Canine Nonulcerative Corneal Disease

Canine Nonulcerative Corneal Disease

Margi Gilmour, Stillwater, Oklahoma

When a corneal lesion is identified the practitioner first should determine if the disease is ulcerative or nonulcerative. Nonulcerative corneal disease usually is not painful, whereas ulcerative corneal disease is painful and is associated with blepharospasm. It is very important to distinguish a primary nonulcerative keratitis from a keratitis secondary to a healed or healing corneal ulcer. For example, the treatment for the former condition often is a topical steroid, but steroids are contraindicated in the presence of a corneal ulcer.

Additionally, the practitioner always should consider the position and function of the eyelids, as well as the quality and quantity of the tear film, whenever corneal disease is diagnosed. The cornea depends on the eyelids, tear film, and aqueous humor for maintaining its health. The tear film and aqueous humor supply nutrients to the avascular cornea, and the eyelids are responsible not only for protection but for proper distribution and restructuring of the tear film. Accordingly, the diagnostic evaluation for nonulcerative keratitis always should include a Schirmer tear test as well as fluorescein staining of the cornea.

Nonulcerative corneal disease can be inflammatory in origin, and this keratitis can be acute or chronic. Inflammatory disease is indicated by the presence of active corneal vascularization. Active vessels can be distinguished from chronic vessels by their multiple branching pattern. Superficial vessels have treelike branching, whereas deep stromal vessels are compacted with bushlike branching or a paintbrush appearance. Granulation tissue and corneal edema are additional signs of active keratitis. The finding of corneal pigmentation, or melanosis, is an indication of chronic corneal disease or corneal irritation.

Congenital Disorders

Dermoid

A corneal dermoid is a choristoma—normal tissue (skin) in an abnormal location (cornea). Corneal dermoids usually are located on the lateral aspect of the cornea. Dermoids are nonpainful; however, they usually contain hair follicles, and the hair from the dermoid may cause irritation of the adjacent normal cornea. The thickened tissue itself interferes with normal tear film spread over the cornea. Keratectomy is the treatment of choice and is curative. Keratectomy should be performed using appropriate microsurgical technique and instrumentation to allow complete excision and is best performed by an ophthalmologist.

Neonatal Dystrophy

Congenital or neonatal corneal dystrophy is a light, gray to white corneal opacity in a patchy or lacy pattern. It may be detected in neonatal puppies and is considered an incidental finding. The opacities usually resolve by 10 weeks of age. There is no associated keratitis and the condition is nonpainful. No treatment is needed.

Noninflammatory Disorders

Epithelial Inclusion Cyst

Corneal inclusion cysts are uncommon and occur when there has been injury to the epithelium. The epithelial cells form an epithelium-lined cyst that accumulates white, yellow, or tan material. The cyst is well circumscribed with normal surrounding cornea. It protrudes from the surface of the cornea and extends into the corneal stroma. Keratectomy is curative.

Lipid Keratopathy

Corneal lipid deposits appear as gray to white, refractile or glitterlike opacities in the superficial stroma. They can be bilateral or unilateral and usually do not significantly enlarge but can become denser over time. Vision rarely is affected, and the lesions are not painful. Causes of these deposits include genetic dystrophy, hyperlipidemia, and lipid degeneration in association with corneal injury, scar, or active keratitis. The long-term topical use of corticosteroids is another association. Diagnostic testing should include measurement of fasting serum cholesterol and triglyceride concentrations, particularly when the opacity is perilimbal. There is no specific treatment for the lipid deposits other than treating any existing hyperlipidemia. If the patient is receiving topical steroid medications, substitution of a topical nonsteroidal medication should be considered when possible.

Calcium-Related Degenerative Keratopathy

Calcium deposits in the epithelial and subepithelial cornea are seen most frequently in geriatric dogs, although dogs of all ages can be affected. The deposits are white, refractile, spicule opacities like an etching in glass. They are nonpainful and not associated with keratitis; however, it is not uncommon for a corneal ulcer to develop adjacent to an area of dense calcium deposits. Superficial vascularization may be seen in or surrounding the area of calcium deposition. Topical ethylenediaminetetraacetic acid (EDTA) 1% has been recommended for treatment in an attempt to chelate the calcium deposits, but even with long-term use, efficacy is variable. Calcium deposits in association with a deep corneal ulcer or descemetocele can be treated successfully with keratectomy and conjunctival pedicle graft.

Superficial Punctate Keratitis

Superficial punctate keratitis manifests as focal or multifocal, punctate, epithelial corneal opacities. The surface of the cornea may have an “orange peel” irregularity in the area of the opacities. Usually the opacities do not stain with fluorescein, but occasionally they can retain a dot of stain in the center. In some dogs the condition is associated with mild to moderate blepharospasm. Rarely there is associated superficial vascularization. The disorder appears to be familial in the sheltie and dachshund breeds. Clinical signs usually are controlled well with topical cyclosporine 1% administered every 12 hours. Lifelong treatment usually is needed.

Endothelial Dystrophy

The endothelium is a single cell layer on the inner surface of the cornea responsible for keeping the cornea dehydrated and transparent. When it is affected by disease the result is diffuse corneal edema. Endothelial dystrophy is a bilateral genetic or age-related loss of endothelial cells. The condition is nonpainful, and usually there is no associated keratitis. Vision loss is rare even with significant edema. With severe corneal edema epithelial bullae can develop on the surface of the cornea. Rupture of the bullae results in painful epithelial ulcers. Hypertonic sodium chloride 5% ointment can be used every 6 to 12 hours to help reduce the severity of edema and lessen the risk of bullae formation. Very severe cases can be referred to an ophthalmologist for thermokeratoplasty or a Gunderson flap procedure.

Florida Spots

Florida spots are a unique condition of unknown etiology seen in dogs living in tropical and subtropical climates. The underlying cause has not been identified definitively. The lesions are round, focal or multifocal, white-gray homogeneous opacities, sometimes overlapping, located in the superficial stroma. There is no associated keratitis. The condition is nonpainful and does not progress to affect vision. No successful treatment has been reported.

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Tags: Kirks Current Veterinary Therapy XV

Jul 18, 2016 | Posted by admin in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off

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