Surgical techniques for the eyelid (Proceedings)
Eyelid function is important in maintaining the health of the cornea and globe. Eyelids distribute tears over the corneal surface, remove foreign bodies from the surface of the eye, control the amount of light entering the eye and protect the globe from trauma. The outer eyelid is haired skin and the inner surface is palpebral conjunctiva. The upper lid is more mobile than the lower. The orbicularis oculi muscle (innervated by a branch of the facial nerve) encircles the eyelids and enables closing of the eyelids; closure occurs laterally to medially. The levator palpebrae muscle (innervated by the oculomotor nerve) is the main muscle responsible for opening the upper lid and the malaris muscle opens the lower lid. The eyelid margin is a mucocutaneous junction. The meibomian gland openings are positioned at the eyelid margin; these play a role in maintaining the tear film and produce the outer lipid component of the tear film (meibum) that prevents evaporation.
There are few congenital abnormalities that require surgical correction. Ankyloblepharon is delayed opening of the eyelids and should be differentiated from neonatal ophthalmia. True anklyloblepharon is infrequent and requires surgical separation of the eyelids. Neonatal ophthalmia results from infection, either intrauterine or at parturition. In these case bulging of purulent material behind the eyelids is usually evident. Careful massaging apart of the eyelids, sometimes using a mosquito hemostat will achieve normal eyelid separation. Culture and cytology of the material should be performed and topical antibiotics dispensed.
Cats may have abnormal/incomplete development of the upper lateral eyelid. Usually the medial quarter to third is normal and the condition is bilateral. The eyelid margin is absent laterally resulting in trichiasis and the palpebral conjunctiva may be absent as well. This results in an adhesion-like situation between the eyelid and the bulbar conjunctiva. Multiple techniques have been described to address this defect; the severity of the agenesis determines the correction that I use. The most simple repair utilizes a strip of haired skin harvested from below the lower eyelid; the lateral aspect of the graft is left attached and the graft is rotated to create the upper lid. This usually results in trichiasis so a graft of mucosa or conjunctiva, if available may be performed at the same time. Alternatively, a second procedure utilizing cryotherapy to address the trichiasis may be planned.Eyelids that are too long, too short, or otherwise incongruent create problems for the ocular surface. Surgical correction is indicated in these patients. Although many of these cases present while still immature, temporary corrective techniques are important until the eyelids finish growing. Too early correction may lead to further problems that require another surgery or to permanent deformity of the eyelids. For patients with entropion, or rolling in of the eyelids and the haired skin is in contact with the globe, temporary eversion of the eyelids is performed until growth is finished. Suture, staples, or glue may be used to create a fold to shorten the eyelid so the normal margin is in apposition to the cornea. As the patient grows the everting material may need to be replaced so that the appropriate amount of tissue is folded into the temporary eversion.
Once the patient is grown the need for a permanent surgery may be assessed. Sometimes, with maturity the eyelid grows to fit the globe and no surgery is indicated. In many instances the incongruity remains and tissue must be removed permanently to create normal eyelid:globe apposition. Permanent eyelid surgery should not be performed if dermatitis is present. The Hotz-Celsus procedure is the most commonly utilized; a new moon or banana shaped piece of tissue is removed. The incision starts 1-2 mm from the eyelid margin. The appropriate width of tissue is removed so that when the incisions are sutured together the eyelid margin is appropriately situated. Measurement is performed when the patient is awake with normal muscle tone; measurement after anesthesia is induced may lead to removal of too much tissue. If uncertainty is present about how much tissue to remove, for instance in a dog that squints when the eye is approached, it is better to be conservative. More tissue may always be removed, but if too much is resected long term complications may occur. Suturing of the incision proceeds with simple interrupted non-absorbable suture material using the law of halves; 4-0 to 6-0 suture is used.
Eyelid laxity may also be present with entropion. This is corrected by performing a wedge resection at the lateral canthus, either before or after the entropion surgery. In breeds with loose eyelids the primary entropion is often a factor of the long eyelids. Failure to shorten the eyelid, even when the entropion is corrected may predispose to problems over the long term. Although the easiest technique is the associated wedge resection many procedures have been described to accomplish this. Reference to an ophthalmology text is recommended for other techniques.