Keratitis Sicca

Keratitis sicca, commonly referred to as dry eye, is a chronic ophthalmic condition in dogs characterized by insufficient production of the aqueous component of the tear film. The tear film is a complex three-layered structure consisting of an outer lipid layer, a middle aqueous layer, and an inner mucin layer. When the lacrimal glands fail to produce adequate aqueous tears, the resulting dryness leads to inflammation of the cornea (keratitis) and surrounding conjunctival tissues. This condition is one of the most frequently diagnosed ocular disorders in canine veterinary practice.

The tear film serves multiple critical functions for ocular health. It provides essential lubrication that allows the eyelids to glide smoothly over the corneal surface during blinking. It delivers oxygen and nutrients to the avascular cornea, removes metabolic waste products and debris, and contains antimicrobial proteins such as lysozyme, lactoferrin, and immunoglobulin A that protect against bacterial and fungal infections. When tear production falls below physiological requirements, all of these protective mechanisms become compromised, leaving the eye vulnerable to progressive damage.

Keratitis sicca affects dogs of all ages but is most commonly diagnosed in middle-aged to older dogs, typically between five and twelve years of age. The condition can affect one or both eyes, although bilateral involvement is far more common, occurring in approximately 80 percent of cases. Without appropriate treatment, keratitis sicca follows a progressive course that can ultimately result in corneal scarring, pigmentation, vascularization, ulceration, and significant visual impairment or blindness.

The prevalence of keratitis sicca in the general canine population is estimated to be approximately one to two percent, though this figure is likely an underestimate due to subclinical cases that go undiagnosed. Among predisposed breeds, the prevalence can be substantially higher. The condition represents a significant welfare concern because it causes chronic discomfort and pain that owners may not initially recognize, as dogs often do not exhibit overt signs of ocular pain until the disease has advanced considerably.

The most common cause of keratitis sicca in dogs is immune-mediated destruction of the lacrimal gland tissue. In this form, the dog's own immune system targets and progressively destroys the acinar cells of the lacrimal glands and, frequently, the nictitans gland (the gland of the third eyelid). This autoimmune process accounts for approximately 80 percent of all keratitis sicca cases in dogs. The exact trigger for this immune-mediated response remains incompletely understood, but genetic predisposition plays a significant role, as evidenced by the markedly increased incidence in certain breeds.

Drug-induced keratitis sicca is another well-recognized cause. Sulfonamide antibiotics, particularly trimethoprim-sulfa combinations, are the most commonly implicated medications. Etodolac, a nonsteroidal anti-inflammatory drug, and atropine, used to dilate the pupil, can also reduce tear production. In some cases, drug-induced dry eye may be reversible upon discontinuation of the offending medication, though prolonged exposure can result in permanent glandular damage. General anesthesia can also temporarily reduce tear production, which is why artificial tear ointments are routinely applied during surgical procedures.

Infectious causes include canine distemper virus, which can damage lacrimal gland tissue during the acute phase of infection and lead to permanent tear deficiency. Traumatic injury to the lacrimal glands or their nerve supply, surgical removal of the nictitans gland (historically performed as treatment for cherry eye, a practice now strongly discouraged), and radiation therapy involving the orbital region can all result in diminished tear production. Congenital absence or hypoplasia of the lacrimal glands, though rare, has been documented in certain toy and miniature breeds.

Neurogenic keratitis sicca results from damage to the parasympathetic nerve fibers that innervate the lacrimal glands. This form is often unilateral and may be accompanied by ipsilateral dryness of the nostril on the same side, since the same nerve branch supplies both structures. Endocrine disorders, particularly hypothyroidism and diabetes mellitus, have also been associated with decreased tear production, likely through metabolic effects on glandular function. Chronic blepharoconjunctivitis and aging-related glandular atrophy represent additional contributing factors in older dogs.

The clinical presentation of keratitis sicca varies depending on the severity and chronicity of the condition. In early or mild cases, owners may notice a subtle increase in mucoid or mucopurulent discharge accumulating in the corners of the eyes or along the eyelid margins. This discharge is often the first and most obvious sign, and it occurs because the mucin and lipid components of the tear film continue to be produced even as the aqueous component diminishes. Without adequate aqueous tears to wash away this material, it concentrates into thick, ropy strands that adhere to the ocular surface.

As the condition progresses, the cornea begins to lose its normal clarity and luster. Affected dogs develop a dull, lackluster appearance to the corneal surface, which may initially be subtle but becomes increasingly evident. Conjunctival hyperemia, or redness of the tissues surrounding the eye, is a consistent finding. Dogs may exhibit blepharospasm, characterized by squinting or keeping the eye partially closed, which indicates ocular discomfort. Excessive blinking, pawing at the eyes, and rubbing the face on furniture or carpet are behavioral indicators of irritation and pain.

Chronic keratitis sicca leads to a cascade of corneal changes that are collectively referred to as keratitis sicca syndrome. Corneal vascularization, the growth of blood vessels from the limbus across the normally avascular cornea, occurs as the body attempts to deliver nutrients to the compromised tissue. Corneal pigmentation, the deposition of melanin within the corneal epithelium and superficial stroma, progressively obscures vision as dark pigment encroaches across the visual axis. Corneal fibrosis, or scarring, adds another layer of opacity. Together, these changes can severely impair or eliminate functional vision.

Recurrent corneal ulceration is a serious complication of keratitis sicca. The dry, compromised corneal epithelium is fragile and susceptible to mechanical injury from normal eyelid movement and environmental exposure. These ulcers may become secondarily infected with bacteria, potentially progressing to stromal melting, descemetocele formation, or corneal perforation, all of which constitute ophthalmic emergencies. Dogs with keratitis sicca may also develop secondary bacterial conjunctivitis due to the loss of the antimicrobial properties normally provided by a healthy tear film.

The diagnosis of keratitis sicca is established through a combination of clinical examination and quantitative tear production measurement. The Schirmer tear test (STT) is the gold standard diagnostic tool and is performed using standardized filter paper strips placed in the lower conjunctival fornix for exactly 60 seconds. The strip wicks tears by capillary action, and the length of wetting is measured in millimeters. Normal canine tear production is typically 15 to 25 millimeters per minute. Values between 10 and 15 millimeters are considered borderline or early dry eye, while values below 10 millimeters are diagnostic for keratitis sicca. Severe cases often present with values below 5 millimeters.

Fluorescein staining is an essential component of the ophthalmic examination in dogs suspected of having keratitis sicca. A sterile fluorescein strip is applied to the corneal surface, and the eye is examined under blue cobalt light. Areas of corneal epithelial loss will retain the fluorescent dye, revealing ulceration that may not be visible on gross examination. This test is critical because corneal ulceration requires additional therapeutic intervention and may necessitate adjustments to the treatment plan. Rose bengal staining can also be used and preferentially stains devitalized epithelial cells and areas of mucin deficiency, providing additional information about corneal surface health.

A thorough ophthalmic examination should include assessment of the eyelids for conformational abnormalities such as entropion or ectropion that may contribute to corneal exposure, evaluation of the third eyelid for prolapse of the nictitans gland, and examination of the cornea for vascularization, pigmentation, fibrosis, and edema. Slit-lamp biomicroscopy, when available, allows detailed evaluation of the corneal layers and anterior segment structures. Tear film breakup time (TFBUT), measured by observing the time between a complete blink and the first appearance of a dry spot on the fluorescein-stained tear film, provides information about tear film stability.

In cases where an underlying systemic cause is suspected, additional diagnostics may be warranted. A complete blood count, serum chemistry panel, and thyroid hormone levels may be recommended to identify concurrent endocrine disease. Review of the patient's medication history is essential to identify potential drug-induced causes. For neurogenic keratitis sicca, assessment of nasal moisture on the ipsilateral side and pharmacologic testing with topical pilocarpine can help confirm the diagnosis. Lacrimal gland biopsy is rarely performed clinically but may be considered in research settings to characterize the nature and extent of glandular destruction.

The cornerstone of medical management for keratitis sicca is cyclosporine A, an immunomodulatory drug that has revolutionized the treatment of this condition since its introduction into veterinary ophthalmology. Cyclosporine works through multiple mechanisms, including suppression of the immune-mediated destruction of lacrimal gland tissue, direct lacrimostimulatory effects that increase tear production in glands with residual functional capacity, and anti-inflammatory properties that reduce corneal and conjunctival inflammation. It is most commonly available as a 0.2 percent ophthalmic ointment and is typically applied twice daily. Response to treatment is assessed through serial Schirmer tear tests, with improvement often noted within two to eight weeks of initiating therapy.

Tacrolimus, another calcineurin inhibitor, is an effective alternative for dogs that do not respond adequately to cyclosporine. Tacrolimus is approximately 100 times more potent than cyclosporine on a per-weight basis and has demonstrated efficacy in some cases refractory to cyclosporine therapy. It is typically compounded as a 0.02 to 0.03 percent ophthalmic solution or ointment and is applied once to twice daily. Both cyclosporine and tacrolimus require long-term, often lifelong administration, as discontinuation typically results in relapse of clinical signs and declining tear production.

Artificial tear supplements are an important adjunctive therapy, particularly in the initial treatment phase before lacrimostimulatory agents take effect and in severe cases where endogenous tear production remains inadequate despite immunomodulatory therapy. Preservative-free formulations are preferred because chemical preservatives can cause additional irritation to the already compromised ocular surface. Viscous formulations containing hyaluronic acid, carboxymethylcellulose, or polyvinyl alcohol provide longer contact time on the corneal surface. Petroleum-based artificial tear ointments applied at bedtime provide extended lubrication during sleep when the blink reflex is absent.

Topical antibiotics may be necessary to manage secondary bacterial infections, which are common due to the loss of the tear film's natural antimicrobial defenses. Broad-spectrum ophthalmic antibiotics such as neomycin-polymyxin-bacitracin or tobramycin are commonly prescribed. Topical anti-inflammatory agents, including nonsteroidal anti-inflammatory ophthalmic drops, may be added to reduce corneal and conjunctival inflammation, though topical corticosteroids must be used with extreme caution and only after confirming the absence of corneal ulceration through fluorescein staining. Mucolytic agents such as acetylcysteine can help break down thick, tenacious mucoid discharge.

In cases refractory to medical management, surgical intervention may be considered. Parotid duct transposition, in which the duct of the parotid salivary gland is surgically relocated to deliver saliva to the ocular surface as a tear substitute, is the most established surgical option. While this procedure can effectively wet the eye, saliva differs from tears in composition, and complications such as mineral deposits on the cornea and excessive moisture during eating can occur. This surgery is generally reserved for severe, unresponsive cases where medical therapy alone is insufficient to prevent progressive corneal deterioration.

The prognosis for keratitis sicca depends on several factors, including the underlying cause, the severity of the condition at the time of diagnosis, the degree of residual lacrimal gland function, and the consistency of treatment administration by the owner. Dogs diagnosed early, before significant corneal changes have developed, and who respond well to immunomodulatory therapy generally carry a favorable prognosis for maintaining comfortable, functional vision throughout their lives. Approximately 70 to 80 percent of dogs treated with cyclosporine show measurable improvement in tear production.

Dogs with moderate to severe corneal changes at the time of diagnosis may show significant improvement with aggressive medical management, though some degree of corneal scarring and pigmentation may be permanent. The cornea has remarkable regenerative capacity, and with consistent treatment, vascularization can regress, pigmentation can lighten, and corneal clarity can improve substantially over months of therapy. However, dense corneal scarring and extensive pigmentation that has been present for prolonged periods is less likely to resolve completely.

Cases caused by drug toxicity may carry a more variable prognosis. If the offending medication is identified and discontinued early, before extensive glandular destruction has occurred, tear production may recover partially or completely over weeks to months. Prolonged exposure, however, can result in irreversible glandular fibrosis. Neurogenic keratitis sicca may respond favorably to oral pilocarpine supplementation, with some cases showing substantial improvement in tear production, though treatment must typically be continued indefinitely.

The most important prognostic factor is owner compliance with the prescribed treatment regimen. Keratitis sicca is a chronic condition that in most cases requires lifelong medication, and lapses in treatment can lead to rapid recurrence of clinical signs and progressive corneal deterioration. Regular veterinary rechecks, typically every three to six months once the condition is stabilized, are essential for monitoring tear production, assessing corneal health, and adjusting the treatment plan as needed. With diligent management, most dogs with keratitis sicca can enjoy a good quality of life with preserved vision.

Keratitis sicca demonstrates strong breed predilections that reflect the genetic basis of the immune-mediated form of the disease. Brachycephalic breeds are disproportionately affected, likely due to a combination of genetic susceptibility to immune-mediated lacrimal adenitis and their prominent eye conformation, which increases corneal exposure and evaporative tear loss. The English Bulldog, Pug, Shih Tzu, Lhasa Apso, and Boston Terrier are among the most commonly affected brachycephalic breeds, with prevalence rates significantly exceeding those in the general canine population.

The Cavalier King Charles Spaniel deserves particular mention as one of the breeds with the highest documented prevalence of keratitis sicca. Studies have reported prevalence rates ranging from 10 to over 20 percent in this breed, suggesting a strong hereditary component. The West Highland White Terrier is another breed with notably high prevalence, and the condition in this breed appears to be associated with a more aggressive immune-mediated process that may be more challenging to manage medically. The Cocker Spaniel, both American and English varieties, also shows increased susceptibility.

Several other breeds have been identified as having elevated risk, including the Miniature Schnauzer, Yorkshire Terrier, Bloodhound, Chinese Crested, English Springer Spaniel, and Pekingese. In contrast, certain breeds appear to have a lower incidence of keratitis sicca, though the condition can occur in any breed, including mixed-breed dogs. The sex distribution of keratitis sicca is relatively equal, though some studies have suggested a slight female predilection, which may relate to hormonal influences on immune function and lacrimal gland activity.

The strong breed predispositions have led to recommendations from breed health committees and ophthalmology specialists that breeding stock in high-risk breeds undergo Schirmer tear testing as part of routine health screening. While no specific genetic test for keratitis sicca susceptibility is currently available, awareness of breed risk allows for early detection through proactive screening, which can significantly improve outcomes by enabling treatment initiation before significant corneal damage occurs.

Managing a dog with keratitis sicca requires a committed, long-term approach from the owner, as this condition typically demands ongoing daily care. Establishing a consistent medication routine is paramount. Most treatment protocols require the application of topical medications twice daily, and these applications should be spaced approximately 12 hours apart to maintain therapeutic drug levels on the ocular surface. Many owners find it helpful to associate medication times with existing daily routines, such as morning and evening meals, to improve compliance and reduce the likelihood of missed doses.

Proper technique for administering topical ophthalmic medications is an important skill for owners to master. The eye should first be gently cleaned of any accumulated discharge using a warm, damp, clean cloth or sterile gauze. Thick mucoid discharge should be removed before applying medication, as it can act as a barrier and prevent adequate drug penetration. When applying ointments, a small ribbon of medication is placed along the inside of the lower eyelid, and the eye is then gently held closed for a few seconds to distribute the medication across the corneal surface. Drops should be applied without touching the dropper tip to the eye to maintain sterility.

Environmental modifications can help minimize exacerbating factors for dogs with keratitis sicca. Exposure to wind, dust, cigarette smoke, and air conditioning or heating drafts should be minimized, as these conditions increase evaporative tear loss and worsen ocular surface dryness. During car rides, windows should be kept closed or dogs should be positioned away from direct airflow. In dry climates or during winter months when indoor humidity drops, using a humidifier in rooms where the dog spends most of its time can provide beneficial ambient moisture.

Owners should be educated about the signs of corneal ulceration, which constitutes a potential emergency in dogs with keratitis sicca. Sudden onset of severe squinting, increased tearing or discharge, marked redness, cloudiness or a visible white spot on the cornea, and behavioral changes suggesting acute pain such as depression, decreased appetite, or reluctance to be touched around the head should prompt immediate veterinary evaluation. Early recognition and treatment of corneal ulcers is critical to preventing serious complications such as corneal perforation. Regular follow-up visits allow the veterinarian to monitor the condition and make timely treatment adjustments.

Corneal ulceration is the most clinically significant complication of keratitis sicca and represents a potentially sight-threatening or even globe-threatening emergency. The chronically dry corneal epithelium becomes thin, irregular, and poorly adherent to the underlying stroma, making it highly vulnerable to mechanical disruption from normal eyelid movement, environmental debris, or self-trauma. Superficial ulcers in dogs with keratitis sicca have a propensity to become complicated, progressing to deep stromal ulcers, particularly when secondary bacterial infection is present. Bacterial enzymes, including collagenases and proteases, can cause rapid stromal dissolution or melting, potentially leading to descemetocele formation or frank corneal perforation within hours.

Secondary bacterial conjunctivitis and keratitis are common in dogs with inadequate tear production because the tear film normally provides critical antimicrobial defense through mechanical flushing, immunoglobulins, and enzymatic activity. Staphylococcus and Streptococcus species are the most frequently isolated organisms, though gram-negative bacteria including Pseudomonas aeruginosa can cause particularly aggressive infections. Cytology and culture with sensitivity testing should be performed whenever bacterial infection is suspected, especially in cases of deep or rapidly progressive corneal ulceration, to guide appropriate antibiotic selection.

Corneal pigmentation is a hallmark of chronic keratitis sicca and, while not itself painful, can lead to significant visual impairment when melanin deposition extends across the central visual axis. Pigmentary keratitis is the cornea's response to chronic irritation and inflammation, and it represents an attempt by the corneal epithelium to protect itself from further damage. While some degree of pigmentation may regress with effective tear stimulation and anti-inflammatory therapy, dense, long-standing pigmentation may be permanent. In severe cases, superficial keratectomy, a surgical procedure to remove the pigmented corneal tissue, may be considered, though pigment frequently recurs if the underlying dry eye is not adequately controlled.

Lipid keratopathy, the deposition of cholesterol and other lipids within the corneal stroma, can occur secondary to chronic corneal vascularization and inflammation associated with keratitis sicca. Corneal mineralization, the deposition of calcium salts within the cornea, is another potential complication of chronic disease. Both conditions can cause corneal opacity and, in some cases, corneal discomfort if the deposits disrupt the corneal epithelium. Additionally, dogs with keratitis sicca may develop symblepharon, the adhesion of the conjunctival membrane to the corneal surface, particularly following episodes of severe ulceration or in cases where treatment is inadequate or delayed.

True prevention of immune-mediated keratitis sicca is not currently possible, as the condition arises from a complex interplay of genetic predisposition and immune dysregulation that cannot be fully predicted or preempted in individual dogs. However, several strategies can facilitate early detection and reduce the risk of preventable forms of the disease. Responsible breeding practices in high-risk breeds, including screening of breeding stock with Schirmer tear testing and removal of affected individuals from breeding programs, can help reduce the incidence of the condition over successive generations.

Regular ophthalmic screening is particularly important for breeds with known predisposition to keratitis sicca. Annual or biannual Schirmer tear testing can detect declining tear production before clinical signs become apparent, allowing for early therapeutic intervention. The Canine Eye Registration Foundation (CERF) examination, now administered through the Orthopedic Foundation for Animals (OFA) Eye Certification Registry, provides standardized ophthalmic screening by board-certified veterinary ophthalmologists and can identify early signs of keratitis sicca along with other heritable ocular conditions.

Prevention of drug-induced keratitis sicca requires awareness and vigilance on the part of prescribing veterinarians. When sulfonamide antibiotics or other medications known to affect tear production are prescribed, baseline Schirmer tear testing before initiating therapy and periodic monitoring during treatment can help detect drug-induced decreases in tear production before irreversible glandular damage occurs. If tear production declines, the medication should be discontinued promptly and an alternative therapeutic agent selected. This approach is particularly important when these medications are prescribed for long-term use.

The practice of surgically removing the prolapsed nictitans gland, known as cherry eye, has been largely abandoned in favor of gland replacement techniques precisely because of the recognized risk of subsequent keratitis sicca. The nictitans gland contributes approximately 30 to 50 percent of total aqueous tear production, and its removal significantly increases the lifetime risk of developing clinically significant dry eye. Current best practice involves surgical repositioning of the prolapsed gland to preserve its tear-producing function while addressing the cosmetic and functional concerns of the prolapse. Owners and breeders should be educated about this important distinction when seeking treatment for cherry eye.