Corneal dystrophy

Corneal dystrophy is a group of disorders, characterised by a noninflammatory, inherited, bilateral opacity of the transparent front part of the eye called the cornea. It is commonly seen in humans as well as dogs. It is rare in cats.

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Signs and symptoms

Corneal dystrophy may not significantly affect vision in the early stages. However, it does not require proper evaluation and treatment for restoration of optimal vision. It can, however, rarely cause corneal ulceration, especially with epithelial dystrophy. It appears as grayish white lines, circles, or clouding of the cornea. Corneal dystrophy can also have a crystalline appearance.

Pathophysiology

A corneal dystrophy can be caused by an accumulation of extraneous material in the cornea - it can be in the form of lipids or cholesterol crystals.

Classification

Corneal dystrophies are commonly subdivided depending on its specific location within the cornea. It can be basically divided into anterior, stromal, or posterior according to the layer of the cornea affected by the dystrophy. [1] [2]

Treatment

Suboptimal vision caused by corneal dystrophy usually requires surgical intervention in the form of corneal transplantation. Penetrating keratoplasty is commonly performed for extensive corneal dystrophy. Corneal dystrophy in dogs usually does not cause any problems and treatment is not required.^[1]

Prognosis

Early stages may be asymptomatic and may not require any intervention. Initial treatment may include hypertonic eyedrops and/or ointment to reduce the corneal edema and may offer symptomatic improvement prior to surgical intervention. With penetrating keratoplasty (corneal transplant), the long term results are good-excellent. Recent surgical improvements have been made which have increased the success rate for this proceedure. However, recurrence of the disease in the donor graft is not ruled out.

Corneal dystrophy in dogs: Commonly affected breeds

Many breeds are affected by corneal dystrophy with many different appearances. These breeds most commonly have these criteria.^[2]

• Afghan Hound
• Airedale Terrier - occurs at 4 to 12 months of age in the central cornea. It is progressive and can cause decreased vision.
• Alaskan Malamute - occurs at greater than two years of age in the central cornea.
• Beagle - has a nebular, race track, or arcing appearance.
• Bearded Collie - occurs at greater than one year of age in the lateral or central cornea and can affect just one eye.
• Bichon Frise - occurs at greater than two years of age in the inferior or central cornea.
• Cavalier King Charles Spaniel - occurs at two to four years of age in the central cornea.
• American Cocker Spaniel
• Rough Collie - occurs at one to four years of age in the inferior or central cornea.
• English Toy Spaniel - occurs at two to five years of age and has a crystalline, circular appearance.
• German Shepherd Dog - occurs at one to six years of age and is usually oval.
• Golden Retriever - occurs at less than two years of age and can be progressive.
• Italian Greyhound - occurs in young dogs and is focal.
• Lhasa Apso - oval appearance.
• Mastiff - oval appearance.
• Miniature Pinscher - occurs at one to two years of age and is oval.
• Norwich Terrier - peripheral cornea.
• Pembroke Welsh Corgi - occurs in young dogs and can include blood vessels and pigmentation.
• Pointer - gray, hazy ring.
• Poodle - occurs at greater than one year of age.
• Samoyed - oocurs at six months to two years of age and is gray and round.
• Shetland Sheepdog - occurs at two to four years of age as multiple gray/white rings. It can develop into a corneal ulcer.
• Siberian Husky - occurs at five months to two years of age and is gray and oval.
• Weimaraner - Occurs at one to eight years of age in the central cornea.
• Whippet - occurs at three to five years of age in the central cornea.

Corneal endothelial dystrophy

Corneal endothelial dystrophy is an age-related change that affects the inner layer of the corneal, the endothelium. Leakage of fluid into the cornea causes edema, causing a bluish appearance. This will eventually involve the whole cornea. Bullous keratopathy (blisters in the cornea) may also form, leading to nonhealing and recurrent corneal ulceration. Hyperosmotic agents are sometimes used topically for treatment, but success with these medications is inconsistent and can cause irritation. Bad cases may require a corneal transplant or thermokeratoplasty, which is a grid of superficial burns to the cornea that causes anterior stromal fibers to contract and prevent fluid uptake by the stroma.^[3] The most commonly affected breeds are the Boston Terrier, Chihuahua, and Dachshund.^[2] The age of onset in the Boston is five to nine years and eight to thirteen years in the Chihuahua and Dachshund.^[4] The disease is similar to Fuch's dystrophy in humans.

See also

• Recurrent corneal erosion
• Keratoconus
• Keratoglobus

References