Understanding canine ocular ulcers

Lateral view of a deep corneal ulcer, or descemetocele in a dog. (Todorean Gabriel/stock.adobe.com)

Dogs develop ocular ulcers for many reasons, including foreign material, distichia, trauma, entropion, trichiasis, endothelial degeneration, autoimmune diseases and keratoconjunctivitis sicca. Although specific treatments vary, preventing infection is critical, so patients should receive a topical antibiotic, such as Tobramycin or Ofloxacin, immediately. In the case of an infected ulcer or one that's particularly deep, a broader-spectrum antibiotic will be used, such as Moxifloxacin.

It's also important to keep patients from rubbing their faces on the floor or pawing at their eyes, causing further trauma to the area. Sending the patients home with Elizabethan collars to protect their eyes is strongly recommended.

4 types of corneal ulcers

The cornea itself is made up of four layers. The epithelium is the outermost layer and acts as a barrier to the rest of the cornea. It's essentially the "skin" of the eye. The stroma is the second and thickest layer of the cornea and is made up of mostly collagen. Thirdly, there is Descemet's membrane and then finally at the bottom is the endothelium.

With superficial corneal ulcers, the epithelium is missing in an area and there is varying stromal involvement underneath. In a healthy eye, small abrasions should heal within three to five days.

If the ulcer becomes infected or is so deep that it reaches Descemet's membrane, or the epithelium can't adhere to the stroma for any reason, then healing is delayed. Medical intervention is warranted in any of these cases, and sometimes surgery with an ophthalmologist will be needed.

With infected ulcers, tear proteases digest stromal collagen, causing the ulcer to become deeper. (Some even become so deep they reach Descemet's membrane!) The eye will have a grey, gelatinous appearance on the surface, and the patient typically holds the eye fully closed.

A descemetocele is an ulcer that's so deep it goes through the stroma to Descemet's membrane. It will not pick up central stain with fluorescein stain, and it looks like there's a divot in the eye. These ulcers require emergency intervention and surgery with an ophthalmologist as the eye will be at risk for perforation. The ophthalmologist will decide which interventions are needed, but conjunctival grafting, third eyelid flaps and tarsorrhaphies are all possibilities.

When deep ulcers are diagnosed or if there's significant stromal involvement, pet owners need to make sure there's no unnecessary pressure on their pets' necks. In other words, no collars or neck leads for these patients! Ocular pressure increases artificially when there's pressure on the neck-and that increases the chance for ocular perforation.

With non-healing corneal ulcers, the epithelium doesn't adhere to the stroma and ends up flipping outwards. Pet owners may have said in the past that the ulcer "comes and goes" as the patient seems to be less blepharospastic at times. In these cases, the epithelium was loosely covering the stroma temporarily and then flipped back out again. These ulcers need a debridement and grid keratotomy or a diamond burr superficial keratectomy to help them heal.

After either of these procedures are performed, it takes another two to three weeks or so for the epithelium to make its way back across the entire cornea. A second, or even third, procedure may be warranted, as these ulcers can be very stubborn.

Last thoughts

Some ulcers have a component of anterior uveitis that should be treated along with the underlying cause. In these cases, corticosteroids should never be used as these increase tear protease activity and inhibit healing.

Sometimes ulcers can take weeks to heal, and clients can get very frustrated and feel overwhelmed. It can be a long time for them to manage the medications and Elizabethan collar use. Offer frequent rechecks, if needed, to help support them and check the pet's progress. Follow-ups are important with ocular ulcers, because things can change in the eyes very quickly-for better or for worse.

Kirstin Lee is a freelance writer and certified veterinary technician who lives and works in Colorado. She started working in ophthalmology because she cares deeply about pets' eyes.