Imaging Behind the Iris
Imaging Behind the Iris
Ultrasound biomicroscopes enable practitioners to obtain a long-hidden view of the anterior chamber.
BY ERIN MURPHY, CONTRIBUTING EDITOR
Ultrasound biomicroscopes (UBMs) give clinicians higher-resolution digital images and video of the anterior segment of the eye behind the iris better than any other technology. This new capability is generating excitement among eyecare practitioners for its potential use in glaucoma and IOL patients and other common conditions and procedures.
This article will discuss how ophthalmologists are using UBMs in IOL applications and in the diagnosis, treatment and management of anterior segment disease.
Comparing UBM and OCT
Anterior-segment imaging with OCT uses light that doesn't penetrate the iris. High-frequency UBM penetrates the iris to offer a clear view of the anterior segment.
"What OCT can do, it does better than ultrasound, but the ultrasound has greater versatility," says Kenneth M. Goins, MD, professor of ophthalmology at the University of Iowa in Iowa City. A cornea specialist, Dr. Goins uses the Aviso (Quantel Medical Inc.). "If you need to view structures in front of the iris, OCT is superior, but to look behind the iris, UBM is superior. So one might use it for trauma, glaucoma, uveitis or tumor."
John A. Vukich, MD, is an associate clinical professor at the University of Wisconsin-Madison Medical School and director of refractive surgery at Davis Duehr Dean, a large private group practice that uses the VuMax-II UBM (Sonomed Inc.) for glaucoma.
"It's a sophisticated tool that delivers a high-quality image of the anterior segment," he agrees. "By the time we're using the UBM, we're looking for a definitive answer. We can't obtain a view this clear with any other technology."
Reviewing the Clinical Advantages
UBM technology is valuable for making clinical diagnoses and helping to guide treatment and disease management decisions primarily for patients with glaucoma or IOL implantation.
Dr. Vukich uses UBM for several applications. "In glaucoma cases, I can get a detailed analysis of the angle, ciliary body and other anterior segment anatomy," he explains.
"I also rely on UBM to assist in properly sizing phakic IOLs, including angle- and sulcus-supported implants. And it excels at imaging irregularities of the iris, occult cysts, melanomas and tumors."
Ike K. Ahmed, MD, FRCSC, an assistant professor at the University of Toronto who practices at Credit Valley Eye Care, uses the VuMax-II UBM (Figure 1).
Figure 1. VuMax-II from Sonomed
"For glaucoma patients, we often use it to evaluate not only the angle, but also what's causing the patient's borderline or narrow closed angles. We can determine if pupil block, plateau iris, lens surgery and/or lens intumescence (phacomorphic glaucoma) play a role," he says. For IOL patients, "we can assess what's going on in the capsular bag, obtain the dimensions of the sulcus and understand the capsular bag morphology, which helps us choose a lens and identify potential issues."
Nicole Fram, MD, is an associate of Samuel Masket, MD, at Advanced Vision Care in Los Angeles, where she's an anterior segment, cornea and external disease specialist. She and Dr. Masket use the UBM Plus (Accutome) for many treatments, including anterior segment reconstruction and IOL exchange.
"The UBM reveals the position of the optic, haptics and relationship to the iris, posterior chamber and ciliary body. This helps pre- and postoperatively in patients with malpositioned IOLs requiring exchange," Dr. Fram says. "The UBM also may be an excellent tool for evaluating pseudo-accommodating lenses and clarifying the anatomical reasons for phenomena, such as negative dysphotopsia, after uneventful cataract surgery."
|UBMs in Optometry|
|In optometry, ultrasound biomicroscopy is becoming an adjunct for diagnosing and comanaging disease.|
At Credit Valley Eye Care, a multidisciplinary private group practice in Mississauga, Ontario, Prit Shoan, OD, director of optometry, uses the Vu-Max II (Sonomed Inc.) ultrasound biomicroscope (UBM). "Within our scope of practice, we don't perform surgical treatment or management, but we can make a diagnosis, develop a recommended treatment plan and send patients with glaucoma or cataract to an ophthalmologist with as much information as possible," Dr. Shoan says.
As a primary care practitioner, Dr. Shoan is most interested in the UBM's ability to assess angles — a common thread among clinicians.
"If you're really interested in glaucoma, beyond primary open-angle disease, and you're treating and comanaging with an ophthalmologist, then this technology is useful. The investment makes sense," he says. "Not many ODs and MDs are completely comfortable performing gonioscopy. In fact, it's generally been noted that not many eye doctors perform this test or perform it well. Newer technologies mean we won't have to rely heavily on it in the future. We have more comfortable alternatives."
Dr. Shoan adds that OCT and UBM together will make it easier to diagnose glaucoma, particularly narrow- angle disease. "Patients will get more timely treatment before the disease gets more complex, which will prevent vision loss," he says.
He offers this example: "If we want to see what's causing the iris to bow forward in a narrow or closed angle, OCT will be limited by its inability to adequately image the anatomy behind the iris, whereas with the UBM, you can appreciate the structures behind the iris more clearly."
Dr. Shoan encounters other situations where UBM images can clarify what doctors are seeing on OCT. "When patients have narrow angles, we routinely do a peripheral iridotomy, and usually we can appreciate its effect nicely with OCT," he says. "But sometimes, the angle still looks narrow or closed despite the peripheral iridotomy. There might be a plateau iris configuration where something behind the iris is continuing to push it forward, but OCT doesn't image this well. UBM fills that need."
In addition to comparing UBM features side by side (See "What Are Your Choices?" below), practitioners may consider the qualities that manufacturers say differentiate their devices.
Cheng-ning Chang, principal software engineer for Accutome, explains, "The UBM Plus design is totally different from other UBMs. Like Accutome's B-Scan Plus, the UBM Plus is a fully USB device. All of the ultrasound parts except the display are inside the probe."
Jim O'Connor, marketing manager at Accutome adds, "We developed a self-contained UBM probe. A doctor or tech hooks it to a laptop and it's ready to go."
The self-contained probe design offers economic advantages, as well as portability, according to Mr. Chang. "We ensure that your hardware isn't falling behind," he says. "If you watch the PCs on the market, you know that every 6 months, the capacity doubles and the price drops. Because the UBM Plus (Figure 2) system simply includes software and a plug-in probe for your computer, you can upgrade your laptop, desktop or monitor relatively inexpensively any time you like, and you won't need to replace your entire UBM system."
Figure 2. UBM Plus from Accutome
Barry Durante, president of Sonomed, explains what sets apart his company's VuMax-II. "With proprietary image-enhancing software, the VuMax-II provides the highest image quality available for the widest range of applications, and the software capabilities and user interface are unmatched in the industry," he says. "Doctors can clearly visualize structures that, until now, they'd only seen in textbooks or in the anatomy lab."
At Quantel, national sales manager Kenneth Dickerson explains the advantages of the Aviso UBM. "Quantel offers true 25 MHz and 50 MHz linear scanning probes," he explains. "The display is unparalleled, and you can readily resize onscreen, not just to one or two fixed magnifications. Doctors are impressed with the DICOM-compatible resolution of the Aviso and with the ClearScan cover (ESI, Inc.), which provides improved ease and comfort when examining the side of the eye."
Finally, Mark Zamorski, marketing specialist at Reichert, Inc., highlights the flexibility of the Reflex UBM (Figure 3). "The Reichert Reflex is truly compact, requiring no added hardware to conduct or review an exam, and the space-saving instrument allows doctors to perform procedures in their offices they previously sent elsewhere," he says. "Users can put the Reflex on the table stand, mount it flush on a wall, or use a multiposition monitor mount. This flexibility means the unit fits into any practice, and the touch screen permits easy navigation of the Reflex's intuitive software."
Figure 3. Reichert Reflex
The use of UBMs is increasingly common among doctors who need to see behind the iris. They're usually attracted by UBM studies and then won over by the images. Manufacturers and users alike predict that UBM use will increase as more doctors are exposed to the technology.
Mr. Durante explains, "Differential diagnosis is easily accomplished with UBM. The devices have become much more user-friendly in the last 2 to 5 years, and the device's multiple capabilities for many specialties are attractive to large and small practices alike."
Mr. Dickerson agrees, adding that enhanced ease of use and financial incentives will give UBMs a boost. "The new ClearScan cover eliminates the drawbacks of the old scleral shell, or shell-and-gel technique, in terms of setup, patient comfort, procedure time, safety and sterility," he says.
"And not only is this a Medicare-reimbursable procedure, it also will help doctors better determine if and when they should refer patients."
Dr. Fram says UBM technology helps keep patients — and billable services — inside her doors. "It's amazing to have this technology. Previously, we'd have to send these cases to a university for testing. Now we can provide state-of-the-art care in the private office setting." OM
|What Are Your Choices?|
|Several ultrasound biomicroscopes (UBMs) are currently on the market, providing variety in terms of portability and features.|
• Aviso (Quantel). The Aviso has many ergonomic features to facilitate image acquisition, such as the intuitive, accessible controls and a touch screen. Its software also helps technicians make measurements, marks and comments.
Two proprietary software features, Cineloop and Varigain, provide automatic image recording and adjustable gain on images, respectively. The Aviso is also portable, so eyecare practitioners can move it between clinics if necessary.
• Reflex UBM (Reichert). Reichert describes the Reflex as "ultra-compact" and "ultra-easy." These terms reflect the device's compact size and easy setup, as well as its touch-screen interface for analysis tools (a keyboard and mouse are also included). Like many new devices, the Reflex has software tools designed to make data and measurement acquisition achievable without extensive training.
The probe design of the Reflex enables technicians to perform the scan without a water bath, while the patient sits or reclines, and a foot pedal enables hands-free image acquisition. The Reflex has a 35 MHz or 50 MHz transducer. The Reflex records 60 seconds of data per eye and six images per scan, and users can export files in AVI, JPEG or DICOM formats.
• UBM Plus (Accutome). Most UBMs have a cart, an arm and a monitor, but in the UBM Plus, all of the ultrasound technology is contained in the freehand probe, which connects by wire to a laptop or desktop computer. According to the manufacturer, this eliminates signal loss for sharper images, and the device's 15-micron electronic resolution is the highest available.
The UBM Plus utilizes what Accutome calls Smooth Zoom technology, which performs 2× full image zoom either during a scan or when you review the images later. You can also capture 34-second film loops.
Doctors can use built-in report templates, easily print or share information, and store images compactly. Accutome continually enriches its software and works to make the UBM Plus easy to use.
• VuMax-II UBM (Sonomed). The PC-based VuMax-II system has an 18.5-mm × 14-mm deep scanning field to capture the entire anterior segment in one scan, which enhances intraocular measuring. Technicians can take 45-second video, adjusting features, such as gain, TGC, contrast, zoom and freeze. The UBM also exports both AVI and JPEG file formats.
Like all imaging devices today, UBMs require the right software to help doctors interpret vast amounts of data. For the VuMax-II, this includes software, such as post-processing tools, auto measuring and image-enhancing focus software. In addition, the VuMax-II's handpiece can be used with a 35 MHz or 50 MHz transducer.
Optometric Management, Issue: July 2009