Canal of Schlemm. | ||
| L. P. Lig. pectinatum, between the fibres of which are the spaces of Fontana. | |||
| Sup. C. Ly. S. Suprachoroidal lymph-space which extends backwards between the choroid and sclerotic. | |||
| M. Longitudinal portion | } of the ciliary muscle. | ||
| C. M. Circular portion | |||
| O. Circulus arteriosus. | S. Lig. Suspensory ligament of the lens. | ||
| E. Epithelium covering the ciliary process. | |||
| Pars Cil. Pars ciliariis retinæ. Pars plana of the ciliary body. | |||
| R. The retina. | } The junction of these with the pars plana is known as the ora serrata. | ||
| C. The choroid. | |||
| J. Iris. | S.M. Sphincter muscle. | Cry. Crypt. | |
| M. M. Pigment epithelium. | S. Cornea. Substantia propria. | ||
| B. M. Bowman’s membrane. | D. M. Descemet’s membrane. | ||
| A. Cap. Anterior capsule of the lens. | C. P. Canal of Petit. | ||
DISCISSION OR NEEDLING
Discission of the lens has for its object the tearing open of the anterior capsule, so that the lens substance may be broken up and absorbed.
Indications. This operation will be required:
(i) For cataract in patients under the age of about thirty. The forms of cataract for which these operations are usually performed are: (i) complete congenital cataract, in which the whole lens is opaque and consists of little more than a shrunken capsule which may have to be extracted if discission is unsuccessful; (ii) lamellar cataract, of sufficient density to interfere seriously with vision; (iii) posterior polar cataract in rare instances; (iv) traumatic cataract, to complete the absorption of the lens by breaking up its fibres.
Before operating on any form of cataract the following facts must be ascertained as far as possible:—
(a) Vision. It must be remembered that in children a defective eye retaining the power of accommodation is often more useful than an eye which sees better but has to wear different glasses for different distances. Vision must be reduced to less than 6/18 in both eyes after correction with glasses before the operation should be undertaken. In rare cases, in children, and in traumatic cataract where the cataract is very dense and confined to one eye, it may be removed partly to improve the personal appearance and partly to enable the patient to see large objects.