Cross-sectional imaging techniques in veterinary ophthalmology.

Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) are useful, complementary cross-sectional imaging modalities of the eye and orbit. High-resolution US provides excellent morphological information of ocular structures but offers limited information on the periocular tissues. CT and MRI provide valuable morphologic and topographic images of both ocular and periocular structures, thereby giving a more complete picture of the pathological process. US can be performed on awake patients, whereas CT and MRI require general anesthesia. In addition, US equipment is readily available and less costly than CT or MRI units. Fine-needle aspirations and biopsies under US or CT guidance can also be performed. This article reviews the technique and normal findings of ocular and orbital structures as displayed in each of these imaging modalities. Representative clinical cases are presented to illustrate the interpretation principles as well as to provide an illustrative reference for common ocular and orbital changes.