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.
There are 2 main types of glaucoma - primary and secondary.
In
primary glaucoma, the cause of the increase in ocular pressure is due
to deceased outflow from the drainage angle. It is frequently an
inherited problem. Beagles, Bassett Hounds, and Cocker Spaniels are
especially prone to this type of glaucoma.
In secondary
glaucoma, the pressure in the eye is too high because something else is
wrong with the eye, such as a lens luxation, bleeding, inflammation, or
tumor.
a red (bloodshot) eye
a painful eye
eyelids held shut
excessive tearing of the eye
eye may
appear cloudy or blue
sudden blindness
a dilated (enlarged) pupil that
does not respond normally to light
enlargement of the eye
appetite
loss
depression
The type of glaucoma treatment chosen (medical vs. surgical) 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 orally and affect
the whole body, while others are put directly in the eye and have a
local effect. These drugs help to reduce the amount of fluid produced
in the eye, and also to increase the outflow of fluid from the eye. The
drugs that work when the problem is first diagnosed and may not work
forever. Therefore, the intraocular pressure needs to be monitored on a
regular basis so 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.
In some cases, surgical procedures are available that may help provide
long-term control of glaucoma. One of these procedures uses a laser to
destroy the part of the eye that produces fluid and thereby reduces the
pressure inside the eye. Another surgery involves the placement of 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
repeat procedures may be requied over several years 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.
Uveitis is defined as an inflammation of the parts of the eye (uvea)
which contain blood vessels, ie. those parts of the eye that are
connected by blood vessels to the rest of the body. The uvea consists
of three parts, the iris, the cliliary body and the choroid. (See
diagram at top of page.) When the blood vessels in these structures
become leaky, then cells and proteins and fats inside the blood stream
can get from the blood to the inside of the eye. Basically, uveitis is
inflammation or infection inside the eye rather than on the external
surface of the eye.
The following are signs of uveitis:
cloudiness
redness
small pupil
decreased vision
painful eye
Dogs, cats, and rabbits usually exhibit one or more of the following signs if an eye is painful:
squinting
tearing
rubbing at the eye with a paw
rubbing the eye on
furniture or the rug
holding the eye shut
elevated third eyelid
decreased
appetite
depression
There are many causes of uveitis. Diseases such a those caused by
viruses, bacteria, parasites or fungus can cause inflammation inside
the eye. Other causes include trauma to the eye, cataracts, cancer
(either in the eye or in the body), and autoimmune disease.
To diagnose uveitis the following tests are often performed:
1. Bloodwork - a CBC and chemistry panel 2. Chest radiograph - to look for tumors or pneumonia 3. Abdominal ultrasound - to evaluate the organs 4. Testing for specific diseases based on location and travel (ie. Lyme disease, Rocky Mountain Spotted Fever, etc. 5. Ocular ultrasound 6. Aspirate of fluids inside the eye
Keratoconjunctivitis sicca (KCS)
is also called dry eye. This condition is due to a deficiency in tear
production that results in a red, itchy eye with thick mucous
discharge. The tear production is measured by the Shirmer 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.
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 case of KCS, 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 results in the thickening of the cornea so that it appears
dull and cloudy. Tears are made or mucus, water and oils. Cry eye is a
deficiency of the watery (or aqueous) part of the tears. Therefore
animals with KCS accumulate a lot of mucus.
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
profuse, ropy, thick discharge that adheres to the eye. without
treatment, the cornea may eventually pigment and scar to the point of
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.)
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.
How is KCS treated?
Animals
with acute dry eye frequently havee 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 forms of KCS
are treated by topical tear substitutes as well as stimulation of the
existing tear production. Cyclosporine ointment or oily drops is used
to increase tear production and reduce inflammation. Sometimes used
alone 2x/day this can control the KCS effectively without any other
medications. Additionally tacrolimus drops have been used successfully
to treat KCS.
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 with antibiotic
therapy. Anti-inflammatory drugs are frequently used to help control
scarring and irritation.
It is important to clean accumulated
mucus from the eyes or lids with eye wash and cotton balls prior to
instilling any medications and to 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 pets 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.
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
expect 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. There is often excessive tearing and
small pupils as well.
A corneal ulcer is diagnosed by using
fluorescein stain to coat the eye. In a normal eye, the orange stain
will wash away when rinsed. In an eye with a corneal ulcer the stain
will stick to the ulceration leaving behind a green glow.
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 necessary. The treatment for a corneal
ulcer is most often medical with the use of topical pain medications
and antibiotics. Deep or infected ulcers may need surgical treatment in
addition to topical therapies.
A cataract is an 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 objuects. A thin capsule (the consistency
of cellophane) covers the lens.
In front of the lens is a clear
fluid called the aqueoud humor, and behind the lens is a clear gel
called the vitrious 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.
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.
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.
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 7 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 a 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 either 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.
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 simlar 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 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.
No effective treatment is available
Complete blindness eventually results
The condition is NOT
painful
PRA is prevented through selective breeding of animals with
normal eyes
Poor vision in dim light is the first sign you will see in
your dog
You may eventually see dilated pupils
Sometimes
cataracts will develop secondary to retinal degeneration, but because
of the retinal degeneration, cataract removal would not help the animal
regain vision
Additional ocular conditions will be covered next month in the May 2009
Monthly Update.
Until then, if you think your pet has an ocular
emergency please call the Roslyn-Greenvale Veterinary Group at 516-621-4010 to schedule an appointment immediately.
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.
The type of glaucoma treatment chosen (medical vs. surgical) 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 orally and affect
the whole body, while others are put directly in the eye and have a
local effect. These drugs help to reduce the amount of fluid produced
in the eye, and also to increase the outflow of fluid from the eye. The
drugs that work when the problem is first diagnosed and may not work
forever. Therefore, the intraocular pressure needs to be monitored on a
regular basis so 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.
To diagnose uveitis the following tests are often performed:
Keratoconjunctivitis sicca (KCS)
is also called dry eye. This condition is due to a deficiency in tear
production that results in a red, itchy eye with thick mucous
discharge. The tear production is measured by the Shirmer 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.
Animals
with acute dry eye frequently havee 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 forms of KCS
are treated by topical tear substitutes as well as stimulation of the
existing tear production. Cyclosporine ointment or oily drops is used
to increase tear production and reduce inflammation. Sometimes used
alone 2x/day this can control the KCS effectively without any other
medications. Additionally tacrolimus drops have been used successfully
to treat KCS.
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
expect 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. There is often excessive tearing and
small pupils as well.
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.
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 7 years of age. The lens will become increasingly
cloudy as the animal ages, but it almost never has an effect on vision.
Fig. 1 - Normal Retina
Fig. 2 - Retina showing signs of Progressive Retinal Atrophy (PRA)
Additional ocular conditions will be covered next month in the May 2009
Monthly Update. 