Chronic superficial (or pannus) keratitis is an immune-mediated keratitis that is influenced by genetic and environmental factors. Altitude and exposure to ultraviolet radiation are the biggest environmental risk factors, with the most serious cases in this country occurring in states like Utah and Colorado. There is an apparent breed predisposition to German Shepherds and German Shepherd crossbreeds, but it can occur in any breed. It is also common in the greyhound. It usually begins as a bilateral pink or red inflammatory lesion of the inferotemporal cornea and is usually symmetrical. However, it can start in other quadrants of the cornea and be asymmetric. Histologically, the corneal infiltrate is characterized by plasma cells, lymphocytes, and blood vessels. As it progresses, the entire cornea can be affected, leading to marked deterioration in vision or blindness. Corneal pigment and fibrosis are prominent features in chronic cases. Nictitants may be involved simultaneously or exclusively (e.g., atypical pannus or plasmoma). The age of onset is usually 3 to 5 years, but can occur at any time. Pannus can be more difficult to control in dogs that are affected at a young age. Diagnosis is based on clinical presentation, breed predilection, and corneal or conjunctival cytology. Cytology usually shows a preponderance of lymphocytes and plasma cells.
Like most immune-mediated diseases, pannus is a disease that requires treatment, not a cure. Topical corticosteroids, cyclosporine, or tacrolimus are the primary treatments. Preferred steroid preparations are those with 1% prednisolone acetate or 0.1% dexamethasone. The required frequency of administration varies with the season and the severity of the pannus, but is generally 2-4 times a day. Subconjunctival steroids can be given as an adjunct to topical treatment, in treatment-resistant cases, or in dogs that are difficult to treat. Triamcinalone, methylprednisolone, and betamethasone are equally effective, but conjunctival granuloma formation may be less likely after betamethasone injection. Topically applied cyclosporine at concentrations of 0.2, 1, or 2% or tacrolimus at concentrations of 0.02 or 0.03% are also effective treatments. Some cases of pannus are effectively controlled with ciclosporin or tacrolimus alone. In other cases, its use allows for a reduction in steroid treatment, thus minimizing unwanted side effects. Treatments can often be reduced in the winter months, but must be increased again in the summer months. Beta radiation and lamellar keratectomy are additional treatment options but are no longer commonly used. Plasma cells and lymphocytes are particularly sensitive to beta radiation, and radiation is an effective treatment for difficult cases. However, the strict licensing requirements for the strontium-90 spacecraft made irradiation an impractical treatment.
This is an immune-mediated condition that presents as nodular to diffuse inflammation of the sclera or episclera. It can be unilateral or bilateral. Often only one quadrant is affected, and because of the nodular appearance, scleritis can be confused with a neoplasm. However, scleral neoplasms other than limbic melanoma are rare. There is a breed preference for the Cocker Spaniel and the Airedale. The condition can be severe in Airedale, where concomitant uveitis (i.e. scleroveitis) is common. Lymphocytes, plasma cells and histiocytes are typical histological features. The adjacent cornea is often affected with variable degrees of vascularization, inflammatory cell infiltrates, and apparent secondary lipid degeneration. Deep necrotizing scleritis is rare but can cause serious intraocular disease (eg, retinal detachment). The diagnosis is based on the clinical appearance. A biopsy can be done but is rarely necessary. Immune function tests (eg, ANA, Coombs, etc.) are often negative and of little use. Treatment usually involves a combination of topical and subconjunctival steroids or systemic treatment. Effective systemic treatments include prednisone, azathioprine, and combination therapy with tetracycline and niacinamide.
Oral or topical ciclosporin may be effective in some cases. Long-term treatment is likely to be required.
Pigmentation of the corneal epithelium or stroma is called pigmentary keratitis (also called corneal melanosis or corneal pigmentation). Several conditions can contribute to corneal pigmentation, including irritation from adnexal hairs (eg, nasal trichiasis), superfluous facial wrinkles, dry eye, or lagophthalmos. Dry eyes are probably the most common cause of corneal pigmentation in most breeds (except the Pug). Pigmentation can occur after an ulcer has healed or in association with inflammatory conditions such as pannus. As a distinct or primary clinical entity, it occurs most frequently in the Pug. In this breed, contributing factors may include breed-related exophthalmos and corneal exposure, lower eyelid nasal entropion, and nasal canthal trichiasis. However, the most important factor is probably genetics, as other breeds with a similar build have much less pigment (e.g. Bulldog, Pekingese, Shih Tzu, etc.). Nasal canthoplasty (or permanent medial tarsorrhaphy) is most commonly recommended to slow or reduce corneal pigment progression in the Pug. The benefits of this procedure include increased eye protection by reducing eyelid fissures, removing trichiasis nasal hair, and correcting nasal angle entropion.
A combination of surgery and topical treatment is usually appropriate for pugs. Topical treatments that can slow or reduce corneal pigment include cyclosporine, tacrolimus, and corticosteroids. There is no evidence that ciclosporin is more effective than tacrolimus or vice versa, so the drug that is best tolerated by the patient must be selected. Steroids used judiciously can be beneficial but should always be used on a brachycephalic breed because of their tendency to ulcerate the cornea. Beta radiation or lamellar keratectomy can be effective treatments but are generally reserved for patients in whom the pigment has progressed to the point of significant visual impairment.
corneal endothelial dystrophy
This condition is caused by defective corneal endothelium and results in excessive corneal edema, which gives the cornea a bluish-gray veil. The main differential diagnosis of edema is a corneal ulcer, uveitis, or glaucoma, which are usually easily distinguished from this condition. Endothelial dystrophy is slowly progressive, usually beginning in the lateral cornea and progressing to affect the entire cornea in middle-aged or older dogs. There is a racial preference for the Boston Terrier and the Chihuahua, but it can be seen sporadically in virtually every breed of dog. In the early stages it is not painful. Advanced endothelial dystrophy results in the formation of fluid pockets in the cornea (ie, blistering or bullous keratopathy), ulcerative keratitis, and pain. Medical management is palliative with a hyperosmotic ointment or suspension containing 5% sodium chloride (Muro-128) used twice daily to minimize edema. Don't expect dramatic callus removal, however. Topical antibiotics or atropine are indicated if the cornea is ulcerated. Conjunctival injection may be prominent in some affected dogs, and the cause is unclear. If the eyes are particularly irritated and there is no ulcer, topical steroids can be used with caution. Topical NSAIDs (eg, flurbiprofen) are sometimes beneficial. Thermal cautery (or thermal keratoplasty) may be beneficial in advanced cases when recurrent ulceration is a problem. This procedure doesn't significantly clean the cornea, but leaves enough scarring to prevent the progressive inflammation and pain associated with recurrent ulcers. The technique involves performing multiple superficial stromal burns of the cornea using a disposable ocular cautery unit or carbon dioxide laser. Surgical discretion is advised as the cornea can "melt like butter" under the heat of the cautery or laser. In selected cases, a penetrating keratoplasty (or corneal transplant) can be performed.
Lipid or calcium keratopathy
Lipid or calcifications in the cornea may appear similar but have different origins and an absolute clinical distinction is not always possible. However, three disorders are generally recognized: corneal dystrophy, corneal degeneration and arcus lipoides corneae. The term corneal dystrophy refers to an inherited, bilateral, and often symmetrical corneal lipidosis, although involvement of one eye may precede the other. Corneal lipid dystrophy occurs in a variety of dog breeds, including Siberian Husky, Samoyed, Cocker Spaniel, and Beagle. Clinically, lipid deposits in the central or paracentral cornea may impart a barely perceptible crystalline opacity, or the affected cornea may be opaque. Lipids are usually subepithelial or stromal and include cholesterol, neutral fats and phospholipids. There is no associated systemic disease. The cornea is usually unulcerated and there is no inflammation or vascularity. Rarely does corneal dystrophy cause significant visual impairment or discomfort in dogs. For these reasons, no special treatment is usually required. If treatment is desired, lamellar keratectomy is often effective in removing lipid deposits, but the condition can recur. Corneal degeneration refers to lipid or calcium deposits or both in the epithelium or stroma of the cornea as a result of a pre-existing eye disease. Previous illnesses can be corneal ulcers, uveitis or pthisis bulbi. Unlike corneal dystrophy, corneal degeneration is usually unilateral. The degenerative zone of the cornea is usually quite opaque, rough, and the epithelium is often torn. This often causes discomfort for the animal. Associated inflammation, vascularity, and pigmentation are common. Lamellar keratectomy is the treatment of choice if the animal is in pain or has vision problems (and the eye is worth saving), but the condition can recur. In some cases, a topically applied chelating agent (eg, 0.4 to 1.38% EDTA solution) may be beneficial in dissolving calcium deposits when used alone or in combination with a keratectomy. Corneal lipid degeneration can occur after prolonged treatment with topical corticosteroids, such as those used after cataract surgery, but this type of degeneration is rarely problematic. After stopping therapy, the degeneration may regress somewhat. Lipid deposits associated with systemic hyperlipidemia at the periphery of the cornea are referred to as arcus lipoides corneae. Clinically, the lipid causes a ring of opacity at the periphery of the cornea. While the condition can occur in any breed, a predisposition to German Shepherds with hypothyroidism has been suggested. Corneal arcus lipoides is usually bilateral, and there may be mild inflammation and vascularity. Treatment aims to resolve the primary disease. For most dogs with lipid or calcified keratopathy, I usually draw a fasting blood sample to assess cholesterol, triglycerides, and thyroid function. If fasting hyperlipidemia is observed, the primary cause should be sought and treated. If the blood test is normal, dietary treatment can reduce the buildup or delay its progression.
This is a relatively uncommon condition that the dachshund appears to be predisposed to. The punctate keratitis appears to be immune-mediated and this is the only case of corneal ulceration for which topical steroids are indicated. Affected eyes often have multifocal, punctured corneal opacities that retain fluorescein staining, and one or both eyes may be affected. Topical ciclosporin drops or ointments can be effective treatments, but more consistent results are usually achieved with topical steroids.
This condition has an apparent racial preference for the Sheltie, and the cause is unclear. Affected dogs have multifocal circular corneal opacities, many of which may retain fluorescein staining. Secondary lipid degeneration can occur. It can look very similar to immune-mediated punctate keratitis and respond similarly to treatment. However, topical steroids should be used with caution in these dogs as their response to steroids is less predictable than in immune-mediated punctate keratitis. Affected eyes may show marginal tear production and reduced tear film break-up time, but overt dry eye is not a feature of this disease.
Corneal (or sclera) tumors are rare. Corneal dermoid melanoma and limbal (epibulbar) melanoma are the most common. Dermoids are benign congenital tumors that most commonly occur in the temporal cornea. They can usually be completely removed by a lamellar keratectomy. Limbic melanomas may present with malignant histology but are almost always benign. They tend to grow slowly, but if ignored they can grow large enough to destroy the balloon. As their name suggests, they usually arise at the corneoscleral (limb) junction. Surgery will remarkably slow the progression of the tumor and may even be curative. However, complete excision is usually not possible without penetration of the eyeball, so there is no consensus on the most effective treatment. Surgical options include full-thickness excision followed by a grafting procedure (i.e., using nick cartilage, etc.) or partial excision followed by laser treatment or cryosurgery. The author achieved good results with the combination of partial excision and cryosurgery.
Chronic spontaneous corneal epithelial defect (indolent ulcer or recurrent erosion)
This represents a specific and unique type of corneal ulcer that is frustrating for both veterinarians and customers. They are generally chronic, superficial, non-infectious (except for feline herpesvirus), and minimally to moderately painful. Most are characterized by redundant corneal epithelial borders and variable corneal vascularity. Indolent ulcers are believed to be the result of an abnormality in the basement membrane of the corneal epithelium. An indolent ulcer is suspected when a superficial ulcer persists for more than 7 to 10 days with no apparent cause or predisposing factor. Any breed can be affected, but most affected dogs are middle-aged or older. Appropriate topical treatment should include an antibiotic (such as Neo-Poly-Bac or Tobramycin) three times a day. and 1% atropine once or twice daily for convenience. Topical hyperosmotic treatment with 5% sodium chloride ointment or drops can promote healing and reduce the risk of recurrence. Topical cyclosporine is useful in reducing corneal vascular infiltrates and scarring. Corneal epithelial debridement and grid keratotomy are more commonly recommended to facilitate healing. The intent of both procedures is to disrupt the abnormal basement membrane to allow for more effective attachment of the epithelium to the underlying stroma. Epithelial debridement is performed after applying topical anesthesia and using a dry, sterile cotton swab. One study estimates that about 40% of indolent ulcers do not heal until after debridement, and this is likely to be an accurate percentage if the ulcer remains relatively small after debridement. If the ulcer is large after debridement, a keratotomy may be necessary.
This procedure is only intended to treat uninfected superficial ulcers and should never be performed on a deep corneal ulcer. After debridement, the keratotomy is performed as described above. General anesthesia is recommended for unruly dogs or when performing this technique for the first time. For obedient animals, all that is required is topical anesthesia and good restraint or sedation. A 22 or 25 gauge needle is used to make shallow incisions or ridges of the anterior stroma in a grid pattern. To do this, the needle is pulled over the cornea at an angle of about 30 to 45 degrees. Deep penetration into the cornea should be avoided. The keratotomy should be extended 1-2 mm beyond the ulcer margins into the normal cornea. The author prefers to use a tuberculin syringe as the handle with a 25 gauge needle attached. The medical treatments continue as before. Oral anti-inflammatories and pain relievers (eg, an NSAID and tramadol) should be administered, and the dog should be fitted with an Elizabethan collar. Most ulcers heal within two weeks after grid keratotomy.