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

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 gla.s.ses for different distances. Vision must be reduced to less than 6/18 in both eyes after correction with gla.s.ses 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.

An eye without a lens (aphakia) will not work with an eye with a lens even if the former be corrected with gla.s.ses.

If the patient be unable to see letters, he should have a ready and quick perception of light, no cataract, however dense, being sufficient to prevent this.

(_b_) A patient should have a good _projection of light_; that is to say, he should be able to locate the light when thrown into the eye with a mirror whatever direction it comes from. Children generally turn the head towards the light, provided that they can see it and that the eye is not defective from other causes.

(_c_) Note whether _the pupils_ are equal and active. In children most useful information can often be obtained as to the condition of the fundus by means of the pupil, which often will not react when the patient is unable to appreciate light.

(_d_) _The condition of the fundus of the other eye_, if observable, should be taken into account, as many diseases of the fundus, such as choroiditis and myopia, are bilateral, and would influence the prognosis considerably.

(_e_) _The lachrymal sac_ and conjunctiva should be free from all signs of inflammation (see p. 181).

[Ill.u.s.tration: FIG. 85. EYE SPECULUM.]

[Ill.u.s.tration: FIG. 86. FIXATION FORCEPS.]

(ii) =For the removal of a lens for high myopia.= In selected cases operation gives very satisfactory results with great improvement of vision; indeed full normal distance vision has been obtained without gla.s.ses. The operation, however, is only justifiable under certain circ.u.mstances, the chief of which are:--

(_a_) The amount of myopia should exceed 18 D.

(_b_) Distance vision should be defective--less than 6/18 with gla.s.ses.

(_c_) Ophthalmoscopically the macular region should be sound.

(_d_) Binocular vision should be absent.

(_e_) The patients should be children or young adults.

(_f_) If there is some serious reason why the patient is unable to wear gla.s.ses.

In emmetropia, if the lens be removed, a gla.s.s of + 11 D. has to be placed before the eye for distance vision and + 14 D. for near vision.

It is impossible to predict the exact amount of correction of myopia which will be produced by the removal of the lens, owing to the surgeon's inability to estimate the refractive power of the lens a.s.sociated with the distortion of the posterior pole of the globe.

Usually a patient with about 22 D. of myopia is rendered emmetropic by the operation.

There are two main objections which have been raised to the operation: first, that there is a slight risk of septic infection, sympathetic ophthalmia even having been known to occur; secondly, that retinal detachment seems rather more common after operation than in ordinary myopia of the same degree. As a rule it is only advisable to perform the operation on one eye, the patient using the other for reading purposes, but under certain circ.u.mstances, as when the operation has been successful for a considerable period of time, it would be justifiable to perform it on the other eye. The operation should never be performed on patients having only one eye.

=Instruments.= Speculum (Fig. 85), fixation forceps (Fig. 86), discission needle.

=Operation.= _First step._ The operation is best performed by artificial light. The pupil having been dilated with atropine and the eye anaesthetized with cocaine (a general anaesthetic being necessary, however, for young children), the speculum is inserted by first drawing up the upper lid, making the patient look down, and inserting the top blade, and then drawing down the lower lid, making the patient look up, and inserting the lower blade. The speculum is opened to its full width without undue strain on the canthus and is kept in position by tightening the screw. The eye is steadied by fixation forceps held in the left hand, which grasp the conjunctiva as close to the cornea as possible directly opposite to the spot at which the puncture is to be made; the puncture is made directly behind the limbus and the needle is pa.s.sed into the anterior chamber.

_Second step._ Using the shaft of the needle lying in the cornea as a fulcrum on which to rotate the needle, an incision is made in the anterior capsule of the lens, and the lens fibres are broken up by a stirring movement. The needle is then rapidly withdrawn in the same plane in which it was inserted so as to avoid making a crucial incision in the cornea with the spear-like end and thereby losing the aqueous.

The best way to make sure of this is to mark one side of the handle so that it may be inserted and withdrawn in the same position. A pad and bandage are then applied.

=After-treatment.= The pupil should be kept dilated subsequently by the use of atropine twice a day until the lens has become absorbed. The bandage may be removed about the fourth day and dark gla.s.ses worn.

The effect of the operation on the lens varies considerably. It may swell up so rapidly that the tension of the eye becomes increased, in which case an evacuation may have to be performed; in other cases, especially in the cases of a patient with high myopia, several needlings may be required before absorption is complete.