Standardized Echography of the Optic Nerve

Because of its size and location, the optic nerve is difficult to image. Although it can be seen with computerized tomography in both axial and coronal images, it is virtually iJnpossible to differentiate the optic nerve from its sheaths axially and difficult at best coronally. Computerized tomography is too insensitive for measuring the size of the optic nerve, and studies cannot be performed in real time. Since the optic nerve must be measured from hard copies of scans, error is increased. It is also difficult to determine if the i.IJlage is oblique to the major axes of the nerve. Magnetic resonance imaging suffers from these same problems. Fat suppression techniques must be used to differentiate the optic nerve from the surrounding intraconal fat. Ultrasonography, however, can offer precise and reproducible measurements of the optic nerve. Dynamic real-time images can be obtained. Standardized echography is essential if fluid filled lesions are to be differentiated from solid ones. Ultrasonography is less stly, and it affords less morbidity to the patient. It can also be used to follow the progress of optic neuropathies, and it can be used to follow patients who have had optic nerve surgery.