The eyelids consist of four parts: 1) the outer very thin and mobile skin; 2) the strong and encircling orbicularis oculi muscle anchored at the medial canthus; 3) the thin and poorly developed fibrous tarsus, which contains the sebaceous Meibomian glands and attaches the lid to the bony orbital rim; and 4) the thin and flexible palpebral conjunctiva, which continues to the conjunctival fornix or conjunctival cul-de-sac. Eyelid disorders may be associated with facial and orbital abnormalities, specific breeds, and adjunct skin diseases, as well as with many systemic diseases.
Entropion is an inversion of all or part of the lid margins that may involve one or both eyelids and the canthi. It is the most frequent inherited eyelid defect in many canine and ovine breeds and may also follow cicatrix formation and severe blepharospasm due to ocular or periocular pain. Inversion of the cilia (or eyelashes) or facial hairs causes further discomfort, conjunctival and corneal irritation, and if protracted, corneal scarring, pigmentation, and possibly ulceration. Early spastic entropion may be reversed if the inciting cause is quickly removed or if pain is alleviated by everting the lid hairs away from the eye with mattress sutures in the lid, by subcutaneous injections (eg, of procaine penicillin) into the lid adjacent to the entropion, or by palpebral nerve blocks. Temporary stay sutures or surgical staples left in place for 2–3 wk may be used to treat entropion in very young puppies. Established entropion usually requires surgical correction.
Ectropion is a slack, everted lid margin, usually with a large palpebral fissure and elongated eyelids. It is a common bilateral conformational abnormality in a number of dog breeds, including the Bloodhound, Bull Mastiff, Great Dane, Newfoundland, St. Bernard, and several Spaniel breeds. Contracting scars in the lid or facial nerve paralysis may produce unilateral ectropion in any species. Conjunctival exposure to environmental irritants and secondary bacterial infection can result in chronic or recurrent conjunctivitis. Topical antibiotic-corticosteroid preparations may temporarily control intermittent infections, but surgical lid-shortening procedures are often indicated. Mild cases can be controlled by repeated, periodic lavage with mild decongestant solutions.
Lagophthalmos is an inability to fully close the lids and protect the cornea from drying and trauma. It may result from extremely shallow orbits (in brachycephalic breeds), exophthalmia due to a space-occupying orbital lesion, or facial nerve paralysis. Corneal scarring, pigmentation, and ulceration usually result. Unless the cause can be corrected, the therapy is frequent topical lubrication and surgical shortening or closure of the lateral canthi either temporarily or permanently. Excessive nasal skin folds and facial hair may aggravate the damage caused by lagophthalmos.
Abnormalities of the cilia include extra (distichia) or misdirected eyelashes on the lid margin. Epiphora, corneal vascularization, and corneal ulceration and scarring may result. In many instances, anomalous cilia are very fine, the same color as the surrounding eyelid hair, and result in neither clinical signs nor damage. However, ectopic cilia protruding through the dorsal palpebral conjunctiva can cause profound pain. If the corneal or conjunctival damage is caused by the extra cilia, excision, cautery, or cryothermy of the cilia follicles is indicated. Anomalies of the cilia are common and probably inherited in some dog breeds but are rare in other animal species. Distichiasis is not treated unless corneal and/or conjunctival disease results. Successful removal of distichia requires destruction of the follicular base of the eyelids while not injuring the eyelid margin. The most popular method is cryotherapy applied at the base of the cilia beneath the palpebral conjunctiva at the eyelid margin. Depigmentation of the eyelid margin may result after cryotherapy but usually re-pigments in the subsequent months. Inadequate cryotherapy can result in distichia recurrence.
Blepharitis (inflammation of the eyelids) can result from extension of a generalized dermatitis, conjunctivitis, local glandular infections, or irritants such as plant oils or solar exposure. The lids can be the original site of involvement for agents that lead to a generalized dermatitis. Dermatophytes (all species), Demodex canis (dogs), D cati or D gatoi (cats), and bacteria such as staphylococci often are involved. The mucocutaneous junction of the skin and conjunctiva can be the site of lesions of immune-mediated diseases such as pemphigus. Skin scrapings, cultures, and biopsies may be required for an accurate diagnosis. Localized glandular infections may be acute or chronic (stye [glands of Zeis and Moll] and chalazion [Meibomian glands]).
In generalized blepharitis, systemic therapy often is indicated in addition to topical treatment. Supportive therapy of hot packing and frequent cleansing is indicated in acute cases. Nonophthalmic preparations can be used to treat the eyelids, but caution in application is indicated to avoid corneal and conjunctival contact and possible irritation.