Ординатура / Офтальмология / Английские материалы / Slatter's Fundemental of Vetrinary Ophthalmology 4th edition_Maggs, Miller, Ofri_2008

ANATOMY, FUNCTION, AND PATHOLOGIC RESPONSES

Anatomy and Function

The eyelids consist of a fibrous tarsal plate and muscle, bounded by skin on the outer surface and conjunctiva on the inner surface (Figure 6-1). In addition, there are a number of adnexal specializations, such as cilia (eyelashes) and glands. These components vary by species; however, some general comments are possible. The skin on the outer surface of the eyelid is thinner, more mobile, and more pliable than skin elsewhere on the body. Cilia are present on the outer surface of the upper eyelid margin in dogs, horses, cattle, pigs, and sheep. A few cilia also are present on the lower eyelids of horses, cattle, and sheep. Cats have no cilia but do have a line of modified hairs that are essentially identical. Modified sweat glands—the glands of Moll—open onto the eyelid margin near the base of the cilia. The glands of Zeis are rudimentary sebaceous glands that open into the follicles that produce the cilia. The tarsal or meibomian glands (Figures 6-1 and 6-2) are modified sebaceous glands that are embedded in the tarsal plate, a layer of fibrous tissue that gives some structural rigidity to the eyelid. The meibomian glands open right at the eyelid margin posterior to the cilia. Their orifices are visible grossly, and a grayish white secretion rich in phospholipids can be expressed from them. This secretion has two functions: It coats the eyelid margins to minimize overflow of tears and it forms the superficial lipid layer of the precorneal tear film. This lipid layer has high surface tension and thereby adds stability to and reduces evaporation of the aqueous layer of the tear film.

Tear film components drain from the ocular surface through the lacrimal puncta, which lie on the inner surfaces of the upper and lower eyelids 3 to 4 mm lateral to the medial canthus, approximately opposite the last of the meibomian gland openings. The lacrimal canaliculi drain into the lacrimal sac, which lies in a fossa of the lacrimal bone. Blinking creates a negative pressure within the sac, thereby drawing tears into it. During the relaxation phase of blinking, pressure is placed on the sac, thereby forcing tears down the nasolacrimal duct. This forms the so-called lacrimal pump. Blinking occurs with contraction of the orbicularis oculi muscle, which encircles and closes the palpebral fissure (Figures 6-3 and 6-4). It is innervated by the palpebral nerve, a branch of the facial nerve

(cranial nerve [CN] VII) (Figure 6-5). Localization of this nerve is important for injection of local anesthetic and induction of akinesia of the upper eyelid in large animals.

The general pattern and innervation of muscles surrounding the eyelids is similar in all species, although the names and relative development differ somewhat among species. The orbicularis oculi muscle is the major muscle responsible for eyelid closure. It is anchored medially to the wall of the orbit by the medial palpebral ligament (see Figure 6-5) and laterally by the retractor anguli oculi lateralis (see Figures 6-3 and 6-4). In cattle and sheep this latter structure is fibrous in nature and is known as the lateral palpebral ligament (see Figure 6-5). In horses it is visible as a fibrous raphe within the orbicularis muscle. The medial and lateral attachments of the orbicularis oculi preserve the elliptical shape of the palpebral fissure and prevent it from becoming circular during contraction of the orbicularis. Excessive muscle tone in the orbicularis oculi muscle, called blepharospasm, may result in spastic entropion.

Opening of the eyelids requires not only relaxation of the orbicularis oculi muscle but also elevation of the upper eyelid and depression of the lower eyelid. The upper eyelid is more mobile than the lower eyelid in mammals, although the opposite is true in birds and reptiles. The major elevators of the upper eyelid are the levator palpebrae superioris, which originates near the optic foramen, inserts into the tarsal plate, and is innervated by the oculomotor nerve (CN III), and Müller’s muscle, which lies posterior to the levator and is sympathetically innervated (see Figure 6-1). The levator and superior rectus muscles have common innervation (CN III), so that elevation of the globe by the superior rectus muscle is coordinated with elevation of the upper eyelid. If it were not, the animal would see the inner surface of the upper eyelid on elevation of the globe. The levator anguli oculi medialis and frontalis muscles are minor elevators of the upper eyelid and are both innervated by the palpebral nerve (see Figures 6-3 and 6-4).

The lower eyelid is depressed by the malaris muscle, which is innervated by the dorsal buccal branch of the facial nerve. Note that different branches of the facial nerve supply the orbicularis, which narrows the palpebral fissure, and the malaris, which widens it. Actions of the muscles of the eyelids are summarized in Figure 6-6. Sensory innervation for the dog, horse, and ox is shown in Figures 6-7 to 6-9. Interference with sensory or motor innervation of the eyelids may result in severe desiccation of the cornea and conjunctiva.

Adipose tissue

Orbital septum

Orbicularis

muscle

Müller’s muscle

Tarsal plate

Meibomian

gland

Cilia

FIGURE 6-1. Anatomy of the normal eyelid. (From Remington LA [2005]: Clinical Anatomy of the Visual System, 2nd ed. Butterworth-Heinemann, St. Louis.)

B

A

FIGURE 6-2. Photomicrograph of the normal eyelid stained with trichrome (Masson) showing tarsal (meibomian) gland (A) and cilium (B). (Courtesy Dr. Richard Dubielzig.)

The eyelids protect the eye in the following ways:

•Sensory and protective effects of the cilia and sensory vibrissae surrounding the eye

•Secretions of the meibomian glands and conjunctival goblet cells, which contribute to the outer lipid and inner

mucopolysaccharide layers of the precorneal tear film, respectively

•Physical protection against trauma

•Reduction of evaporation of tears

•Distribution of the precorneal tear film by eyelid movements

•“Pumping” of tears down the nasolacrimal duct, preventing epiphora and promoting a precorneal tear film of uniform thickness and optical properties

Pathologic Responses

The eyelids show pathologic reactions and diseases characteristic of skin. However, these may be modified by the extremely vascular nature of eyelids and by the numerous associated specialized structures (glands, cilia, etc.). In addition, malfunction and poor conformation of the eyelids are very common causes of ocular disease in animals, especially dogs, and frequently result in painful and potentially blinding secondary ocular disease, especially of the conjunctiva and cornea.

DELAYED OR PREMATURE OPENING OF THE EYELIDS IN NEONATES

In the newborn foal or calf the eyelids are open at birth; whereas in the kitten and puppy they open at about 10 to 14 days of age. Premature opening occurs infrequently in dogs and cats but when it does, it results in corneal desiccation, keratitis, corneal ulceration, and conjunctivitis because tear production takes several weeks to reach adequate levels. If these consequences are left untreated, corneal perforation and endophthalmitis may occur. Treatment consists of frequent application of a topical lubricating ophthalmic ointment. Rarely, a temporary tarsorrhaphy may be necessary to further limit evaporation of tears and aid in corneal healing (see Chapter 10). A small gap should be left at the medial canthus to permit administration of bactericidal antibiotic or bland lubricating ointment. Sutures are removed after 7 to 10 days, but topical treatment may be necessary for a few days longer.

More commonly, delayed opening of the eyelids (ankyloblepharon) occurs in dogs or cats. This is often associated with accumulation of mucus and sometimes with infection (ophthalmia neonatorum). Typical infectious agents vary somewhat by species: Chlamydophila felis or feline herpesvirus is common in cats, and Staphylococcus spp. may infect dogs or cats. Ankyloblepharon can be treated conservatively with warm compresses for a short period in the expectation that the eyelids will open. However, if they do not open within a day or so, the eyelids should be gently pried open with firm digital pressure or by inserting the nose of a closed pair of small mosquito hemostats at the medial canthus, where there is often a small gap between the eyelids. The hemostats can then be gently opened in this position but should not be reclosed while inserted between the eyelids, so as to avoid damage to surface ocular structures. A sharp instrument should never be used for this purpose, and the fused eyelid margins should never be incised to separate them, because either action would cause irreversible damage to the eyelid margins themselves and/or the meibomian glands with subsequent lifelong keratitis. After the eyelids are pried apart, the ocular surface should be liberally irrigated with saline or dilute (1:50) povidone-iodine solution (not povidoneiodine scrub) and the cornea checked with fluorescein stain for evidence of ulceration. A topical antibiotic ointment with a

spectrum appropriate for the suspected organisms should be applied a few times daily for approximately 1 week.

EYELID AGENESIS (COLOBOMA)

Eyelid coloboma refers to congenital absence of a portion of an eyelid. It can occur in all species but it is most common in cats, in which it usually affects the lateral portion of the upper eyelid (Figure 6-10). In piebald and Karakul sheep it has been described as affecting the middle of the upper eyelid. Coloboma is believed to be a hereditary condition. Dermoids may be seen in association with coloboma (see Chapter 10). Eyelid colobomas are associated with excessive evaporation and inadequate dispersion of the precorneal tear film, and sometimes with trichiasis. Together, these lead to secondary keratoconjunctivitis, pain, and sometimes corneal ulceration. If the lower eyelid is affected, epiphora may occur owing to escape of tears through the defect. With time, corneal scarring, pigmentation, and vascularization are common.

Eyelid colobomas are repaired with a variety of blepharoplastic procedures; the choice depends on the size and position of the defect. Larger defects require more extensive reconstructive procedures and are best referred to a veterinary ophthalmologist. However, simple defects affecting less than one third of the eyelid margin can be restored by removal of the edges of

the defect so as to create a wedge defect (Figure 6-11). This is then closed in two layers with special care to accurately appose the sides of eyelid margin without leaving sutures that may abrade the cornea (Figure 6-12). Sutures are removed 10 days later. Postoperatively, an Elizabethan collar is used. The twolayer eyelid closure also should be used for reapposition of any incisions or lacerations involving the eyelid margin, including traumatic injuries, medial canthoplasty, tumor resection, and treatment of some cases of entropion or ectropion.

PROMINENT NASAL FOLDS

In Pekingese, pugs, English bulldogs, Boston terriers, and similar brachycephalic breeds the nasal folds may be unusually prominent. When this feature is combined with a shallow orbit and prominent globe, the hair on these skin folds may contact the cornea with resultant epiphora, corneal melanosis, vascularization, and, in some cases, ulceration. A careful inspection should be made for other causes of irritation (e.g., distichiasis, medial entropion) that also are common in these same breeds. When this syndrome is seen in young puppies of breeds at risk but before the development of keratitis, the owner should be advised to observe the eyes carefully for signs of ocular disease as the animals mature.

Occipitalis

Cervicoauricularis prof. major

Interparietoscutularis

Interparietoauricularis

Interscutularis

Frontalis

Buccinator

Maxilionasolabialis pars labialis pars nasalis

Cervicoscutularis

Cervicoauricularis

superf.

Anterior part of cervicoauricularis superf.

Scutuloauricularis superf. accessorius

Scutuloauricularis superf. medius

Scutiform cartilage

Scutuloauricularis superf. dorsalis

Zygomaticoauricularis

Zygomaticus and sphincter colli prof. -pars intermedia

Retractor anguli oculi

Orbicularis oculi

Levator anguli oculi medialis

Levator nasolabialis

Lacrimal nerve

Frontal nerve

Infratrochlear

nerve

Infraorbital

nerve

Auriculotemporal nerve

Zygomatic nerve

Mental nerve

FIGURE 6-7. Sensory innervation of the canine periocular area. (Modified from Westhues M, Fritsch R [1964]: Animal Anaesthesia, Vol 1: Local Anaesthesia. Oliver & Boyd, London.)

Frontal nerve

Infratrochlear

nerve

Infraorbital

nerve

Superficial temporal nerve

Mental nerve

FIGURE 6-8. Sensory innervation of the equine periocular area.

If nasal folds are causing keratitis, they should be removed either partially (Figure 6-13) or totally (Figure 6-14). In partial removal, only the medial portion of the fold is removed, where it touches the cornea, resulting in less alteration from the breed “norm” desired by some owners. The wound is closed with simple interrupted sutures of 4/0 silk placed 2 mm apart. In both methods the suture ends should be short enough to prevent corneal irritation. Sutures are removed 10 days later. Postoperatively, an Elizabethan collar is used. Nasal fold removal should be performed in conjunction with reconstructive medial canthoplasty when there is associated corneal drying, corneal exposure, and keratitis due to macropalpebral fissure and lagophthalmos or lower medial entropion (see later discussion of brachycephalic ocular syndrome).

DISORDERS OF THE CILIA

Normally positioned cilia emerge from the dermal side of the eyelid margin (Figure 6-15, A). The three common disorders in which aberrant cilia or hair cause corneoconjunctival irritation are as follows:

•Distichiasis (Figure 6-15, B): Cilia emerge from the openings of the meibomian glands. A few soft distichia can be seen in many dogs, especially poodles and cocker spaniels. Without clinical evidence of irritation, they are considered insignificant. The typical clinical appearance of distichiasis is shown in Figure 6-16.

•Ectopic cilia (Figure 6-15, C): Cilia arise from the meibomian glands and emerge through the palpebral conjunctiva where

FIGURE 6-9. Sensory innervation of the bovine periocular area.

FIGURE 6-10. Eyelid agenesis of the right eye in a cat. Note the congenital absence of upper eyelid margin laterally and the subsequent chronic keratitis evident as superficial corneal vascularization due to trichiasis. (Courtesy University of California, Davis, Veterinary Ophthalmology Service Collection.)

A B

C D

FIGURE 6-11. Eyelid wedge resection. This general technique may be used for correction of some cases of entropion or ectropion and smaller eyelid colobomas, freshening and closure of eyelid lacerations, and removal of eyelid tumors. A, The extent of eyelid margin to be resected may be identified by gently crimping the eyelids with hemostats or with a dermatologic marker pen. B, The apex of the triangle or “wedge” to be resected is then marked in a similar manner. Usually the height of this triangle is approximately twice its base. C, The skin incision is made with a No. 15 Bard-Parker scalpel while the eyelid is supported by a Jaeger lid plate. D, The subcutis and conjunctiva are cut with straight Mayo or Stevens tenotomy scissors, so that the tissue wedge is completely resected. The method of closure is described in Figure 6-12.

A

3

2

B C D

1 4

FIGURE 6-12. Standard two-layer closure technique. A, This technique is used for all eyelid wounds or incisions that involve the eyelid margin. B, A buried 3/0 to 5/0 absorbable horizontal mattress suture is placed without penetrating the skin, the margin itself, or the conjunctiva. The suture is placed so that the appositional forces are at the margin, but the knot is distal from it so as to avoid corneal contact. This buried suture may be continued if necessary in a continuous or interrupted pattern from the eyelid margin to the apex of the incision so as to close the subcutis. C, The skin is closed using a figure-of-eight suture of 3/0 or 4/0 silk or braided nylon. Numbers identify order of needle passage through the tissue so that appositional forces are again at the margin but the knot is distal from it. Both suture ends are left long at this stage. D, The rest of the skin incision is closed with a series of closely spaced simple interrupted sutures. The ends of the figure-of-eight suture are incorporated into the knot of the first simple interrupted suture so that they are directed away from the eye.

they cause marked corneal irritation and usually ulceration. Cilia may be white or pigmented, and considerable diligence may be needed to find them. On occasions, they are visible only with the illumination and magnification provided by a slit-lamp or operating microscope.

•Trichiasis (Figure 6-15, D): Cilia or adjacent skin hairs arising from a normal location are misdirected so that they touch the cornea. This may be a primary condition but is also a consequence of nasal folds, eyelid coloboma, eyelid agenesis, and entropion.

Cilia disorders can be bilateral or unilateral and can affect upper or lower eyelids. However, ectopic cilia are more common on the upper eyelid. Although not necessarily congenital, disorders of the cilia usually are seen early in life and rarely make their first appearance after full maturity. Disorders of cilia are most common in dogs, in which they are breed-related and familial. Horses are sometimes affected with ectopic cilia; however trichiasis acquired following eyelid trauma is the most frequent cilia disorder in horses. Cats are uncommonly affected by cilia disorders.

Clinical Signs of Cilia Disorders

All cilia disorders produce similar signs, as follows:

•Epiphora: Excess tearing and staining of facial hairs is usually present despite patency of the nasolacrimal apparatus. Purulent discharge is unusual except with corneal ulceration.

•Blepharospasm: Pain associated with constant irritation and sometimes corneal ulceration is evident as blepharospasm and occasionally rubbing. In some dogs pain and epiphora are intermittent.

•Chronic conjunctival hyperemia: The surface vessels of the conjunctiva are engorged, and a reddish pink capillary flush is present. It is unusual for clinically significant disorders of cilia to be present without this sign.

•Corneal ulceration: Disorders of the cilia, particularly ectopic cilia, can cause corneal ulceration. Ulcers caused by cilia are usually shallow and are frequently eccentrically placed on the cornea, corresponding to the position of the cilia. As with ulcers due to any other cause, secondary

A B

C D

FIGURE 6-15. A, Normal eyelid. Note the position of cilia in relation to the orifice of the meibomian gland. B, Distichiasis. Cilia emerge from the meibomian gland orifice. C, Ectopic cilium. The cilium arises from the meibomian gland but emerges through the palpebral conjunctiva. D, Trichiasis. Normal cilia or hairs arising from a normal location reach the cornea due to altered facial or eyelid conformation.

A

infection may cause corneal malacia or stromal loss (see Chapter 10). In all cases of corneal ulceration a thorough search for cilia should be undertaken, with magnification and use of general anesthesia if necessary.

Adequate magnification is essential for detecting abnormal cilia.

Treatment of Distichiasis

Numerous methods have been advocated for the correction of canine distichiasis. “Eyelid-splitting” and partial tarsal plate excision techniques have been abandoned because of postoperative cicatricial entropion, scarring of the eyelid margin, and destruction of the meibomian glands. Cryoepilation or electroepilation is used most commonly now. Electroepilation is useful for treating a small number of follicles but tends to be less reliable and convenient than cryoepilation, especially when large numbers of follicles are to be treated. Simple epilation by forceps without adjunctive cryotherapy or application of an electric current is a temporary measure because the cilia regrow within 3 to 4 weeks. However, it can be useful to determine the clinical significance of the epilated cilia.

Cryoepilation

Cryoepilation takes advantage of the selective susceptibility of hair follicles to cold. A nitrous oxide or liquid nitrogen cryoprobe is applied to the conjunctiva overlying the meibomian glands that contain the offending cilia (Figure 6-17). The ice ball is observed as it advances over the line of gland openings on the eyelid margin. Two rapid freeze–slow thaw cycles are used. Following thawing of the second freeze, all visible cilia

B

FIGURE 6-16. Distichiasis in two dogs. A, This dog has distichia on both upper and lower eyelids, which are best seen when viewed against the third eyelid or sclera. B, Retroillumination also provides an excellent method of detecting more subtle distichia. (Courtesy University of Missouri, Columbia, Veterinary Ophthalmology Service Collection.)

FIGURE 6-17. Cryoepilation for distichiasis. The tarsal glands from which the distichia originate are isolated with a chalazion clamp. The clamp assists with exposure and slows thawing to enhance follicular cell death. The lid is everted and the cryoprobe is applied over the tarsal gland from the conjunctival surface. The ice ball is allowed to advance to the eyelid margin. A double freeze-thaw cycle is performed. Care must be taken to avoid corneal contact. After thawing of the second freeze, all visible cilia are manually epilated.

are manually epilated. Postoperatively, the eyelid swells and the meibomian glands undergo cryonecrosis. However, eyelid tissues other than the follicle are relatively spared. By 4 weeks, the treated meibomian glands have regenerated without cilia; however, new cilia may appear from untreated areas.

Postoperative swelling can be reduced by perioperative use of a systemically administered corticosteroid or nonsteroidal antiinflammatory drug (NSAID). An oral NSAID may be continued postoperatively for analgesia. An antibiotic-steroid ophthalmic ointment may also help diminish conjunctival swelling. Some depigmentation of the eyelid margin may occur, but most of this pigment returns within 6 months.

Failures with cryoepilation may be attributed to the following:

•Use of a “counting” or timed technique to determine the size of the ice ball rather than actual, precise observation of the frozen area through the operating microscope

•Failure to appreciate the spherical nature of an ice ball, and the potential for inadequate freezing at depth when adjacent areas are frozen. Overlapping of frozen areas avoids this problem.

•Departure from the principles of controlled cryonecrosis. The ideal is a double cycle of rapid freeze–slow thaw. A Desmarres chalazion clamp with screw lock (see Figure 6-17) helps speed the freeze and slow the thaw by reducing blood supply to the area being treated.

•Failure to identify all aberrant cilia

Electroepilation

The ideal electroepilator supplies direct current (1 to 5 mA) to the offending meibomian gland, destroying it by electrolysis. A fine needle (25 or 26 gauge) can be used as the applying electrode. It is passed alongside the cilium and into the follicle with use of adequate magnification. Current is applied for 20 to 30 seconds. Easy removal of the cilium, which often adheres to the epilation needle, indicates follicle destruction. Low currents, supplied by a small battery, prevent contraction of the orbicularis oculi, excessive damage to surrounding structures, as well as postoperative scarring. High-frequency alternating current supplied by electrosurgical units must not be used for epilation, because it may cause severe necrosis and scarring.

Treatment of Ectopic Cilia

Ectopic cilia are treated with resection of the affected cilium and meibomian gland under magnification. An elliptical Desmarres chalazion clamp with screw lock is placed around the cilium for hemostasis, and the eyelid is everted. A block of tissue containing the offending follicle and meibomian gland is removed with a small (No. 65 Beaver) scalpel blade (Figure 6-18), leaving the eyelid margin intact. No sutures are placed. Digital pressure for several minutes is sufficient to control hemorrhage. A topical broad-spectrum antibiotic ointment is applied three times daily for 5 to 7 days postoperatively. If correctly performed, this technique is highly effective and is rarely associated with recurrence, although follicles may arise in the future from different sites.

Focal tarsoconjunctival resection is the method of choice for removal of ectopic cilia.

FIGURE 6-18. Resection of an ectopic cilium. The eyelid surrounding the cilium is clamped with a chalazion clamp for hemostasis, and the eyelid is everted. A wedge of palpebral conjunctiva including the ectopic cilium and its follicle is resected en bloc.

Treatment of Trichiasis

Depending on location of the offending hairs, trichiasis is treated with any of the following:

•Regular trimming of the periocular hairs by the owner. This is often neglected by inexperienced owners and is important in breeds such as the poodle, shih tzu, and Lhasa apso.

•Cryoepilation of the offending hairs (Figure 6-19). This method is especially useful at the medial canthus when there are a large number of hairs on the inner surface of the canthus and on the medial caruncle. As with cryotherapy elsewhere on the eyelids the owner must be warned that the frozen area may be depigmented for up to 6 months.

•Surgical correction of the deformity causing the trichiasis (e.g., entropion, nasal folds, eyelid coloboma).

FIGURE 6-19. Cryoepilation for trichiasis. The offending hairs are identified and the cryoprobe is applied over the dermal surface. A lid plate is necessary to protect the cornea. The ice ball is allowed to advance to the eyelid margin. A double freeze-thaw cycle is performed. After thawing of the second freeze, offending hairs are manually epilated.

ENTROPION

Entropion, or inward rolling of the eyelid margin, is common in many species. It may be conformational, spastic, or cicatricial or may occur subsequent to alteration in globe position (enophthalmos) or size (phthisis/microphthalmos). Conformational entropion occurs most frequently in dogs and sheep but is uncommon in cats, horses, and cattle. Conformational entropion usually affects both eyes, although occasionally only one eye is affected or there is marked asymmetry in severity of the entropion. The upper eyelid is less commonly affected than the lower. The whole length of the eyelid may be affected in severe cases, but the affected area is usually restricted to one portion of the margin. In brachycephalic animals entropion is more notable medially, whereas in large, broad-skulled dogs conformational entropion frequently affects the lateral part of the lower eyelid and the lateral canthus. Conformational entropion is believed to be inherited in a large number of dog breeds, including the chow chow, English bulldog, Irish setter, Labrador and golden retrievers, Saint Bernard, shar-pei, Rottweiler, Great Dane, and Chesapeake Bay retriever. Although conformational entropion may be manifest soon after eye opening, it often does not become clinically evident in many affected breeds until later in life as the skull and associated facial skin gain their adult conformation. Occasionally maturation is associated with reduction or sometimes even resolution of entropion. For these reasons, surgery is always delayed until facial maturity is achieved.

Spastic entropion occurs with spasm of the orbicularis oculi muscle (blepharospasm) due to painful ocular conditions such as ulcerative or nonulcerative keratitis, conjunctivitis, or uveitis. It is relatively common in cats, possibly owing to the frequency with which feline herpesvirus causes corneal disease and associated pain in this species. However, because clinically significant entropion—regardless of cause—is always associated with some degree of trichiasis, spastic entropion is a component of all cases of entropion. It is important to eliminate this spastic component before permanent surgical correction of entropion; otherwise postoperative ectropion may occur. Therefore thorough assessment of entropion includes determination of the cause and relative contribution of blepharospasm through the use of the following steps:

1.Examination of the patient before and after the application of a topical anesthetic.

2.Assessment of the tear film with the Schirmer tear test.

3.Fluorescein staining. (Ulcers may be the cause or result of entropion. Regardless, they will exacerbate the spastic component.)

4.Examination with magnification for coexistent cilia disorders.

5.Assessment of aqueous flare and intraocular pressure.

Although treatment of the underlying condition sometimes relieves the spasm, surgical correction, as for conformational entropion, may be necessary.

Clinical Signs of Entropion

•Rolling in of the eyelid (Figure 6-20). This can be very subtle in some mild cases, especially if the dog is excitable in the examination room.

•Blepharospasm with further rolling in of the eyelid (“spastic entropion”)

FIGURE 6-20. Entropion of the lower eyelid of a dog with consequent epiphora and conjunctival hyperemia.

•Excoriation and maceration of the eyelid surface from constant contact with tears

•Rubbing of the affected area

•Corneal ulceration

•Corneal melanosis and vascularization in chronic cases

•Conjunctival hyperemia

•Epiphora or mucoid discharge

Treatment of Entropion

The various methods of treating entropion are summarized here. The choice of procedure depends on the level of facial maturity, species, severity and position of eyelid abnormality, and (in lambs) economic factors. Although there are surgical techniques specific to each procedure, the following general principles apply to all:

1.Always eliminate other causes of spastic entropion before deciding on the extent of surgical resection.

2.Accurately assess extent of skin resection before sedation, premedication, or induction of anesthesia. Consider use of a dermatologic marker pen. If bilateral surgery is planned, make careful preoperative note of whether the extent of resection required is symmetric.

3.Undercorrection, with the need for a second operation, is preferable to overcorrection, which causes cicatricial ectropion.

4.Minimize surgical tissue trauma.

5.It is not necessary to remove orbicularis oculi muscle; doing so increases hemorrhage, operating time, postoperative edema, and risk of infection.

6.Use fine suture material (4/0 or smaller in dogs and cats).

7.Use fine, swaged-on, cutting suture needles.

8.Place multiple, closely spaced sutures of small “bites.”

9.Use an Elizabethan collar until 2 to 3 days after suture removal.

10.Provide adequate postoperative analgesia for the first 7 to 10 days.

11.For the first few days after surgery, while the tissues are swollen, the eyelid may appear overcorrected, but as swelling subsides (over 5 to 7 days) the correction can be better evaluated. Delay any decision regarding a second operation for at least 4 to 6 weeks, when wound contraction is complete.