Glaucoma

Glaucoma is increased eye pressure caused by fluid buildup in the eye. Glaucoma is due to an obstruction to the drainage of aqueous humor from the eye. Continued fluid secretion into the sealed eye elevates the intraocular pressure.It is a serious disease that can lead to partial or total blindness. Signs include redness, cloudiness, excessive tearing, eyeball swelling, pain, and sensitivity to light. After diagnosing glaucoma by measuring eye pressure with a tonometer, veterinary ophthalmologists treat the disease with pressure- relieving medication or laser surgery In some cases, surgical removal of the eye is necessary.

Glaucoma is a very common disease in humans and also very common in dogs. Glaucoma means that the pressure fluid inside the eyeball (or globe) is excessively high. When this occurs, internal structures are destroyed. It is similar to high blood pressure causing a vessel within the brain to rupture and blood flooding into the surrounding tissue crushing brain cells. In the eye, the elevation of the pressure of the internal fluid to dangerous levels affects almost every tissue inside the globe. In most cases, this renders the eye blind and useless.

The fluid that develops the excessive pressure associated with glaucoma is the aqueous humor, the liquid found in front of the lens. It is produced by the ciliary body (1), flows past the lens (2), through the pupil (3), across the inner surface of the cornea and front side of the iris (4), and then drains from the eye at the angle formed where the cornea meets the iris (5). The cornea and lens are living tissues but they have no blood vessels going to them to supply the needed oxygen and nutrition. These life-sustaining materials are brought to them through the aqueous humor.

In glaucoma, elevations in the pressure of the aqueous humor are most frequently caused by this fluid not being able to drain correctly from the eye. Additional fluid is constantly being produced and if an equal amount does not leave the globe, then the pressure starts to rise. It is very similar to a water balloon. As more water is added, the balloon stretches more and more. In the case of the balloon, it finally ruptures. The eyeball is strong enough that it does not stretch to any great degree so the force of the increasing pressure is felt by the eye’s internal structures. They are either crushed or displaced. In either case, they are rendered nonfunctional.

We refer to glaucoma as being primary or secondary.

Primary Glaucoma: Primary glaucoma occurs in an animal because it possesses physical or physiologic traits that predispose it to glaucoma. This is usually predetermined by genetics. For instance, eyes may have drainage pores that are too small or naturally narrow angles such that the fluid has a difficult time making its way out of the globe.

Primary glaucoma is most common seen in Beagles, Cocker Spaniels, and Basset Hounds. It also occurs many of the breeds listed below:

DOG BREEDS WITH A PREDISPOSITION TO GLAUCOMA

• Afghan
  
  
• Akita
  
  
• Alaskan Malamute
  
  
• Basset Hound
  
  
• Beagle
  
  
• Border Collie
  
  
• Boston terrier
  
  
• Bouvier des Flandres
  
  
• Cairn terrier
  
  
• Cardigan Welsh corgi
  
  
• Chihuahua
  
  
• Chow Chow
  
  
• Cocker Spaniel
  
  
• Dachshund
  
  
• Dalmatian
  
  
• Dandie Dinmont terrier
  
  
• English springer spanielv
  
  
• Giant schnauzer
  
  
• Great Dane
  
  
• Maltese
  
  
• Manchester terrier
  
  
• Miniature pinscher
  
  
• Norfolk terrier
  
  
• Norwegian elkhound
  
  
• Norwich terrier
  
  
• Pembroke Welsh corgi
  
  
• Poodle
  
  
• Saluki
  
  
• Samoyed
  
  
• Scottish terrier
  
  
• Sealyham terrier
  
  
• Shih tzu
  
  
• Siberian husky
  
  
• Skye terrier
  
  
• Smooth-coated fox terrier
  
  
• Welsh Springer spaniel
  
  
• Welsh terrier
  
  
• West Highland white terrier
  
  
• Whippet
  
  
• Wire-haired fox terrier
  
  

CAT BREEDS WITH A GENETIC PREDISPOSITION FOR GLAUCOMA:

• Persian
  
  
• Siamese

The exact cause of primary glaucoma is slightly different in each of these breeds, but suffice to say that the end result is the same. In these breeds, even though the animal carries the trait for this disorder, the disease itself does not usually develop until the dog is two or three years of age or older. It appears that developmental changes continue to occur until the animal is mature and then an additional period of time is necessary for clinical signs to appear. With primary glaucoma, both eyes are rarely effected equally or at the same time. The disease usually occurs in one eye months or even years before it affects the second one.

Secondary Glaucoma: Secondary glaucoma means that the disease is secondary to, or caused by, another condition. A common example is a penetrating wound to the eye. This often causes an inflammation and the fluid may become too thick to flow out through the drainage pores, or it might cause scar tissue to form with the drainage angle, itself, closing.

A brief list of the causes of secondary glaucoma would include bleeding in the eye, inflammation within the eye, luxation or displacement of the lens, attachments or scarring between the iris and the lens, degeneration of the structure within the drainage angle, or anything that causes the angle to narrow or close. With inflammation or bleeding into the eye, glaucoma is simply caused by the drainage pores or angle becoming so clogged that adequate fluid cannot escape the eye.

Luxation of the lens means that the small attachments holding it in place have weakened or broken down and the lens has moved forward. When this happens, it rests against the iris and blocks the opening (or pupil). An attachment or growing together of the lens and the iris can happen with or without luxation, but the result is the same - the pupil is closed and the fluid cannot pass through. The cells and tissue of the drainage angle can degenerate or wear out with age, causing them to lose their ability to function correctly. In these cases, the cells sometimes change type or scar, preventing drainage. As can be imagined, a narrowing of the drainage angle can be caused by many different events. If the base of the iris or ciliary body becomes swollen or enlarged, the iris and cornea are pushed together and the fluid will be unable to make it to the deeper reaches of the angle. Drainage will be impossible. This can be caused by tumors, infections, inflammations, etc.

All of this information will hopefully give you an understanding of why or how glaucoma occurs. What is even more important for you, the owner, is to be able to recognize the earliest signs of glaucoma. Just so there is no misunderstanding, if treatment for glaucoma in the dog is not started within a few days or in some cases a few hours of the pressure increase, vision will probably be lost completely from the affected eye. The pressure can crush the cells of the retina and optic nerve, rendering them nonfunctional. It can break down the structures holding the lens in place and it can cause damage to the iris and cornea. After these internal changes have occurred, the eyeball itself swells in size, tilts off to the side, and all the surface blood vessels enlarge giving it the appearance of a large, ugly, bruised radish.

The early signs of glaucoma that an owner may watch for or notice are pain, a dilated pupil, cloudiness within the cornea and/or an increase in the size of the blood vessels in the white portion of the eye. You may notice that one eye seems larger or protrudes more than the other. Most animals will not display all of these signs initially, maybe only one or two.

Often glaucoma has advanced and the pet is displaying obvious symptoms (very red painful eyes, cloudy corneas, markedly swollen, protruded eyes) before the owner is aware of the problems. Once it has reached this point is it almost always too late to save the animal’s sight and in many cases it is too late to even save the eye.

Early diagnosis is best made by measuring the pressure within the eye. This is a painless procedure and done with a tonometer. Unfortunately, the “normal” measurement has a wide variation, and it is best to establish a “normal for that individual”. Ideally, this is done when the animal is young. Once the normal is established, the pressures should be checked annually for changes which would be an early warning of glaucoma. The measurement can easily be done when the animal receives its vaccinations.

Veterinary ophthalmologists are recommending monitoring the eye pressure in all breeds of dogs, and especially for those breeds with established genetic predispositions for glaucoma. Pressures should be monitored in adult animals annually even if puppy/kitten normals are not available for comparison.

Eye pressure can be tested using a tonopen.

The pain may be indicated by the dog rubbing his eye with his paw, against the furniture or carpet, or your leg. This is a common, and often unnoticed, early sign. Some dogs will also seem to flutter the lids or squint with one eye.

The pupil of the affected eye will usually dilate early in the course of the condition. It may still react to all bright light shining in it, but it will do so very slowly. Remember that glaucoma, even primary glaucoma, is usually going to initially affect just one of the eyes. If the pupil in one eye is larger than in the other, something is definitely wrong and it may be glaucoma.

The cornea is normally perfectly clear, you cannot really see it. Its main function is to hold the liquid portion of the eye in place but at the same time allow light to easily pass through. Glaucoma causes it to lose this clearness and become cloudy. This can occur with other disorders and all deserve medical attention. With glaucoma, the elevated pressure stretches the cornea and tears apart the small protein fibers that give it strength. This change in its internal structure is what causes the initial cloudy appearance. Later in the course of the condition, fluid (or edema) enters the layers of the cornea along with tiny blood vessels.

Early in some glaucoma cases, the vessels on the white portion of the eye (the sclera), enlarge and increase in number. This would be similar to 'bloodshot eyes' in a person, only much worse. Usually, when this occurs major changes have already taken place inside the eyeball and vision may have been lost.

If you observe any of these signs, take your dog to the veterinarian for a physical exam, immediately - that same day. In many cases, your veterinarian will initiate treatment immediately, but may also refer you to a veterinary ophthalmologist, who specializes in eye disorders. This is important because every case of glaucoma is different and only with a lot of experience can the correct decisions be made. If we delay at all, or an incorrect therapy is chosen, the animal may go blind. We may not be able to prevent blindness from occurring, but we can learn from the first eye so that preventive measures can be taken to control or prevent the condition in the second eye. This is especially important in primary glaucoma.

Treatment

Glaucoma that has been present for less than 48 hours requires emergency treatment. Although only a small percentage of dogs regain vision in an eye that has glaucoma, emergency treatment helps relieve the extreme pain associated with this condition. If your

dog has had glaucoma for more than 48 hours, emergency treatment may not be effective. Emergency treatment generally requires one day of hospitalization. Long term treatment is often needed to control glaucoma requiring oral medication and/or eye drops for the rest of your pets life. A surgery to relieve increased eye pressure is frequently recommended instead of long term medication if the eye is permanently blind.

The treatment for glaucoma depends on its cause and severity. There are three goals:

1. Reduce the pressure within the eye
2. Reduce the amount of aqueous humor that is produced
3. Increase the drainage

There are specific medications used to try to accomplish these goals. Most of the therapies are used topically (e.g.; ointment in the eye), but some are also given orally. Those given topically often have to be administered 3 or more times a day.

Medical treatment of glaucoma in dogs does not work as well as it does in people. In most cases, the only long-term control of glaucoma is achieved through surgery. Various procedures including cyclocryotherapy (liquid nitrogen) can be used depending on the underlying cause of the glaucoma.

If neither medical or cyclocryotherapy treatments are effective, there are two options. If there is no pain, infection, or neoplasia present, an intraocular prosthesis can be inserted. In this procedure, the internal contents of the eye are removed and replaced with a silicone ball. There is generally a high rate of success with this procedure. If all other treatments have failed or the glaucoma is a result of neoplasia or intractable infection, the eye may need to be removed (enucleated).

In cases of secondary glaucoma, treatment of the underlying cause is also necessary. This may include antibiotics for bacterial infection, or surgery for the removal of a tumor.

Surgeries for Glaucoma

• The Eye With a Potential for Vision
  
  Laser: Laser energy can be directed into the eye to selectively destroy the fluid producing cells. This "turns down" the flow of fluid into the eye and subsequently reduces intraocular pressure. Laser surgeries are about 75% effective in keeping an eye comfortable, amount of vision restored to the eye is dependent on the amount of damage done during the pressure spike.
  
  
• The Blind Eye
  
  Eye Removal (enucleation): Although this surgery seems drastic, enucleation is the most reliable way to alleviate the source of your pet's pain. The eyeball is removed, a silicone ball is placed in the eye socket, and the eyelids are permanently sutured over the ball.
  The ball prevents the skin over the eye socket from sinking in.
  
  Intraocular Evisceration & Implantation: The inner contents of the eye are removed and replaced with a black silicone ball. The outer portions of the eye remain. The eye is sutured shut for 4 weeks while the eye heals. This surgery is often chosen by pet owners who cannot tolerate eye

Prognosis

Glaucoma has a guarded to poor prognosis, especially if untreated in its early stages. In people, ophthalmologists perform yearly eyeball pressure tests to detect early symptoms and initiate therapy as soon as possible. Glaucoma is definitely a disease where early treatment is critical.

While your dog is on preventative glaucoma treatment, you should have his/her eyes examined 4-6 times each year. If you notice redness, irritation, or a decrease in vision in the normal eye, you should seek veterinary assistance immediately! Your veterinarian or local emergency clinic will begin emergency treatment.

Don't Delay

Glaucoma is an emergency! If your dog is showing ocular (eye) pain, a dilated pupil, a cloudy cornea, and/or a bloodshot eye – get your dog into a veterinary clinic immediately. In most cases, these signs indicate an emergency.

Notify your veterinarian if any of the following occur:

• An eye shows sudden or chronic redness
• An eye is painful, watery, or squinting
• One or both eyes change in size
• One or both pupils are dilated
• Your pet's vision seems poor