4. Subconjunctival tissue and conjunctiva.
It is most important for successful results that flaps and incisions should be made accurately down to and in the correct layer of the lid.
Along the lid margin, between the eyelashes and the posterior border of the eyelid, is a white line (intermarginal line) formed by the edge of the tarsal plate. In the many operations in which the lid is split the incision is carried along this line.
The blood-supply to the eyelids is derived from arterial arches—two in the top lid, and one in the lower—which run parallel to the margins. As far as possible, therefore, flaps should be planned with their bases at right angles to the course of the vessels. The extreme vascularity of the lid, together with the small amount of subcutaneous fat, allows of almost complete detachment of flaps of skin without fear of necrosis, but at the same time every care should be taken to avoid injuring these flaps when manipulating them. Hæmorrhage is controlled during the operation by means of clamps or by direct pressure of the lid between the finger and thumb. As a rule a general anæsthetic is required for most of the operations.
SUTURE OF WOUNDS OF THE EYELIDS
Wounds which involve the skin only are brought together in the ordinary way with a few fine sutures. In wounds of the upper lid care should be taken to suture the levator palpebræ, if divided, as otherwise traumatic ptosis may result.
Suture of wounds involving the lid margin.
(a) In simple division the margins of the lids are brought together by means of a fine suture; the conjunctival surface is first approximated, and then the skin by a deep suture which includes the tarsal cartilage. Accurate apposition of the lid border is very essential. Unfortunately a certain amount of ectropion frequently follows, which may require for its relief one of the operations given below (see [p. 284]).
(b) Occasionally the lid margin carrying the lashes may be torn off. As a rule, the strip remains attached to the lid. It should then be accurately sutured in position, taking care that the lashes take their correct turn outwards. In cases where the strip is torn off entirely, the skin and conjunctiva should be sutured together. When large portions of the lid are lost, some form of plastic operation, such as is performed for making a new lid, is required (see [p. 287]).