Part 34 (1/2)

[Ill.u.s.tration: FIG. 105. IRIDOTOMY BY ZIEGLER'S METHOD. Showing the first incision and the position of the second.]

[Ill.u.s.tration: FIG. 106. IRIDOTOMY BY ZIEGLER'S METHOD. Final step; the triangular flap of iris attached at its base is turned downwards.]

Apart from being one of the stages of removal of a cataract, already described, it is performed as an independent operation in the following conditions:--

1. For optical purposes (optical iridectomy).

2. For the relief of glaucoma, primary and secondary (glaucoma iridectomy).

3. For small growths at the free margin of the iris.

4. For prolapse of the iris through a wound.

OPTICAL IRIDECTOMY

=Indications.= Iridectomy for optical purposes is performed for a centrally situated nebula of the cornea and in some very rare cases of small central opacities in the lens. In the latter condition it is rarely of much value, as nearly all the rays which enter the eye pa.s.s through the central portion of the lens. Further, in this condition the lens may be removed and better sight obtained with gla.s.ses. Optical iridectomy should always be performed opposite a clear portion of the cornea, the lower segment of the eye being chosen, otherwise the coloboma may be subsequently covered by the upper lid. The site of election for the operation is downwards and inwards, but in all cases the patient should be carefully examined in the following ways: (1) the vision is tested, any refraction being corrected without a mydriatic; (2) the pupil is then dilated, and the best situation for the iridectomy determined by means of a stenopaic slit. The vision must be definitely improved by the use of these before operation can be advised. The disadvantage of an iridectomy is that it allows more light to enter the eye, and, if the periphery of the lens be uncovered, spherical aberration may result. For both these reasons, therefore, it is advisable to make the iridectomy as small as possible. Tattooing of the central scar in the cornea will often diminish the amount of light entering the eye, but before undertaking the latter operation, the eye should be cocainized and the area covered with a piece of black paper to see if the vision is improved thereby.

[Ill.u.s.tration: FIG. 107. OPTICAL IRIDECTOMY. The incision being made with a keratome.]

=Instruments.= Speculum, fixation forceps, bent broad needle or small keratome, Tyrrell's hook, iris forceps, scissors, and spatula.

=Operation.= The operation is usually performed under cocaine.

_First step._ The eye is fixed by grasping the conjunctiva directly opposite the spot at which the incision is to be made. The incision is then made by means of a keratome or bent broad needle directly behind the limbus, and enlarged laterally if desired (Fig. 107).

_Second step._ A Tyrrell's hook, bent at the correct angle, is pa.s.sed on the flat into the anterior chamber. When the margin of the iris is reached the handle is rotated and the hook is made to engage the free border of the iris, which is then withdrawn from the wound; a small portion is removed with scissors, which should be held at right angles to the wound when dividing the iris (Fig. 108).

[Ill.u.s.tration: FIG. 108. OPTICAL IRIDECTOMY. Method of removing the iris to produce a small coloboma.]

_Third step._ The iris should be carefully replaced and the pupil kept under the influence of eserine until the anterior chamber has re-formed, when atropine should be subst.i.tuted.

Care must be taken to see that the Tyrrell's hook presents no sharp angle, and great care is required in its manipulation, otherwise the lens capsule may be damaged, and traumatic cataract will result. If the iris slips from the grasp of the Tyrrell's hook, iris forceps should be used, the iris being grasped near its free margin and as small a portion as possible withdrawn.

=Brudenell Carter's method.= The ordinary optical iridectomy divides the sphincter iridis and so inhibits the activity of the pupil. With the idea of obviating this, Brudenell Carter removed a small portion of the iris (b.u.t.ton-hole), leaving the pupillary margin intact. On the whole the results of the latter operation are no more satisfactory, and the operation is more dangerous to perform owing to the likelihood of wounding the lens, and to the fact that monocular diplopia occasionally results.

The pupil should be under the influence of eserine. The incision is made as in the previous operation. De Wecker's iris scissors are inserted open into the anterior chamber, closed, and the piece of iris which bulges up between the blades cut off; this can usually be withdrawn with the scissors; or if not, it should be removed subsequently by forceps.

[Ill.u.s.tration: FIG. 109. OPTICAL IRIDECTOMY. Showing the coloboma.]

GLAUCOMA IRIDECTOMY

=Surgical and pathological anatomy.= The fluid in the anterior and posterior chambers of the eye is secreted from the ciliary body by a process of modified filtration. The fluid pa.s.ses partly direct into the posterior chamber and partly behind the suspensory ligament of the lens, making its way forward into the posterior chamber through the fibres of the suspensory ligament. From the posterior chamber it pa.s.ses into the anterior through the pupil; from the anterior it filters at the angle of the anterior chamber through the ligamentum pectinatum into the ca.n.a.l of Schlemm; thence it is carried into the blood-stream by the venous anastomosis in that region (Fig. 110).

The essential change found in all cases of primary glaucoma is the blocking of the angle of the anterior chamber owing to the root of the iris being applied to the back of the cornea, and thus preventing the filtration of the fluid into the ca.n.a.l of Schlemm, as a result of which the tension of the eye is raised, either acutely (acute glaucoma) or slowly from time to time (chronic glaucoma) (Fig. 111). The aim of every operation for the permanent relief of glaucoma is the opening up of Schlemm's ca.n.a.l at the angle of the anterior chamber or the creation of a new lymph channel between the anterior chamber and the subconjunctival tissue (filtrating cicatrix). Although this latter condition is not unattended by the risk of the spread of inflammation from the conjunctiva to the interior of the globe, it is not an inadvisable condition to obtain in some cases of chronic glaucoma if the scar be small and free from iris tissue; in this disease the opening up of the ca.n.a.l of Schlemm by iridectomy is often impossible. (See Sclerectomy, p. 231.)

=Indications.= Since the days of von Graefe, who first performed iridectomy empirically for the relief of glaucoma, the operation has held the first place in its treatment.

(i) =In primary glaucoma.= Iridectomy should be undertaken as early as possible in the disease. _In acute cases_, unless the tension is relieved, the disease ends in rapid destruction of the sight. Operation should always be undertaken as quickly as possible, provided the patient has not lost his perception of light for longer than about ten days.

[Ill.u.s.tration: FIG. 110. THE NORMAL ANGLE OF THE ANTERIOR CHAMBER.

A. Cornea.