Corneal ulceration in dogs and cats: Diagnosis and treatment

Ruth Marrion, DVM, PhD, DACVO
Bulger Veterinary Hospital, North Andover, MA
Posted on 2016-12-20
 

Corneal ulceration is one of the most common ophthalmic problems seen in our canine and feline patients. This post covers the causes and diagnosis of corneal ulceration in dogs and cat, as well as medical and surgical treatment.

History

A history is certainly an important part of the diagnostic process for any patient presented to a veterinarian. But I have found that in many cases, owners will try to attribute the cause of a corneal ulcer to a specific event: Another pet scratched the patient in the eye, the dog was running through the woods and got a stick in her eye, the cat was cleaning himself and his claw caught the cornea, etc. – an exogenous cause. Consider the history when looking for the cause of the ulcer, but suspect an endogenous cause.

Some of the most common endogenous causes are:

• Mechanical irritants
  • Distichiae
  • Ectopic cilia
  • Trichiasis (including trichiasis from entropion)
  • Foreign bodies
• Tear film problems
  • Dry eye
  • Inability to blink completely
• Glaucoma
• Exophthalmos
• Mass preventing complete blink
• Neuropathies
• Infectious disease
  • Feline herpesvirus infection in cats
• Crystalline deposits
  • Calcareous degeneration of the cornea in older dogs
  • Corneal dystrophy of Shetland Sheepdogs

Initial examination: Step away from the eye!

I cannot stress enough the importance of a complete ophthalmic examination no matter what the presenting problem. Owners will often point to the affected area and want you to look at that immediately. That’s fine, but then make sure that you perform a complete examination.
 

Complete ophthalmic examination

• Observe pet from a distance
• Examine eyelids
  • Entropion
  • Distichiae
  • Ectopic cilia
  • Masses
  • Abscesses
• Neuroophthalmic examination
  • Vision
  • Ability to blink
  • Pupillary light response
• SCHIRMER TEAR TEST
• Fluorescein
• Tonometry
• Adnexal examination
• Anterior and posterior segment examination

Start by looking at the pet from across the room. Is it squinting one eye? Does one eye appear more prominent (exophthalmos or buphthalmos)? Does one eye appear displaced from the midline? Does the pet blink one eye (completely or partially) but not the other?

Spend a minute examining the eyelids. We see cases of undiagnosed entropion in cats and older dogs; veterinarians miss this because they are not looking for it. You will need to use magnification to visualize distichiae and ectopic cilia; try an otoscope without a cone, or a magnifying loupe.

An absent or incomplete blink can cause exposure keratitis. Neuropathic keratitis may involve pathology of the afferent or efferent nerves. If sensation is absent because of pathology involving the trigeminal nerve, the menace response will be intact, but not the palpebral response. If the pet is unable to blink because of a problem with the facial nerve, it will not have either a menace or palpebral response.
 

Take a second look

Still do not know what caused the ulcer? Take a second look, but first consider the area of the ulcer. Is the ulcer in the superior cornea? If so, take another look on the conjunctival aspect of the upper lid for ectopic cilia. Is the ulcer in the horizontal axial cornea? This suggests an incomplete blink, from a neuropathy, buphthalmos, or exophthalmos.

Is it indolent or infected?

If an ulcer is indolent (non-healing, superficial chronic corneal erosive defect), it will not heal on its own. This condition only occurs in middle-aged to older dogs. An indolent ulcer is superficial (epithelium only) and has loose epithelial margins. The pathogenesis of this condition is that the superficial corneal stroma becomes unhealthy and unable to maintain attachments to the overlying corneal epithelium. The hallmark is the presence of loose epithelial margins at the edge of the ulcer. Indolent ulcers are common; I see several of these every week, so your index of suspicion for this condition should be high in an older dog.

An infected ulcer is a serious condition that can become a descemetocele or perforation in only a day or two. Most pets with corneal ulcers with secondary bacterial infections will exhibit considerable pain (blepharospasm). Upon close inspection, the area of the stroma surrounding the ulcer may be opaque with a white to tan infiltrate. Corneal ulceration causes a reflex uveitis which can be severe in cases of secondary infection. Signs include miosis relative to the fellow eye, aqueous flare, and hypopyon. The presence of hypopyon in an eye with a corneal ulcer typically indicates an infection on the corneal surface, not inside the eye. In contrast, bacterial endophthalmitis is very rare in small animals.

Sometimes it’s complicated…

The conditions mentioned above are not mutually exclusive. If you find an indolent ulcer, take an extra look to make sure that there is not a bristly distichia or a small eyelid mass in the area of the ulcer. And if an ulcer is indolent, it can still be infected. If you see an ulcer that appears to be indolent but the dog is particularly painful, consider the possibility that it may be infected, and err on the side of caution when planning treatment.

Crystalline deposits causing corneal ulceration

There are numerous causes for the development of crystalline deposits in the canine cornea. Many do not cause ocular morbidity in terms of either pain or vision loss. Two exceptions to this general rule are corneal dystrophy in Shetland Sheepdogs, and calcareous corneal degeneration in geriatric dogs. Both of these conditions have the potential for areas of the crystalline deposits to slough and thereby cause ulcerations of the cornea. Dogs that you suspect of having either condition should be watched closely for signs of pain. I have seen several cases of calcareous degeneration in older dogs lead to stromal ulcers and perforations, so early recognition is crucial. There is no universally recognized treatment that is effective, but some cases will respond to treatment with 1% EDTA ointment in artificial tears to chelate the mineral component, or tacrolimus preparations to improve tear film quality.

Treatment of corneal ulcers

The goals of treatment of corneal ulcers are to:

• Prevent/treat infection
• Prevent/stop progression through the corneal stroma
• Prevent/treat pain
• Provide structural support or facilitate healing when necessary

For a simple ulcer with no apparent underlying cause, treatment with a topical antibiotic three to four times daily may be all that is needed. Most owners find it easier to apply drops than ointments, so I typically prescribe/dispense antibiotic solution unless there is a specific condition that is an indication for use of ointments (dry eye, poor blink etc.). A topical aminoglycoside or triple antibiotic combination are good choices. For pain relief, if a dog is only minimally painful, I may apply one dose of topical atropine in the exam room. This will last for a few days in a dog, and this should be sufficient for an ulcer that one expects to heal. If the ulcer is more painful, supplement with your choice of oral pain relievers, an NSAID and/or tramadol and/or gabapentin.

Certainly, if you find an underlying cause such as an aberrant hair or entropion, address this, in conjunction with your ophthalmologist if needed.

Recommend that the owner makes a recheck within a week, and prior to that time if the pet is painful, as judged by blepharospasm.

Indolent ulcers

Middle-aged to older dogs commonly develop superficial (loss of epithelium only) ulcers that do not heal, because of a defect in epithelial-stromal attachment. These ulcers are known as indolent, non-healing, or Boxer ulcers; also as superficial chronic corneal epithelial defects (SCCED). The pathogenesis involves degeneration of the superficial stroma, thus impairing attachment to the overlying epithelial cells. The result is a superficial ulcer characterized by the presence of loose epithelial margins. The cornea responds by vascularizing, in some cases resulting in an impressive buildup of granulation tissue.

This is an anatomic problem, and thus requires a surgical procedure to allow epithelial cells to attach to healthy stroma that underlies the degenerated superficial corneal stroma. A grid or punctate keratotomy, diamond burr debridement, or superficial keratectomy can be used to accomplish this goal.

Cats do NOT develop indolent ulcers. Infection of corneal epithelial cells with feline herpesvirus in cats causes an ulcer that is identical in appearance to an indolent ulcer; however the pathogenesis is completely different, and therefore none of the above procedures is indicated for a cat with a superficial ulcer that has loose epithelial margins.

Ulcers from dry eye

Keratoconjunctivitis sicca is a common cause of surface ocular disease, including corneal ulceration, in dogs. The mainstay of treatment is a topical lacrimal stimulant, either tacrolimus or cyclosporine. I most commonly prescribe 0.03% tacrolimus in artificial tear ointment, three times daily for severe dry eye, and twice daily for mild to moderate dry eye. The ointment forms of tacrolimus and cyclosporine play “double duty” in that they stimulate lacrimation and provide lubrication – so they are ideal for moderate to severe dry eye.

Other medications may be indicated depending upon the severity of dry eye and co-morbid conditions. Owners should be instructed to use over the counter eye wash, prior to applying medications, when discharge accumulates on the surface of the eye. They should be administering lubricants if the eye appears dry between applications of tacrolimus or cyclosporine.

Infected ulcers

An infected ulcer is a serious condition that can progress to a perforated cornea, unless treated promptly and effectively. I recommend treating an ulcer as infected if you are at all suspicious based on signs of stromal infiltrate, uveitis or an excessively painful ulcer. Ideally, hospitalize a pet with an infected ulcer to ensure adequate treatment. If overnight care is not available at your facility, or if the owner is not willing to hospitalize, I recommend daily rechecks until the ulcer is stabilized (not deepening, and epithelializing at the edges). It is certainly reasonable to consider referral for these cases, but I strongly encourage starting treatment unless an owner will bring the pet to an ophthalmologist immediately.

Antibiotics – Good choices are a fluoroquinolone, such as ofloxacin, or a triple antibiotic combination with polymyxin. I tend not to culture because by the time I obtain results, typically the infection is resolved. Treatment is indicated every two to four hours.

Serum – The reason that infected ulcers are so dangerous is that collagenases, from both host leukocytes and invading bacteria, digest corneal stroma and thereby deepen ulcers. Serum contains alpha-2 macroglobulin, which is the universal protease inhibitor. Application of topical serum blocks enzymatic destruction of corneal stroma, so it is indicated in cases of infected ulcers, ideally every two to four hours.

Pain relief – I use topical atropine to effect, keeping in mind the potential systemic effects of this medication. In a very small dog I may apply one drop myself during the course of the examination; while it is reasonable to treat a large breed dog topically two to three times daily. Atropine drops can cause profuse salivation in cats and some dogs; so I use atropine ointment in cats. There are several approaches to treating ocular pain, including use of topical atropine, and oral NSAIDS, tramadol and gabapentin. Avoid application of topical NSAIDS because they have some potential to delay epithelialization.

What about that new miracle drop?

There are several commercially-available preparations that have been marketed to facilitate healing of corneal ulcers. At this point, there is no credible evidence that any of these preparations is more useful than any other artificial tears. So, is it worth recommending these medications for treatment of ulcers? These are not likely to cause any harm, with the caveat that owners will not always administer all medications as directed. If owners are having difficulty administering medications, they may skip some doses, and they often do not know which medications are the most important (topical antibiotics) so may skip them, instead going with the medication with the coolest label.

Surgery for infected ulcers

I recommend surgery for ulcers that reach Descemet’s membrane. Different ophthalmologists recommend different surgeries; options include grafts of cornea, conjunctiva, and commercially available products such as swine urinary or intestinal submucosa. It is essential that any infection be resolved prior to placing a graft. I have found that if an area of ulcerated cornea still has stroma that it will fill in and epithelialize.
 

Corneal ulceration in cats – Diagnosis and treatment

Feline herpesvirus is the cause of surface ocular disease in many cats. The virus is unusual in that it is actually capable of causing corneal ulceration, by infecting and killing corneal epithelial cells. Since recrudescence of herpesvirus is triggered by stress, overly aggressive treatment can actually be counterproductive. So, treatment of a corneal ulcer suspected to be caused by feline herpesvirus is a balancing act between adequate medical treatment and decreasing stress in our feline patients.

One cannot say conclusively that any cat has surface ocular disease attributable to herpesvirus infection. The reason is that there is no reliable test for this pathogen. Even the most accurate test, polymerase chain reaction (PCR), has false positives and false negatives. It is reasonable to attribute any ulcer that persists for more than a few days, in the absence of a perceptible underlying cause, to infection with feline herpesvirus.

For any cat I suspect to have ocular disease from feline herpesvirus, I recommend treating with L-lysine 500 mg daily (dose for an adult cat, decrease dosage in small/young cats). Feliway may be helpful in decreasing the incidence and severity of outbreaks.

Famcyclovir at a dosage of 40 mg/kg TID has been shown to be safe and effective in treating outbreaks of feline herpesvirus. I have found that many owners will administer the medication BID much more readily than TID, and I have seen many cats do very well with this treatment. For cats refractory to oral medication, treatment with topical cidofovir 0.5% BID is a good alternative. This is available from the Prescription Center in North Carolina 800 682-4664, potentially from other compounding pharmacies as well. This is the only topical herpesvirus treatment that I recommend for cats because of the treatment being only BID. Other topical antivirals need to be administered more frequently to be effective.

I almost never recommend Elizabethan collars for cats, the exception being after a surgical procedure such as lens extraction. I have never seen a cat damage its own cornea and few would argue that these apparatus cause cats considerable stress.
 

Appendix

Sample discharge instructions for owners for different types of corneal ulceration right eye:

1. Simple corneal ulcer right eye

• Apply one drop of tobramycin to right eye three times daily – two more applications tonight
• Tramadol – give one tablet orally twice daily with food – one dose tonight
• Gabapentin- give one 100 mg capsule orally twice daily with food – one dose tonight
• You may give the oral medications together, and you may give with food

 
2. Infected corneal ulcer right eye (after ulcer stabilized)

• Apply one drop of ofloxacin to right eye four times daily – three more applications today
• Apply one drop of atropine to right eye once daily – one more application tonight
• Apply one drop of serum to right eye four times daily through tomorrow (Sunday February 8, 2015) – three more applications today

Use the medications in the order written above. Wait 3-5 minutes between drops. Spread out the time between applications of medications as much as you can during waking hours (you do not need to get up at night to apply eye medications).

Oral medication – see instructions for simple ulcer right eye
 
3. Ulcer associated with dry eye

• Rinse off eye PRIOR to applying medications whenever discharge develops with over the counter eye wash/eye irrigating solution/saline solution for eyes
• Tobramycin – apply one drop to right eye three times daily
• Tacrolimus ointment – apply a small amount to right eye three times daily

Use the medications in the order written above. Wait 3-5 minutes between drops. Spread out the time between applications of medications as much as you can during waking hours (you do not need to get up at night to apply eye medications).

Over the counter artificial tear GEL or OINTMENT (not drops) – apply to right eye whenever needed for dryness, in between applications of tacrolimus ointment.
 

Compounding pharmacies

This is a list of the compounding pharmacies that I use. There are many others.

• IVG Compounding Pharmacy, Woburn, MA (781-897-6936)
• Prescription Center, Fayetteville, NC (800-682-4664)
• Wingate’s Pharmacy, Nashua, NH (603-882-9733)

Further reading

• Bentley E. Spontaneous chronic corneal epithelial defects in dogs: a review. J Am Anim Hosp Assoc 2005;41:158-65.
• Cooley PL, Dyce PF (1990): Corneal dystrophy in the dog and cat. Vet Clin North Am Small Anim Pract 3:681-92.
• Kern TJ. Ulcerative keratitis. Vet Clin North Am Small Anim Pract 1990;3:643-66.
• Maggs DJ. Antiviral therapy for feline herpesvirus infections. Vet Clin North Am Small Anim Pract 2010;40:1055-62.
• Maggs DJ. Cornea and Sclera. In Slatter’s Fundamentals of Veterinary Ophthalmology, Saunders (2008), p 175.
• Sansom J, Blunden T. Calcareous degeneration of the canine cornea. Vet Ophthalmol 2010;13:238-43.
• Thomasy SM, Lim CC, Reilly CM, et al. Evaluation of orally administered famcyclovir in cats experimentally infected with feline herpesvirus type-1. Am J Vet Res 2011;1:85-95.
• Thomasy SM, Covert JC, Stanley SD, et al. Pharmacokinetics of famcyclovir and pencyclovir in tears following oral administration of famcyclovir to cats: a pilot study. Vet Ophthalmol 2012;15:299-306.

Image credit: By Joel Mills (Own work) , via Wikimedia Commons.