Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002

A thorough ophthalmic examination is requisite of both involved and fellow eye, including tonometry, gonioscopy, and dilated examination of the posterior segment. Imaging techniques including ultrasound, CAT scan, or MRI are particularly valuable in determining the presence of a proliferative lesion in the presence of opaque media due to such factors as severe corneal edema or intraocular hemorrhage. Imaging modalities also can be useful in determining if there is involvement of the ciliary body or peripheral choroid, which can be difficult to directly visualize. A thorough physical examination is indicated with emphasis on palpation of the regional nodes (while the eye itself lacks lymphatics, the conjunctiva does and the orbit may possess them) and lymph nodes in general and determination of the presence of a primary lesson elsewhere that might have metastasized to the eye or a potentially malignant primary ocular tumor that has spread beyond the globe. If there is a clinical suspicion of a malignant ocular tumor, chest radiographs and clinical biochemistry to evaluate organ function may be helpful.

5. Can a biopsy be taken of an intraocular tumor?

Fine-needle aspiration biopsy of the aqueous or vitreous cavities or of observable ocular tumor masses has both its critics and its advocates and in general is likely underutilized as a diagnostic tool. Some neoplasms, such as lymphoreticular tumors and melanomas, tend to have noncohesive cells that are shed into the aqueous or vitreous and can be obtained by aqueous or vitreous centesis. Uveal lymphoma is one tumor that is likely to lead to an accurate cytologic diagnosis following a fine-needle aspiration of the mass itself. Other tumors are more likely to provide samples that are low in cellularity and to be problematic for critical interpretation even by experienced cytopathologists. Putting needles into eyes is not an innocuous procedure and can be accompanied by complications such as hemorrhage, rupture of the lens capsule, and potential seeding of neoplastic cells (Figs. 3-5).

Incisional biopsy likewise has the potential for significant intraand postoperative complications. In some instances, biopsy may provide an indication of tumor morphology at the time of biopsy but is not predictive of future transformation. Diffuse iris melanoma in cats, for example, may undergo a prolonged premalignant stage with relatively bland melanocytic cells confined to the iris surface that at a future point in time can undergo transformation to a malignant invasive neoplasm. A few intraocular tumors, those that are confined to the iris stroma or the ciliary body processes, may lend themselves to excisional biopsy (see question 7).

6.What is the prognosis for ocular neoplasia?

Prognosis depends on the nature ofthe neoplasm and stage of tumor development. Two ques-

tions need to be addressed: what is the prognosis for the globe both in terms of visual potential and cosmesis? and what is the prognosis for the general well-being of the patient? In general, eyes that harbor secondary intraocular tumors should be considered within the perspective of the whole animal. Less aggressive means should be used to control ocular complications; topical and sys-

Figure 3. Ocular lymphoma in a canine and feline; the left eye of this dog shows a dyscoria related to a space occupying iridal stromal lesion and diffuse thickening of the bulbar conjunctiva of the third eyelid.

Figure 4. The gray vascularized superior anterior chamber mass demonstrated is shown with a fibrohemorrhagic anterior chamber reaction.

Figure 5. Iris intrastromal thickening seen in the temporal quadrants of the right eye of a feline patient. The diagnosis was malignant melanoma.

temic corticosteroids can control uveitis, and hypotensive agents should be used to treat glaucoma. The majority of canine melanocytic neoplasms-roughly 90%-are benign in terms of their morphology. Of the remaining 10% that have morphologic features of malignancy, probably only about half actually metastasize. Both nodular and diffuse iris melanomas in cats are aggressive, with metastatic rates as high as 50% reported. Whereas metastatic disease tends to manifest within months in canine malignant uveal melanoma (although isolated cases with long latent periods prior to detectable metastasis have been documented), latency up to 2 years following enucleation is characteristic of diffuse iris melanomas in cats. When it occurs, metastatic disease in either species can affect any of the body's organ systems (Figs. 6 and 7).

In the dog, benign and malignant tumors of ciliary body epithelium occur with approximately equal frequency. In the cat, the majority demonstrate worrisome histologic features. However, although malignant tumors of the ciliary body epithelium do possess malignant potential, actual metastasis has been documented rather infrequently in both species (Figs. 8 and 9).

Primary ocular sarcomas in cats are very aggressive neoplasms, with mortality rates approaching 100%. These tumors typically will invade the optic nerve to gain access to the central nervous system, extend through the sclera into the orbit and beyond, and commonly metastasize to distant sites.

Even benign intraocular neoplasias can grow slowly and expansively along the planes ofleast resistance and result in complications that cause ocular pain or blindness. Preiridal fibrovascular membranes may form associated with benign and malignant neoplasms. Even limbal melanocutomas can extend into the globe if neglected, and an intractable glaucoma invariably develops in dogs with diffuse melanocytosis. Thus, as a rule of thumb, ocular neoplasia, either benign or malignant, carries a guarded prognosis for the involved eye.

Figure 6. Diffuse malignant melanoma of the left iris in a cat.

Figure 7. Melanomas most commonly present as a diffuse velvety thickening of the anterior surface of the iris.

Figure 8. Ciliary body epithelial tumors. Ciliary body adenomas typically present as proliferative lesions extending into the posterior segment or anterior vitreous as evidenced in the nasal quadrant of this patient. (Photograph courtesy of Dr. RIE Smith).

7.What are the management options for ocular neoplasia?

Management options are limited to observation; excisional biopsy, laser ablation, enucle-

ation, and, if the tumor has extended beyond the glove, exenteration. Localized lesions in eyes without tumor-associated complications may be managed by excisional biopsy, if amenable, or by observation over time in order to gain a sense of their biologic behavior. Tumor size should be carefully documented by photography or drawings. Notable increase in size over a relatively short period of time (weeks) suggests more aggressive biological behavior and demands intervention. In addition to excisional biopsy, laser ablation of tumors has been proposed as an effective means

Figure 9. Adenocarcinomas tend to invade the iris root as seen in the temporal quadrants in this Brittany spaniel.

of treatment for these tumors, and some success has been reported using trans scleral diode laser application or direct application of diode laser energy using an indirect ophthalmoscope or operating microscope attachment. A disadvantage of laser ablation is the failure to obtain a specific tissue diagnosis, without which it is impossible to unequivocally recommend management options. In addition, some neoplasms, notably diffuse iris melanomas in cats, may "seed" by shedding cells into the aqueous that become entrapped in the trabecular meshwork, beyond the reach of laser energy and excisable only by enucleation. Observation of slow-growing lesions in eyes without tumor-associated complications might also be indicated in an elderly canine patient or a one-eyed canine patient. In this species, the odds are favorable that conservative therapy is not likely to adversely affect general health and well-being. In general, cat eyes with diffuse primary iris hyperpigmentation or nodular pigmented lesions that demonstrate rapid increase in size should be enucleated. Some controversy exists as to whether cats can acquire a benign diffuse primary iris hyperpigmentation that never undergoes malignant transformation; the data that has been collected indicates that, although the premalignant stage may persist for years, malignant transformation is likely inevitable at some point in time. Until proven otherwise, the axiom that early enucleation will minimize the metastatic potential should be adhered to. Canine eyes with rapidly growing lesions or eyes that have experienced tumor-associated complications should be enucleated. Cat eyes with suspected primary ocular sarcoma, based on history of prior trauma, change of appearance in a blind or phthisical, or the observation of a gray to white vascularized tumor mass, should be promptly enucleated or exenterated, although prognosis for general health is bleak. Indeed, the aggressive nature of this tumor and the strong association with ocular trauma provide suggestions for prevention that are likely to be much more effective than treatment. Blind phthisical eyes in cats should be enucleated, and cosmetic globe sparing procedures such as pharmacologic ablation of the ciliary body with intravitreal Cidofovir or gentamicin and evisceration with an intraocular prosthesis are, in the opinion of the author, contraindicated in cats. Once the tumor is characterized by pathology, consult with an oncologist regarding additional treatments available.

either cryo or laser theoretically should be effective but more often than not fall short in terms of controlling intraocular pressure and preserving vision. Topical and systemic hypotensive agents are likewise likely to be unsuccessful in controlling the glaucoma, and visual prognosis in these eyes should be guarded (Figs. 12 and 13).

Figure 12. Uveal melanocytosis is a bilateral condition seen in elderly cairn terriers. In this patient, the left eye demonstrates diffuse iris hyperpigmentation, intercalary hyperpigmentation of the sclera, and pigment flecks on the anterior lens capsule.

Figure 13. In the fellow eye, chronic secondary glaucoma is present.

10.What type of follow-up is indicated in a patient with an ocular tumor?

All tissues obtained at surgery should be submitted for histologic interpretation, and mor-

phology can provide guidelines for prognostication. Uveal melanocytomas in dogs have an excellent prognosis and have not been demonstrated to recur even if the tumor has extended transsclerally into the orbit. Transscleral extension and involved surgical margins in malignant tumors are ominous harbingers of either locally recurrent or metastatic disease. The tendency for some of these tumors to demonstrate long latency prior to metastasis has been discussed, and regular follow-ups should be conducted over a 2-year period before the animal can be pronounced "cured" of this disease. One-eyed animals function quite well with an excellent quality of life, but enucleation or exenteration places a premium on the remaining fellow eye, and pet owners should be instructed about the sensitivity of the globe to insult and to seek attention promptly at the earliest suspicion of any problems with the remaining eye.

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