Mastering corneal ulcers (part 1)

Joshua Broadwater, DVM, DACVO, veterinary ophthalmologist at the Charlotte Animal Referral & Emergency in North Carolina, recognized that ophthalmology cases can be difficult, however corneal ulcers are quite common in veterinary medicine, and therefore, important for veterinary professionals to brush up on their knowledge of the disease. He also explained how to tell the difference when infected corneal ulcers can be medically managed by a general practitioner or when a case is more severe and needs to be sent to an ophthalmologist for surgery, which will be discussed in part 2.

What’s normal

During his session at the 2024 Fetch dvm360 conference in Charlotte, North Carolina,¹ Broadwater said to attendees, “I like to go into what's normal before we jump into what's abnormal.” So, what would look normal? First, the tear film of the eye has an oily layer which is the meibomian glands of the eyelids. Then, there is an aqueous layer, which is the third eyelid gland and lacrimal gland. And finally, there is the mucus or glycoprotein layer, which comprises of the goblet cells of the cornea and conjunctiva. “We've learned to understand the importance of the tear film is super for these [patients], because dry eye is probably the most common underlying condition that I see that leads to a lot of ulcers in a lot of dogs. So, understanding that we need to have all these layers intact is super important,” Broadwater continued.

Along with the tear film layers, there are also the corneal layers which includes the epithelial layer, basement membrane, stromal layer, Descemet’s membrane, and the endothelial cells. “The bulk of the cornea is going to be the stroma that makes up 95% of the corneal thickness,” Broadwater said.

A normal corneal anatomy consists of a 0.5-0.6 mm thickness and no blood vessels. Broadwater stated, “So you can imagine we don't have a large margin of error when we get an ulcer, and it starts to get deep into the cornea, it starts to be a little scary that the cornea is going to get thinner and thinner. We have no blood vessels. It’s one of the only things in our body that doesn't have blood vessels in it. Which is great because we have to be able to see out really well, but it's not so good when we get an infection because we want those blood vessels there to get white blood cells to the site to fight the infection…and they take a long time to get there.”

Normally functioning corneas should also have the ophthalmic branch of trigeminal nerve (CN V1), and this helps with sensory innervation and signals the brain for discomfort if something is bothering the eye.^1,2 “It's also the most painful so when you get an ulcer, especially even a superficial ulcer, they're really sensitive,” Broadwater said.

The final thing that should be present in a normal cornea is a type of defense system. An intact epithelium can act as a barrier against bacteria, eyelashes help catch debris before they enter the eye, and the tear film coupled with functioning blinking can help wash away any debris.

What’s not normal (corneal ulcers)

Corneal ulcers may arise due to insufficient eye lubrication (inadequate tear production) or because of trauma, such as scratches or other injuries.³ Corneal injuries can also occur from a foreign object getting caught in the eye like dirt, sand, an eyelash, wood shavings, etc. The ulcers can escalate in severity if infections take hold. A superficial corneal ulcer would affect the top layer (epithelium) and a stromal ulcer goes below the epithelial layers. A majority of infected corneal ulcers are deeper, stromal ulcers and these cases need a more aggressive, immediate treatment.^1,4

Deep infected stromal ulcer

To diagnosis, Broadwater recommended examining the patient for any underlying pathology that may have caused the ulcers such as dry eye, entropion, foreign body, distichia, allergies, or trauma (scratch). However, take everything into consideration. For example, Broadwater reminded attendees, “It's tough to diagnose in these cases right away. Why would dry eye be tough to diagnose? It hurts, right? So you're tearing a lot more…you can still do your tear test, as long as this thing is not too deep. Because that might not be a true indication of tear production, that might be a reflex tearing.” In general, Broadwater recommended being extra cautious with all diagnostics when an ulcer looks very deep. Instead, cytology and a bacterial culture can be a good option in these cases.

Most infected ulcers are going to be bacterial, however a small amount could be fungal. The most common bacteria will be Staphylococcus, followed by Streptococcus and Pseudomonas.^1,5

Brachycephalic breeds and other dogs with larger exposed eye sockets are more susceptible to corneal ulcerative disease.⁶ Broadwater also stated that patients with underlying metabolic diseases such as diabetes and Cushing’s disease, can be predisposed to getting an infected ulcer because the body cannot fight off the infection as easily as those without these conditions.

Check out part 2 to learn more about when to use medical management for these cases and when surgery is necessary.

For more coverage from Fetch Charlotte, visit our dedicated conference news page at dvm360.com/conference/fetch-charlotte.

References

1. Broadwater J. Infected corneal ulcers: Medical and surgical management. Presented at: Fetch dvm360 conference; Charlotte, North Carolina; March 15-17, 2024.
2. Huff T, Weisbrod LJ, Daly DT. Neuroanatomy, Cranial Nerve 5 (Trigeminal). In: StatPearls. Treasure Island (FL): StatPearls Publishing; November 9, 2022.
3. Gelatt K. Eye emergencies. Merck Veterinary Manual. November 2022. Accessed February 27, 2024. https://www.merckvetmanual.com/special-pet-topics/emergencies/eye-emergencies
4. Stromal corneal ulcer FAQs. University of Tennessee College of Veterinary Medicine. Published December 6, 2021. Accessed April 2, 2024. https://vetmed.tennessee.edu/wp-content/uploads/sites/4/UTCVM_Ophthalmology-StromalCornealUlcer_FAQs.pdf
5. Verdenius CY, Broens EM, Slenter IJM, Djajadiningrat-Laanen SC. Corneal stromal ulcerations in a referral population of dogs and cats in the Netherlands (2012-2019): Bacterial isolates and antibiotic resistance. Vet Ophthalmol. 2024;27(1):7-16. doi:10.1111/vop.13080
6. O’Neill DG, Lee MM, Brodbelt DC, Church DB, Sanchez RF. Corneal ulcerative disease in dogs under primary veterinary care in England: epidemiology and clinical management. Canine Genetics and Epidemiology. 2017;4(5). doi: 10.1186/s40575-017-0045-5