2020–2021 BCSC Basic and Clinical Science Course™
7 Oculofacial Plastic and Orbital Surgery
Part I: Orbit
Chapter 2: Evaluation of Orbital Disorders
Orbital ultrasonography may be used to examine patients with orbital disorders. The size, shape, and position of normal and abnormal orbital tissues can be determined by means of contemporary ultrasound techniques. B-scan ultrasonography captures 2-dimensional images of these tissues, while standardized A-scan ultrasonography provides 1-dimensional images rendered as a series of spikes of varying height and width that demonstrate the particular echogenic characteristics of each tissue. Areas of edema can sometimes be used to discern the degree of disease activity. Ultrasonography has high resolution in the area of the sclera and optic nerve insertion and is useful for evaluating scleritis and other types of anterior inflammation that produce fluid in the sub-Tenon space. Localization of foreign bodies is possible with ultrasonography. Doppler ultrasonography can provide specific information regarding blood flow and can demonstrate arterialization, retrograde flow in the orbital veins in cases of dural cavernous fistula or arteriovenous malformation, or vascular abnormalities associated with increased blood flow. Vascular tumors can be identified by active pulsation or, in the case of venous lesions, by compressibility and change in size with the Valsalva maneuver.
However, ultrasound analysis of orbital tissues and diseases requires specialized equipment and experienced personnel, and office-based equipment is generally not suitable for this purpose. Ultrasonography is of limited value in assessing lesions of the posterior orbit (because of sound attenuation) or the sinuses or intracranial space (because sound does not pass well through air or bone).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.