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Advances in Orbital Imaging

Successive years have provided the ophthalmologist with increasingly useful tools for imaging the orbit and its contents. The use of plain radiographs has largely been supplanted by imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), that provide information about anatomical structures along planar sections. During the last decade, CT scanning has become a routine imaging modality for patients with orbital disorders. The 1990s will likely demonstrate the value of orbital MRI for many of these patients in the clinical setting. In addition, specialized techniques for MRI, such as surface coils and fat-suppression sequences, will become routine. Other innovative applications of wellunderstood technology, such as three-dimensional reconstructions of CT images or color coding of Doppler imaging in orbital ultrasound, will become more widespread. This chapter provides an introduction to what can be expected for orbital imaging during the next decade. Basic principles of data collection and image reconstruction for MRI will not be discussed; these are better described in a recent tutorial [ l , 21 or more technical introductions [3]. The focus is on current methods for imaging the orbit as well as a survey of more classical methods and their application to common and uncommon lesions. It is hoped that the information contained here will allow the clinician to choose the most appropriate imaging modality for the patient as well as to interpret it knowledgeably. Several of the most up-to-date technologies for imaging the orbit will be discussed first, followed by a situation-based guide to choosing CT or MRI for various orbital conditions. Understanding the radiographic findings of various orbital lesions should allow the clinician to identify major classes of orbital processes preoperatively.