Second step. An incision is carried directly outwards from the external canthus. The length of this incision should be 1¼ times the length of the lid margin. An incision is then carried downwards from its outer end parallel to the outer limb of the V by which the lower lid has been excised. This flap is then raised freely (Fig. 161).
| Fig. 161. Modified Dieffenbach’s Operation to replace the loss of the whole lower lid. First step. The whole lower lid, together with the growth, is removed by the V-shaped incision and the flap to form the new lid is dissected up from the outer canthus. The diagram shows the incision marking out the flap. | Fig. 162. Modified Dieffenbach’s Operation. Third step. Showing the flap turned down, to the free border of which is attached the flap of skin and ear cartilage. The inset shows the proportion of skin and cartilage (light area) to be removed from the back of the ear. |
Third step. The ear is turned forward and a semilunar portion of the skin is marked out and deepened down to the cartilage. The base of this semilunar portion should be equal in length to the upper margin of the flap that is to form the new lid (Fig. 162). The skin is then dissected up for about 3 millimetres from the crescentic part of the incision back towards the straight one forming the base of the semilune. When this part of the skin has been raised the cartilage is divided, first by a curved incision, 3 millimetres behind that through the skin, and then along the straight incision joining the ends of the curved one. It is separated from the skin on the anterior surface of the ear, and the semilunar piece of skin and cartilage is thus removed. The portion of cartilage removed with the skin is smaller than the latter; the two portions coincide in length along their straight margins, but the depth of the crescent of cartilage is considerably less than that of the skin (Fig. 162). The cartilage is usually too thick to form the new tarsus and must be pared down until the right thickness is obtained. It is then applied to the inner surface of the flap to form the new lid, the skin surface being directed inwards to help to form the lower conjunctival sac. It is fixed firmly by sutures at its margin, which are passed through the whole substance of both flaps, and tied on the outer surface of the new lid.
Fourth step. The flap forming the new lower lid is sutured in position. The surface from which the flap is taken is closed as far as possible with sutures after undermining the edges, any raw area being covered by skin grafts taken from the arm.
CHAPTER X
OPERATIONS UPON THE LACHRYMAL APPARATUS
Operations upon the lachrymal apparatus are divided into—
| I. | Operations upon the lachrymal canals. |
| II. | Operations upon the lachrymal gland. |
The majority of operations are undertaken for the relief of obstruction to some portion of the canal which leads from the conjunctival sac to the nose, obstruction to which causes an overflow of tears (epiphora)—a condition which must be distinguished from hypersecretion (lachrymation).
The obstruction may occur in any part of the canal, that is to say, in the puncta, canaliculi, lachrymal sac or duct; and it is most important to determine the cause and position of the obstruction in every case before undertaking an operation for its relief. Hence it need hardly be said that the nose should be carefully examined in every case unless the cause is obvious. The operations are divided into two classes:—