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Corneal Dystrophy in Dogs

 

Contributors:

Julie Gionfriddo DVM, Dip.ACVO, ACVO Genetics Committee/CERF Liaison.
Michael Zigler DVM, CertVOphthal.

Distinction between Corneal Dystrophy and Corneal Degeneration

Confusion often arises over the use of the term "corneal dystrophy" in dogs. Technically, "corneal dystrophies" are diseases of the cornea that are bilateral, non-inflammatory and inherited 1,2. The confusion arises because the term "corneal dystrophy" is sometimes used to refer to a disease with similar clinical signs but is not hereditary. A more appropriate term for the non-inherited conditions is corneal degeneration.

Clinical Appearance

In most breeds, corneal dystrophy appears as gray-white, crystalline or metallic opacities in the center of the cornea or close to the periphery. These opacities may affect any layer of the cornea, the epithelium (outer layer), the stroma (the thick, middle layer), or the endothelium (the inner layer). The opacities are usually oval or round and are sometimes doughnut-shaped. The age of onset of the disease varies within and among dog breeds and may range from 4 months in Airedale Terriers, to up to 13 years in Chihuahuas. The opacities usually progress but in some cases they remain static. Their progression may be very slow and may or may not lead to blindness (common in Cocker Spaniels, Poodles, Samoyeds, Siberian Huskies, Pointers, German Shepherds, and Bichon Frises). On the other hand, progression may be rapid and lead to blindness (more common in Airedale Terriers, Boston Terriers, Chihuahuas and Dachshunds) 2. The mode of inheritance varies among breeds and in many breeds it is unknown. In the airedale terrier it is thought to be a sex-linked trait 1,3 and in the Siberian Husky, Corneal Dystrophy has been shown to be a recessively inherited trait with variable expression 4.

Corneal dystrophies are usually not painful. In a few breeds, however, a dystrophy can lead to secondary breaks in the epithelial (outer) layer of the cornea. When this occurs a painful corneal ulcer develops requiring intense treatment. In other breeds, a painful ulcer may not develop and the dystrophy itself is not treatable. No medication will "dissolve" the opacity. Surgical removal of the dystrophic area may temporarily decrease the opacity in cases of epithelial dystrophy. Often, however the opacities will reform in the healed cornea.

Characteristics of corneal dystrophy in 6 dog breeds:

Shetland Sheepdogs have corneal dystrophy which may begin as early as 4 months of age and usually progress throughout life 5. It usually manifests as small gray or white rings which start in the center of the cornea and later other spots develop peripherally. This condition is an epithelial dystrophy, meaning it is in the superficial layer of the cornea. This corneal dystrophy is inherited but the mode of inheritance is unknown. In Shelties this disease can cause corneal ulcers.

In Beagles, corneal dystrophy may begin as early as 3.5 years of age 6. Beagles usually have either an anterior stromal opacity or one which involves all layers of the stroma. The opacity progresses from an oval "nebula" (cloud-like lesion), to a racetrack-shaped lesion, to an arc-shaped opacity. In Beagles dystrophy rarely causes corneal ulcers and the mode of inheritance is unknown.

Siberian Huskies have a form of corneal dystrophy which is properly called "crystalloid corneal dystrophy." it is inherited as a recessive trait and appears round or horizontally oval 4. It begins as a diffuse, gray haze in the anterior stroma and may progress to crystals or gray-brown smudgy deposits in the anterior stroma, or involve the posterior part of the stroma or the entire stroma 2. This form of dystrophy usually begins between 5 and 27 months of age.

Boston Terriers and Chiuhuahuas have a form of endothelial dystrophy which usually begins later in life (5 to 9 years) 7. Its mode of inheritance is unknown. This disease begins as a fluid build-up (edema) in the cornea due to the inability of the endothelium to act as a water barrier to keep the fluid inside the eye from percolating into the corneal stroma. The fluid build-up causes the cornea to look white. It begins at the edge of the cornea, progresses centrally and often involves the entire cornea, causing the cornea to appear thickened. The fluid can accumulate under the epithelium and lift it off, thus causing a painful corneal ulcer which is very difficult to treat.

Airedale Terriers have a dystrophy which is presumably sex-linked inherited and affects male dogs as young as 9-11 months of age. It is located in the anterior stroma of the cornea and consists of an infiltration of lipid (fat). This form of dystrophy often progresses to decreased vision by 4 years of age and is not treatable.

References

  1. Cooley, P.L. and Dice, P.F.: Corneal dystrophy in the dog and cat. Vet Clin No Am 20:681-692, 1990.
  2. Whitely, D.: Canine cornea. In. Gelatt KN, editor. Veterinary Ophthalmology 2nd ed. Pages 307-356; 1991.
  3. Dice, P.F.: Corneal dystrophy in the Airedale. Proc Am Coll Vet Ophthalmol. 7:36, 1976.
  4. Waring, G. O.; MacMillan, A; Reveles, P.: Inheritance of crystalline corneal dystrophy in Siberian Huskies. J Am Anim Hosp Assoc 22:655, 1986.
  5. Dice, P.F.: Corneal dystrophy in the Shetland Sheepdog. Am Coll Vet Ophthalmol, 15:241, 1984.
  6. Ekins, M.B.; Waring, G.O.; Harris, R.R.; et.al.: Oval corneal opacities in Beagles, PartII: Matural history over 4 years and study of tear function. J Am Anim Hosp Assoc 16:601, 1980.
  7. Dice, P.F.: Corneal endothelial-epithelial dystrophy in the dog. Am Coll Vet Ophthalmol 7:36, 1976.

Breeds Affected with Corneal Dystrophy

BREEDING ADVICE
BREED NO* BREEDER'S OPTION* UNKNOWN*
Afghan Hound . spacer .
Airedale Terrier spacer . .
Australian Shepherd . . spacer
Bichon Frise . spacer .
border Collie . . spacer
Boston Terrier spacer . .
Cavalier King Charles Spaniel . spacer .
Chihuahua spacer . .
Cocker Spaniel - American . spacer .
Collie . . spacer
Dachshund spacer . .
English Toy Spaniel . spacer .
German Shepherd . . spacer
Golden Retreiver . . spacer
Labrador Retreiver . . spacer
Miniature Pinscher spacer . .
Old English Sheepdog . . spacer
Papillon . spacer .
Samoyed . spacer .
Shetland Sheepdog spacer . .
Shiba Inu . spacer .
Siberian Husky spacer . .
Vizsla . . spacer
Whippet . . spacer

* Definitions

(abstracted from Ocular Disorders Proven or Suspected to be Hereditary in Dogs, ACVO, revised 1994)
No - Substantial evidence exists to support the heritability of this entity and/or the entity represents potential compromise of vision or other ocular function.
Breeder's Option - Entity is unknown or suspected to be inherited but does not represent potential compromise of vision or other ocular function
Unknown - Diseases under consideration with inadequate information available to give breeding advice.

Reference
Severin, G.A., Severin's Veterinary Ophthalmology Notes 3rd edition, 1995.

Frequently Asked Questions

Corneal Dystrophy

I have been trying to find the latest information about the effects of Hypothyroidism on Labrador Retriever eyes. If you have any information I would appreciate receiving it. My yellow lab has developed cloudy spots on her corneas in both eyes. Since she has been receiving treatment for hypothyroidism, I am concerned that it is not as under control as I had thought.

Labrador Retreiver's are occassionally are presented with Corneal Dystrophy, a condition that is thought to be inherited. It is usually bilateral (both eyes) and is usually axial (right in the centre) and appears as a non-painful opaque whitish or grey deposit. It is unrelated to hypothyroidism.

Hypothyroid dogs with elevations of serum cholesterol will occasionally develop a cholesterol plaque in the cornea, but this tends to occur at the site of a corneal injury or irritation where blood vessels have grown into the cornea. It is therefore unlikely that such a lipid dystrophy would be bilateral and axial.

Your best method to determine what is really happening is to have the blood checked for thyroid levels and cholesterol. The sample should be drawn approximately six hours after the morning dose of thyroid medication and after a 12 hour fast. If necessary, your vet will recommend a dosage adjustment if he is not controlled well on his present dosage.

A veterinary ophthalmologist can recognise corneal dystrophy on the basis of a routine "slit lamp" examination. Ask for a referral.

Corneal Endothelial Dystrophy

My 10 year old Boston Terrier has been diagnosed as having Corneal Endothelial Cell Dystrophy. His eyes have a bluish color. He is in no distress, but I can tell that his vision is lessened. Is there a way to slow the progress of this? What is his future?

Corneal endothelial dystrophy is an uncommon condition, but is seen most frequently in the Boston Terrier and Chihuahua. Age of onset is generally 7 to 9 years of age. This is a slowly progressive disease, for which there is no definitive cure.

The corneal endothelium is a layer of cells which line the inner surface of the cornea. The endothelial cells are responsible for pumping fluid out of the cornea. The cornea is normally clear despite being bathed in tear on the the outer surface and bathed in aqueous humor on the inner surface. This clarity is maintained by the function of the endothelial cell layer.

If the endothelial cell numbers are reduced, the clarity of the cornea cannot be maintained. This is called corneal edema, which progresses at varying rates in different dogs, and is often, but is not necessarily blinding. What causes this loss of endothelial cells is not known although the breed distribution suggests an inherited predisposition, along with age related degeneration of the endothelial cells. The condition resembles Fuch's endothelial dystrophy in humans.

In severely affected dogs, the cornea contains enough fluid that bullae - or water bubbles - form. These come to the surface of the cornea and break resulting in corneal ulceration and pain. Application of topical hyperosmotic eye ointment containing 5% NaCl, may help reduce bullae formation, but the corneal edema does not clear.

Corneal transplantation, the treatment of choice for Fuch's dystrophy in humans, has been tried in dogs, but the success rate is less than desirable. The reason that the success rate is less than stellar includes the fact that the dog's cornea vascularizes more readily that the human cornea, and this promotes rejection of the graft. In addition techniques for procuring and preserving donor graft tissue is a fine tuned art in humans, but is rarely pursued in animals.

Corneal Lipid Dystrophy

My 31/2 year old Sheltland Sheepdog was recently diagnosed as having corneal lipid dystrophy. I have never heard of this and would like some more information on it. I was told that it could be a symptom of hypothyroid or it could be genetic so I am awaiting the results of a thyroid test on him. I would appreciate any other info you may have on this condition.

Corneal dystrophy is seen quite commonly in the Sheltie. It is an inherited disease which results in the deposition of cholesterol and sometimes calcium in the corneal tissue just under the surface epithelium. In most dogs the central part of the cornea is involved. In Shelties, it is not uncommon for multiple spots to develop. The condition progresses up to a certain point, and then stops and is rarely blinding.

Of all the breeds of dogs, the Sheltie is most likely to have problems with the dystrophy. Sometimes little pieces of the dystrophic plaque will come to the surface and slough off resulting in a painful corneal ulcer. If not managed properly, the ulcer may get infected and complications develop.

Dogs with corneal dystrophy should have a thorough blood evaluation done including thyroid, cholesterol and triglyceride tests.

The use of topical steroid eyedrops may help, but steroid drops should not be used if there is any corneal ulceration. Ocular lubricants generally help make the dog more comfortable and reduces the episodes of plaque sloughing. Topical EDTA drops help in some cases, especially if the plaque has a significant Calcium component. Low fat dietsocassionally help. In cases where repeated episodes of painful sloughing occur, a surgical keratectomy may be beneficial.

Re: Corneal Lipid Dystrophy

My labrador bitch was recently (has been CERFed four years prior to this) screened and diagnosed, according to the CERF form as "dystrophy--epithelial/stromal", doctors notes include; "Possible genetic corneal dystrophy, possible systemic lipid abnormalities. Recommend fasting blood cholesterol and triglycerides.." She previously suffered a corneal abrasion in the one eye, however the doctor said lipids were present in both. Can I assume this has a genetic cause. If so, what is the genetic inheritance pattern for this disorder?? Although she will be eliminated from the breeding program, what is the prognosis for the puppies she already has on the ground??

Corneal dystrophy is presumed to be heritable in the Labrador Retreiver. It is more likely to be passed as a recessive trait, but this is not known for certain. If this were the case, her pups from previous litters would have a degree of risk of being affected which depends upon the genetic status of both parents, for example a Normal (RR) X Affected (rr) breeding would produce 100% carriers (Rr) while a Carrier (Rr) X Affected (rr) breeding would result in 50% carriers (Rr), 50% affected (rr).

I would recommend that you have the blood work done before making major decisions.

Corneal Dystrophy

My Australian Terrier pup of 5 months has been diagnosed by a local Opthamologist as having Corneal Dystrophy. He has had this ever since we have had him. I would just like to know how this condition may progress and whether it will make him blind. I have heard conflicting reports on this condition and the Opthamologist was a little vague.

Neonatal corneal dystrophy often improves quickly with time, and usually is gone or hardly noticable by 5 or 6 months of age. I would suggest a recheck visit if spontaneous improvement is not occurring. There are reasons other than corneal dystrophy that young dogs might develop a whitish spot on the cornea. These include scarring from an injury, persistent pupillary membranes, and abnormalities in the tearfilm or in the ability to blink.

Siberian eyes - White Filmy Covering

My 5 year old female red & white siberian has developed a white filmy covering on both of her eyes. Last year she was checked for cataracts by a certified opthalmologist, and cleared with no signs of cataracts developing at all. She had an eye infection last year around that time, so her vessels were very red and showed, the vet had her on drops. The opthalmologist indicated that he believed that it was caused by something caught in her third eyelid that scratched her lense at the bottom of her eye. There was a small scar there. The vet indicated later that this condition might come back and be something that she always has, although it is not hereditary. My question is what does it sound like to you?? The whiteness looks like a film, like when there's gas on water. It's on the actual external part of her eyeball, like you could wipe it off.

I don't understand the signs of cataracts, but I don't think this could be what it is. I guess I'll need to take her to Dr. Christmas and see what he thinks, but I thought I'd try to get an idea of what I might be dealing with.

I suspect you are describing Corneal Dystrophy - a heritable disease in the Siberian. I would suggest that you see Dr. Christmas to rule out other possibilities.

Corneal Dystrophy

Our Golden Retriever was just in to see the vet today. She has developed cloudy spots on her corneas in both eyes. What is the treatment recommended for this, and how serious is it? I'm so scared.

Corneal dystrophy in the Golden is presumed to be a heritable disorder which rarely progresses to impair vision, and rarely causes any problems with discomfort. It is generally not treated unless irritation is noted. In the Golden, it may be prudent to have the dog checked for hypothyroidism.

Our Sheltie has spots on her eyes

Our four year old Shetland Sheepdog has developed whitish spots near the surface of both eyes. The spots are uneven in shape and size, and are more opaque around the edges than in the centers, which are more translucent. The spots (one in each eye) are somewhat oval in shape, and are not exactly centered in the eye, although they are generally centered. These spots developed a month or two ago, and at first I thought they were just odd reflections. I have read the other postings on this site, and I am suspicious of corneal dystrophy, although my veterinarian diagnosed the problem as dry eye, and recommended I treat my dog with artificial tears every few hours.

My veterinarian performed one test on my dog's eyes -- the one with the green dye and the blacklight. He said there was no ulceration present and the spots were on the surface of my dog's eyes.

My vet is on vacation until mid-week, and I plan to bring my dog in to see him again as soon as he is back in his office. Do you have any suggestions as to what may be wrong with my dog? Obviously, I don't expect you to diagnose a dog you haven't seen, but any suggestions you can make would be very helpful, because I will ask my vet to test my dog for any conditions you suspect. If he is unfamiliar with any conditions you suggest, I will ask for a referral to a veterinary opthalmologist (or should I see one anyway, just to be safe?)

I would suspect you are indeed describing Corneal dystrophy. It is most common, in my experience, in the Sheltie and the Sheltie seems to be the breed that has the most problems with corneal dystrophy.

Until your vet gets back, I would suggest that you use a high quality ocular lubricant such as lacrilube, duratears, tear gel or hylashield, and if irritation continues then perhaps you should be seeing an ophthalmologist.

Corneal Dystrophy in Shiba Inu

I have a 18 mth old male shiba (japan imort). He has a definite blue cloudy film in both eyes. Recently he was CERF examined and was diagnosed with corneal dystrophy. After reading all the info available on your fab.. website I am still confused about the treatment and heretiary factors. Also is this a major problem in the breed to start with? The breeders of this dog have been involved in the breed for a very long time and they have not had this perticular problem before. The vet who examined the dog was not very experienced, by her own admission, could there be another cause? I would appreciate any help on this problem.

There is insufficient data on the Shiba Inu to make any assessment of heritability. By definition, corneal dystrophy is a heritable problem. I am certain the the ophthalmologist would have no difficulty diagnosing corneal dystrophy and differentiating it from other conditions that produce white lesions in the cornea. Since many heritable problems are influenced by other factors, you might want to try feeding a low fat diet (8 or 9% fat) to see if this makes a difference.