A horse's eye is designed to help them easily spot predators, footing, and food. Check out these very interesting articles and learn about the unique capabilities of your horse’s eyes and how it can help you better understand his/her behavior.
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Most owners are diligent about giving their horses a once-over for scrapes and swellings while grooming. This includes checking the eyes for subtle changes and early indicators of problems. Squamous cell carcinoma (SCC), for instance, is something an owner might notice; it is one of the most common cancerous tumors of the equine eye. Fortunately, with early intervention it's treatable.
Amber Domino Labelle, DVM, MS, Dipl. ACVO, assistant professor and veterinary ophthalmologist at the University of Illinois Veterinary Teaching Hospital, in Urbana, says the most common locations for periocular (around the eye) SCC include the eyelid skin, third eyelid, and the limbus (the junction between the cornea--the clear surface of the eyeball--and the conjunctiva that covers the white of the eye).
"On the eyelid, SCC generally appears as a pink mass, often ulcerated or bloody," she explains. "On the third eyelid or at the limbus it generally appears as a pink proliferative mass that can distort the tissues or create a mass on the surface of the eye. The tumor is generally pink or red in color." The affected eye might squint or emit a yellow or white discharge; this is typically what the owner notices first.
Brendan Mangan, DVM, MS, Dipl. ACVO, clinical assistant professor in comparative ophthalmology at the University of Florida College of Veterinary Medicine, says SCC lesions and the adjacent tissue typically appear more red and inflamed than the surrounding normal tissue.
Causes and Risk Factors
Some horses are more vulnerable to SCC than others. "There are several known risk factors," says Labelle. These have to do with pigmentation around the eye and ultraviolet (UV) light exposure.
"Horses that spend a lot of time in the sun are at higher risk, especially if eyelid skin and conjunctiva are nonpigmented," says Mangan. "Living at higher altitudes and closer to the equator results in more intense and longer periods of sun exposure and UV radiation."
Labelle says some breeds seem more predisposed to developing SCC than others, including Haflingers and some draft breeds. Appaloosas and Paint horses also are prone to SCC, but primarily because of the nonpigmented skin around their eyes.
Mary Lassaline Utter, DVM, PhD, Dipl. ACVO, assistant professor of ophthalmology at the University of Pennsylvania's New Bolton Center, is conducting research with Rebecca Bellone, PhD, associate professor of biology at the University of Tampa, to investigate Haflingers' genetic tendency toward SCC. "This breed appears to be overrepresented among horses with limbal SCC, and they are often diagnosed with SCC at a younger age than other breeds," Utter says. "Affected Haflingers are closely related, suggesting a possible heritable basis for this type of SCC. Our research is currently investigating the association of candidate genes with disease status, which may help clarify both the genetics and the pathophysiology of limbal SCC."
Labelle cites another recent study suggesting that equine papillomavirus might contribute to SCC development. "Infection with this virus may be why some lesions develop," she says. "There is convincing evidence that SCC in other locations, particularly the penis, may be due to equine papillomavirus, but we are not yet sure if this is also the case in lesions of the eye."
Diagnosis and Treatment
Have your vet examine any abnormality in a horse's eye area. He or she might takes samples and order tests. "It may be possible to arrive at a diagnosis of SCC with cells taken from the surface of the lesion, but a more definitive diagnosis requires a biopsy," says Mangan. "A biopsy also allows more effective surgical -planning."
The size, stage, and location of the mass dictate treatment options; the smaller the lesion, the easier it is to treat. Unfortunately, by the time they're noticed, many SCC tumors, especially those located on the third eyelid that is tucked underneath the outer surface, have become quite large. And the longer the lesion is present, the more likely the cancer will invade surrounding tissues, and the more it invades those tissues, the harder it is to treat.
"Lesions on the third eyelid or the eyelid itself can sometimes be treated in the field, without bringing the horse to a hospital facility," Labelle says. "There are many ways to treat these, including topical chemotherapy creams, injectable chemotherapy, freezing the lesion, radiation (which is highly effective), and surgical removal."
Mangan notes that large eyelid masses might require reconstructive surgery due to the amount of tissue removed.
Growths that occur at the limbus, on the eyeball itself, are more likely to be referred to an ophthalmologist for surgical intervention. "These are often treated with surgical excision, followed up with either chemotherapy or cryotherapy (freezing) to make sure there are no stray cancer cells left in the area," Labelle explains. "When we excise those kinds of lesions, we always submit them for biopsy to make sure that we removed the entire tumor (the lab looks for SCC cells close to the edges of the sample)."
Veterinarians might also use a variety of SCC therapies in conjunction with or in place of surgery, including:
Cryotherapy Mangan says veterinarians commonly freeze affected areas to -13°F as an adjunct to surgery. This method can be used on all tissues.
β-irradiation (Sr90) "This is an ideal treatment for corneal lesions, since the radiation travels a very short distance and is -almost completely absorbed by the cornea," says Mangan.
Brachytherapy (Ir192), during which radioactive beads or rods are inserted into the tumor for a period of time, is an effective treatment for eyelid SCC, but it carries with it radiation hazards.
Radiofrequency hyperthermia raises the temperature of the treated tissue to 122°F. Mangan notes that this damages tumor cells but allows normal cells to recover.
Intralesional immunotherapy involves injecting the immunomodulator Bacille Calmette-Guérin into eyelid tumors to treat large SCC.
Intralesional chemotherapy commonly involves using cisplatin and carboplatin with or without surgical debulking.
Topical chemotherapy agents mitomycin C and 5-fluorouracil can be used effectively following surgical mass removal.
Carbon dioxide (CO2) LASER therapy can be used on SCC in all locations and might be useful as a primary procedure or as an adjunct to conventional surgical removal, Mangan explains.
Piroxicam is a non-steroidal anti-inflammatory drug (NSAID) that "may have anti-neoplastic (tumorous) properties, but the effectiveness against SCC in the horse has not been completely validated," says Mangan.
Photodynamic therapy (PDT) is an evolving treatment for eyelid SCC that involves using a drug that photosensitizes tumor cells with a specific wavelength of light. After the practitioner injects the photosensitizing agent, he or she exposes the mass to a specialized light source, such as a laser, that destroys tumor cells and associated blood vessels.
Elizabeth Giuliano, DVM, MS, Dipl. ACVO, an associate professor in the Department of Veterinary Medicine and Surgery at the University of Missouri, has been studying the use of local PDT to treat eyelid SCC. She first introduced the concept of using local PDT for equine eyelid SCC in 2003 and has treated more than 30 affected horses using the therapy.
Giuliano first began using PDT when presented with an SCC case that had already undergone five different treatment modalities to no avail. The cancer was limited to the eyelid, and the horse had retained his vision, so she could not yet bring herself to remove the eye.
"Horses' eyes present a unique challenge because if you can't save the eyelid you can't save the eye," she explains. "The horse is not amenable to eyelid flaps like other species. Eyelid reconstruction surgery for a horse is extremely difficult to perform successfully because their skin is tightly adhering to the underlying bone--unlike that of a dog whose skin is much looser."
When performing PDT Giuliano first debulks the eyelid tumor surgically, then she injects the photoactive agent into the tumor bed, and finally she uses a laser to irradiate the area and kill any residual tumor cells.
"In people, photoactive agents are typically administered intravenously and have been used to treat a variety of conditions including age-related macular degeneration and bladder cancer," she explains. "The volume of drug needed for a horse (if we were to give it systemically) would be too expensive, and we don't know how horses would react. Local PDT is believed to be a much safer approach at this time."
She says one of the reasons PDT is appealing for treating periocular cancers in horses is that it is not toxic to the people handling the drugs, unlike potentially dangerous intralesional chemotherapy agents like cisplatin.
"Additionally, PDT typically does not require multiple treatments," she says. "Therapeutic modalities that require repeat treatments can become very costly. Even if the individual treatment cost is low, if you have to repeat it five or six times in order to be effective, and add the costs associated with trailering the horse to a veterinary facility several times, the total cost is comparable to what you'd spend on one treatment of PDT." The one treatment also means less hassle and stress for the client and the horse.
"For me, the advantages of local PDT are that it is nontoxic, there is no cumulative drug effect, and usually one treatment is sufficient," she concludes. "The disadvantage of PDT is its limited use by veterinary ophthalmologists currently and the initial cost. The drug itself is very expensive."
One of the best ways to prevent potentially cancer-inducing UV light exposure is to keep horses out of intense sunlight. "Anything you can do to minimize exposure will help decrease risk of SCC, especially in areas of the country with a lot of UV light," says Labelle. "Using a fly mask (especially the type with UV blocking material) is often the easiest thing to do if your horse has pink eyelids and you live in the Southwest. In summer when UV light is most intense, you might consider turning that horse out at night and putting him in a stall during the day."
Before the use of fly masks, some owners tried to reduce sun glare by putting dark color around their horses' eyes if they had white face markings. Dark color materials included mascara and theatrical grease paint, but these can be dangerous for the horse. Thus, these old "home remedies" might do more harm than good.
"Also, tattooing the eyelids does not help," Labelle says. "The tattoo ink localizes deeper in the skin than the layer where the tumor occurs, and does not protect the layers where the tumor actually arises."
Never neglect an abnormality on your horse's eye, as it can go from something insignificant to serious rather quickly. As with any type of skin cancer, prevention is preferable to treatment, and early treatment assures a better chance for a positive outcome. "The best thing owners can do is look at their horse closely every day and have any abnormality examined by a veterinarian," Labelle advises.
Article courtesy of Heather Smith Thomas
Unless your mare has had a bad breakup with the stallion next door, her watery eyes could indicate a serious problem. While there are many reasons for a horse to have excessive tear production, it's a classic sign of equine recurrent uveitis, also known as moon blindness.
Although years ago it was thought that the disease came and went with the cycles of the moon, today we know that it has nothing to do with the lunar calendar. Unfortunately, "equine recurrent uveitis is the most common cause of vision loss in horses," said Amber Labelle, DVM, an ophthalmology resident at the University of Illinois Veterinary Teaching Hospital in Urbana. Since the disease affects approximately one in 10 horses, it's important that a complete ophthalmic examination be performed during pre-purchase exams to detect the disorder.
Uveitis simply means that there is inflammation within the uveal tract of the eye. This area includes three parts: the iris, the ciliary body (which is found around the iris), and the choroid (a layer of tissue that supplies blood to the eye located beneath the retina).
Although they might sound similar, uveitis is not really related to UV radiation. Experts do believe that sunburn-causing UV wavelengths from the sun might exacerbate uveitis, but it is not suspected to be the inciting cause. So those fancy sunglasses you bought for your Saddlebred probably won't help with prevention.
One of the reasons equine uveitis is so widespread is because the early clinical signs are very subtle and often are not detected right away.
"Extra tearing or occasional squinting are symptoms owners should watch for," Labelle explained. But she also noted that, "owners often think their horse just has allergies," although in reality it is the beginning signs of the disease.
There are many causes of uveitis. Leptospirosis, a bacterial disease that can also affect humans, is one culprit. However, in many cases the inciting cause is not found, and regardless of the cause, the end result is destruction of sensitive eye tissue by the horse's own immune system.
Unfortunately, Labelle said, "equine recurrent uveitis is one of the most difficult diseases to treat." The standard protocol of anti-inflammatory medications to decrease inflammation in the eye certainly helps, but it rarely prevents the disease from recurring.
Even with this mainstay of treatment, many horses will eventually lose vision, or at the least, will experience repeated, painful episodes of the disease. But there is hope for better treatment in the future. A veterinary ophthalmologist, Brian Gilger, DVM, MS, Dipl. ACVO, has developed a device that is impregnated with a drug that suppresses the immune system and can be surgically placed into the eye of an affected horse. Although the implant is not yet commercially available, it is being used at specialty veterinary hospitals across the country and is showing a great deal of promise.
Because a teary-eyed horse might be the first sign of a much bigger problem, contact your veterinarian immediately if you notice any changes in your horse's eye.
Article courtesy of --Ashley Mitek
Many horse people don't know that much about leptospirosis. If you have heard of it, it is probably in reference to cattle, other livestock, or maybe dogs. However, leptospirosis does affect horses, and it can be the cause of some serious health problems, including abortion in pregnant mares and chronic uveitis (moon blindness). It is a disease that has not been studied much in the horse, but several scientists have been calling for further research and for the development of an effective equine vaccine.
What is it?
Leptospirosis is a zoonotic (transmitted between animals and man) bacterial disease found worldwide that can affect any mammalian species, including humans, wildlife, rodents, livestock, and, yes, horses. The disease is caused by leptospires, which are motile (capable of moving) bacteria called spirochetes. Leptospires are subdivided into serovars and serogroups (subgroups). Those of importance to the horse include pomona, grippotyphosa, hardjo, bratislava, canicola, and icterohaemorrhagiae. They are very common in both domestic and wild animals.
Craig Carter, DVM, PhD, director of the University of Kentucky's Livestock Disease Diagnostic Center (LDDC) and professor of epidemiology, College of Agriculture, tells us horses become infected through mucous membranes of the eyes or mouth and sometimes through broken skin by contact with infected urine, blood, or tissues. Horses can become infected by eating hay or grain that has been contaminated by infected urine, or they can contract it by drinking from standing water that has been similarly affected. In some cases horses are affected by the direct splashing of infected animals' urine into the eyes or mouth.
The incubation period for leptospirosis in horses is one to three weeks. Horses might experience a variety of clinical signs, including fever, loss of appetite, swelling of the eyes, light sensitivity, tearing, ocular discharge, eye cloudiness, and redness around the eye, as well as lethargy and mid- to late-term abortion. Adult horses have been known to develop jaundice and even die from kidney and/or liver failure. Diagnosis of leptospirosis can often be overlooked because the clinical signs of the disease are common to other diseases. Only laboratory tests of blood or urine can confirm if leptospirosis is present.
Another unique factor in this disease is that the bacteria seem to cluster in different parts of the body, such as the eye, kidney, liver, or reproductive tract. An article on leptospirosis-induced uveitis in Cornell University's newsletter recommends "prompt treatment, which may include steroids, antibiotics, and medications to dilate the eye."
Drugs of choice, according to Carter, are oxytetracycline, streptomycin, or penicillin. Although leptospirosis vaccines are available for dogs, cattle, and pigs, there are no approved vaccines for horses. Cattle vaccines have been tried in horses, but they are not proven to be effective and might produce negative side effects.
The primary conditions associated with leptospirosis in horses are chronic uveitis (moon blindness) and abortion. Chronic uveitis occurs when the leptospira bacteria enter the eye, creating an immune reaction. The clinical signs, as touched on above, are ocular inflammation, redness, cloudiness, tearing, light sensitivity, and strong muscle spasms closing the eyes. In severe cases, it can cause a calcification of the cornea, permanent blindness, atrophy (wasting away) of the eye, and glaucoma (an increase in intraocular pressure that can cause blindness). Leptospirosis-induced uveitis is often a painful condition for the horse, and veterinarians recommend that treatment begin as soon as possible.
An Ontario Ministry of Agriculture, Food and Rural Affairs Fact Sheet discusses a variety of treatments, including steroids given topically or systemically to reduce inflammation. Atropine is recommended to dilate the iris, which will help relieve the muscle spasms, photosensitivity, and tearing.
German researchers isolated leptospires from the eyes of infected horses and were able to identify them as belonging to the grippotyphosa subgroup and a few from the australis subgroup.
Equine abortions occur when the bacteria migrate to the uterus or placenta, then to the fetus, resulting in fetal death. Abortion is most often associated with the L. pomona subgroup infections. Some research suggests that leptospirosis infection is a vastly underreported cause of abortions.
Precautions and Preventions
So what can we do about leptospirosis? Prevention is the best option available at this point. Good management techniques at the farm can help reduce the risk of infection. Keep wildlife away from feed sources and do not allow standing water to accumulate (or at least do not allow the horses to drink from stagnant water sources). Standing water might be contaminated with leptospirosis-tainted urine from wildlife or cattle.
Good disinfection programs will help reduce the risk of exposure to leptospirosis (and many other diseases).
So why don't we have a vaccine for horses? Several factors contribute to the lack of a vaccine, with two topping the list.
The first is a lack of data to support the need for a vaccine. There have only been limited studies on leptospirosis in horses, most of which have been epidemiologic studies on a limited scale. No one really knows how many horses are affected each year, so it has been difficult to generate interest and funds to research the disease. For this reason you might consider donating money for leptospirosis research.
Second, there are many subgroups of leptospirosis that can affect horses. Researchers in Northern Ireland, including Professor William A. Ellis, found that horses were susceptible to far more strains than animals such as cattle and dogs. In other species, one serogroup is overwhelmingly present. In horses there are seven serogroups, and there was no clear indication which one(s) was (were) predominant. This might explain why the cattle vaccine is not particularly effective in horses, as cattle are affected almost exclusively by the sejroe serogroup.
Yung-Fu Chang, DVM, MS, PhD, Dipl. ACVM (veterinary microbiology), a professor in the department of population medicine and diagnostic sciences at Cornell University, has been developing an equine leptospirosis vaccine. His group has experimented with a DNA vaccine for leptospirosis.
Several scientists are working to place a national focus on leptospirosis. Recent Kentucky research from Carter and his colleagues has been at the forefront because it showed a significant number abortions were caused by leptospirosis in 2006 and 2007. The scientists diagnosed 41 cases of leptospirosis at necropsy using fluorescent antibody testing on fetal kidney and placental tissue. The predominant serovars found though antibody testing on the aborting mares' serum were L. pomona and L. grippotyphosa.
Carter feels that the number of cases diagnosed at the laboratory might represent just the tip of the iceberg. As many as five to 10 times more abortion cases might have occurred around the area.
In 2007 there was a follow-up survey conducted on economic loss of the affected farms. Less than half of the farms responded, but those that did reported $3.5 million in lost revenues as a result of the abortions caused by leptospirosis. This is an indication of the economic impact a disease like this can have on a region like Central Kentucky, where a single foal can potentially mean millions in profit. Another study by K.B. Poonacha et al. in 1993 in Veterinary Pathology identified 67 cases of leptospirosis in 51 fetuses and 16 stillborn foals in Kentucky.
Current and Future Work
Carter presented the 2006-2007 data to the American Association of Veterinary Laboratory Diagnosticians annual meeting in Reno, Nev., in October 2007. This group comprises the leadership in laboratory medicine for animals in the United States. Carter and others are now studying 14 years of equine leptospiral abortion cases received by his laboratory to better understand the conditions under which horses are at a high risk, such as high rainfall. He hopes this and other studies will underscore the need for more research on equine leptospirosis and provide the impetus for development of a vaccine.
To that end, the University of Kentucky recently developed a working group combining the resources of area practitioners, the Livestock Disease Diagnostic Center, scientists at the Gluck Equine Research Center, and the College of Public Health's statistics resources to conduct an epidemiological study and a nationwide impact study of equine leptospirosis.
Carter urges owners and veterinarians to recognize leptospirosis as a disease that is here to stay. He also urges horse breeders to keep in mind that an abortion could be caused by leptospirosis, especially in a year with high rainfall or when wildlife have been present. Prevention includes minimizing contact between horses and wildlife/rodents, and especially keeping these creatures out of feed areas.
Make an effort to reduce stagnant water and recognize the risk of commingling horses with cattle and sheep, as the latter two could introduce infected urine into ponds and other standing water. If you have an abortion or a case of uveitis on the farm, send in samples of the affected horse's blood or urine (or fetus and placenta, in the case of abortion) for testing. Talk to your veterinarian about leptospirosis and work with him or her on collecting samples if you think it is indicated. Until we fully understand the epidemiology of this disease--which might be increasing in prevalence--the industry won't be able to develop a vaccine.
Article written and courtesy of author Liza Holland of Lexington, KY
Hi - I came across this article on CSNB from Dr. Brooks. I think this could definitely be another use for the Recovery Vizor. The vizor (without the fly jacket) would provide superior protection to the horse's eyes to help prevent injury at night... If you know of anyone whose horse suffers from CSNB please share with them this article.
Congenital stationary night blindness (CSNB) is found mainly in the Appaloosa, and it is inherited as a recessive trait. Cases are also noted in Thoroughbreds, Paso Finos, and Standardbreds. CSNB appears to be caused by a failure of neurotransmission in the middle retina. Clinical signs include visual impairment in the dark with generally normal vision in daylight. There is behavioral uneasiness and unpredictability at night. CSNB does not generally progress, hence its name, but horses with progression to vision difficulties in the daytime have been noted. An ophthalmoscopic examination of horses with CSNB will look normal to the veterinarian's eyes. Diagnosis is by clinical signs, breed type, and electroretinogram (ERG). The ERG is a test of retinal function commonly performed by veterinary ophthalmologists. There is no therapy for this condition, but affected animals should not be bred because the condition is heritable. Keeping horses stalled at night with a light on and avoiding exercise in the dark can help the horse feel more comfortable.
Taken from * By Dennis E. Brooks, DVM, PhD, Dipl. ACVO<http://www.thehorse.com/authors/140/dennis-e-brooks-dvm-phd-dipl-acvo>
* Dec 1, 2002
This is a very informative article about Equine Recurrent Uveitis - specifically how it relates to the Appaloosa but it certainly applies to all horses. As the article mentions, "Much more study is needed to determine why Appaloosa horses have a different type of disease and why they tend to go blind more frequently than other horses." Click on the LINK to read the whole story.
A truly great moment when I was able to bring my blind horse Dawnica back into the spot light and onto the parade route. She was absolutely stellar! I had an Equivizor fly mask on her - but that was just for aesthetics. Our motto is 'never give up'. I added a video of our day - enjoy! Gayla.
I am passionate about sharing inspirational, innovative, and educational information with my readers. I know from personal experience just how important and needed having this type of information is to horse owners.