Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002

tween recurrences. L-Iysine is an arginine inhibitor that slows the replication of FRV -1. This amino acid is commonly used by humans with oral herpes problems.

13.If after using these medications, the eye has not responded, what should be done next?

FHV infections can be very frustrating for the clinician, the owner, and the animal. Refrac-

tory or nonresponsive cases should be referred to a veterinary ophthalmologist. New antiviral medications along with the use of oral or topical interferon may provide some control of FHV -I. Although it is recommended never to administer topical or systemic corticosteroids with FHV-l infections, some forms of stromal herpetic keratitis require anti-inflammatory therapy or nonsteroidal anti-inflammatory solutions.

14.Conjunctivitis is present, but white plaques have formed on the conjunctiva and cornea of a cat. What should I do?

A conjunctivial or corneal scraping is warranted. This is a common presentation of an eosinophilic conjunctivitis and keratitis. The predominate cell type is usually the eosinophil, although plasma cells and lymphocytes may be present (see Chapter 9).

15.What causes this and how should it be treated?

The etiology of eosinophilic conjunctivitis/keratitis is unknown; however, a large percentage

of these cats are positive for FHV-I. Allergies and other viruses have been implicated but never confirmed. The treatment is directed toward decreasing the immune response around the eye. Topical corticosteroids (0.1% dexamethasone phosphate) may be all that is needed to control the inflammation. Treatment should be started every 8 hours and tapered by the response. Concurrent FHV-I must be monitored, and, if suspected, antiviral medications may need to be administered. If the infiltrates are nonresponsive to therapy, give 20 mg of methylprednisolone (Depo-Medrol) subcutaneously, and a dramatic response is seen. Occasionally, systemic megestrol acetate can be used at the dosage of 5 mg PO every 24 hours for 5 days and then tapered. Megestrol acetate is a last resort for control of feline eosinophilic conjunctivitislkeratitis because of the systemic effects caused by long-term usage, such as diabetes mellitus and pyometra.

16.Is canine conjunctivitis as difficult to treat as it is in the feline patient?

No. Vary rarely is canine conjunctivitis associated with a viral infection. Bacterial and fun-

gal conjunctivitis is uncommon and usually secondary to eyelid abnormalities and keratoconjunctivitis sicca. Allergic conjunctivitis is also commonly seen and is often associated with atopy. The use of a topical antibiotic and corticosteroid solution (neomycin-polymixin-dexamethasone) is usually sufficient to control inflammation. Of course, it is necessary to rule-out a corneal ulceration with a fluorescein stain test before application of a topical corticosteroid. Corneal cultures may be warranted if infectious conjunctivitis is suspected. Other causes of conjunctivitis in the dog need to be explored.

The ocular examination is very important. Any conformational eyelid abnormality such as entropion or ectropion could cause conjunctival irritation. If they are present, appropriate surgical correction is warranted. The presence of distichiasis, trichiasis, or ectopic cilia will cause significant irritation. Very close ocular examination is needed because these cilia are difficult to visualize. The use of Rose Bengal stain is helpful in the localization of the offending cilia. Rose Bengal stains devitalized corneal epithelial cells. A corneal ulceration does not need to be present to have a positive Rose Bengal stain. Always be careful not to overlook a conjunctival foreign body. Grass awns or other plant material hide behind the nictitans and cause an intense hyperemia (Fig. 4).

17. Excessive mucoid discharge is present. In fact, the owners reports that they need to clean the discharge from the eye hourly. What should I do?

A Schirmer tear test (STT). An STT ofless than 10 mmlmin for dogs and less than 5 mmlmin for cats is diagnostic of keratoconjunctivitis sicca (KCS). Many breeds such as cocker spaniels, West Highland white terriers, bulldogs, shih tzus, and Lhaso apsos are predisposed and KCS

should be considered in any red eye problem. Treatment of topical cyclosporine (Optimmune) should be started. Adjunct therapy of tear supplementation, antibiotic, or antibiotic-corticosteroid combination therapy should be used as indicated by the severity of the inflammation.

18. Are there any other causes of KCS?

Yes. Iatrogenic causes of KCS include the systemic use of sulfonamides and the surgical removal of the third eyelid. Systemic disease such as hypothyroidism, diabetes mellitus, Cushing's syndrome, canine distemper, and chronic blepharoconjunctivitis should be considered. Systemic nonsteroidal anti-inflammatory medication has recently been implicated as a cause of KCS. Further data are needed to confirm the association of KCS with their administration. KCS is rare in cats but can be associated with chronic FHV-l infections (see Chapter 10).

19.Along with the red eye, the globe appears to be pushed forward. What should I do?

Exophthalmos is an indication of orbital disease. A common mistake is to confuse exoph-

thalmia with buphthalmia (enlargement of the globe). If the globe itself is normal, the possibility of retrobulbar disease needs to be explored. Anatomic variations can give the appearance of exophthalmos and must be considered in the brachycephalic breeds. Lagophthalmia can also contribute to this variation.

20.What diagnostic tests should be done?

A complete ophthalmic examination is needed to assess the extent of the pathology present.

Increased resistance on digital retropulsion indicates an orbital mass. Pain observed on manual opening of the oral cavity may indicate a retrobulbar lesion. A thorough examination is needed to evaluate the soft palate especially in the area of the second molar. Ocular or orbital ultrasonography will help to define the retrobulbar lesions. Radiographs, MRI, and CT scan may be warranted (see Chapter 3).

21. What are the major categories of the orbital disease?

Inflammatory, cystic, and neoplastic causes should be considered. Orbital abscesses can cause a red, exophthalmic globe. Once the diagnosis is obtained, appropriate therapy should be initiated.

22.Are there any extraocular neoplastic disease that can cause a red eye?

As previously discussed, orbital neoplasia needs to be considered. Although rare, conjuncti-

val neoplasia is possible, and any mass identified should be biopsied and resected. Appropriate adjunct therapy should be considered as determined by the type of neoplasia. Neoplasia of the nictitans is more commonly observed. Biopsy should be considered prior to removal of the entire third eyelid because the gland is responsible for 20-30% of tear production. Therefore, the removal of the third eyelid could predispose the animal to KCS (Fig. 5).

Figure 5. A melanoma located at the leading edge of the nictating membrane.

23. Neoplastic cells were not reported on my conjunctival biopsy. A diagnosis of episcleritis was given. What does it mean?

Inflammatory diseases of the episcleral tissue are rare and can be difficult to define. The first thing to do is to eliminate other causes of episcleral tissue inflammation. Keratitis, uveitis, and glaucoma must be ruled out. Episcleritis is thought to be an underlying autoimmune disorder although the etiology is frequently not determined. Episcleritis is defined as generalized, necrotizing, or nodular. Generalized episcleritis is usually responsive to topical corticosteroids. Necrotizing episcleritis is extremely challenging, rare, and a topic unto itself. Nodular episcleritis is more difficult to treat and is characterized by raised nodules usually at the limbus. Many names such as nodular episcleritis, nodular fascitis, fibrous histiocytoma, and others have been given to this condition. The criteria for naming this condition can be confusing, and the type and number of cell types (plasma cells, histiocytes, lyrnphoytes, and fibroblasts) are used to classify the lesion. It is possible that all these lesions are essentially the same, just at different stages of development (see Chapter 48).

24. Although naming the condition of episcleritis is important, how do you treat it?

This can be a very difficult disease to manage. Along with topical corticosteroids, systemic immunosuppressive medications are warranted. Topical 0.1 % dexamethasone can be used 3-4 times daily along with a tapering dose of oral prednisolone (I mg/kg every 12 hours for 4 days, than I mg/kg every 24 hours for 4 days, and then I mg/kg every other day). If the inflammation is severe, use azathioprine at a dosage of 1-2 mg/kg daily for 2 weeks and then taper as dictated by response to the medication (Fig. 6).

25.It appears nodules could just be surgically resected. Is medical treatment necessary?

For isolated nodules. the inflammatory tissue can be debulked surgically followed by use of

liquid nitrogen to freeze the area of concern. However, systemic immunosuppressive medication should still be used in conjunction with the surgery. Reoccurrence is commonly observed, and multiple cryosurgery procedures may need to be performed (Fig. 7).

26. What is scleritis?

Scleral inflammation is associated with the stromal elements of the sclera. This has a deep red or bluish-red appearance. The engorged vessels are not movable. Scleritis can be quite uncomfortable and, when the necrotizing form is present, quite devastating to the eye. Etiology is assumed to be autoimmune, and systemic immunosuppressive medications should be used as discussed with episcleritis (Fig. 8).

27.Are engorged, deep episcleral or scleral vessels always considered scleritis?

No. Glaucoma and uveitis are also possibilities that need to be considered. The redness can

be intense and associated with considerable discomfort with both of these disease processes. The

Figure 6. Episcleritis in a mature cat. It was partially responsive to topical corticosteroid therapy.

Figure 7. Nodular episcleritis in a collie.

Figure 8. Generalized scleritis in a

Labrador retriever.

measurement of intraocular pressure (lOP) is critical to differentiate uveitis from glaucoma. Glaucoma is associated with lOP> 22-25 mmHg. Corneal edema, epiphora, and light sensitivity can be associated with both disease processes. However, the presence of a dilated nonresponsive pupil is usually indicative of glaucoma. The measurement of lOP in conjunction with clinical signs should help you to key in on your clinical diagnosis. (For further discussion on glaucoma and uveitis, see Chapters 13-15.)

28. Are there any other external ocular causes of a red eye?

Of course, we cannot forget to discuss the most common corneal problem. Corneal abrasions or ulcerations are very common and can cause an intensely red and painful eye. The use of fluorescein stain will help to aid in this diagnosis. The type of ulceration is important to discern so appropriate therapy can be started. Ulcers that are refractory to treatment and do not heal within

Figure 9. Indolent ulceration in a boxer. Note the epithelial lipping present.

Figure 10. Infected corneal ulceration in a canine. Pseudomonas aeruginosa was cultured.

5-7 days may be considered an indolent ulcer or erosion. Indolent ulcers require epithelial debridement and a superficial punctate keratotomy to be performed to help stimulate healing. Appropriate antibiotic and anticollagenase medication may be necessary for treatment of infected ulcerations (see Chapter 7) (Figs. 9 and 10).

29.What is hyphema?

Hyphema, or blood within the eye, will definitely cause the eye to appear red. Hyphema can

result from trauma, retinal detachment, coagulopathies, or vasculitis from uveitis or neoplasia. Retinal detachment as a sequela to systemic hypertension can result in hyphema. A very thorough physical examination is warranted to evaluate for other systemic problems. If systemic problems are identified, proper treatment should be started immediately. Ocular treatment is focused on decreasing any existing uveitis to prevent secondary glaucoma (see Chapter 35).

4.Nasisse MP: Feline herpesvirus ocular disease. Vet Clin North Am Small Anim Pract 20:667, 1990.

5.Nasisse MP: Ocular feline herpesvirus-I infection. In Bonagura J (ed): Kirk's Current Veterinary Therapy, 13th ed. Philadelphia, W.B. Saunders, 2000, p 1057.

Figure 2. Elliptical (race track) superficial lipid corneal dystrophy. No neovascular response, which is typical of these dystrophies.

7. What is the biochemical composition of the infiltrate in corneal dystrophy?

The infiltrate in the cornea consists of a combination of cholesterol, cholesterol esters, phospholipids, and neutral fat.

Figure 3. Multiple punctate lipid corneal dystrophy.

8. What additional diagnostic tests should be performed?

A biochemistry profile including cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides is recommended. Evaluation of adrenal and thyroid function may be indicated as well. Addressing any abnormalities found may help arrest the dystrophy.

9. Describe the treatment for corneal dystrophy.

Medical treatment is usually not effective in corneal dystrophy. A superficial keratectomy may be used to remove the affected area of the cornea. Excimer laser therapy has been used to treat selected cases of corneal dystrophy.

Some superficial epithelial dystrophies exfoliate the outer layers of the cornea enough to cause hypersensitivity to the sensory nerves, inducing squinting and possibly tearing. These cases heal in a matter of days. Artificial tears used frequently reduces the sensitivity and aids in the healing process.

10. Which breeds of dogs are most commonly affected?

Although this disease has been reported in many breeds, the breeds in which this disease has been described in most detail are the beagle and the Siberian husky. Other breeds include the Shetland sheepdog, Cavalier King Charles spaniel, and Airedale terrier.

Corneal Dystrophy in the Dog: Affected Breeds'-!"

Other Breeds Affected6,l O

11.Describe the clinical appearance of corneal dystrophy in the beagle.

The lesions are oval, horizontal and on average 3 X 5 mm in size. Three clinical types have

been described.

I. The nebular form is located in the anterior third of the stroma and has a uniform ground glass appearance.

2.The race-track form involves the stroma full thickness and has a dense outer ring surrounding a lighter center.

3.In the white-arc form, white plaques located subepithelially are overlying a nebular or race track form lesion. The epithelium is usually intact.

The opacities may progress from nebular through race-track to white-arc patterns.

12.What is the clinical appearance of corneal dystrophy in the Siberian husky?

Corneal dystrophy in the Siberian husky can manifest itself in five different patterns de-

pending on the location within the corneal stroma. The infiltrate may be present (I) in the anterior part of the stroma, (2) as refractory crystals in the posterior stroma, (3) as homogenous deposits in the posterior stroma, (4) as a combination of both anterior and posterior stroma, or (5) as fullthickness corneal dystrophy (the most severe form). The infiltrates are present in a doughnutshaped pattern (Fig 4).

13.Why is corneal dystrophy in the Shetland sheepdog different from corneal dystrophy in most other breeds of dogs?

Corneal dystrophy in the Shetland sheepdog is characterized by muItifocal, superficial irregular rings 1-3 mm in diameter that are initially located in the (para)central cornea. Recurrent corneal erosions may occur associated with the dystrophic lesions, making this a potentially painful disease. Distichiasis, decreased tear film break up time, low T4 levels, and abnormal lipid profiles have been reported in affected dogs. Treatment consists of treating the corneal ulcerations associated with the dystrophy using topical antibiotics with or without atropine, cyclosporine, or hyperosmotic agents. These ulcers may behave as indolent ulcers and additional treatments such as grid keratotomy, punctate keratotomy, or soft contact lens placement may be required. A viral etiology has been suggested, but not proven, to be present. Antiviral therapy, such as idoxuridine, has been suggested in treatment of this disease.

14.Do dogs go blind from corneal dystrophy?

Corneal dystrophy rarely results in visual impairment with the possible exception of the

Siberian husky and the Airedale terrier. The dystrophy can involve a large area of the cornea in these breeds resulting in visual impairment.

15.Is corneal dystrophy inherited?

There appears to be a genetic predisposition in certain breeds. It is presumed to be caused by

Figure 4. Siberian husky corneal dystrophy. This dystrophy is deep stromal and a little more difficult to visualize.

a recessive gene with variable expression in the Siberian husky. A possible sex-linked, recessive inheritance has been suggested in the Airedale terrier. A recessive mode of inheritance is suspected in the miniature poodle.

16.Do I need to recommend against breeding a dog that has corneal dystrophy?

The Canine Eye Registration Foundation (CERF) in cooperation with the American College

of Veterinary Ophthalmologists has established guidelines for breeding advice for each individual breed of dogs. Contact your veterinary ophthalmologist for further details on specific breeds.

17. What are the characteristics of corneal degeneration?

Corneal degeneration may affect one eye or both eyes. It is a secondary change in the cornea. It is often asymmetrical if it involves both eyes. It is usually associated with inflammation in the cornea, and it may be associated with systemic diseases. In addition to lipids and cholesterol, calcium may be present in corneal degeneration as well. Corneal ulceration and vascularization of the affected area is common.

18. Name a few systemic diseases that may be associated with corneal lipid or calcium infiltration.

19.What is the treatment for corneal lipid infiltration?

Diagnosis and treatment of the underlying disease mayor may not result in spontaneous res-

olution of the lipid infiltration. Corneal lipid infiltration secondary to hypercholesterolemia may respond to a fat-restricted diet.

20.What is endothelial dystrophy?

Endothelial dystrophy or endothelial degeneration refers to the premature loss of endothelial

cells that is most commonly seen in the Chihuahua, Boston terrier, and dachshund. The loss of endothelial cells results in progressive corneal edema and may lead to bullous keratopathy and nonhealing corneal ulcers (Figs. 5 and 6).

21.How do you determine that endothelial dystrophy is the cause of corneal edema?

This is a diagnosis by exclusion. Other important causes of corneal edema such as glaucoma,

anterior uveitis, anterior lens luxation, or corneal ulceration need to be excluded. Diagnostic tests include measurement of the intraocular pressure, fluorescein staining of the cornea, careful ex-

Figure 5. Boston terrier with endothelial dystrophy. The graying of the cornea is stromal edema. Note the clear (normal) zone ventrally.