What is Ocular Neoplasia ?
Ocular neoplasia is basically an abnormal growth of cells in the ocular adnexa and in this case, it occurs in and around the tissues that surround the eye of the horse. These masses or tumors have been shown to be malignant in approximately 80% of the time when found and identified. These neoplasms tend to show up in horses who are about 8 to 10 years old and most frequently are found in those horses whose eyelids have either no pigment or are lightly pigmented. Neoplasms of this type are usually found on the eyelids and conjunctival areas of the equine eye. If detected early, it is very easily treated.
Ocular neoplasia is the abnormal growth of cells in or around the eye; the growth can be classified as either malignant or benign.
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Symptoms of Ocular Neoplasia in Horses
A careful examination, done on a regular basis, will go a long way toward early detection of suspicious areas that could be early stages of neoplastic development. As noted above, if these neoplastic areas are detected early enough, treatment of them is very successful. Here are some things to look for:
- Small bumps on or around the eyes and eyelids
- Areas that appear raw or abraded and are oozing
- Any of the above noted areas which have enlarged after having been previously observed
- Any area of ulceration or abrasion which does not heal over an acceptable period of time
- Suspicious areas may appear alone or in groups anywhere on the eyeball, eyelids, and areas surrounding the eyeball
These are types of cancer (neoplasia) that are commonly found in horses:
- Melanoma - This can occur in any dark-skinned horse but is most commonly detected in gray horses ranging in age from 4 years to 15 years old
- Squamous cell carcinoma (SCC) - Easily seen around the eyes and eyelids, especially in those areas which have little to no pigment
- Sarcoid tumors - This is the most common tumor found in horses and certainly epitomizes the proliferation of cells requirement of the definition of cancer; it is believed to be caused by the bovine papillomavirus and is one of the most common skin tumors (usually doesn’t spread internally and is easily removed unless allowed to become very large)
- Lymphosarcoma - This is a lymph system related cancer that can present anywhere in the body where lymph nodes are found, including the eyelids and other tissues around the ocular adnexa (depending on the location and size, this can be deadliest of ocular neoplasms in the horse)
Causes of Ocular Neoplasia in Horses
The primary cause of most ocular neoplasia is exposure to sunlight, ultraviolet light and elements. Here are some things that can increase the risk of development:
- Many of the above types of neoplasia commonly found in horses result from a lack of protection of tissue by the pigment of the skin or hair of the horse
- These neoplasms occur in areas around the eyes and eyelids where the pigment of the skin is lighter or nonexistent and where the protective hair is also thin
- Higher altitudes can place horses in a higher risk category because the higher altitude puts them closer to the sun and those damaging ultraviolet light rays
- Horses having little to no pigment surrounding the eyes are at higher risk for development of squamous cell carcinoma; for example Appaloosa and Paint breeds
- Equine papillomavirus is believed to be a cause of SCC found in some areas of the equine body but the jury is still out on possible ocular involvement
Diagnosis of Ocular Neoplasia in Horses
To determine the etiology (origin) of any suspicious areas observed and reported by you, your vet will need to take a sampling in some manner to have it evaluated. This sampling may be a simple scraping or collection of cells from the surface of the lesion or bump or may require an excisional biopsy be taken surgically. Regardless of the type or method of collecting the sample or biopsy, it will have to be closely examined under laboratory conditions to determine what it is and whether it is benign or malignant.
If it is determined to be a malignancy, a determination will be made regarding whether if only portion of the lesion was collected or if the whole lesion was obtained. In the case of a malignancy, the vet will use the pathologist’s report to determine surgical excision options as well as other possible treatment options and the extent to which those options should be utilized for each area identified.
Treatment of Ocular Neoplasia in Horses
Of course, it must be noted here that the size, shape and location of the lesion will determine the best treatment option. Because SCC lesions are usually fairly large before they are detected and identified, the opportunity is present for it to have invaded surrounding tissues and hence, the increased difficulty in treatment and removal. The smaller the lesion, the easier it usually is to treat successfully. Here are some of the options available:
- Cryotherapy involves freezing the tissue involved; this can be done prior to surgery and can be used on any type of tissue
- Sr90 irradiation - Its very short wave length makes this option ideal for corneal lesions as the cornea absorbs most of the energy
- Brachytherapy (lr192) - This procedure involves insertion of radioactive pieces shaped like rods or beads directly into the tumor for a specific period of time; it is usually effective but not without its radiation hazard risks
- Radiofrequency hyperthermia - This procedure increases the temperature of the tissue to approximately 122 degrees F to damage the tumor cells while allowing the normal cells to recuperate
- Intralesional immunotherapy involves the injection of specific immunomodulating medications directly into the tumor tissue, mainly used to treat large SCC tumors located on the eyelids
- Topical chemotherapy involves using several chemotherapy medications postoperatively to discourage the regeneration of tumor cells at the surgical site
- Carbon dioxide (CO2) laser can be used like topical chemotherapy as an after-surgery treatment or as a primary removal option
- Photodynamic therapy (PDT) involves using a special injectable medication to highlight and attract the laser energy to the tumor tissue, destroying it along with any associated blood vessels
Recovery of Ocular Neoplasia in Horses
Identifying and treating the potential cancer lesion as early as possible in the cancer’s developmental process is very important for the best post-cancer prognoses. Since the eyelids are a primary site for cancer development, surgical removal and the subsequent repair is quite challenging. The equine, unlike humans and other species, can’t adapt to some of the eyelid or flap repairs which will be needed in the event that large portions of the eyelid need to be removed to get all of the cancer. This will necessitate the removal of the equine eye since the eyelid cannot be repaired to allow it to do the job for which it was designed (protection and lubrication primarily).
The most prudent thing you, as the owner and caregiver, can do for your horse is to make every effort to reduce the exposure of the horse to the damaging UV rays of the sunlight. This might mean allowing the horse to spend less time in open pastures without appropriate shade. Additionally, incorporating a change in your daily regimen to include a daily thorough and close examination of your horse’s face for any unusual or abnormal areas and then take the step to call your vet to get him involved as soon as possible to ascertain if the lesion warrants further invention. This is definitely one of those cases in which an ounce of prevention is worth a pound of cure.