Eye on Opthalmology
EYE ON OPHTHALMOLOGY:
ADVANCEMENTS IN HUMAN AND ANIMAL TREATMENTS
HOLD GREAT POTENTIAL
Published in Veterinary Practice News, October, 2003
An exciting array of technological and pharmaceutical
advancements – many borrowed from human medicine – are
helping veterinary ophthalmologists cure small-animal eye
diseases that just a decade ago would have left many of their
patients blind or vision-impaired. And the future looks even
brighter, researchers and practitioners report.
“Human ophthalmology and animal ophthalmology both benefit
from what we learn in our fields,” said Tanja Nuhsbaum, DVM,
MS, Dipl. ACVO, staff ophthalmologist at Animal Eye Specialists,
a branch of VRCC in Englewood, Colorado. “Although the eye is
unique for every animal, there is a lot of crossover from animal
to human eyes, from dog to cat eyes and from cat to horse
eyes. We all learn from whatever species it may be.”
Veterinary ophthalmologists nationwide said they’re treating an
eclectic assortment of small-animal eye disorders these days.
Among the most common are:
A thorough medical history is required to direct therapy, which
can range from dispensing a topical antibiotic for a superficial
corneal injury to surgery for a deep corneal ulceration or
laceration. Cats may also receive a topical anti-viral medication
to stabilize infection, said Dr. McNabb.
Cataracts are another commonly-seen eye disorder in dogs,
veterinary ophthalmologists reported. Some cases, particularly
those in purebred dogs, are hereditary, while older dogs may
develop the disease as a result of diabetes, said Dr. McNabb.
The treatment options for cataract illustrate just how dramatic
the advancements in veterinary ophthalmology have been in
recent years – and how much the field owes to human medicine.
In the past, treatment typically consisted of making a 180-
degree incision in the top half of the cornea and expressing the
lens in one piece using microsurgical instruments, a technique
known as extracapsular lens extraction. Today, most
ophthalmologists use an instrument known as a
phacoemulsifier, which breaks up the cataract with ultrasound
vibrations. The device also removes residual cortical fragments
of the cataract using irrigation and aspiration after the densest
nuclear portion is removed.
“All of this is linked to a computer which senses the fluids going
in and out of the eye so that the eye remains in a state of
homeostasis,” said Dr. Nuhsbaum. “The eye doesn’t feel as if it’
s collapsing or expanding, it just stays very calm.”
Dr. Warren employs a related procedure known as a “phaco
chop,” which offers good results using reduced ultrasound
power. “I learned this procedure by sitting in with human
ophthalmologists and watching videotapes on human patients,”
she noted. “It’s being adopted by more and more veterinary
ophthalmologists, but there’s a learning curve.”
Once the cataract is removed, the patient typically receives an
acrylic lens – just like human patients do. Traditional rigid
lenses require a 7 millimeter corneal incision. However, newer
soft intraocular lenses, which are folded and open up like a
flower once in place, can be inserted through an incision as
small as 3 millimeters.
Never before have veterinary ophthalmologists had access to
such an eclectic array of new diagnostic and treatment
technologies. Dr. McNabb, for example, frequently relies on
magnetic resonance imaging to diagnose orbital disease and
neuro-ophthalmology cases, ocular ultrasound to examine eyes
with surface obstructions and a test known as an
electroretinogram to evaluate electrical retinal activity.
“I’m very lucky to have access to this equipment because I’m
often able to provide a diagnosis to an owner within hours and
then direct treatment,” said Dr. McNabb. “The eye is often
unforgiving. If it’s in trouble, you don’t have a lot of time to figure
out what the problem is.”
In addition, more and more veterinarians are turning to lasers
to treat a wide range of problems, including intraocular pressure
from glaucoma, retinal detachment, cysts on the iris and
potentially cancerous eyelid growths, noted Dr. Hamilton.
Veterinary ophthalmologists also have a growing selection of
drugs from which to choose for the treatment of small-animal
eye diseases, the majority of them borrowed from human
medicine.
“There are several new medications that have had a
tremendously positive impact on canine glaucoma,” said Dr.
McNabb. “One of the newer medications is Xalatan, which is
used to treat primary glaucoma. It’s a medication that is often
prescribed on a once-a-day basis, maybe every 12 hours at the
most. Our clients appreciate that because it isn’t a high-
frequency drug, and it’s very effective.” Trusopt and Azopt,
which are carbonic anhydrase inhibitors, are also used in the
treatment of glaucoma in both animals and humans.
Topical cyclosporine is commonly used to treat canine dry eye
because it helps stabilize and improve tear production. In an
interesting reversal, human medicine recently picked up the
drug for a similar purpose, noted Dr. McNabb.
Veterinary ophthalmology has achieved significant strides in
recent years, but there are many things on the horizon that
promise to take the specialty to even greater heights in years to
come. One of the most impressive is a cyclosporine eye implant
developed at North Carolina State University that provides a
constant infusion of medication for the treatment of chronic
inflammation. The implant was first developed for use in horses,
but also shows great promise in treating inflammation in the
canine patient, said Dr. Nuhsbaum.
“Also important is genetic testing for purebred dogs,” Dr.
Nuhsbaum added. “We have a lot of inbreeding going on, and
that’s where many (eye) diseases are being perpetuated.”
On the forefront of this technology is a company called
Optigen, which uses a blood sample to test for a variety of
inherited eye diseases. “If you have two adult dogs that you
would like to breed, genetic testing can determine if they carry
the genes for certain eye problems,” Dr. Nuhsbaum explained.
“If they both carry the genes, they shouldn’t be bred together.
You can see where such testing has implications for a healthier
pool of puppies.”
What the future holds for veterinary ophthalmology remains to
be seen, but specialists are monitoring ongoing research and
development with great anticipation.
“Veterinary ophthalmology has a very bright future,” concluded
Dr. Warren. “The eye is the window to the body, and I’ve
diagnosed a lot of systemic problems from an eye exam. It’s not
just diseases that affect only the eye – we’re dealing with the
patient as a whole through the eye. It’s an exciting field, and I
think it’s going to continue to grow.”
ADVANCEMENTS IN HUMAN AND ANIMAL TREATMENTS
HOLD GREAT POTENTIAL
Published in Veterinary Practice News, October, 2003
An exciting array of technological and pharmaceutical
advancements – many borrowed from human medicine – are
helping veterinary ophthalmologists cure small-animal eye
diseases that just a decade ago would have left many of their
patients blind or vision-impaired. And the future looks even
brighter, researchers and practitioners report.
“Human ophthalmology and animal ophthalmology both benefit
from what we learn in our fields,” said Tanja Nuhsbaum, DVM,
MS, Dipl. ACVO, staff ophthalmologist at Animal Eye Specialists,
a branch of VRCC in Englewood, Colorado. “Although the eye is
unique for every animal, there is a lot of crossover from animal
to human eyes, from dog to cat eyes and from cat to horse
eyes. We all learn from whatever species it may be.”
Veterinary ophthalmologists nationwide said they’re treating an
eclectic assortment of small-animal eye disorders these days.
Among the most common are:
- Corneal disease. “This is one of the most frequent
reasons I see patients,” observed Noelle McNabb, DVM,
Dipl. ACVO, staff ophthalmologist at Massachusetts
Veterinary Referral Hospital in Woburn, Massachusetts.
“The cause depends on species. If it’s a dog or a horse,
most commonly the patient has sustained some kind of
corneal trauma resulting in infection. Cats are a bit of a
different story – they more often develop spontaneous
corneal disease due to herpes virus infection.”
A thorough medical history is required to direct therapy, which
can range from dispensing a topical antibiotic for a superficial
corneal injury to surgery for a deep corneal ulceration or
laceration. Cats may also receive a topical anti-viral medication
to stabilize infection, said Dr. McNabb.
- Regional vector-borne diseases such as tick fever and
Lyme disease. These are systemic diseases that often
present themselves via eye problems, noted Christi T.
Warren, DVM, Dipl. ACVO, a partner at Eye Care For
Animals in Tucson, Arizona. Treatment typically involves
a regimen of antibiotics such as doxycycline or
tetracycline. - Environmentally-mediated diseases such as valley fever,
which is caused by a fungus found in the soil. “This
disorder is predominantly seen in dogs, and less
commonly in cats,” said Dr. Warren. “After all, who has its
nose to the ground? It’s the dog. They will pick up valley
fever just by sniffing around.” This disorder responds well
to antifungal medications such as fluconazole. - Chronic superficial keratitis (Pannus). This genetic
disease, which is most commonly seen in German
shepherds, results in fibrosis and scarring of the cornea.
It is exacerbated by UV light, which makes it a serious
problem in states that receive a lot of sunlight year round.
Believed to be an immune-mediated disorder, Pannus is
commonly treated with medications that suppress immune
function, such as cyclosporine. - Sudden acquired retinal degeneration (SARD). Seen
exclusively in dogs, SARD results in a fairly rapid loss of
vision through degeneration of the retina. “No one knows
what causes this disease, so we can’t prevent it, we can’t
treat it and we can’t cure it,” said Dr. Warren. “Dogs lose
their vision, but otherwise the condition doesn’t seem to
affect their health or their lifespan.” - Drug-related eye disorders. “We’re seeing an increase in
the number of dogs with secondary low tear production
associated with the use of oral nonsteroidal medications
for arthritis,” noted Holly Hamilton, DVM, MS, Dipl. ACVO,
an associate at Veterinary Vision in San Mateo,
California. “We’re also seeing cats with an idiosyncratic
reaction to the oral antibiotic Baytril. Sometimes they
develop a retinal degeneration from that.”
Cataracts are another commonly-seen eye disorder in dogs,
veterinary ophthalmologists reported. Some cases, particularly
those in purebred dogs, are hereditary, while older dogs may
develop the disease as a result of diabetes, said Dr. McNabb.
The treatment options for cataract illustrate just how dramatic
the advancements in veterinary ophthalmology have been in
recent years – and how much the field owes to human medicine.
In the past, treatment typically consisted of making a 180-
degree incision in the top half of the cornea and expressing the
lens in one piece using microsurgical instruments, a technique
known as extracapsular lens extraction. Today, most
ophthalmologists use an instrument known as a
phacoemulsifier, which breaks up the cataract with ultrasound
vibrations. The device also removes residual cortical fragments
of the cataract using irrigation and aspiration after the densest
nuclear portion is removed.
“All of this is linked to a computer which senses the fluids going
in and out of the eye so that the eye remains in a state of
homeostasis,” said Dr. Nuhsbaum. “The eye doesn’t feel as if it’
s collapsing or expanding, it just stays very calm.”
Dr. Warren employs a related procedure known as a “phaco
chop,” which offers good results using reduced ultrasound
power. “I learned this procedure by sitting in with human
ophthalmologists and watching videotapes on human patients,”
she noted. “It’s being adopted by more and more veterinary
ophthalmologists, but there’s a learning curve.”
Once the cataract is removed, the patient typically receives an
acrylic lens – just like human patients do. Traditional rigid
lenses require a 7 millimeter corneal incision. However, newer
soft intraocular lenses, which are folded and open up like a
flower once in place, can be inserted through an incision as
small as 3 millimeters.
Never before have veterinary ophthalmologists had access to
such an eclectic array of new diagnostic and treatment
technologies. Dr. McNabb, for example, frequently relies on
magnetic resonance imaging to diagnose orbital disease and
neuro-ophthalmology cases, ocular ultrasound to examine eyes
with surface obstructions and a test known as an
electroretinogram to evaluate electrical retinal activity.
“I’m very lucky to have access to this equipment because I’m
often able to provide a diagnosis to an owner within hours and
then direct treatment,” said Dr. McNabb. “The eye is often
unforgiving. If it’s in trouble, you don’t have a lot of time to figure
out what the problem is.”
In addition, more and more veterinarians are turning to lasers
to treat a wide range of problems, including intraocular pressure
from glaucoma, retinal detachment, cysts on the iris and
potentially cancerous eyelid growths, noted Dr. Hamilton.
Veterinary ophthalmologists also have a growing selection of
drugs from which to choose for the treatment of small-animal
eye diseases, the majority of them borrowed from human
medicine.
“There are several new medications that have had a
tremendously positive impact on canine glaucoma,” said Dr.
McNabb. “One of the newer medications is Xalatan, which is
used to treat primary glaucoma. It’s a medication that is often
prescribed on a once-a-day basis, maybe every 12 hours at the
most. Our clients appreciate that because it isn’t a high-
frequency drug, and it’s very effective.” Trusopt and Azopt,
which are carbonic anhydrase inhibitors, are also used in the
treatment of glaucoma in both animals and humans.
Topical cyclosporine is commonly used to treat canine dry eye
because it helps stabilize and improve tear production. In an
interesting reversal, human medicine recently picked up the
drug for a similar purpose, noted Dr. McNabb.
Veterinary ophthalmology has achieved significant strides in
recent years, but there are many things on the horizon that
promise to take the specialty to even greater heights in years to
come. One of the most impressive is a cyclosporine eye implant
developed at North Carolina State University that provides a
constant infusion of medication for the treatment of chronic
inflammation. The implant was first developed for use in horses,
but also shows great promise in treating inflammation in the
canine patient, said Dr. Nuhsbaum.
“Also important is genetic testing for purebred dogs,” Dr.
Nuhsbaum added. “We have a lot of inbreeding going on, and
that’s where many (eye) diseases are being perpetuated.”
On the forefront of this technology is a company called
Optigen, which uses a blood sample to test for a variety of
inherited eye diseases. “If you have two adult dogs that you
would like to breed, genetic testing can determine if they carry
the genes for certain eye problems,” Dr. Nuhsbaum explained.
“If they both carry the genes, they shouldn’t be bred together.
You can see where such testing has implications for a healthier
pool of puppies.”
What the future holds for veterinary ophthalmology remains to
be seen, but specialists are monitoring ongoing research and
development with great anticipation.
“Veterinary ophthalmology has a very bright future,” concluded
Dr. Warren. “The eye is the window to the body, and I’ve
diagnosed a lot of systemic problems from an eye exam. It’s not
just diseases that affect only the eye – we’re dealing with the
patient as a whole through the eye. It’s an exciting field, and I
think it’s going to continue to grow.”