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Corneal Ulcers

Education > Dog Health & Behaviour 1st April 2019
 


The cornea is the clear, transparent part of eye that lets light into the globe, much like the aperture in a camera. The outer layer comprises several layers of epithelial cells which protects the rest of the cornea.

WHAT IS A CORNEAL ULCER?

Corneal ulcers are painful defects to one or more layers of the cornea – like a scrape wound on your skin. Superficial ulcers involve just the outer layer (epithelium). Uninfected ulcers heal within days as the epithelial cells grow into the defect and new skin sticks to the underlying tissue. Deep ulcers extend into the middle layer (stroma) and take longer to heal. With deep ulcers, vision may be severely compromised or even lost. Often, intensive antibiotic therapy and surgery is required.



SOME CAUSES OF CORNEAL ULCERS

­Trauma: scratches, abrasions, puncture wounds
Entropion: eyelids rolling inwards
Keratoconjunctiva sicca: dry eyes
Ectopic cilia: fine eye lashes that grow inwards
Foreign body: an object sitting on the eye surface, e.g. a seed

Signs and symptoms include: squinting, excessive blinking, tearing, eye discharge, pawing at eyes, redness of the conjunctiva. A slit lamp allows our vet to evaluate your pet’s cornea with a high degree of magnification and resolution to determine the extent and depth of an ulcer.



FLUORESCEIN STAIN TEST

Most ulcers can be diagnosed using a fluorescein stain. A green, non-toxic dye is applied to the surface of the cornea. On normal healthy eyes, the dye does not stain the corneal layer. If there is an ulcer, the dye adheres to the ulceration and illuminates bright green under a special light.



WHAT IS AN INDOLENT CORNEAL ULCER?

Indolent ulcers are usually superficial and non-infected but take a very long time to heal. New skin tries to grow over the ulcer but fails to adhere to the underlying tissue. With careful examination, a thin layer of loose tissue can be seen surrounding the ulcerated area. Indolent ulcers are also known as chronic epithelial erosion, refractory superficial ulcer, Boxer ulcer and epithelial basement membrane dystrophy.



Because the epithelial cells do not stick down to the tissue underneath, it is not possible for indolent ulcers to heal with just the use of antibiotic eye medications and artificial tears. Without appropriate treatment, indolent ulcers persist for months, causing ongoing discomfort and pain, and may lead to severe corneal ulcers, secondary bacterial infections, cornea perforation and loss of sight.

CORNEAL DEBRIDEMENT

In order for an indolent ulcer to heal, the loose tissue needs to be removed in a process called debridement. After local anaesthetic eye drops are applied, dry sterile cotton-­tipped swabs are used to gently remove the loose abnormal epithelium surrounding the ulcer. This procedure may have to be repeated several times.



GRID OR LINEAR KERATOTOMY

If needed, grid or linear keratotomy is performed after debridement. A hypodermic needle is used to make superficial parallel incisions in the underlying exposed stroma. Simply put, we scratch the cornea with a needle to provide a rough surface for new epithelial cells to anchor onto and allow for proper healing. Grid keratotomy can be performed on calm and cooperative patients under topical anaesthesia. Otherwise, sedation or general anaesthesia is necessary.

Medications will be dispensed to prevent infection and control pain, and your dog will return for reviews until the ulcer is fully healed. Surgery for an indolent ulcer has to be considered if it fails to heal after several attempts at debridement and keratotomy.