Part 30 (1/2)

The dressings should not be disturbed for at least 24 hours. The lids are then cleansed with 1-6,000 perchloride of mercury lotion, and the lower one is pulled down so as to allow the escape of tears and to see if any discharge be present. The upper lid should not be touched. If no discharge be present the eye is re-dressed. If discharge be present the conjunctival sac should be washed out carefully with boric lotion. Most wounds with conjunctival flaps are shut off in 48 hours, after which time it is advisable to wash out the conjunctival sac twice a day with boric lotion. Great care should be taken to see that no undue pressure is made on the globe. The patient should be warned not to screw up the eyes or strain whilst the dressing is being performed.

CHAPTER II

OPERATIONS UPON THE LENS

=Surgical anatomy.= The lens consists of fibres which are developed from cells originating in an inclusion of the ftal epiblast. A normal lens is surrounded by a capsule, the anterior half of which is lined with a single layer of epithelial cells on its inner surface. In ftal life the cells which line the posterior half of the capsule go to form the lens fibres, so that after birth the lens capsule is lined by cells only on its anterior surface. The lens capsule, which is deposited from the epithelial cells lining it, consists of a highly elastic membrane; small wounds in its continuity, therefore, gape widely. Throughout life the cells lining the capsule continue to become new lens fibres, but at the same time the bulk of the lens does not increase markedly. This is due to the fact that the lens fibres become more closely packed together and lose some of their watery const.i.tuents (sclerosis). The older central part of the lens is the first to undergo this process, with the result that a definite hard nucleus is found in the lenses of people about the age of thirty to thirty-five and upwards.

[Ill.u.s.tration: FIG. 83. A LENS THREE WEEKS AFTER NEEDLING. The section shows the swelling and breaking up of the lens in the anterior chamber.

The iris has become adherent to the needle puncture.]

Chemically the lens fibres are composed of crystallin, which is closely allied to a serum globulin and is therefore soluble in salt solution.

When the lens capsule has been opened, by operation or accident, the saline aqueous is admitted to the lens, which becomes opaque, swells up, and is gradually absorbed (Fig. 83). In those under the age of thirty, therefore, a simple incision into the capsule is all that is required to cause it to be absorbed. But, as has already been pointed out, the lens develops a hard nucleus after that age and will not then be absorbed satisfactorily by simply opening its capsule; to remove it, as is done in senile cataract, the hard nucleus must be extracted from the eye.

[Ill.u.s.tration: FIG. 84. ANATOMY OF THE ANTERIOR SEGMENT OF THE EYE.

Cil. P. Ciliary process.

S. Ch. Ca.n.a.l of Schlemm.

L. P. Lig. pectinatum, between the fibres of which are the s.p.a.ces of Fontana.

Sup. C. Ly. S. Suprachoroidal lymph-s.p.a.ce 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 retinae. Pars plana of the ciliary body.

R. The retina. } The junction of these with the pars plana is known as C. The choroid.} the ora serrata.

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. Ca.n.a.l of Pet.i.t.

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.

DISCISSION OR NEEDLING