UBM

The Sound of Pathology: UBM's Diagnostic Echoes

Ultrasonic biomicroscopy finds increasing proponents as its ophthalmic clinical applications expand.

By Robert J. Murphy

Ultrasound biomicroscopy (UBM) has grown in popularity in recent years perhaps due to its capacity to clearly image the anterior segment extending beyond the iris to the angle, ciliary body, crystalline lens, or intraocular lens with a procedure that is easy to perform and equipment that is relatively inexpensive.¹

Well within the capability of any ophthalmic technician knowledgeable in ocular anatomy and pathology, the UBM's examination techniques — scleral shell or the newer ClearScan cover methods — can be readily learned in less than a day. Vendor representatives may be the most helpful teachers, while online videos as well as regional and national conferences provide useful training as well.

“It's a very simple technique,” says longtime ultrasound technician and educator Rhonda G. Waldron, MMSc, COMT, CRA, ROUB, CDOS, Diagnostic Echographer and Senior Associate in Ophthalmology at Emory Eye Center in Atlanta. “I want to stress how easy it is, because people sometimes try to make it sound more complicated than it is.”

Ultrasound biomicroscopy serves many diagnostic imaging purposes, some of which cannot be captured using any other technology such as coherent light.

UBM indications

Ultrasound biomicroscopy captures high-quality anterior segment images thanks to the use of high-frequency sound waves ranging from 20-80 MHz.² A transducer emits a short acoustic pulse and displays echoes as it passes through various tissue structures, each with its own acoustic density.³

UBM is useful in the event of certain signs, symptoms, and historical factors that suggest anterior segment involvement in ocular disease — most notably angle assessment in glaucoma — as well as measurements that are useful prior to cataract or refractive surgery as well as postoperatively.

With glaucoma patients, UBM lets users detect and visualize numerous structures and events: angle assessment, aqueous misdirection, and ciliary body position in those with plateau iris. Users can also evaluate iris/ciliary body cysts and identify ciliary body tumors, clefts, and anterior retinoschisis or synechia.¹

UBM's applications extend to cataract and refractive surgery where users can visualize phacomorphic lens changes, dislocated IOLs, misplaced haptics, and perform sulcus-to-sulcus measurements for implantable contact lenses (ICLs). Beyond that, UBM allows users to detect ciliary body cysts before lens implantation, fibrin and retained lens fragments, and anterior suprachoroidal effusions.¹

“I use UBM routinely for visualization of iris/ciliary body lesions and cysts, evaluation for plateau iris configuration, localization and evaluation of anterior chamber tube patency, multifocal and monofocal IOL positioning/haptic localization,” says Kelly Babic, MSc, CDOS, Diagnostic Services Manager/Eye Ultrasonographer at the University of California at San Francisco Medical Center Department of Ophthalmology.

“In addition, I use UBM to examine for evidence of ciliary process atrophy, ciliochoroidal detachments, cyclodialysis clefts, peripheral retinal tears and extraocular muscle insertion, as well as examination of conjunctival lesions and external adnexa,” Ms. Babic says.

Other indications include seeing if Descemet's membrane is detached when the cornea “is so edematous,” Ms. Waldron says.

“Or if you're looking for a foreign body after an injury; I've found a piece of metal in the ciliary body and in the lens after injury.” Add to these indications uveal melanomas of the ciliary body or iris, and you've got a pretty full plate,” she adds.

The scleral shell technique

The device can be used to perform either of two safe and effective UBM techniques. The traditional method involves the use of an open scleral shell filled with saline.²

“You can use what's called a scleral shell filled with soft contact lens saline and place that on the anesthetized eye and hold the probe in the saline,” Ms. Waldron says.

The technique is fairly straightforward. “Basically, what you want is to center the pathology in the cup,” Ms. Waldron says. “In other words, if the patient has a lesion at six o’clock in the iris, I would have [the patient] look up a little bit so that I could get six o’clock centered under that little cup of saline. And then the probe just goes directly over that area.”

Depth of focus hinges on the probe's positioning in the saline. “There's a very small zone of focus on the images,” Ms. Waldron says. “It has to do with how deep the pathology is, and how close to the pathology you are.”

The farther the probe is from the eye, the more anterior the focus. “If something is in the cornea vs. the iris vs. the lens, those are three different depths,” Ms. Waldron says. “To focus on one vs. the other, it just depends on how deep into the saline you go. You need to get into the zone of focus. Depending on where you are from the eye, the cornea may be in focus; if you go a little deeper into the saline, the iris is in focus; if you go a little deeper, you get the lens in focus.”

Gain adjustment allows the of capture images including anterior retinoschisis or far-peripheral uveal melanomas difficult or impossible to image with a standard B-scan probe.

ClearScan cover technique

The so-called bag/balloon technique using the ClearScan cover (ESI Inc., Plymouth, MN) utilizes a sterile, single-use, water-filled bag covering the end of the UBM probe. A flexible collar, also serving as a valve to adjust internal bag pressure, secures to the ultrasound probe and creates a watertight seal. As you gently applanate the eye, the water-filled bag readily conforms to the contour of the eye. Inserting the probe into the bag creates positive pressure keeping the waggling probe tip from making contact with the eye. (2)

Since just a drop of saline is required as an interface, patients can be examined while sitting, in the same orientation as when anterior anatomy is evaluated at the slitlamp, as opposed to the reclined (supine) position necessary with the scleral shell as anatomical changes may occur in patients due to positional changes.

“You have to make sure that the probe is placed over the structure of interest,” says Thomas C. Prager, PhD, a Clinical Professor at the University of Texas Medical Branch, Galveston, who holds a patent on the ClearScan cover. “So, you have to identify the pathology's location and then have [patients] rotate their eyes so that the structure is directly below the transducer.”

Education and training

In a scene from The Marx Brothers' movie “Duck Soup,” Groucho scans a financial report and says, “A four-year-old child could understand this. Go out and find me a four-year-old child — I can't make head or tail of it!” No one pretends a four-year-old will be performing UBM anytime soon. Yet, its proponents say it's as easy to learn.

“With both techniques there is a short learning curve,” says Ms. Waldron, who lectures on UBM at regional, national, and international venues, as well as providing instruction at private practices. “Neither one is hard to do. They're both going to give you good image quality. We don't use gel in the scleral shells anymore, so there is no eye irritation afterward as in the old days. Comfort-wise to the patient, neither one is uncomfortable.”

The best bet might be to invite a vendor representative to demonstrate proper UBM technique. Lectures at conferences or regional training programs are also ideal options for learning one or both UBM techniques. Numerous online videos, including those by Dr. Prager, provide practical and effective hands-on training.

Certain fundamentals remain paramount. Before learning the specifics of UBM technique, you must come to the table with a solid understanding of ocular anatomy and pathology and be able to distinguish normal from abnormal.

In determining the right technique for your patients, Dr. Prager suggests technicians try a taste of their own medicine. “In comparing technologies it would be advisable for technicians to be patients themselves and see what they prefer,” he says.

UBM takes center stage

Due to the many clinical entities that can be identified, beyond coherent light machines where the iris blocks more posterior structures, eyecare providers have embraced ultrasound biomicroscopy. Use has migrated from academic and hospital settings to the private practice. Even as its present indications provide numerous clinical applications, it's safe to say innovative researchers, clinicians, and technicians will discover further diagnostically fruitful uses for UBM in years to come. OP

1. Prager TC. How to succeed with ultrasound biomicroscopy. Ophthalmol Mgt 2011;October:73-9.2. Bell NP, Feldman RM, Zou Y, Prager TC. New technology for examining the anterior segment by ultrasonic biomicroscopy. J Cataract Refract Surg 2008;34:121-25.
3. Bell NP, Nagi KS. High-frequency UBM. Glaucoma Today 2010;October:54-56.