Eyelid coloboma (eyelid agenesis)
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Domino presented to us with eyelid “coloboma”, an unusual condition where part of the eyelid is missing not as a result from an injury but just because the normal process of eyelid development has failed. In the cat this tends to be bilateral and affect the upper lids. It results in skin hairs coming into direct contact with the eyeball, causing irritation and inflammation of the cornea (the window of the eye). Domino was particularly unlucky with both eyes affected and to make matters worse the defects were very substantial. The exact cause of eyelid coloboma is not exactly known but a genetic predisposition or possible teratogenic factor has been suggested. This means that development of the eyelid tissues before birth has gone wrong, either due to a malfunction of a gene necessary for normal development or due to an event or with a disturbing effect on normal development. In some cases with eyelid coloboma there are other problems or defects such as KCS, cataracts and retinal abnormalities.
Defects in eyelids may be treated by direct closure but this is generally not possible with very large ones (i.e. extending beyond a third of the lid length). In Domino’s case more than ½ of the eyelid length was missing. In these cases tissue from around the eye can be mobilised to re-create an eyelid but these “grafts” do not have a smooth inner lining (such as the conjunctiva) or normal eyelid margin and skin hairs form mobilised grafts may bear down on the cornea. This can be adjusted by relining the grafts with conjunctiva but an alternative approach to re-create an eyelid involves a more complicated technique where the lower eyelid is used as a “donor” for the upper lid. This can obviously leave a substantial defect in the lower lid, which in some may be closed directly so that the final result is a smaller eyelid opening but with more or less normal lid function and no more problems with irritation from hairs. If the defect left in the lower eyelid is too extensive then “second stage” surgery is needed to correct this, using sliding skin grafts or in Domino’s case, tissue from the lip. The lip to some extent resembles the eyelid: it has a smooth margin and an inner mucosal surface similar to the conjunctiva. A small section of lip tissue is freed, rotated around and used to reconstruct the lower eyelid defect.
The end result was a much happier and comfortable cat, with a particularly good outcome for the left eye. The right eye cosmetically did not as well but was comfortable and with functional repair and after several (3) surgeries a further “tidy” up procedure was decided against.