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Figure 1: The skull of a dog showing the bony orbit. The orbit is essential for protection of the eye and other structures.
Figure 2: This side-on (lateral) view of a dog's eye shows obvious protrusion of the eyeball or exophthalmos due to inflammation of the extraocular muscles (extraocular myositis). This was successfully treated medically.
2. Where is the orbital mass? Although the extent of exophthalmos provides some clues as to the size and position of the orbital mass, an accurate assessment of where and how large the mass is requires advanced imaging techniques. Depending on the clinical exam findings, your veterinarian may recommend a combination of ultrasonography, computed tomography (CT scanning) magnetic resonance imaging (MRI), or radiographic examination of the eye, orbit, and surrounding tissues. We are pleased at the UCD VMTH to be able to offer all these techniques and to have a highly skilled group of radiographers and radiologists to conduct and interpret these tests in collaboration with the veterinary ophthalmologist. Figure 3 shows a CT image of a dog with a mass in her right orbit.
3. What is the orbital mass? The final step in the diagnosis of orbital disease is to assess the composition of the mass. This can differ widely and each type of disease has a different treatment. In some cases, the treatment for one disease may make another disease worse, therefore this is a critical phase of the diagnosis. This requires the collection of a small sample of the tissue for microscopic diagnosis by a board certified veterinary pathologist. Again, the UCD VMTH is fortunate to have such specialists on its faculty. The biopsy samples are usually collected under general anesthesia and can be done with a needle or through a very small incision.
Figure 3: This is a computed tomographic image ("CAT scan") of a dog with a mass in her right orbit. A biopsy revealed that the mass was due to inflammation and cystic enlargement of a salivary gland. The mass was removed by surgery and she retained normal vision and use of her right eye.
Treatment of orbital disease may be surgical or medical depending on the diagnosis. Some orbital disease, particularly that due to infection or immune-mediated inflammation may be treated with orally administered drugs (Figure 2). In other cases, particularly neoplasia (cancer) surgical removal may be required. In some cases it may be possible to remove the mass while retaining a normally functioning eye (Figure 3). In more advanced or malignant neoplasia, chemotherapy, radiation therapy, or surgical removal of the eye along with the tumor may be necessary.
What to look for
As with most diseases, early diagnosis and treatment of orbital disease is likely to minimize discomfort and provide the best prognosis. Watch for early signs such as altered appearance of your pet's eye, especially being able to see more of the whites (sclera) of the eye; difficulty seeing, blinking, or moving the eye; or altered pupil size or direction of gaze. If you see any of these conditions, please call your local veterinarian. He or she will want to examine your pet and may run some of the initial tests described above. Ultimately, you may be referred to a veterinary ophthalmologist. In this case, the ophthalmologists at the UC Davis VMTH, along with the associated specialties of anesthesia, radiology, and pathology will be happy to provide you, your pet, and your local veterinarian with specialist assistance.