Ultrasound Biomicroscopy (UBM) is a specialized diagnostic imaging technique used in ophthalmology. It offers a detailed view of the eye’s anterior segment. UBM helps eye care professionals visualize areas that are otherwise difficult to examine directly, providing valuable information for various eye conditions. This non-invasive method is a valuable tool in understanding and managing ocular pathologies.
Understanding Ultrasound Biomicroscopy
Ultrasound Biomicroscopy operates on principles similar to sonar, using high-frequency sound waves to generate detailed images of internal eye structures. The UBM device emits ultrasound waves, in the range of 50-100 MHz, which are much higher frequencies than conventional ultrasound. These high-frequency waves penetrate the eye’s tissues and reflect differently depending on the density and type of tissue encountered.
The reflected sound waves, or echoes, are captured by the transducer. A signal processor converts these echoes into a two-dimensional, grayscale image displayed on a screen, creating high-resolution images with up to 50 micrometers resolution. This enables near-microscopic visualization of ocular tissue. UBM’s imaging depth is limited to about 4-5 millimeters, making it effective for examining the anterior segment, including the cornea, iris, ciliary body, lens, and the drainage angle. Its ability to visualize structures hidden behind opaque tissues or those that are extremely small gives it an advantage over other imaging modalities.
Conditions Diagnosed with UBM
UBM is valuable for diagnosing and managing a range of eye conditions, especially those affecting the anterior segment. For glaucoma, UBM is used to evaluate the drainage angle, helping to distinguish between different types of angle closure, such as pupillary block and plateau iris configurations. It can provide quantitative measurements of the anterior chamber angle, including angle opening distance and angle recess area, which are useful for accurate diagnosis and management.
In cases of ocular trauma, UBM is effective for assessing damage to internal structures like the iris, ciliary body, or lens, even when the media is opaque due to conditions like hyphema or corneal edema. It can detect cyclodialysis clefts, angle recession, and identify intraocular foreign bodies. UBM also aids in identifying and characterizing growths such as cysts and tumors in the anterior segment, helping to determine their size and potential invasion of surrounding tissues.
For lens abnormalities, UBM can visualize subluxation or dislocation of natural or intraocular lenses, and assess the integrity of the posterior capsule. It is also useful in visualizing inflammation in structures like the ciliary body, which can occur in inflammatory conditions such as uveitis. UBM’s ability to provide detailed cross-sectional views of these hidden or small structures makes it a valuable tool for evaluating these conditions.
What to Expect During a UBM Exam
Undergoing a UBM exam is a straightforward, non-invasive procedure that requires no special preparation. Patients are positioned lying down on their back, facing the ceiling, to facilitate the examination. To ensure comfort, topical anesthetic eye drops are applied to numb the eye.
A small, specially designed eye cup, between 22 to 24 mm in diameter, is placed on the eye to separate the eyelids and create a fluid-filled environment. This cup is filled with a viscous, sonolucent coupling fluid, such as methylcellulose or sterile distilled water, which helps in the transmission of sound waves. The UBM probe, which emits the high-frequency sound waves, is immersed into this fluid within the eye cup.
The examiner manipulates the probe with fine movements while observing real-time images on a screen, guiding the scanning over areas of interest. The entire examination takes between 10 to 30 minutes per eye, depending on the case’s complexity and the number of areas investigated. Patients experience minimal discomfort during the procedure. After the exam, there might be temporary blurriness from the eye drops, but normal activities can be resumed shortly after.