Ulcerative Keratitis

Ulcerative keratitis is a common and potentially sight-threatening condition in dogs characterized by a defect or erosion in the corneal epithelium that may extend into the deeper layers of the cornea. The cornea is the transparent, dome-shaped structure at the front of the eye that serves as the primary refractive surface and acts as a protective barrier for the internal ocular structures. It consists of four distinct layers in dogs: the outermost epithelium, the stroma which comprises approximately 90 percent of the corneal thickness, Descemet's membrane, and the innermost endothelium.

When the corneal epithelium is disrupted, the underlying stroma becomes exposed to the environment, bacterial colonization, and enzymatic degradation. This exposure triggers an inflammatory response and causes significant pain because the cornea is one of the most densely innervated tissues in the body. The severity of ulcerative keratitis ranges from superficial epithelial erosions that heal within days with appropriate treatment to deep stromal ulcers and descemetoceles that threaten the structural integrity of the globe and require emergency surgical intervention.

Ulcerative keratitis is one of the most frequently encountered ophthalmic conditions in veterinary practice. It can affect dogs of any age, breed, or sex, though certain breeds face dramatically higher risk due to their ocular conformation. The condition can be unilateral, affecting one eye, or bilateral, affecting both eyes, depending on the underlying cause. Prompt recognition and appropriate treatment are essential to prevent progression, minimize pain, preserve vision, and avoid potentially devastating complications such as corneal perforation and loss of the eye.

The classification of corneal ulcers is based on depth, cause, and behavior. Superficial ulcers involve only the epithelium and anterior stroma. Deep ulcers extend into the mid or posterior stroma. Descemetoceles occur when the stroma has been completely lost and only Descemet's membrane remains intact, bulging forward under intraocular pressure. Each category carries different prognostic implications and demands a tailored therapeutic approach.

Ulcerative keratitis in dogs arises from a wide array of causes that can be broadly categorized as traumatic, infectious, anatomical, neurological, and immune-mediated. Trauma is the most common inciting factor and includes direct mechanical injuries such as scratches from cat claws, contact with plant material or foreign bodies, self-inflicted trauma from rubbing the face, and chemical or thermal burns. Even seemingly minor injuries to the corneal surface can initiate an ulcerative process if the epithelial barrier is compromised.

Anatomical predisposition plays a major role in the incidence of ulcerative keratitis. Brachycephalic breeds with prominent, protruding eyes and shallow orbits are at substantially increased risk because their ocular conformation results in greater corneal exposure, inadequate eyelid coverage, and often compromised blink reflexes. These dogs may have lagophthalmos, the inability to fully close the eyelids, which leads to chronic corneal drying and vulnerability. Macroblepharon, or excessively large palpebral fissures, further compounds the problem. Entropion, distichiasis, ectopic cilia, and other eyelid or eyelash abnormalities can cause chronic mechanical irritation of the corneal surface, predisposing to recurrent ulceration.

Infectious agents can both initiate and complicate corneal ulcers. Bacterial organisms, particularly Staphylococcus, Streptococcus, and Pseudomonas species, are frequent secondary invaders of compromised corneal tissue. Pseudomonas aeruginosa is of particular concern because it produces potent proteolytic enzymes that can rapidly destroy corneal stroma, leading to the feared complication known as a melting ulcer or keratomalacia. Fungal keratitis, while less common in dogs than in horses, can occur, particularly in geographic regions with warm, humid climates.

Keratoconjunctivitis sicca, commonly known as dry eye, is a significant predisposing factor for ulcerative keratitis. Deficiency in the aqueous component of the tear film compromises the cornea's natural defense mechanisms, including mechanical flushing of debris and delivery of antimicrobial proteins such as lysozyme, lactoferrin, and immunoglobulin A. Neurological conditions affecting the trigeminal nerve can reduce corneal sensation, diminishing the protective blink reflex and allowing injuries to go unnoticed. Endocrine diseases such as hypothyroidism and hyperadrenocorticism may impair corneal healing and increase susceptibility to infection.

The clinical signs of ulcerative keratitis in dogs are typically readily apparent and reflect the significant pain associated with corneal injury. Blepharospasm, or involuntary squinting and forceful closure of the eyelids, is one of the earliest and most consistent signs. Dogs may hold the affected eye partially or completely closed, and attempts to examine the eye may be met with resistance. Excessive tearing, known as epiphora, is another hallmark sign, as the eye produces increased tear volume in response to corneal irritation and pain.

Ocular discharge is common and its character can provide clues about the nature and severity of the ulcer. Serous or clear watery discharge suggests uncomplicated superficial ulceration, while mucopurulent or purulent discharge with a yellow or greenish color indicates bacterial infection. The conjunctiva, the pink tissue lining the inner eyelids and covering the sclera, typically becomes hyperemic and swollen, contributing to a reddened, irritated appearance of the eye. Protrusion of the third eyelid may occur as a protective response to pain.

Visible changes to the cornea itself may be observed depending on the severity and duration of the ulcer. A focal area of cloudiness, haziness, or whitening of the corneal surface may be apparent. In more advanced cases, corneal edema manifests as a diffuse blue-gray discoloration of the cornea surrounding the ulcer. Neovascularization, the ingrowth of blood vessels from the limbus into the normally avascular cornea, develops in response to chronic or deep ulceration and appears as visible red vessels extending across the corneal surface.

Behavioral changes frequently accompany the ocular signs. Dogs may paw at the affected eye, rub their face against furniture or carpet, become photophobic and avoid bright light, or show reduced activity and appetite due to discomfort. Some dogs become head-shy and resist being touched around the face. In cases of deep or perforating ulcers, aqueous humor leakage may be observed, and the anterior chamber may appear shallow or collapsed. Any sudden worsening of signs, particularly a change from squinting to a wide-open eye with a dilated pupil, may indicate globe rupture and constitutes an ophthalmic emergency.

Diagnosis of ulcerative keratitis begins with a comprehensive ophthalmic examination, ideally performed in a dimly lit room to facilitate visualization of corneal details and to reduce the dog's discomfort from photophobia. A thorough history helps identify potential causes such as recent trauma, exposure to irritants, existing ocular conditions, or current medications. The examination should evaluate both eyes for symmetry, assess menace response and pupillary light reflexes, and evaluate the eyelids, eyelash position, and third eyelid for abnormalities that might have contributed to corneal injury.

Fluorescein staining is the cornerstone diagnostic test for corneal ulcers. Fluorescein is a water-soluble, orange dye that is applied to the ocular surface. Intact corneal epithelium is lipophilic and repels the water-soluble dye, while exposed stroma is hydrophilic and absorbs the dye, producing a bright green fluorescence when illuminated with cobalt blue or Wood's lamp light. A positive fluorescein stain confirms the presence of an epithelial defect and helps delineate the size, shape, and depth of the ulcer. Importantly, descemetoceles do not retain fluorescein because Descemet's membrane, like the epithelium, is lipophilic, though the surrounding stromal shelf will stain positively, producing a characteristic ring pattern.

Schirmer tear testing should be performed prior to application of any topical solutions to obtain an accurate measurement of basal tear production. Values below 15 millimeters per minute are suggestive of keratoconjunctivitis sicca, which may be an underlying or contributing factor. Intraocular pressure measurement using tonometry is important to rule out concurrent glaucoma, which can complicate ulcerative keratitis, and to detect low intraocular pressure that might suggest globe perforation.

Cytology and culture of the corneal surface or ulcer bed are indicated for deep, rapidly progressive, or infected ulcers, and especially for melting ulcers where identification of the causative organism is critical for guiding appropriate antimicrobial therapy. Samples should be collected before applying any topical medications that might interfere with culture results. Slit lamp biomicroscopy provides magnified, cross-sectional evaluation of the cornea, allowing precise assessment of ulcer depth, stromal thinning, and anterior chamber status. In complicated cases or when surgical planning is needed, referral to a board-certified veterinary ophthalmologist is strongly recommended.

Corneal ulcers in dogs are classified into several distinct types based on their depth, underlying pathology, and clinical behavior, and each type requires a specific management approach. Superficial corneal ulcers involve only the epithelium and minimal anterior stroma. These are the most common type encountered in practice and typically result from minor trauma. With appropriate medical therapy and elimination of the inciting cause, superficial ulcers generally heal within five to seven days through epithelial cell migration and proliferation from the surrounding healthy epithelium and the limbal stem cells.

Indolent ulcers, also known as spontaneous chronic corneal epithelial defects or Boxer ulcers due to their breed predilection, represent a distinct category of superficial ulcers characterized by their failure to heal despite apparently adequate treatment. The pathophysiology involves an abnormality in the adhesion between the corneal epithelium and the underlying stroma. A hyaline, acellular membrane forms beneath the epithelium, preventing normal attachment. On examination, these ulcers typically display loose, redundant epithelial edges that can be debrided with a dry cotton-tipped applicator. Indolent ulcers are exclusively superficial but can persist for weeks to months without targeted intervention addressing the adhesion defect.

Deep stromal ulcers extend beyond the superficial stroma into the mid or deep stroma, representing a significant loss of corneal tissue and structural integrity. These ulcers may result from progression of inadequately treated superficial ulcers, aggressive bacterial infection, or severe trauma. The risk of perforation increases as the ulcer deepens, and surgical intervention is often required to provide structural support and promote healing. Descemetoceles, in which only Descemet's membrane remains intact, represent a pre-perforation emergency requiring immediate surgical stabilization.

Melting ulcers, also termed keratomalacia or collagenolysis, are among the most aggressive and dangerous corneal ulcers. They are characterized by rapid, progressive stromal dissolution caused by proteolytic enzymes released by bacteria, particularly Pseudomonas and beta-hemolytic Streptococcus, as well as enzymes produced by the dog's own inflammatory cells and degenerating corneal cells. Clinically, the corneal surface takes on a gelatinous, translucent, or liquefied appearance, and the ulcer can progress from superficial to full-thickness perforation within 24 to 48 hours without aggressive treatment. Melting ulcers constitute a true ophthalmic emergency.

Medical management of ulcerative keratitis involves a multifaceted approach aimed at controlling infection, reducing inflammation, managing pain, supporting corneal healing, and addressing underlying predisposing conditions. The specific treatment protocol depends on the type, depth, and cause of the ulcer, and must be tailored to the individual patient. Topical broad-spectrum antibiotic therapy is the foundation of medical treatment for virtually all corneal ulcers, serving both therapeutic and prophylactic roles.

For uncomplicated superficial ulcers, a topical broad-spectrum antibiotic such as a triple antibiotic combination of neomycin, polymyxin B, and bacitracin, or a fluoroquinolone such as ofloxacin or ciprofloxacin, is typically applied three to four times daily. More severe or infected ulcers require intensified antibiotic therapy, sometimes as frequently as every one to two hours around the clock. When culture and sensitivity results are available, the antibiotic regimen should be adjusted accordingly. For Pseudomonas infections, fortified tobramycin or gentamicin may be compounded at concentrations higher than commercially available preparations.

Atropine, a topical parasympatholytic agent, is used to manage the ciliary spasm and reflex anterior uveitis that accompany corneal ulceration. By dilating the pupil and paralyzing the ciliary muscle, atropine reduces pain caused by iris and ciliary body spasm and helps prevent the formation of posterior synechiae, adhesions between the iris and lens. Atropine has a prolonged duration of action in dogs, typically 24 to 48 hours, and is usually applied once to twice daily. Owners should be advised that atropine has a bitter taste that dogs may detect through the nasolacrimal duct, potentially causing transient drooling.

Anticollagenase therapy is critical for melting ulcers to inhibit the proteolytic enzymes responsible for stromal dissolution. Autologous serum, prepared from the patient's own blood, contains natural protease inhibitors including alpha-2 macroglobulin and provides growth factors that support corneal healing. Serum drops are typically applied every one to two hours for melting ulcers. Acetylcysteine and EDTA are also used as anticollagenase agents. Systemic pain management with oral nonsteroidal anti-inflammatory drugs or other analgesics complements topical therapy. Topical corticosteroids are strictly contraindicated in the presence of any corneal ulcer, as they inhibit healing, potentiate infection, and accelerate collagenolysis.

Surgical intervention becomes necessary when medical therapy alone is insufficient to achieve healing or when the structural integrity of the cornea is compromised. The choice of surgical procedure depends on the ulcer type, depth, location, and the overall condition of the globe. Early surgical intervention can prevent corneal perforation, preserve the eye, and optimize visual outcomes. Referral to a veterinary ophthalmologist is recommended for surgical cases.

Grid keratotomy and diamond burr debridement are procedures specifically indicated for indolent ulcers that have failed to respond to medical management and epithelial debridement alone. Grid keratotomy involves creating a crosshatch pattern of superficial incisions in the anterior stroma with a needle, providing channels for epithelial cell adhesion. Diamond burr debridement uses a battery-powered rotary diamond burr to remove the abnormal hyaline basement membrane and create a roughened stromal surface that promotes epithelial attachment. Both procedures are performed under topical anesthesia, often with sedation, and success rates typically exceed 85 percent with a single treatment.

Conjunctival grafting is one of the most commonly performed corneal surgeries in veterinary ophthalmology and involves mobilizing a section of the patient's own conjunctiva to cover and support a deep corneal ulcer or descemetocele. The graft provides structural reinforcement, delivers blood supply directly to the damaged cornea to deliver antibodies, white blood cells, and growth factors, and acts as a biological bandage. Conjunctival grafts can be configured as pedicle grafts, which maintain a connection to the conjunctival base, island grafts, hood grafts, or complete 360-degree grafts depending on the ulcer's location and extent.

Corneoconjunctival transposition involves rotating a full-thickness section of healthy, adjacent cornea along with attached conjunctiva to cover the ulcer defect, preserving corneal transparency over the visual axis when possible. Corneoscleral transposition is a variation of this technique. For emergency stabilization of perforating or near-perforating ulcers, temporary tarsorrhaphy, which involves partially suturing the eyelids together, or placement of a contact lens bandage may be employed as bridging measures. More advanced options include biosynthetic corneal grafts, amniotic membrane transplantation, and porcine small intestinal submucosa grafts, which serve as scaffolds for corneal regeneration.

The corneal healing process following ulcerative keratitis involves a coordinated sequence of biological events including epithelial migration, stromal remodeling, and in many cases, neovascularization and scar formation. Understanding this process helps set appropriate expectations for owners and guides the monitoring and treatment decisions made during the recovery period. Superficial ulcers that involve only the epithelium heal rapidly, with epithelial cells migrating at a rate of approximately 0.6 millimeters per day from the ulcer margins to cover the defect.

Deep ulcers and those that have undergone surgical repair heal more slowly and through more complex mechanisms. Stromal healing involves fibroblast proliferation and the deposition of new collagen fibers, a process that takes weeks to months and results in some degree of permanent scarring and corneal opacity. The extent of scarring depends on the depth of the original ulcer, whether infection was present, and the type of surgical repair performed. Neovascularization, while initially beneficial for delivering nutrients and immune mediators to the healing cornea, eventually regresses as healing completes, though ghost vessels may remain visible.

During recovery, owners play a crucial role in administering prescribed medications consistently and on schedule, which can be demanding given that treatment for complicated ulcers may require drops every one to two hours. An Elizabethan collar must be worn at all times to prevent self-trauma to the healing eye. Recheck examinations with fluorescein staining are typically scheduled at three to five day intervals for uncomplicated ulcers and more frequently for deep or infected ulcers to monitor healing progress and detect complications early.

Complications during recovery can include ulcer progression despite treatment, secondary infection, corneal perforation, persistent corneal edema, anterior uveitis, glaucoma, and phthisis bulbi in severe cases where the eye is irreparably damaged. Failure of a superficial ulcer to show healing progress within five to seven days of appropriate therapy should prompt reconsideration of the diagnosis, evaluation for underlying causes such as dry eye or eyelid abnormalities, and possible reclassification as an indolent ulcer requiring procedural intervention.

Prevention of ulcerative keratitis focuses on identifying and managing risk factors, protecting vulnerable eyes, and maintaining optimal ocular surface health. For brachycephalic breeds with inherent anatomical predispositions, proactive measures are particularly important. Regular ophthalmic examinations by a veterinarian can identify early signs of corneal compromise, tear film deficiency, or eyelid abnormalities before ulceration occurs. Corrective surgery for entropion, ectopic cilia, or distichiasis should be performed when these conditions are identified to eliminate chronic corneal irritation.

Maintaining adequate tear production is essential for corneal health. Dogs diagnosed with keratoconjunctivitis sicca should receive consistent lacrimogenic therapy, typically with topical cyclosporine or tacrolimus, which stimulates natural tear production, along with supplemental artificial tear preparations. Compliance with these medications is critical, as interruptions in therapy can quickly lead to corneal drying and subsequent ulceration. Schirmer tear testing should be performed at regular intervals to monitor treatment efficacy and adjust therapy as needed.

Environmental modifications can reduce the risk of traumatic corneal injury. Dogs should be restrained or supervised in environments with potential ocular hazards such as dense brush, thorny vegetation, or areas where other animals might inflict scratches. Protective eyewear designed for dogs, such as goggles or visors, can be used during activities that pose increased risk, including riding in vehicles with open windows, running through wooded areas, or during hunting activities. Keeping the hair around the eyes trimmed prevents it from contacting and irritating the corneal surface.

Owner education is a cornerstone of prevention. Teaching owners to recognize the early signs of corneal disease, including squinting, tearing, redness, cloudiness, and behavioral changes, enables prompt veterinary consultation before a minor problem becomes a serious one. Owners of predisposed breeds should be counseled about the ongoing nature of ocular health management and the importance of seeking immediate veterinary attention at the first sign of eye discomfort rather than waiting to see if the condition resolves on its own.

The long-term prognosis for dogs with ulcerative keratitis varies widely based on the type, depth, and cause of the ulcer, the timeliness and appropriateness of treatment, and the presence of predisposing conditions that may lead to recurrence. Uncomplicated superficial ulcers that receive prompt and appropriate medical treatment carry an excellent prognosis, with complete healing expected within one to two weeks and minimal to no residual scarring or visual impairment. Most dogs with superficial ulcers recover fully without long-term consequences.

Indolent ulcers have a good prognosis once the adhesion defect is addressed through appropriate debridement and keratotomy or diamond burr polishing. Some dogs require more than one procedure before complete healing is achieved, and a small percentage may experience recurrence in the same or contralateral eye. Boxers and other predisposed breeds may benefit from long-term prophylactic lubrication therapy to support corneal surface health and reduce the risk of recurrent erosions.

Deep stromal ulcers, descemetoceles, and melting ulcers carry a more guarded prognosis. While many can be successfully managed with aggressive medical therapy and surgical intervention, complications such as corneal scarring, persistent opacity, irregular astigmatism, and reduced vision are common sequelae. Dense corneal scarring over the visual axis can significantly impair vision in the affected eye, though many dogs compensate well using their contralateral eye and other senses. In some cases, corneal scarring gradually becomes less dense over months to years, allowing partial visual improvement.

The most serious complications of ulcerative keratitis include corneal perforation with iris prolapse, endophthalmitis or panophthalmitis resulting from intraocular infection, secondary glaucoma from anterior uveitis and inflammatory debris blocking aqueous outflow, and phthisis bulbi representing end-stage globe shrinkage and dysfunction. Enucleation, or surgical removal of the eye, may be necessary when the globe is irreparably damaged, painful, or at risk of serving as a source of ongoing infection. Despite these potential complications, the majority of dogs with ulcerative keratitis respond well to appropriate treatment and maintain a good quality of life with preserved or functionally adequate vision.