The eyelids are important in protecting the globe, contributing to and spreading the tear film, and preventing the buildup of ocular pathogens and environmental debris.
The eyelids of domestic animals have many important functions. They are important in protecting the globe, contributing to and spreading the tear film, and preventing the buildup of ocular pathogens and environmental debris. This article will review the basics of eyelid anatomy and function as well as discuss common problems associated with these structures
The eyelids near the margin are thought to be composed of four primary layers: the conjunctiva, the tarsus and stroma, the orbicularis oculi muscle, and the dermis/epidermis. The margin is a mucocutaneous junction that connects the conjunctiva on the bulbar surface with the haired skin of the external surface. The primary muscle involved in eyelid closure is the circumferential orbicularis oculi muscle, innervated by the facial nerve (CN VII). The primary muscle involved in opening of the eyelid is the levator palpebrae superioris innervated by the oculomotor nerve (CN III). The tarsus (stroma) is comprised of connective tissue, levator muscles, and the tarsal or meibomian glands. These glands secrete the lipid component of the tear film and the openings for the secretory ducts are visible along the eyelid margin. The palpebral conjunctiva is the smooth, inner lining of the eyelid. It is continuous with the bulbar conjunctiva and contains lymphoid follicles, goblet cells (secrete the mucous portion of the tear film) and lymphatics.
Congenital abnormalities of the eyelids are occasionally seen in both dogs and cats. Physiologic ankyloblepharon is typically present until 10-14 days after birth. Premature opening of the palpebral fissure can result in severe ulceration since the lacrimal tissue is not fully developed. Ophthalmia neonatorum is a condition where a bacterium, often a staphylococcus, gains access to the conjunctival sac and results in purulent material building up beneath the closed eyelids. The eyelids must be opened in this case, by gentle massage if possible or scissors if necessary. The globe and conjunctiva should be aggressively flushed and topical antibiotics and ocular lubricants used frequently. Eyelid aplasia (agenesis) is a condition where a portion of the eyelid margin fails to form. This is most common in cats and typically involves the lateral dorsal eyelid. Other congenital anomalies are often associated with this condition. Various reconstructive surgical techniques have been described, depending on the severity of the defect. Dermoids are ectopic islands of skin that develop at abnormal locations. They can be present along the eyelid margin, palpebral or bulbar conjunctiva, or the cornea. Surgical excision is curative.
Eyelid cilia and aberrant hair abnormalities are common in dogs. Distichia are hairs emerging from the meibomian gland openings and are oriented parallel to the corneal surface. They arise from undifferentiated portions of the meibomian glands. The clinical significance varies. Many dogs have multiple distichia that cause no clinical signs. The vast majority of cocker spaniels have multiple fine distichia, but treatment is rarely needed. Distichia that result in clinical signs are typically shorter, stiffer hairs. These commonly result in excessive lacrimation and epiphora, blepharospasm, and corneal ulceration. Various treatment options are available. Manual epilation can be used in cases of few distichia to determine if the clinical signs are actually due to the hairs. The hairs will regrow in most cases necessitating a more permanent option. Common techniques include electrolysis, electrocautery, cryotherapy, CO2 laser ablation, and surgical resection of the distal tarsal plate. Of these, I prefer cryotherapy, especially in cases of multiple hairs. This technique is effective at destroying the hair follicle without damaging the eyelid margin. Some temporary swelling and depigmentation of the margin is common however. Laser ablation and electrolysis are useful where there are few offending hairs. Ectopic cilia are a completely different matter. In most cases, this involves a single cilium emerging from the palpebral conjunctiva and oriented perpendicular to the cornea. These are typically seen in young dogs (rarely over 2 years old) are cause severe blepharospasm and lacrimation. A corneal ulcer that is unresponsive to medical therapy is often present. They are most commonly present in the center of the dorsal eyelid, several millimeters from the margin. They are most damaging and painful when they first emerge from the conjunctiva and act like little spikes rubbing on the cornea each time the dog blinks. Unfortunately, this is also when they are the most difficult to find, and often cannot be seen without magnification. Treatment involves removal of the cilia, either through direct excision or laser ablation, followed by cyrotherapy of the eyelid to destroy the follicle.
Entropion is another common condition in dogs. In this condition, a portion of the eyelid is inverted such that the normal eyelid skin and hair makes contact with the cornea. This is usually a congenital or hereditary condition and typically requires surgical correction. There are several common exceptions. Pugs and Pekingese very commonly have a mild entropion of the medial lower eyelid. This often results in pigmentation of the medial cornea in these breeds, but typically does not cause signs of discomfort. Permanent surgery is not recommended in young puppies for several reasons. Some dogs may grow out of the condition as they age due to differences in the speed of development between the skull and skin. Furthermore, any permanent correction performed at too early an age may prove to be excessive or insufficient as the dog grows, necessitating a second surgery. In these cases, temporary eyelid tacking with either suture or surgical staples is effective at keeping the eyelid margin away from the cornea as the dog grows. Multiple tacking procedures may be necessary until the dog is old enough for surgery. Eyelid tacking is also useful in treating spastic entropion, a form of secondary entropion induced by a primary corneal injury or irritation. Relieving the eyelid contact with the cornea will allow the initiating corneal injury to heal and the eyelid will then return to a normal position. Surgery for entropion involves the removal of skin in appropriate areas to evert the eyelid margin. This is typically done by the Hotz-Celsus procedure. A strip of skin and orbicularis parallel to the margin in the affected area is removed and the edges sutured. It is important with this procedure to stay close to the margin (2-3mm) to minimize scar and ensure that sufficient eversion will occur. Removing too wide a strip of skin may result in cicatricial ectropion which can be unsightly and difficult to correct. Therefore, it is best to err on the side of caution and aim for the desired amount or slightly less. It is easier to remove more skin at a later date than to attempt to fix an overcorrected eyelid. The skin is sutured with 5-0 to 7-0 suture in an interrupted pattern, making sure the knots are a sufficient distance from the cornea. Many modifications of this surgery have been described depending on the location of the affected eyelid. Often, a full thickness wedge resection is combined with the Hotz-Celsus procedure. Many forms of hereditary entropion result from excessive length of the eyelid and thus benefit from shortening. I perform the wedge resection near the lateral canthus prior to the Hotz-Celsus and have obtained good results with this combination. Important with any eyelid margin resection techniques is precise apposition of the margin upon closure. This is achieved with a 2 layer closure involving an absorbable conjunctival layer and non-absorbable skin layer with a figure-8 suture at the margin.
Ectropion is the eversion of a portion of the eyelid away from the cornea such that there is excessive exposure of the conjunctiva. Surgery is often not necessary for this condition, except in severe forms, such as with severe macroblepharon in Mastiffs, St. Bernard's, and Bloodhounds. In these cases, a simple wedge resection of the everted areas is effective at improving the dog's comfort and reducing chronic conjunctival exposure. Cicatricial ectropion can result from overcorrected entropion surgery or trauma. This is typically corrected with a V→Y plasty but can be difficult due to significant fibrosis of the eyelid stroma. In most cases of mild ectropion, as is often seen in English bulldogs, does not require correction. The everted eyelid may result in increased conjunctival irritation and mucoid discharge due to environmental debris collecting in the ventral conjunctival sac. Treatment with topical corticosteroids is often helpful.
Macroblepharon is an oversized palpebral fissure. In brachycephalic breeds, this results in the "bulgy" eye appearance. As mentioned earlier, these dogs can have several abnormalities, including lower eyelid medial entropion, lagophthalmos and pigmentary keratitis. A permanent medial or lateral tarsorrhaphy is a common procedure for reducing the palpebral fissure length and improve eyelid coverage of the cornea. Lateral tarsorrhaphies are technically easier to perform but medial procedures result in a better cosmetic appearance. There is risk of damage to the nasolacrimal duct with medial procedures. While multiple surgical techniques have been described for shortening the palpebral fissure, I find the simplest technique the most effective and efficient. For a medial tarsorrhaphy, the eyelid margin and medial canthus are excised to a point 1-2 mm from the nasolacrimal puncta. A 2 layer closure using absorbable suture for the conjunctiva and nylon for the skin is performed. As always, careful apposition of the margin with a figure 8 suture is important. To relieve tension on the sutures, one or two temporary tarsorrhaphy sutures through the eyelid margin just lateral to the figure 8 suture is recommended and left in place for several weeks.
Trichiasis is a condition involving abnormal deviation of normal eyelid hairs. This is distinguished from entropion by observing the eyelid margin making normal contact with the cornea behind the offending hairs. I have seen this as a hereditary condition in some young dogs as well as an aging change due to loss of eyelid connective tissue in some older dogs. Nasal fold trichiasis is also common in brachycephalic breeds. Treatment is by excision of the affected skin and hair. Often this is performed as a Hotz-Celsus procedure, as for entropion. Severe trichiasis has been treated with excision of the affected skin and the wound left to heal by second intention. I have also utilized the CO2 laser to ablate the affected area in mild cases.
Blepharitis is inflammation of the eyelid tissue. There are multiple potential etiologies, including bacteria, fungi, parasites, and autoimmune. Bacterial blepharitis due to Staphylococcus or Streptococcus hypersensitivity results in significant swelling and ulceration of the eyelid and purulent discharge. Topical and systemic antibiotics are usually effective. Autoimmune blepharitis commonly involves periocular alopecia and crusting, depigmentation and ulceration of the mucocutaneous junctions, and eyelid swelling. Often all four eyelids are affected, but this may be variable. Lymphocytes and plasma cells on histopathology suggest this etiology. Topical and systemic corticosteroids are usually effective, and I will sometimes add azathioprine to reduce the amount of systemic prednisone that is necessary long term. Oral cyclosporine may also be beneficial.
Chalazia are smooth, tan colored swellings along the palpebral conjunctiva near the margin. They are inflammatory swellings that result from meibomian secretions leaking into the surrounding tissue. They are a common incidental finding and treatment is rarely necessary. They can grow to be large and irritating to the cornea in some cases. Treatment involves in incision in the chalazion with a scalpel or CO2 laser and curettage. Topical antibiotics are used after surgery. I cases of multiple chalazia, there may be signs of qualitative tear deficiency due to a lack of the lipid component of the tear film. A Schirmer Tear Test would be normal, but fluorescein would reveal that the tear film breaks up sooner than it should. Clinical signs similar to KCS (pigmentary and vascular keratitis, mucoid discharge, dull corneal appearance) may be present.
Eyelid neoplasms are very common in the dog. Fortunately, the vast majority of these tumors are benign in this species, with meibomian adenomas and papillomas among the most common. Multiple tumor types have been reported in the eyelid, however, including melanoma, adenocarcinoma, squamous cell carcinoma, and basal cell carcinomas. Histiocytomas are seen occasionally in young dogs as a smooth, pink mass on the skin surface. Fortunately, most masses are easily biopsied for definitive diagnosis. For typical eyelid masses that appear to arise from the meibomian glands, several options are available. CO2 laser ablation of the mass is a technique that is increasing in popularity. It can be performed from the palpebral conjunctival surface often with little or no disruption of the eyelid margin. Sutures are not necessary and the cosmetic result is excellent. Regrowth of the mass may occur all of the neoplastic tissue is not destroyed. Cryptherapy has also proven effective with some tumors. Simple wedge resection is also an effective technique, as long as the mass is no more than one third of the eyelid length. It is recommended that the V shaped wedge is twice as long as the base is wide to achieve the best cosmetic results. Larger tumors will require one of several reconstructive blepharoplastic techniques to fill in the resultant eyelid defect. In cats, eyelid neoplasms are usually malignant. Complete excision with complete margins is recommended in this species.