The cornea is the transparent windshield-like structure of the eye. The cornea serves to protect the internal parts of the eye, while allowing light to enter for vision. The endothelium is a single layer of cells that line the inner aspect of the cornea. These cells are responsible for keeping the cornea transparent by pumping excess fluid out of it. However, if there is a problem with the endothelial cells, water will start to build up inside the cornea, making it more thick and cloudy.
Endothelial cells in most domestic animals are not able to replicate. Therefore, when endothelial cells die, the remaining cells will stretch to compensate for the area lost by the dead cells. As long as the number of functional endothelial cells remains above a critical threshold number, they will be able to prevent a gap in this lining and successfully keep the cornea clear. However, if the number of cells fall below this threshold, they will not be able to pump out enough fluid from the cornea to keep it dehydrated and clear. As a result, the cornea will become progressively more cloudy and blue, as it fills with fluid.
Spontaneous endothelial cell death has been shown to occur as part of an inherited condition in certain breeds, such as Dachshunds, Chihuahuas and Boston Terriers. In these breeds, the condition is referred to as endothelial dystrophy and usually affects both eyes.
Endothelial cells can also die following damage from different intraocular disorders. Examples of such conditions include inflammation (uveitis), elevated intraocular pressure (glaucoma) or mechanical damage from a luxated lens.
Fluid accumulation within the cornea is not a painful condition by itself. However, this fluid can sometimes cause the formation of small “water blisters” in the cornea called bullae. If these bullae pop, they may leave a crack (ie ulcer) in the cornea, which tends to be very uncomfortable. These ulcers will typically heal quickly with appropriate medications. However, if they become a recurrent problem, we may recommend a surgical procedure to stop them from forming.Treatment of Endothelial Dystrophy/Degeneration
Unfortunately, there is no cure to this condition. In humans, the definitive therapy is a clear corneal transplant. In our companion animals, the success rate for this procedure is much lower than in the human, so medical management is typically Initiated In the dog. A hyperosmotic salt ointment is often prescribed to help dehydrate the cornea. In so doing, this medication may cause the cornea to become clearer, however, the cloudiness will get worse again as the endothelial cells continue to die off. Unfortunately, there is no way of predicting how quickly this condition will progress and whether or not corneal bullae will ever form.
Other medications are occasionally used depending on the underlying cause for the endothelial cell death. For example, if the endothelial degeneration is secondary to inflammation or glaucoma, medications may be used to treat these conditions as well. In addition, topical antibiotic drops may be used if corneal ulcers are found.
If corneal bullae and ulcer formation becomes a recurrent problem, we may recommend a procedure called “Laser Keratoplasty” or “Thermokeratoplasty”. These procedures create scars within the cornea, which helps prevent the cornea from thickening with fluid. These procedures typically do not help to improve the clarity of the cornea, but rather prevent the corneal bullae from forming. This way, ulcers will be less likely to form, leaving your pet more comfortable.
It is important to realize that, although the above keratoplasty procedures are considered to have low risk, the chance for complication is possible. For example, there is always a risk associated with being under general anesthesia. Other potential complications include, but are not limited to:
- •Infection of the surgical site
- Corneal ulcerations
- Rupture of the eye, secondary to ulceration
- Corneal scarring, vascularization, or mineralization
- Inflammation inside the eye (uveitis)
- High pressure within the eye (glaucoma), secondary to uveitis
- Retinal detachment or degeneration, secondary to uveitis or infection
- Ocular or orbital pain, secondary to uveitis, glaucoma or infection
- Lens luxation, secondary to uveitis, glaucoma or infection
- Conjunctivitis
- Itchiness
- Bleeding inside the eye (hyphema)
- Excessive tearing
In rare instances, some of these complications can lead to blindness.
If you have any questions about Corneal Endothelial Dystrophy/Degeneration, please do not hesitate to call us at Eye Care for Animals.
