What is corneal dystrophy?
Corneal dystrophy is a term used to describe several conditions that occur in dogs and cause the corneas to become opaque (cloudy). There are three major categories of corneal dystrophy: epithelial, stromal, and endothelial. Each is named based on the anatomic location of the abnormal tissue and opacity. All corneal dystrophies are primary, inherited conditions not associated with any other eye disease or systemic (body- wide) medical problem. Corneal dystrophy is very rare in cats.
What are the three types of corneal dystrophies? How do they differ from one another?
The three types of corneal dystrophy are named by their anatomic location in the cornea, and consequently the clinical signs of each differ.
1. Epithelial corneal dystrophy
This opacity occurs in the superficial layers of the cornea. It has been found in many breeds of dogs. Many dogs with epithelial corneal dystrophy have no clinical signs other than corneal opacity. However, some dogs may have corneal pain causing sensitivity to light, and squinting. The surface of the eye may develop patches of white or gray—these are the opaque lesions—and some of the lesions may reflect erosions in the corneal surface. The erosions are what lead to eye pain.
2. Stromal corneal dystrophy
The stroma is the middle layer of the cornea, and stromal corneal dystrophy is associated with the deposit of fat droplets into this layer of the cornea. Multiple breeds are affected including (but not limited to): airedales, Cocker spaniels, bearded collies, Cavalier King Charles Spaniels, samoyeds, and weimaraners
These dogs tend to be young when diagnosed, and most dogs have no associated inflammation or pain. The opacity tends to occur in one of several patterns, most commonly as a gray, white, or silver opacity at or near the center of the cornea. Alternately, the opacity may appear as a ring around the outer border of the cornea, or the entire cornea may become diffusely opaque. Vision may be affected when the opacity is diffuse.
3. Endothelial corneal dystrophy Endothelial corneal dystrophy affects the deepest layer of the cornea. This condition is most common in middle-aged or older Boston terriers, Chihuahuas, and Dachshunds. In the early stages of endothelial dystrophy, there may be no easily observable signs. As it progresses, fluid accumulation (edema) starts at the lateral edge of the cornea and spreads across the rest of the cornea over time. These dogs may develop painful corneal ulcers, and may lose their vision with advanced disease.
Is there any treatment for corneal dystrophy?
Advanced epithelial or endothelial corneal dystrophy may result in corneal ulceration that requires treatment. That treatment may require referral to a veterinary ophthalmologist. Otherwise, no treatment is described or required for the various corneal dystrophies. It is worth noting that most dogs with corneal dystrophy never experience compromised vision.