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

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FIGURE 17-34. Enucleation. A, A lateral canthotomy is performed. B, The globe is dissected free from the conjunctiva via a perilimbal incision. Extraocular muscle insertions and periorbita are dissected from the globe back to the optic nerve. No traction is placed on the globe or optic nerve. C, The optic nerve is transected near the globe and the eye removed. D, The cavity is packed with sponges for temporary hemostasis, and the third eyelid is removed completely. E, The lid margins are removed. F, The sponges are removed, and the conjunctiva is sutured with 3/0 or 4/0 absorbable material. G, The lid incision is sutured completely with 4/0 or 5/0 nylon or polypropylene (Prolene).

Insertion of an Intraorbital Prosthesis

Silicone or methyl methacrylate spheres may be used to prevent unsightly postoperative depressions in the orbit (Figure 17-36). Insertion of an implant is a safe and inexpensive method of improving postoperative appearance. An implant should not be placed if the reason for enucleation was neoplasia outside the globe or infection inside the globe, or if the patient has foci of possible hematogenous bacterial infection elsewhere (e.g., severe periodontal or gingival disease, pyoderma, prostatitis, chronic otitis externa, or blepharitis). Bacterial invasion of the

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implant can be minimized by prophylactic use of systemic bactericidal antibiotics. The size of the implant is determined by the depth and diameter of the orbit—generally 16 to 22 mm in dogs and cats, up 35 mm in horses.

In some patients the intact sphere may simply be placed in the orbit with acceptable cosmetic results. In many patients, however, shaping a silicone sphere to the contours of the orbit offers a superior cosmetic result and puts less tension on the skin incision. If a shaped sphere is to be used, the diameter of the sphere is typically chosen according to how closely it approximates the diameter of the orbit. One then determines

the proper depth of the sphere by placing it within the orbit and estimating the amount of the sphere required to approximate the depth of the orbit (e.g., meet the orbital rim), allowing an additional 1 to 2 mm for postoperative contraction of orbital tissues. The excess portion of the sphere that would project

17-35. The importance of histopathologic examination of enucleated globes. Amelanotic melanoma was seen histologically in the eye of this cat, which had a history of chronic, nonresponsive anterior uveitis and secondary glaucoma. (Courtesy University of Wisconsin– Madison Veterinary Ophthalmology Service Collection.)

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FIGURE 17-36. Preparation of the orbital implant. A, Approximately one third of the silicone sphere is removed so that the flat surface protrudes 1 to 2 mm above the level of the orbital rim when placed in the orbit. B and C, The cut edge is contoured and smoothed with Mayo scissors or a scalpel blade.

beyond the orbital rim is then trimmed away with a clean horizontal slice with a No. 10 scalpel blade, and the sharp edges are smoothed and contoured with a Mayo scissors or scalpel blade. The implant is inserted with the flat side uppermost. The implant is then secured firmly in place by suturing of the periorbital fascia with a continuous absorbable 3/0 suture. A subcuticular suture layer and simple interrupted sutures close the incision. The success rate with orbital prostheses in dogs is high (98% to 99%), with a higher extrusion rate in cats (up to 5%).

Transpalpebral Enucleation-Exenteration Technique

Transpalpebral enucleation-exenteration, which can be used in all species, differs from the lateral conjunctival approach in that the lids are sutured closed and dissection into the orbit is made through the skin and initially outside the extraocular muscles. Once the orbit is entered the extraocular muscles may be cut free of the globe at their insertions on the sclera if only an enucleation is required, or the entire orbital contents may be removed if an exenteration is appropriate. This approach is preferable to a subconjunctival approach if the ocular surface is infected or if ocular neoplasia has escaped from the globe. A silicone sphere may be placed as previously described.

The transpalpebral approach is useful in the field for enucleation of bovine eyes with advanced squamous cell carcinoma. The cow is restrained in a head gate or chute, or against a strong railing fence, and tranquilized with xylazine. The recommended method of local anesthesia is to infiltrate the upper and lower lids with 10 mL of lidocaine 1 to 1.5 cm from the margin, and to perform a four-point block consisting of placing 5 to 10 mL of lidocaine into the orbit by retrobulbar injection with a 5- or 6-cm needle at each of four sites adjacent to the globe at the 12, 3, 6, and 9 o’clock positions (Figure 17-37). Gently bending the needle prior to insertion into the orbit may facilitate avoidance of the globe. An auriculopalpebral nerve block may also be useful. This produces anesthesia, akinesia, and exophthalmos, which aids in surgical exposure (Figure 17-38). As the globe is removed, additional local anesthetic may be infiltrated into orbital tissues as required. General anesthesia is

FIGURE 17-37. Injection sites for local anesthesia prior to transpalpebral enucleation in cattle. Five to 10 mL of lidocaine is injected at each site to produce anesthesia and proptosis. The needle may be slightly curved before injection to facilitate entry of the orbit and avoidance of the globe.

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FIGURE 17-38. Transpalpebral enucleation/exenteration. A, The eyelids are sutured with a simple continuous suture tied at either end and are held with hemostats. B, A periocular incision is made, and dissection is performed initially outside the conjunctival sac and extraocular muscles. If an enucleation is to be performed, the extraocular muscles are severed at their insertion on the sclera. If an exenteration is to be performed, the dissection continues to the orbital apex. C and D, The optic nerve and associated vessels may be cut with scissors or clamped, ligated, and transected. E, The remaining periorbita and deep subcutaneous tissue are sutured with 3/0 or 4/0 absorbable suture, and the skin is closed with simple interrupted nonabsorbable sutures appropriate for the size and environment of the patient.

used in dogs, cats, and horses. The plane of dissection in this technique may be extended to perform an exenteration.

Enucleation in Birds

Techniques for removal of the eye in birds are modified because of the presence of scleral ossicles and the limited space in the avian orbit, into which the eye fits snugly. A transaural approach is suitable for owls (Figure 17-39), which allows retention of the globe for histologic analysis, and a globecollapsing technique is suitable for all birds, although it may interfere with histologic examination (Figure 17-40). Meticulous hemostasis (including cautery, bovine thrombin, absorbable gelatin sponges, chilled saline, etc.) is also required for enucleation in a bird, because the large orbits are capable of sequestering large fractions of the animal’s blood volume. Traction on the extraocular muscles is to be avoided in birds because it could invoke a lethal oculocardiac reflex.

Exenteration

Exenteration refers to removal of the globe and as much of the ocular contents as possible. It is performed in cases of orbital infection, orbital neoplasia, and ocular neoplasia that has extended beyond the globe. For orbital neoplasms, far better exposure is gained for exenteration by lateral orbitotomy. For

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ocular neoplasms, an extension of the transpalpebral approach is used, with wider removal of orbital tissues. If large amounts of periocular tissues are also removed, the resulting skin defect may be repaired with a caudal auricular axial pattern flap.

Evisceration and Intrascleral Prosthesis

Evisceration (see Figure 17-33, C)—removal of the contents of the globe leaving only the corneoscleral shell—is appropriate for insertion of an intrascleral prosthesis in dogs and cats and, occasionally, in horses (see later).

OCULAR PROSTHESES

Ocular prostheses are of the following three types:

•Intrascleral: Used in the treatment of chronic glaucoma and to prevent phthisis bulbi in the early stages after severe trauma

•Extrascleral: Placement of porcelain shell on the surface of the globe for cosmesis

•Intraorbital: Used to replace an enucleated globe

Intrascleral Prosthesis

In the past, intrascleral prostheses in dogs and cats were associated with persistent infection and extrusion. Use of a silicone sphere and careful technique have greatly reduced these complications. The procedure is particularly useful in the treatment of blind glaucomatous eyes and after severe ocular trauma, in the absence of infection or severe contamination, to prevent phthisis bulbi. The diameter of the implant is equal to the horizontal corneal diameter of the contralateral normal eye plus 1 mm.

After thorough evisceration of the intraocular contents, a silicone sphere (Figure 17-41) is placed in the corneoscleral shell. Care should be taken to avoid trauma to the corneal endothelium if possible. After insertion into buphthalmic eyes, the sclera and cornea contract to the size of the prosthesis, the time for contraction depending on the original size of the eye. In very large eyes, contraction may take up to 6 weeks, and often the cornea has a bluish cast postoperatively. If the cornea is in better condition before surgery it may remain clear, but even then, corneal vascularization in the 2 to 3 weeks after insertion of the prosthesis is not uncommon. This vascularization resolves over the first postoperative 6 weeks but may alarm owners and therefore must be explained to them in advance. After insertion the cornea frequently pigments, usually with an improved cosmetic outcome, but the extent of pigmentation is unpredictable. The complication rate with this procedure is also low when it is performed in correctly chosen cases. Complications include corneal mineralization, ulceration, extrusion of the implant, and keratoconjunctivitis sicca. Although implants of different colors are available, the cosmetic result in cats is generally less satisfactory than that seen in dogs with dark irides because of the normal bright coloration of the feline iris and a vertically elliptical pupil. In select cases, especially in cats, “pupils” may be tattooed onto the cornea to improve cosmesis.

Extrascleral (Shell) Prosthesis

The extrascleral prosthesis, as commonly used in humans, is a porcelain shell inserted into the conjunctival sac over a

disfigured cornea or phthisical globe. Typically an eye (i.e., conjunctiva, cornea, and iris) is painted onto the external surface of the shell, although in some animals the dark conformer can be cosmetically acceptable in and of itself (Figure 17-42). Shell prostheses are used mainly in horses but are available for dogs. The manufacture and insertion of a shell are time consuming and expensive but the shell has gratifying results for clients prepared to bear the cost and time commitment. Each shell is individually cast to fit the affected eye, fitted over a period of several weeks, then painted to match the remaining eye. The services of a specially trained oculist are invaluable. After insertion the shell must be removed daily and washed by the owner (a relatively simple procedure in a tractable horse). A technique has also been described for insertion of a customized prosthesis into a bed of polyvinylsiloxane within the orbit of fish to improve appearance and allow public display after disfiguring eye disorders.

Intraorbital Prosthesis

See earlier discussion of intraorbital prosthesis insertion in the enucleation section.

ORBITOTOMY AND ORBITECTOMY

A detailed discussion of orbitotomy techniques is beyond the scope of this text, as the procedure is performed by veterinary ophthalmologists or specialist veterinary surgeons on an elective basis. The choice of approach to the orbit depends on the size and position of the lesion being excised, as follows:

•Superior, medial, and lateral transconjunctival approaches are used for small lesions anterior to the equator of the globe.

•Limited orbitotomy involving transection of the orbital ligament is used when limited exposure to the orbit is

FIGURE 17-42. Extrascleral (shell) prosthesis in a horse. A custom-made prosthesis that fits between the conjunctival fornices may be placed over unsightly phthisical globes or after enucleation. The prosthesis may be simple, as in this case, or an oculist may paint a cosmetically convincing eye on a porcelain shell. (Courtesy University of Wisconsin–Madison Veterinary Ophthalmology Service Collection.)

FIGURE 17-40. Globe-collapsing procedure for enucleation. 1, The bird is anesthetized and placed in lateral recumbency. The orbital region is plucked and prepared for aseptic surgery. A fine-wire lid speculum is placed under the membrana nictitans and lower lid. A lateral canthotomy extends dorsal to the anterior auricular margin. 2, A 180-degree dorsal limbal incision is made, and a stay suture is placed in the incised cornea. A 360-degree subconjunctival dissection undermines the conjunctiva, membrana nictitans, and periorbital fascia. 3, The region deep to the auricular skin is gently undermined. 4, Mayo scissors are placed carefully between the uveal tract and sclera so that only the sclera and its associated ossicles are severed. 5, Forceps are used to collapse the cut margins of the sclera inward, allowing access to the posterior aspect of the orbit. To prevent damage to the optic chiasm, excessive traction should be avoided. The extraocular attachments to the globe and the optic nerve are severed, and the eye is removed. 6, The conjunctiva and membrana nictitans are removed, and a 2-mm strip of lid margin is resected. Closure is accomplished with the use of a fine (5/0 to 7/0) absorbable suture in a simple interrupted pattern. (Modified from Murphy CJ, et al. [1983]: Enucleation in birds of prey. J Am Vet Med Assoc 183:1234.)

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FIGURE 17-43. Exposure of the inferior lateral orbit by limited orbitotomy. The globe, zygomatic salivary gland, and transected orbital ligament are visible. (Modified from Bistner SI, et al. [1977]: Atlas of Veterinary Ophthalmic Surgery. Saunders, Philadelphia.)

required (Figure 17-43), as for removal of a well-delineated zygomatic mucocele.

•Orbitotomy with zygomatic arch resection is used to completely expose the orbit, as for neoplasia (Figure 17-44).

•Extensive partial and total orbitectomy is used for invasive periorbital neoplasms, such as multilobular osteosarcomas and squamous cell carcinomas (Figure 17-45). Temporalis

FIGURE 17-44. Exposure of deep orbital tissues by orbitotomy with zygomatic arch resection.

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muscle flaps and the medial mucosa of the lip may be used to reconstruct orbital margins, protect exposed brain, and reestablish oral, nasal, and orbital cavities. Adjuvant chemotherapy or radiation therapy may

be useful for osteosarcomas, squamous cell carcinomas, and hemangiomas of the orbit because of the

tendency for both local recurrence and metastasis, although protocols based on prospective studies are unavailable.

Temporalis Muscle Flap

The temporalis muscle originates from the parietal, temporal, frontal, and occipital bones and inserts onto the coronoid process of the mandible. It is the largest muscle in the head of the dog. The muscle is covered by a strong fascial sheet and supplied by the superficial temporal artery. Although the process is time consuming and technically challenging to perform, flaps from the temporalis muscle have been used to reconstruct the lateral wall of the calvarium, orbital rim, and the medial wall of the orbit. In cats, such flaps are used to obliterate the space within the frontal sinus, in combination with autogenous fat grafts.

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Systemic diseases commonly cause associated ocular lesions and signs in all domestic species as well as in humans. Recognition of ocular signs assists both ocular and systemic diagnosis, because the eye can be examined readily. Such recognition allows earlier and more accurate diagnosis of systemic disorders as well as more effective evaluation of treatment. Ocular signs of some of the less common systemic diseases are poorly documented. Therefore this chapter focuses on the ocular manifestations of the more common systemic diseases. Ocular manifestations of neoplastic, nutritional, and dermatologic conditions as well as uncommon diseases are not discussed in this chapter; the reader is referred to standard internal medicine, oncology, and dermatology texts for discussion of these diseases.

Ocular examination is an essential part of a complete physical examination.

This chapter is divided into three sections. The first deals with ocular manifestations of systemic diseases in the dog and cat. Most of the diseases are discussed separately for these two species. For some diseases, however, the discussion of both species has been combined because the interspecies differences are minute; the heading of each subsection indicates the orientation of the discussion. The first section also includes a number of tables that provide systemic differential diagnosis for ocular signs in the two species. These tables are arranged in the anatomic order of the ocular structures to which they refer (i.e., disorders of the eyelids, conjunctiva, cornea, sclera, uvea, etc.) in order to facilitate finding the list of differential diagnosis for a given disorder. The following two sections, also containing similar tables, are devoted to ocular manifestations of systemic diseases in horses and ruminants.

It should be noted that for each systemic disease, the ocular manifestations and their treatment are described rather briefly. For detailed discussion of these manifestations, the reader is referred to the respective chapters in this book. Systemic pathogenesis, signs, diagnosis, and treatment of the diseases are discussed in greater detail. However, this discussion is not intended to replace the relevant textbooks. Rather, it is intended as a teaching and diagnostic aid to students and practitioners, who are also urged to consult the numerous tables in this

chapter for lists of systemic differential diagnosis of the various ocular disorders.

OCULAR MANIFESTATIONS OF SYSTEMIC DISEASES IN DOGS AND CATS (Tables 18-1 to 18-16)

Infectious Diseases

Canine Viral Diseases

CANINE DISTEMPER. Distemper is a disease of wo rldwide prevalence afflicting many canids, including the dog. It is caused by a paramyxovirus (Morbillivirus) designated canine distemper virus (CDV) that is spread by aerosol and droplet exposure.

The systemic and ocular clinical signs vary with the stages of the disease and depend on the immune status of the dog (i.e., age, vaccination status, individual variation), the virulence of the virus, and environmental conditions. Most (50% to 70%) of the infections are subclinical.

The ocular signs are the earliest manifestations of the systemic disease; they include acute, mild to severe, bilateral, serous to mucopurulent conjunctivitis, mostly with involvement of the palpebral conjunctiva. With the progression of disease, respiratory and/or gastrointestinal signs appear. CDV may also cause lacrimal gland adenitis with decreased tear production leading to blepharospasm, keratoconjunctivitis sicca (KCS), and possible corneal ulceration. Corneal ulceration may be severe and may not respond well to routine therapy. KCS may resolve after recovery from the systemic disease.

Anterior and posterior uveitis often accompany distemper encephalomyelitis and may be observed even if the dog is clinically asymptomatic for the latter. A high incidence (41%) of multifocal, nongranulomatous chorioretinitis has been found in the neurologic forms of canine distemper. Choroidal exudation may induce retinal detachment. Retinal atrophy and scarring are the chronic sequelae of chorioretinitis. In the tapetal fundus they are characteristically observed as circumscribed, hyperreflective areas with clumps of pigment in the center, whereas the nontapetal lesions are characterized by depigmentation (see Chapter 15, Figure 15-34).

CDV has a predilection for the central nervous system (CNS), including the central visual pathways. It may cause inflammation or demyelinization of the optic nerve and tract,

18-1. Optic neuritis in a dog. Note the blurry disc margins, hemorrhages, and loss of detail on the disc surface caused by edema of the nerve head. (Courtesy University of California, Davis, Veterinary Ophthalmology Service Collection.)

lateral geniculate nucleus, optic radiations, and visual cortex. Patients may present with actue, bilateral blindness and fixed, dilated pupils due to severe optic neuritis (Figure 18-1). The inflammation may be isolated, prodromal, or concurrent with other neurologic signs of canine distemper.

The diagnosis of canine distemper is complicated because many dogs are infected but not clinically ill. Cytoplasmic inclusion bodies may be present in conjunctival epithelial cells

5 to 21 days after exposure and may be demonstrated in cytologic smears. Immunofluorescence (IF) techniques for the detection of these inclusion bodies may be used on different cytologic smears, including conjunctival epithelial smears. Recently, CDV amplicons were detected by reverse transcriptase– polymerase chain reaction (RT-PCR) of conjunctival swabs of all dogs experimentally with CDV, from day 3 to 14 after infection. The detection rate of these amplicons in conjunctival swabs was significantly higher during most of the experimental period compared to other tissue samples. Ocular treatment, which is essentially symptomatic, consists of topical ophthalmic antibacterial preparations for conjunctivitis and corneal ulcers. Cases of KCS may be treated with artificial tears, topical antibiotics, and lacromimetics. Treatment of severe corneal ulceration may require surgical intervention. Systemic and topical steroids as well as topical atropine are indicated in cases of uveitis. However, atropine should be used with extreme caution if the animal is also suffering from KCS, and steroids may not be used if the cornea is ulcerated. Systemic administration of antiinflammatory dosages of glucocorticosteroids is indicated in an animal with acute optic neuritis following confirming diagnosis of distemper, even if there is no other sign of clinical disease.

INFECTIOUS CANINE HEPATITIS. Caused by canine adenovirus 1 (CAV-1), infectious canine hepatitis affects dogs and foxes. The virus is shed in the feces and urine of infected animals, and dogs are exposed through the oronasal route. After an incubation period of 4 to 7 days, seronegative animals infected by CAV-1 exhibit systemic clinical signs that range from those of a mild upper respiratory disease to those of a severe systemic disease, including hepatomegaly, icterus, and

bleeding that may progress to disseminated intravascular coagulation. The prevalence of the disease has been dramatically reduced with the introduction of vaccination. Immunization with attenuated CAV-1 and, to a lesser extent, CAV-2 strains led to ocular signs of anterior uveitis and corneal edema in some animals. Dogs are currently vaccinated mostly with attenuated strains of CAV-2.

Ocular signs of infectious canine hepatitis are seen within 7 to 21 days of infection or vaccination. The signs are due to the presence of immune complexes in the eye and occur during convalescence. The initial signs include blepharospasm, miosis, hypotonicity, and anterior chamber flare (Figure 18-2) due to anterior uveitis. Corneal edema (“blue eye”) may develop within 1 to 2 days, although it is bilateral in only 12% to 28% of cases. The edema may be severe and lead to formation of keratoconus. Such cases may progress and cause corneal scarring and pigmentation. Persistent or long-lasting corneal edema may also occur, and the Afghan hound has been described as predisposed to chronic edema and glaucoma. However, in most cases the edema is transient, and animals recover spontaneously within a few days to 2 to 3 weeks.

The diagnosis of the ocular disease is based on the signalment, history, and clinical signs. Treatment is symptomatic, including topical glucocorticoids or nonsteroidal antiinflammatory drugs (NSAIDs) and atropine. Hypertonic solutions and ointments may be used to resolve severe corneal edema.

Feline Viral Diseases

FELINE HERPESVIRUS INFECTION. Feline herpesvirus 1 (FHV-1) infection, also called feline rhinotracheitis (FRV), is caused by a member of the Alphaherpesvirinae subfamily that affects all members of the Felidae, and all isolates belong to the same serotype. The virus is widespread in the domestic cat population, especially in colonies and catteries. Cats are infected

after direct and indirect contact with sick and carrier animals; the infection occurs through the oronasal and conjunctival routes. Cats that recover from the disease probably remain persistent carriers, a state characterized by latent infection and intermittent periods of virus shedding.

Secondary bacterial infections are common complications, especially with Chlamydophila felis. Unilateral or bilateral conjunctivitis with hyperemia, ocular discharge, chemosis, and blepharospasm are the most common lesions in adult cats with no respiratory disease. Other ocular signs are dendritic (Figure 18-3) or geographic corneal ulcers, KCS, and stromal keratitis. Symblepharon is a common sequel of infection (Figure 18-4), and FHV-1 may also play a role in the pathogenesis of corneal sequestration and eosinophilic keratitis. Vascularization of the cornea and pain may be severe or absent.

Confirmatory diagnosis of FHV-1 can be made through virus isolation in feline cell cultures. Serology is not very useful owing to the presence of antibodies from vaccination; however, immunofluorescent antibody (IFA) techniques can be used on cytologic and histologic specimens. PCR analysis has been used successfully to identify infected cats, but it is of limited use in a clinical setting because of the high prevalence of the infection in the general feline population.

In vitro sensitivity studies have identified several effective antiviral drugs—in decreasing order of potency, they are trifluridine, 5-iododeoxyuridine, and vidarabine. However, treatment is hampered by drug irritancy and availability. Trifluridine is commercially available but is topically irritating and needs to be administered at high frequency. The other two drugs are less irritating and administered less frequently but are difficult to obtain because they are not available commercially. Bromovinyldeoxyuridine and acyclovir are not effective against FHV-1, whereas valacyclovir is toxic in felines. Promising in vitro results have been reported with ganciclovir, cidofovir, and penciclovir, but large-scale clinical studies with these drugs are still lacking.