Ultrasound Biomicroscopy (UBM) is a technique primarily used for imaging the anterior segment of the eye. It was first introduced in 1990 as a way to obtain microscopically detailed cross-sections of the eye. In comparison to regular ultrasound methods like A-Scan or B-Scan (10 MHz), UBM utilizes a much higher frequency range (35-100 MHz) [2]. As a result, it achieves high resolutions, although the penetration depth into tissues is low. UBM can be used to visualize most of the anatomy of the anterior segment, including associated pathologies such as angle-closure glaucoma, ciliary body cysts, tumors, and angle trauma.
Structures visible using UBM:
1. Cornea
2. Iris
3. Anterior chamber angle
4. Scleral Spur
5. Ciliary body
6. Posterior chamber
7. Anterior chamber
8. Lens
Clinical Applications
UBM is a valuable tool for assessing narrow-angle glaucoma, angle-closure glaucoma, and pathology of the ciliary body. It often complements clinical gonioscopy, especially when monitoring abnormal gonioscopic findings. Studies have shown a correlation between UBM and gonioscopy in evaluating the angle of the anterior chamber.
The analysis and interpretation of images start with identifying the structure called the SCLERAL SPUR, which is the protrusion of the sclera into the anterior chamber, connecting anteriorly to the Trabecular Meshwork. UBM can diagnose angle-closure glaucoma by demonstrating contact between the iris and the cornea anteriorly to the SCLERAL SPUR. Using this technique, different types of angle closure can be distinguished, including Pupillary Block, Plateau Iris, and other causes. UBM can also identify factors contributing to open-angle glaucoma, such as pigment dispersion syndrome.
Additionally, UBM can be used for corneal imaging, enabling the identification of pathologies such as keratoconus, corneal dystrophies, scars, and opacities. It can also visualize post-LASIK corneal flaps. UBM is clinically beneficial for diagnosing and managing anterior eye trauma, anterior chamber cysts and tumors, uveitis, and scleritis, as well as the positioning of intraocular lenses (IOLs) in cases of uveitis-glaucoma-hyphema syndrome.