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               EYE PROBLEMS IN DOGS               

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Glaucoma
Keratoconjunctivitis Sicca (Dry Eye)
Corneal Ulceration
Progressive Retinal Atrophy (PRA)
Cataracts
Nuclear Sclerosis

Lens Luxation
Corneal Dystrophy
Retinal Dysplasia & Retinal Folds
Uveitis
Melanomas in the Eye

GLAUCOMA
Glaucoma is defined as excessive pressure inside the eye. The eye is full of a fluid called the aqueous humor, which is constantly produced and drained away from the eye and supplies nutrition for all interior structures. Glaucoma is caused by a decrease in the amount of fluid that flows out of the eye. It is a serious disease and without proper treatment can result in blindness. Unfortunately, even with aggressive medical and surgical therapy, dogs and cats with glaucoma will often lose their vision. Glaucoma is one of the most frequent causes of blindness in adult dogs.

Types of Glaucoma:
There are two main types of glaucoma, primary and secondary. In primary glaucoma, the cause of the increase in pressure is due to decreased outflow from the drainage angle. It is frequently an inherited problem. Beagles, Basset Hounds, and Cocker Spaniels are especially prone to this type of glaucoma. In secondary glaucoma the pressure is too high because something else is wrong in the eye, such as a lens luxation, bleeding, inflammation, or tumor.

glaucomadiag


Aqueous humor made in the ciliary body flows through the pupil into the anterior chamber. Aqueous then drains into the bloodstream through the iridocorneal angle.

Signs of Glaucoma:
1. A red (bloodshot) eye
2. A painful eye
3. Lids may be held shut
4. Excessive tearing
5. Eye may appear cloudy or blue
6. Sudden blindness
7. A dilated (enlarged) pupil that does not respond normally to light
8. Depression
9. Appetite loss
10. Enlargement of the eye

Treatment:
The treatment chosen (i.e. surgery and/or medical therapy) will be influenced by what the goal of therapy is: to stop pain in a blind eye or to preserve vision. Medical treatment consists of a number of different drugs used in combination. Some are given by mouth and effect the whole body, while others are put directly into the eye and have a local effect. The drugs that work when the problem is first diagnosed may not work forever. Therefore, the intraocular pressure needs to be monitored on a regular basis so that the medication regimen can be altered to fit the needs of the patient. Unfortunately glaucoma cannot be cured, only controlled. When medical treatment fails, surgical therapy can help prolong vision, or eliminate pain.

Medical Therapy:
The following categories of drugs are frequently used:

Carbonic anhydrase inhibitors: Oral and topical formulations reduce the amount of fluid produced inside the eye. (Methazolamide, dorzolamide or Trusopt )

Miotics (Parasympathomimetics): Used on the eye, they help to increase the outflow of fluid from the eye. They may cause a temporary redness, burning or stinging in the eye. (Pilocarpine)

Beta-adrenergic blockers: reduces the amount of fluid produced inside the eye. (Timolol)

*By using very small amounts of several of the drugs, the risks of side effects can be reduced.

*Please keep these drugs out of the reach of children.

Surgical Treatment:
In some cases, surgical procedures are available that may help to provide long-term control. One of these procedures uses a laser to destroy the part of the eye that produces fluid and thereby reduces the pressure. Another surgery inserts a tube into the eye that shunts the fluid under the conjunctiva (pink tissue) deep in the eye socket. Neither surgery is 100% effective and multiple surgeries over several years may be required to preserve vision.

A blind, painful eye can be removed to eliminate discomfort for your pet and to avoid the need for medicines that are expensive and affect the whole body. The surgery to remove the eye is called enucleation. After the eye is removed, the eyelids are permanently sewn shut. This means that the dog will look like he or she is winking at you.

Blind painful eyes may also have an intraocular prosthesis placed after a procedure called evisceration. With this surgery the contents of the eye are removed and silicone prosthesis is placed inside the eye. The outward appearance of the eye is preserved but no longer has the pain from high pressure. Afterwards, the eye looks fairly normal, but remains blind.

EVISCERATION WITH PLACEMENT OF AN INTRASCLERAL PROSTHESIS
 This surgical procedure is a cosmetic alternative to enucleation and is performed on blind and painful eyes. The contents of the eye are removed and a sterile silicone ball (the prosthesis) is placed within the eye. The looks fairly normal, moves normally, remains blind, but is no longer a source of pain. The photographs below show a dog with prostheses in both eyes (the smaller photo is a closer view.

glaucoma1
glaucoma2
 

Remember:
Each case is different and therapy must be tailored to the individual patient. Intraocular pressure must be measured regularly and the eye should be treated as prescribed. Do not stop any medication unless directed to do so by your veterinarian.
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KERATOCONJUNCTIVITIS SICCA (DRY EYE)
Keratoconjunctivitis sicca (KCS) is also called dry eye. This condition is due to a deficiency in tear production and results in a red, itchy eye with a thick mucous discharge. The tear production is measured by the Schirmer Tear Test. In this test a standardized paper strip is gently placed on the eye and allowed to absorb tears for one minute. Wetting values of less than 15 mm per minute are abnormal.

DRY EYE: Below are two dogs with dry eye.

kcs1
kcs2

The cornea is the front window of the eye. In the normal eye it is kept clear, moist, and smooth, by the tear film. In the condition of dry eye, the cornea is vulnerable to exposure, dry air, and bacteria. In order to protect itself, scar tissue starts to cover the normally clear cornea. This tissue consists of blood vessels, and pigment and results in a thickening of the cornea so that it appears dull and cloudy (photo on the left below). Tears are made of mucus, water and oils. Dry eye is a deficiency of the watery (or aqueous) part of the tears. Therefore, animals with KCS, accumulate a lot of mucus (photo on the right).

Why does this happen?
Acute KCS results in a very red and painful eye with a lot of discharge. The condition may be associated with viral diseases, trauma, drug toxicity (some types of antibiotics and some types of non-steroidal anti-inflammatory medications for example), allergy, or general anesthesia.

Chronic KCS results in intermittent redness with a profuse, ropy, thick discharge that adheres to the eye. Without treatment, the cornea may eventually pigment and scar to result in loss of vision. This can be familial in certain breeds, associated with immune-mediated diseases, secondary to chronic inflammation of the eye, or idiopathic (no known cause).

How long will this problem last?
Sometimes the condition resolves and spontaneous tear production resumes. The acute form is more likely to resolve. Chronic KCS may or may not resolve, and those animals with lower tear values (near zero) are harder to control. Medical therapy may need to be given for the lifetime of the animal. If medical therapy fails, surgery to transplant a salivary gland duct into the eye can sometimes help control the problem.

The importance of reexamination:
The tear test should be repeated to monitor progress and improvement in tear production. Premature discontinuation of the treatment can allow the condition to worsen. Due to corneal pigmentation and scarring, the condition can cause blindness if left untreated.

How is this treated?
Animals with acute dry eye frequently have corneal ulcers and they must be treated aggressively with antibiotics and tear replacement to avoid perforation and loss of the eye. Both acute and chronic KCS are treated by topical tear substitutes as well as stimulation of existing tear production. Cyclosporine ointment (Optimmune , Schering Plough) is used to increase tear production and reduce inflammation. Sometimes cyclosporine used 2x/day can control the KCS effectively without additional medications.

In some cases, topical antibiotics and/or corticosteroids are used in the treatment of KCS. The tear film has natural antibacterial action that must be replaced by antibiotic therapy. Anti-inflammatory drugs are frequently used to help control scarring and irritation.

It is important to clean accumulated mucus from eyes or lids with eye wash and cotton balls prior to instilling medications.

Be sure to keep all medications out of the reach of children.

Follow the medication schedule that you have been given. Premature discontinuation of medication is the most common cause of treatment failure.

Important Note:
If your pet is on a topical steroid (hydrocortisone, dexamethasone, or prednisolone), always call your veterinarian if your pet exhibits signs of pain (squinting, or rubbing at the eye). If a corneal ulcer develops, topical steroids must be discontinued immediately. When in doubt, stop topical steroids until your veterinarian checks the eye.
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CORNEAL ULCERATION
The cornea is the front clear part of the eye and is covered with a clear epithelium (skin layer). The corneal epithelium is like our skin except that it is clear and smoother. If the corneal epithelium is scratched, scraped or rubbed off, the resulting defect is called a corneal ulcer. This condition is painful and animals with ulcers often squint and rub at their eyes.

ulceration

A corneal ulcer can be a sight-threatening emergency if it deepens or becomes infected. This can happen rapidly (overnight), so prompt attention to a painful eye is essential.
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PROGRESSIVE RETINAL ATROPHY (PRA)
Progressive retinal atrophy (PRA) is a name given to a group of eye diseases of similar character. PRA causes no pain or discomfort but may result in permanent blindness. The word atrophy means wasting away.

PRA develops after birth and in some breeds has been determined to be inherited from both parents. It affects the retina, which lines the back portion of the inside of the eye. The retina contains the light-sensitive rods and cones that change light into energy for transmitting messages to the brain. The retina is similar to the film in a camera; the image or picture is received on it.

PRA can occur in all breeds of dogs and cats although certain breeds are at higher risk. It appears earlier in some breeds and can take several years to cause complete blindness. An early sign of PRA is inability to see in dim light or at night. For example, an animal with PRA may hesitate to go from a well-lighted room into a darkened room.

Due to PRA's slow progress, most pets adapt very well to the gradual loss of sight. Many owners do not realize their pet is becoming blind. Animals compensate well for blindness, because their senses are much more acute than those of people

Important Points about PRA:
  1. No effective treatment is available.
     2. Complete blindness eventually results.

     3. The condition, however, is not painful

     4. PRA is prevented through selective breeding of animals with normal eyes.

     5. Sometimes cataracts develop secondary to the retinal degeneration. But because of the retinal                              degeneration, cataract removal would not help the animal regain vision.

     6. Poor vision in dim light is the first sign you will see in your dog.

     7. You may also eventually see dilated pupils.

Notify the Vet if Any of the Following Occur

 You notice a sudden change in your pet's vision or in the appearance of the eyes.

 Your pet shows pain or discomfort.

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CATARACTS
A cataract is opacity of the lens of the eye. The lens is behind the iris (the brown or blue part of the eye) and can change its shape allowing animals to see close objects. A thin capsule (the consistency of cellophane) covers the lens.

cataract

In front of the lens is a clear fluid, called aqueous humor, and behind the lens is a clear gel, called the vitreous humor. The vitreous helps keep the retina attached. The retina is a layer of cells that functions in a manner similar to the film in a camera; it receives light and allows animals to see.

Causes of Cataracts
Cataracts may develop because of an inherited defect, with age, or secondary to inflammation, trauma, diabetes, or retinal degeneration.

Cataract Progression
As cataracts progress, they go through different stages: immature, mature and hypermature. In the later stage cataracts may leak proteins into the eye. These proteins can incite inflammation. The term for inflammation inside the eye is uveitis. Lens-induced uveitis is inflammation inside the eye caused by a leaky lens. The eye has an allergic-like reaction to this lens material. Lens-induced uveitis can damage the eye leading to complications such as glaucoma, retinal degeneration or retinal detachment, all of which can result in blindness.

Cataract Surgery
In cataract surgery the lens (cataract) is removed along with the front part of the lens capsule. The capsule covering the back of the lens is usually left in place to maintain the normal arrangement of the structures in the eye. In some cases an intraocular lens implant may be inserted to improve close-up vision after surgery.

To perform cataract surgery the patient must be under general anesthesia. Then, an incision is made in the cornea and the lens is removed. Two types of surgery are used in animals. In most cases a small incision is made and phacofragmentation performed. Phacofragmentation (also called phacoemulsification) utilizes hi-frequency sound waves to break up the lens and then the small fragments are removed.

The second type of surgery is performed in cases where the lens is too hard to be broken up by the phacofragmenter. Very old animals may need this type of surgery. A larger corneal incision is made and after removal of the capsule, the lens is gently expressed from the eye in one piece.

Patient Selection and Preparation
In order for your pet to be considered for cataract surgery, he or she must be relatively free of serious illnesses, skin disease and dental disease. Pre-operative blood tests are performed in all animals to help rule out any undetected kidney or liver problems.

In order for your pet to benefit from surgery, the retina, the tissue in the back of the eye that receives light, must be intact and functioning. Ocular ultrasound is performed before surgery to make sure the retina is attached. An electronic retina test called an electroretinogram (ERG), is also performed to make sure the retina is functioning well enough to go ahead with surgery.

Owner Participation
After cataract surgery, you will have a lot of work to do to help achieve a successful outcome. Several types of eye drops need to be given 4 times a day for at least a few weeks after surgery. Also, oral medications are given for a few weeks after surgery. Eventually these medications are decreased, discontinued or used in very small amounts. Sometimes, however, an animal may need some medication for extended periods of time.

An Elizabethan Collar is necessary for two weeks to keep your pet from rubbing its eyes after surgery.

Several recheck visits are required after surgery. Typically there are 2-3 visits during the first two weeks following surgery and then every few weeks- months for the first 6 months. Then we may recommend rechecks 1-2 times per year. These rechecks are necessary to detect and avoid any complications of surgery that may decrease vision.

see also Cataracts-fred Lanting

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NUCLEAR SCLEROSIS
Nuclear Sclerosis is a normal aging change of the lens. The lens is made up of several layers of cells arranged somewhat like the layers of an onion. Layers of cells are added continually throughout the animal's life. As your dog or cat gets older, new layers are added and the cells become packed together more tightly in the center of the lens (the nucleus). The increased density of the lens causes it to look more cloudy in dogs over seven years of age. The lens will become increasingly cloudy as the animal ages, but it almost never has an effect on vision.

Nuclear Sclerosis should not be confused with CATARACT (a complete opacity of the lens). A cataract is a different problem that is also characterized by a cloudy lens. While a cataract is an abnormality that can cause blindness and irritation inside the eye, nuclear sclerosis is normal for an older dog, and the condition usually does NOT interfere with vision! There is no medical treatment that will cure wither a cataract or nuclear sclerosis. Surgical removal of a cataract may be indicated to regain vision, but surgical removal of a lens with nuclear sclerosis would not be helpful.

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Lens Luxation

 The lens of the eye is the clear structure which focuses the image onto the retina. When the lens pathologically loses it's clarity, we call it a cataract.

The lens is located behind the iris, the central portion being exposed by the pupillary opening. The lens is normally held in position by small fibers called zonules, or the suspensory ligaments. The zonules are attached to the equatorial perimeter of the lens and to the ciliary body to keep it in position. Aqueous fluid (aqueous humor) fills the anterior chamber of the eye, and the vitreous, a jelly like material fills the vitreous chamber behind the lens. The aqueous fluid is manufactured in the ciliary body and flows through the pupil into the anterior chamber and exits the eye through the ciliary cleft or drainage angle where the cornea and the root of the iris meet in the periphery of the anterior chamber. Here, the aqueous fluid re-enters the general circulation of the body. The aqueous humor maintains the normal pressure of the eye known as intraocular pressure (IOP). A disruption or blockage of the flow of the aqueous fluid often results in glaucoma.

What is a Luxated Lens?
Should the zonules break the lens can either become loosened (subluxated) or completely detached (luxated). When the lens completely tears free of its zonular attachments and falls forward into the anterior chamber, we call this an anterior luxation. It is also possible for the lens to luxate posteriorly into the vitreous body.

lensluxa
(a)
normal lens position
(b)
anterior luxation forcing the iris forward. This results in a very shallow anterior chamber
(c)
lens is partially through the pupil. If the lens touches the cornea, edema of the cornea will result
(d)
complete anterior luxation. The anterior chamber is very deep as it contain the whole lens. Pupillary block is present.


Several causes of zonular rupture are recognized.

Primary (heritable) lens luxation seen in many Terrier breeds.

Secondary to trauma

Secondary to inflammation (uveitis)

Secondary to glaucoma

Congenital due to abnormal development

Idiopathic

Breeds with heritable lens luxation
Australian Cattle Dog Bedlington Terrier Border Collie Brittany Spaniel Deutsche Jadgterrier Fox Terrier German Shepherd Jack Russel Terrier Manchester Terrier Miniature Bull Terrier Norwegian Elkhound Scottish Terrier Shar-Pei Tibetan Terrier Welsh Terrier West Highland White Terrier Whippet . .

Since lens luxation may cause glaucoma, and since glaucoma may cause lens luxation it is important to determine which disease came first. When lens luxation occurs secondarily to glaucoma, it usually occurs late in the disease once the elevated pressure within the eye has caused the sclera to stretch, and the zonular ligaments to tear. This does not occur until long after vision has been lost. In such a case, attention must be given to resolving the pain associated with glaucoma.

What happens when the lens luxates?
An anteriorly luxated lens is extremely serious, because it blocks the flow of the aqueous fluid in the eye. This often results in the acute onset of glaucoma. We often use the term pupillary block glaucoma since the luxated lens itself and some displaced vitreous obstructs the flow of aqueous through the pupil. There are, however, other causes of pupillary block glaucoma. In dogs, it is generally accepted that within 72 hours, the elevated pressure in the eye will cause irreversible damage to the optic nerve and retina. In addition, the anteriorly luxated lens may cause corneal damage by injuring the endothelial layer of cells which help keep the cornea clear. Corneal edema of varying severity may be the result.

A posteriorly luxated lens can also cause glaucoma since the vitreous is displaced forward and can block the drainage angle.

Treatment
The first step in planning treatment for a dog or cat with a lens luxation is a careful assessment of the prospect for vision in the eye. If the lens luxation is longstanding and if there is glaucoma greater than 72 hours in duration, or if there is hemorrhage in the eye the chances of saving vision is reduced. If the lens luxation is recent, and if the glaucoma is not severe, and the retina and optic disc still look healthy, then there may be a reasonable chance of saving vision with surgery. In this case the surgery done is called an intracapsular lens extraction where the lens is removed with its capsule or covering intact. This requires a larger incision into the eye than traditional cataract surgery, and since the lens capsule is being removed, it is difficult, but not impossible, to replace the lens with an artificial lens (IOL). In many cases, it is also necessary to remove some of the vitreous which has also herniated forward. This is called a vitrectomy.

In some cases the patient is presented with the lens subluxated (partially luxated). If there is no pupillary block or glaucoma present, then medications may be used in an effort to keep the pressure low, and to keep the pupil relatively constricted to reduce the chance of anterior luxation. In some cases, where mild or intermittent glaucoma is present, laser surgery may help stabilize the intraocular pressure. Frequent re-examinations are required as the situation may change to true luxation in some cases.

If the eye has been blinded as a result of the glaucoma caused by the lens luxation, then emergency lens removal surgery will not benefit the situation. If the eye is painful, something must be done to relieve the pain. The two main solutions (also discussed on the glaucoma page), are enucleation (removal) of the eye, or an intrascleral prosthesis procedure where the contents of the eye are removed and replaced with a silicon ball, in many cases resulting in a comfortable blind eye with a very reasonable cosmetic appearance.

What about the other eye?
Examination of the fellow eye, especially in the terrier breeds predisposed to lens luxation may reveal a looseness or wobble to the lens as the head moves. This is due to weakness in the zonular ligaments and in such a case future luxation is likely. In these cases, preventative lens removal may be best, in an effort to prevent a crisis. Medical management by an observant owner is also an option, but should lens luxation occur, emergency surgery will be required.

What about future generations?
Dogs affected with primary lens luxation should not be used for breeding. Since this is a late onset disease, the breeder may encounter a situation where a dog who has already produced a number of litters of pups develops a lens luxation. This is disconcerting since it would be advisable not to use any of the second generation for breeding either. Routine eye certification examinations will not, in most cases, detect a dog predisposed to lens luxation, unless the ligaments have already started to weaken and the slight wobble of the lens is detected by the ophthalmologist during the examination.

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CORNEAL DYSTROPHY

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
Cooley, P.L. and Dice, P.F.: Corneal dystrophy in the dog and cat. Vet Clin No Am 20:681-692, 1990.
Whitely, D.: Canine cornea. In. Gelatt KN, editor. Veterinary Ophthalmology 2nd ed. Pages 307-356; 1991.
Dice, P.F.: Corneal dystrophy in the Airedale. Proc Am Coll Vet Ophthalmol. 7:36, 1976.
Waring, G. O.; MacMillan, A; Reveles, P.: Inheritance of crystalline corneal dystrophy in Siberian Huskies. J Am Anim Hosp Assoc 22:655, 1986.
Dice, P.F.: Corneal dystrophy in the Shetland Sheepdog. Am Coll Vet Ophthalmol, 15:241, 1984.
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.
Dice, P.F.: Corneal endothelial-epithelial dystrophy in the dog. Am Coll Vet Ophthalmol 7:36, 1976.


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RETINAL DYSPLASIA AND RETINAL FOLDS

Written by Dr. Julie Gionfriddo, D.V.M., Dip. A.C.V.O.


Anatomy and Physiology
The retina is the neurological structure in the back of the eye which receives light and converts it into an electrical signal. This electrical signal is transmitted to the brain by way of the optic nerve and is interpreted by the brain as vision. The embryological development of the retina is quite complex. It forms from a small part of the front of the primitive neural tube, the structure that becomes the nervous system (brain and spinal cord) of the adult. Malformations of the retina before birth are rare but can be due to either hereditary or environmental (in the uterus) influences.

Pathology
Retinal dysplasia is a type of retinal malformation. The word "dysplasia" simply means "a defective development of an organ or structure". Retinal dysplasia occurs when the 2 primitive layers of the retina do not form together properly. Mild dysplasia manifests as folds in the inner retinal layer. These are called "retinal folds". In "geographic" retinal dysplasia there are larger areas of defective retinal development. In the severe form of dysplasia, the 2 retinal layers do not come together at all and retinal detachment occurs. Retinal dysplasia is not progressive. It is a congenital defect and animals are born with as severe a condition as they will ever get. Retinal dysplasia can be detected as early as 6-8 weeks on a CERF examination. However, because the size of the eye is small and young puppies are often wiggling during examination, a 6 month recheck is recommended in order for the ophthalmologist to better see the back of the eye. The cause of retinal dysplasia in most breeds is genetic although prenatal infections with herpesvirus and parvovirus may also lead to it.

Affected Breeds
Retinal dysplasia is reported in 25 of the 100 breeds of dogs listed in the 1996 edition of the CERF book Ocular Disorders Presumed to be Hereditary in Purebred Dogs. Twenty-four of these breeds had retinal folds reported, and 11 had geographic areas of dysplasia and/or retinal detachment. Simple autosomal recessive inheritance has been suspected in Akitas, American Cocker Spaniels, Australian Shepherds, Bedlington Terriers, Beagles, Dobermans, English Springer Spaniels, Labradors, Rottweilers, Old English Sheepdogs, Sealyham Terriers, and Yorkshire Terriers. The means of inheritance has not been determined in many breeds. In Labradors and Samoyeds a combination of retinal dysplasia and skeletal defects has been described. This condition is known as oculoskeletal dysplasia. In this condition an autosomal dominant gene is thought to be responsible for the genetic defects. Homozygous animals have skeletal changes and mild to severe retinal dysplasia while heterozygous animals usually have mild retinal dysplasia.

Retinal folds rarely cause vision problems for the individual dog. They represent small blind spots which are probably not even noticed by the dog. However, large areas of dysplasia (geographic dysplasia) may lead to large deficits in the visual field and dogs with retinal detachments are completely blind.

There have been many questions recently about the certifiability of dogs with retinal folds. Retinal folds may be seen in many breeds and still pass a CERF examination and receive a CERF number. This is due to the fact that the condition is thought either not to be hereditary in the particular breed or has never been shown to be connected to serious (blinding) forms of dysplasia. In some breeds, particularly Labrador Retrievers, Samoyeds, and English Springer Spaniels, individuals with retinal folds are NOT given a CERF number. Since retinal dysplasia is common in these breeds and dogs and bitches with retinal folds can have puppies with blindness and/or skeletal problems the gene should not be perpetuated. In all breeds, individuals with geographic and retinal detachment forms of retinal dysplasia are NOT certifiable.

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UVEITIS 

Inflammation of the Eye

written by Dr. Dennis Hacker
Edited by Dr. Michael Zigler


To understand what uveitis is and how serious it is, it is helpful to know basic anatomy of the eye. The outer layer that encloses the eye is composed of the clear cornea and the white sclera. The innermost layer is the nerve layer or the retina. The middle layer (uvea or uveal tract) is the nutritional layer rich in blood vessels. It is made up of: the iris (colored portion in the front part of the eye), the ciliary body that produces the fluid inside the eye (aqueous humor) and the choroid that provides nutrition to the retina inside the eye. When inflammation attacks specific segments of the uveal tract the disease is further classified depending on the affected structure. Iritis is inflammation of the iris. Cyclitis is inflammation of the ciliary body. Anterior uveitis or iridocyclitis is inflammation of both the iris and ciliary body. Choroiditis or posterior uveitis is inflammation of the choroid. If all three structures (iris, ciliary body and choroid) are inflamed then it is called panuveitis.

Due to its rich blood supply, the uvea or uveal tract is a natural target for diseases originating in other parts ofuveitis the body. Because the cornea is normally clear, signs of these diseases may be seen first in the eye often before signs develop elsewhere in the body. Additionally, uveitis may have causes within the eye such as cataract or changes in the lens.
Click on photo to enlarge image

Diagnosis of Uveitis
Uveitis may cause vague clinical signs that can include blinking, squinting, watery discharge, and fear of light (photophobia) without any obvious changes to the eye itself. The normally clear cornea may appear dull or very blue due to uveitis. In other cases, the cornea becomes cloudy due to white blood cells accumulating on the inside of the cornea. The conjunctiva (white of the eye) becomes red and swollen. In some cases of uveitis, the iris (coloured portion of the eye) becomes red or changes colour. Uveitis is usually diagnosed by an examination of structures of the eye using instruments that magnify and illuminate. In more advanced cases, changes are visible without special instruments. Once uveitis is diagnosed, a general evaluation of the patient should be performed if uveitis is suspected to be a sign of internal disease. Blood profiles or other tests may be necessary if a certain disease is suspected or to find the cause of the uveitis. An ophthalmic examination consists of a visual inspection of the external and internal portions of the eye and the measurement of ocular pressure.

Ocular pressure is maintained by fluid (aqueous humor) which is continually produced by the ciliary body and drains from the eye. If the ciliary body is inflamed fluid production should slow down and the ocular pressure should drop. The aqueous humor produced in the eye flows through the pupil then drains into an 'angle' between the iris and the cornea where it leaves the eye. Cellular debris produced in uveitis can block this drainage angle. Alternatively, the iris may adhere to the lens and block fluid flow and result in increased ocular pressure - glaucoma. Once uveitis resolves, glaucoma may persist if drainage structures were permanently damaged by the inflammation. Recheck of the eyes following the resolution of uveitis is important for this reason.

Causes of Uveitis
Uveitis may be caused by many different diseases. Diseases in the dog include ehrlichiosis, Rocky Mountain Spotted fever, Lyme's disease and brucellosis. In the cat, uveitis can be a consequence of Feline Leukemia Virus (FELV), Feline Infectious Peritonitis (FIP), Feline Immunodeficiency Virus or Feline AIDS (FIV), toxoplasmosis or other diseases. In any animal, penetrating injuries such as cactus spines, porcupine quills, pellets or b.b.'s or a scratch may result in uveitis. Inflammation of the uveal tract can occur when the lens leaks some of its contents into the eye. The lens may cause uveitis when injured, when a cataract is rapidly forming, when cataract is dissolving or following certain types of surgery. Further possible causes are local bacterial infection, immune mediated (autoimmune) diseases, cancer and parasitic diseases. Treatment can be more specific if the actual cause of uveitis is known. Unfortunately, in up to 75% of the cases the cause of uveitis is never determined.

Medical Treatment
Medical treatment of uveitis must be aggressive to prevent glaucoma, to prevent scarring of the structures inside the eye and to prevent possible blindness. Different medications are used to control the original cause of the uveitis, if known, and to minimize the inflammation itself.

Aspirin (not aspirin substitutes), indomethacin, Profenal(R) and corticosteroids (cortisone drugs) minimize the inflammatory process. Corticosteroids may be administered by injection under the conjunctiva (movable white tissue of the eye), by eye drops, or as an oral medication depending on the location of uveitis. Eye drops are most often used for anterior uveitis. Injections and oral medication are used for posterior uveitis or panuveitis. Drops in the eye must be postponed if damage to the corneal surface is present (ulcer) because the corticosteroids prevent healing of the ulcer or lead to a worsening of the ulcer. If certain systemic diseases are suspected, oral corticosteroids may be postponed until laboratory test results become available. Aspirin can be used in dogs and cats by mouth and helps reduce inflammation. Indomethacin or Profenal(R) drops are a non-steroidal anti-inflammatory agent that will help reduce the inflammation of the eye.

Dilating drops or ointments widen the pupil and relax the muscles within the eye. These two actions result in fewer adhesions and less pain for the patient. This medication may not be used if glaucoma is present as it may further decrease the fluid drainage from inside the eye and lead to increased pressure.

Oral and topical antibiotics are only given when a bacterial infection is present within the eye. Antibiotics are not often used as bacterial infections are not commonly found as the cause of inflammation.

Prognosis
The treatment of uveitis requires therapy to halt the inflammation of the uveal tract along with a search for the cause of the condition. Diagnostic tests may be needed to determine possible causes. The results of these tests are very important for proper treatment to be given. Follow-up examinations ensure optimal therapy is being given and guard against possible complications. Uveitis, if caught early and treated diligently and aggressively, will often resolve without serious consequences. Unfortunately, in certain individual patients the cause of uveitis is never determined and treatment may be life-long. In other patients, the uveitis is so severe that removal of the eye is necessary.

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MELANOMAS IN THE EYE

First broadcast on www.provet.co.uk   
 
This information is provided by Provet for educational purposes only.
You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.


Melanoma of the eye occurs in both cats and dogs, but there are some significant differences between these tumours in the two species.

The main differences between melanoma of the eye in cats and dogs are as follows :


CAT
DOG
Frequency of occurrence
Uncommon
Uncommon - but it is the most common intraocular neoplasm in dogs
Most common site
Iris (anterior face usually)
Iris (anterior surface) or ciliary body (difficult to see in early stages).
Most common form
Diffuse infiltrate
Diffuse infiltrate Raised nodule
Colour
Brown usually
Brown to black
Rate of growth
Often very slow.
It can take months-years before secondary effects develop. Slow
Secondary effects
Glaucoma.
Corneal oedema, glaucoma, lens luxation
Predisposed breeds

German Shepherd Dogs, Labrador Retrievers
Genetic inheritance

Possibly
Metastatic spread
High - 30-60% spread
Usually less than 5% spread post-enucleation follow-up.
Treatment Enucleation.
Laser treatment? Enucleation.
Surgical resection occasionally. Laser treatment ?
Differential diagnosis
Melanosis of the iris in middle-aged cats can be difficult to differentiate

Metastasis
Radiograph chest for secondary spread
Radiograph chest for secondary spread


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chloebutton  talabutton  

The above information is simply informational. It's intent is not to replace the advice of a veterinarian nor to assist you in making a diagnosis of your pet. Please consult with your own veterinarian for confirmation of any diagnosis. Your pets life may depend on it.