What is the cornea?
- The cornea is the clear front part of the eye.
- The cornea is elliptical in shape and made up 4 layers – the anterior epithelium with a
- basement membrane, the Stroma, Descemet’s membrane, and the Corneal Endothelium.
- The cornea has many functions one of which is to bend and transmit light to the back of the
- eye thus assisting with vision. If the cornea is scratched or ulcerated this is not only painful
- but can be vision impairing as well.
- The cornea is avascular (no blood vessels) which helps maintain its clarity.
- Corneal thickness varies between species but is typically less than 1 mm thick (Dogs and cats
- range from 0.45mm to 0.55mm centrally and 0.50mm to 0.65 mm peripherally).
What types of corneal ulcers can affect my animal?
A corneal ulcer occurs when one or more of the layers of the cornea become lost, causing an open wound on the cornea.
- Broadly speaking there are 2 types of corneal ulcers: Superficial and Deep.
- Superficial corneal ulcers occur when there is a loss of only the epithelium and typically, these ulcers heal quickly. A small, superficial ulcer in a healthy animal should heal within hours to a few days.
- The exception to this rule is a non-healing ulcer called an “indolent ulcer” or a superficial chronic corneal epithelial defect (SCCED). These ulcers are superficial however can take weeks to months to heal without intervention. Often a surgery or procedure is required to achieve healing (Keratectomy, Diamond Burr debridement, or Grid Keratotomy).
- A deep corneal ulcer involves the stroma. The stroma heals by having the cells called keratinocytes transform, proliferate, and synthesise collagen and an extracellular matrix referred to as “glue.” This process can take weeks or longer.
- The corneal healing process is a series of complex and coordinated cellular processes involving proteinases, growth factors, cytokines from epithelial cells, stomal keratocytes, inflammatory cells and the lacrimal glands. This relies on a delicate balance of synthesis, degradation, and remodelling.
- If the degradation is faster than the synthesis this is called a “melting ulcer”
- Deep stromal or melting ulcers can heal with medications, but often require a surgical procedure to heal, especially if there is infection present.
What causes corneal ulcers?
There are many causes of corneal ulcers. Damage to the cornea can occur due to external traumatic forces, environmental irritants, or due to primary anatomic issues with the eyelids or eyelid function. Systemic disease and tear film abnormalities also can result in deterioration of the corneal health and integrity.
Typical causes of ulcer are:
- Abnormal hairs, eyelashes or foreign bodies irritating the cornea
- Decreased tear production
- Infectious agents
- Immune mediated
- Endocrine disease, including hypothyroidism, Cushing’s disease, and diabetes mellitus
- Endothelial cell dystrophy (corneal edema) Neurologic deficiency, such as loss of sensory innervation of the cornea
- Radiation therapy near the eye
- Chemical or traumatic injury
How is a corneal ulcer diagnosed?
The most common clinical signs of a corneal ulcer include squinting, redness, cloudiness of the cornea, tearing, or discharge. A special stain called fluorescein can be used to help identify the ulcer on the cornea. Corneal ulcers are characterised according to location, depth, associated diseases, and cause.
How are corneal ulcers treated?
Treatment for a corneal ulcer depends on the type and depth of the ulcer. Simple ulcers can often be managed with medication alone to prevent infection and relieve pain. However, more severe or deep ulcers may require surgical intervention.
Deep ulcers pose a higher risk of progressing to a corneal rupture, necessitating surgical intervention to stabilise the cornea. Treatment often involves a combination of topical and systemic medications, along with a surgical graft. The choice of graft depends on the ulcer’s location, depth, and infection status.
If the eye has already ruptured, a synthetic graft like Biosis or Acell is typically used to achieve a watertight seal. Additional support and nutrition are provided by tissue surrounding the eye, such as the cornea and/or conjunctiva. Various surgical options are available for treating deep corneal ulcers, which are discussed below.
The Conjunctival Pedicle Graft (also called ‘CPG’)
The conjunctival pedicle graft is one option for the treatment of deep corneal ulcers. The conjunctiva is the pale pink tissue that covers the “white” of your pet’s eye. It is a thin and strong tissue which contains many blood vessels. These qualities make it an ideal tissue for grafting purposes.
Conjunctival grafting surgery is performed under general anaesthesia. Using advanced surgical equipment and techniques, a portion of the conjunctival tissue is relocated to cover the corneal ulcer. It is then secured in place with specialised dissolvable sutures, which will be removed during a follow-up visit.
Corneo-conjunctival transposition graft (also called ‘CCT’)
In this grafting procedure, a partial-thickness piece of healthy corneal tissue adjacent to the wound is harvested along with some attached conjunctiva. This tissue is then mobilised and sutured into the defect. This type of graft is particularly suitable for large or deep defects, as it provides superior stability. Additionally, it offers excellent cosmetic and functional results, as the grafted corneal tissue typically becomes clear again.
However, in cases of severe infectious corneal ulceration, a conjunctival corneal transposition (CCT) may be discouraged, as it could be susceptible to destruction by the infection.
For both of these grafting procedures, it is crucial that the retrieval and suturing of the graft be performed under an operating microscope. Our ophthalmologists are specially trained in microsurgical techniques, allowing them to handle the delicate tissue and suture material—barely thicker than a hair—with minimal trauma.
Synthetic grafts (Acell or Biosis)
Synthetic grafts, such as Acell or Biosis, are acellular tissues that can be sutured into a malacic (melting) ulcer or a full-thickness corneal defect to provide a watertight seal with excellent structural support. These grafts can be used alongside conjunctival pedicle grafts or corneoconjunctival transpositional grafts. Below, the image on the left shows a melting ulcer, while the image on the right depicts the same ulcer after surgical debridement, with necrotic or “dead” tissue removed and a synthetic graft sutured into place.
Corneal crosslinking (CXL) for strength and sterilization of the cornea
In addition to the previously discussed surgical procedures, ECA is proud to offer a cutting-edge, non-surgical treatment called corneal cross-linking. This procedure uses UV light to kill harmful organisms, such as bacteria, and to strengthen the bonds between the layers of the cornea. It is an excellent option for treating infected corneal ulcers and “melting” ulcers. Corneal cross-linking can be used as a stand-alone therapy or in conjunction with other treatments or surgeries.