Causes and Treatment of Canine Eye Tumors

" Most canine eye tumors or ocular tumors are benign, which means that they are not cancerous or dangerous to the health of your dog. Benign tumors can be left alone if they are not causing any discomfort or interfering with eye function. Malignant or cancerous tumors can originate in the eye or spread from neoplasms (growths) in other areas of the body. Diagnosis is made after examining a small  tumor sample under a microscope. Tumors behind the eye or malignant tumors (cancerous and fast growing) can be problematic and require surgical removal or other treatments such as laser therapy or cryotherapy (freezing). "

Canine eye tumors often appear as spots or discolorations on the eye. These are not necessarily tumors, but can be. Tumors can be in the eye, on the surface of the eye, behind the eye or on the eyelid.

Canine eyelid tumors are usually not cancerous and do not spread to other parts of the dog.  Most tumors are located on the anterior (front) of the uvea (middle part of the dog eye containing the choroid, ciliary body and iris.

Dog Eye Anatomy
Source: Hill's Pet Nutrition, Atlas of Veterinary Clinical Anatomy

Types of Canine Eye Tumors

• Iris Melanoma: This is the most common type of dog eye tumor.  The condition starts with a change in the pigmentation or color of the iris (the round colored part of the eye). It can take from years to just a few months to form. As the tumor grows in size it can restrict the ability of the iris to function (let's light into the eye), causing it to change shape (a condition called dyscoria).  An iris melanoma can trigger secondary glaucoma.  This type of tumor or neoplasia can spread to a dog's lungs, spleen and liver, where tests often first determine the presence of cancer.  A type of iris melanoma, focal iris melanoma, can be treated with a procedure called laser coagulation.
• Orbital Neoplasia (the cavity that holds the eye): This type of neoplasia or tumor occurs in the tissues that line the cavity that holds the eye (most common type is a osteosarcoma). The neoplasia can spread from nearby locations such as the dog's nasal cavity or sinuses. Symptoms of canine orbital neoplasia include swollen eyelids, a buildup of the tissue behind the eye (exophthalmos).   Other types include squamous cell carcinoma (starts on the eyelid), orbital adenocarcinoma (spreads from the dog's nasal cavity) and a epibulbar melanoma (mass on eye sclera often seen in German Shepherds).  Treatment depends on the specific type, location and size of the tumor.
• Cilary body neoplasia: This type of dog eye tumor appears as a reddish pink mass in the eye pupil, towards the rear of the iris.  Cilary body neoplasia can trigger glaucoma.  If this dog eye condition can be diagnosed early, it can be correct with surgery. a swollen conjunctiva (membrane that lines the eyelids and that covers the dog eyeball),  a prominent third eyelid, a dilated pupil, or if the dog retina is detached. 
• Uveal Canine Lymphoma (canine ocular lymphoma): This is a common type of tumor that is the result of a neoplasia or cancer that has spread from another area of the dog's body.  The condition appears asa pinkish white mass on the front of the uvea.  As the tumor grows it can trigger canine glaucoma.  The cornea can also appear blue/white in color. Tumor cells can spread to other areas of the eye including the retina and vitreous.
• Ocular Metastases: This type of cancer occurs in the uvea and choroid.  The presence of this type of tumor may indicate cancer (adenocarcinoma) in a dog's mammary glands, cancer in the uterus, the presence of a squamous cell carcinoma or a hemangiosarcoma.  This type of tumor is commonly found in the part of the eye referred to as the ciliary body.
• Posterior Segment Neoplasia: This is a one of the rare canine eye tumors where a tumor forms in the part of the eye called the posterior (rear) segment.  They are sometimes a type of dog eye tumor called a astrocytoma. Symptoms include a brown mass beneath the retina.
• Limbal Melanoma: This type of melanoma appears as a brown mass the appears on the limbus (the part of the eye between the white sclera and the colored iris).  The eye tumor can reach from the limbus to the sclera (white part of the eye). Treatment is possible with procedures such as cryotherapy (freezing), sclerectomy (removal of a portion of the sclera),  or a keratectomy (removal of part of the cornea).
  
  
  
  This is a type of dog eyelid tumor referred to as a meibomian gland adenoma, which is a type of sebaceous gland tumor.  The meibomian gland secretes a substance that prevents a dog's eyelids from sticking together.
  Source: Washington State University
• Canine eyelid neoplasia: The most common type of dog eyelid tumor or neoplasia is referred to as a sebaceous gland adenoma.  Other types are papiloma and melanoma. Most tumors are benign.  Dog eyelid tumors are treated with surgery.

Canine Eye Tumors such as this one are referred to as a hemangioma of the third eyelid, a type of dog eye tumor that is usually benign or not cancerous.
Source: Washington State University

Symptoms of Canine Eye Tumors

Redness, itching or tearing of the eye can mean your dog has an eye tumor.  Changes in eye pigmentation can also indicate the presence of a primary or secondary (spread from another part of the body) dog eye tumor.

Diagnosis of Eye Tumors in Dogs

To make a diagnosis for the canine eye tumors mentioned, your veterinarian will want to take a small sample of the tumor for testing in a lab.  The dog should undergo a complete physical examination.

If the tumor is inside the eye a veterinarian has a special scope (opthalmoscope) that can look into a dilated eye (done with drops). If the tumor is behind the eye, there is a special tool (fine-needle aspirate) that will allow your veterinarian to take a sample (biopsy).  Other methods include ultrasound, x-rays, MRI, CT scan and blood tests.

Treatment of Canine Eye Tumors

Not every eye tumor requires treatment. If your veterinarian believes it is small, and with monitoring it is not growing, it can be left alone without treatment. Other options include removing the tumor or in more drastic cases removal of the entire eye. If your dog needs its eye removed, most dogs adapt well and heal completely.

Tumors behind the eye can be a problem. They tend to grow quickly so removal of the eye is often called for. Radiation after the eye is removed is often prescribed in case any cancer cells were not surgically removed.  Other methods for treating canine eye tumors includes laser ablation, hyperthermia, cryosurgery, chemotherapy and radiation.

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References for Canine Eye Tumors:

Canine Ocular Tumours
Ingrid Allgoewer
European College of Veterinary Ophthalmologists
Animal Eye Practise

Nutrition and Cancer: New Keys for Cure and Control 2003!
Gregory K. Ogilvie, DVM, DACVIM (Internal Medicine & Oncology)
Colorado State University
Ft. Collins, CO, USA

Prostatic Disease in the Dog
Peter E. Holt, BVMS, PhD, ILTM, DECVS, CBiol, FIBiol, FRCVS
Professor of Veterinary Surgery, University of Bristol,
Department of Clinical Veterinary Science
Langford, Bristol, UK

Lymphoma
Antony Moore, BVSC
Diplomate ACVIM
Director, Veterinary Oncology Consultants
379 Lake Innes Drive
Wauchope NSW 2446
Australia

Canine Brain Tumors: Improvements in Diagnosis and Treatment
R Chun
School of Veterinary Medicine
University of Wisconsin-Madison

Neoplasia of the Nervous System (spinal tumors)
S. Long
School of Veterinary Medicine
University of Pennsylvania

Current Therapy for Canine Oral Tumors
M. Kessler
Tierklinik Hofheim, Germany

Dog Owner’s Home Veterinary Handbook
James M. Giffin
Liisa D. Carlson DVM

Hound Health Handbook
Betsy Brev itz, DVM

Ophthalmic Neoplasia
Michael H. Brown, DVM, MS, Diplomate ACVO
Veterinary Ophthammology Services

Washington State University