Scanning the Future of OCT

Despite reimbursement cutbacks, OCT technology is expected to diversify, leading to expanded use in practice.

By Sean McKinney, Contributing Editor

As OCT continues its rapid evolution, some experts wonder if cuts in Medicare reimbursement for OCT scans will stifle future innovations. The 2011 Current Procedural Terminology codes for Scanning Computerized Ophthalmic Diagnostic Imaging require a single reimbursement for two eyes (instead of the single-eye reimbursements of the past) and disallow the application of OCT for retina and optic nerve evaluation during the same patient visit. (See “New CPT Codes for OCT.”) David Huang, MD, PhD, a co-inventor of OCT, says these changes could reduce reimbursements by 50 to 60%.

“OCT has been in a virtual cycle—more applications leading to a larger market, leading to more research, leading to better technology,” says Dr. Huang, the Weeks Professor of Ophthalmic Research and Professor of Ophthalmology and Biomedical Engineering, Casey Eye Institute, Oregon Health and Science University, Portland, Ore. “Now, the clamp on reimbursements may limit innovation. There will be more of a gap between the laboratory and the patient care environment in the future.”

Nonetheless, Dr. Huang says cutbacks can't reverse OCT's surging growth. By 2009, 17,000 OCT units had been put into service, representing $1 billion in sales, he notes. The number of scans paid for by Medicare per year increased from $1 million in 2001 to nearly $7 million by 2008, far surpassing the number of reimbursed fundus photographs and fluorescein angiograms, Dr. Huang adds.

“I think we can cope. The systems will need to be less expensive, easy to use and have many functions. OCT will continue to expand,” he says.

Many doctors and industry insiders share this belief that practitioners and the market will adapt at this critical juncture.

Driving Rapid Evolution

OCT generates high-resolution, cross-sectional and three-dimensional (3D) images of the retina and anterior segment of the eye. The technology operates analogously to ultrasound except that it uses interferometry to measure the echo time delay of backscattered light, according to James G. Fujimoto, co-inventor of OCT and a professor of electrical engineering at the Massachusetts Institute of Technology. Professor Fujimoto says the technology draws upon advances in photonics such as broadband lasers, frequency swept lasers and line-scan cameras. State-of-the-art OCT systems have imaging speeds hundreds of times faster than previous-generation technology, acquiring comprehensive volumetric data and enabling 3D visualization of pathologies in a manner similar to MRI and CT.

The original form of OCT, time domain (TD-OCT), captures one pixel at a time and acquires 400 axial scans per second. Most manufacturers now produce newer spectral domain (SD-OCT) devices (also known as Fourier domain (FD-OCT), high definition (HD-OCT) or 3D-OCT). These much faster units can capture roughly 2,000 pixels simultaneously and perform 20,000 to 40,000 axial scans per second, eliminating the motion artifact that is commonly seen in TD-OCT images, Dr. Huang says.

Researchers are now advancing beyond spectrometer-based technology with systems that use different wavelengths and operating principles. For example, swept-source OCT, at 1050 nm, can provide speeds of up to 40,000 axial scans per second.¹ This speed allows full 3D volumetric scanning over a 12 mm x 12 mm area of the retina.² Tomey, Cannon and Bioptigen are awaiting FDA approval of this type of OCT technology for use in clinical practice.

“These scans provide tremendous detail over a broad area,” Dr. Huang says. “At longer wavelengths, you have less scattering and enhanced penetration through cataract and the retinal pigment epithelium. You can achieve imaging of the choroid in both hyperopes and emmetropes.”

There is a growing trend toward the use of OCT in the operating room. For example, the newer portable iVue FD-OCT (Optovue, Inc.) has been deployed on a surgical stand during procedures to correct Peter's anomaly (congenital and corneal lenticular opacity), Dr. Huang says. He adds that OCT is also being explored as a method of visualization during femtosecond laser cataract surgery and vitreoretinal procedures.

Expanding Applications

The use of OCT increased as growing numbers of patients were treated for wet AMD with anti-VEGF therapies. “Injection with anti-VEGF once a month can be a daunting prospect for patients,” says Dr. Huang. “OCT is used on a regular basis as a high-volume application to assess results of previous treatments and determine when other treatments are needed.”

OCT scans are also used to help clinicians manage other types of retinal disease, as well as glaucoma and disorders of the anterior segment. For most OCT units, a special adaptive unit, or module, is used to scan the cornea and external structures of the eye.

“Doppler OCT for retinal angiography and blood flow measurement is an emerging area that is still under investigation,” says Brian A. Francis, MD, MS, an associate professor of ophthalmology at the Doheny Eye Institute, Keck School of Medicine, University of Southern California. “This has fascinating potential to improve standards of care, possibly allowing us to measure retinal blood flow in diabetic retinopathy, retinal vein occlusion, neuro-ophthalmology and glaucoma. For example, a certain number of patients are likely to have compromised blood flow or deficient autoregulation in the optic nerve, especially in low-tension glaucoma. Cross-sectional studies can evaluate glaucoma suspects, those with glaucoma and normals. Longitudinal studies can evaluate the effect of medical therapy and surgical pressure lowering on blood flow. We may find, through the use of doppler OCT, that some IOP-lowering therapies also decrease retinal circulation and are counter-productive.”

Focusing on Glaucoma

In 2003, it was found that macular imaging was less sensitive and specific in detecting disease than imaging the circumpapillary retinal nerve fiber layer (RNFL).^3,4 Breakthroughs in using OCT to recognize glaucoma occurred when investigators began to use the 3D SD-OCT to measure sublayers in macular scans. They were able to detect glaucoma with high sensitivity and specificity, measuring retinal layers most affected by glaucoma, including the nerve fiber layer, ganglion cell layer and inner plexiform layer, otherwise known as the ganglion cell complex (GCC).^5,6

E. Randy Craven, MD, a glaucoma specialist in Denver, says the Optovue and Cirrus SD-OCT units have contributed significantly to the improvement of his glaucoma practice. “We now have much better nerve imaging that complements the Heidelberg Retinal Tomograph (HRT),” he notes. “The new SD-OCT has nerve topography that looks similar to what we are used to seeing when looking at the HRT. We now have both cup parameters, such as those provided by HRT, and RNFL, as provided by the Zeiss GDx VCC Retinal Scanner and TD-OCT. You can now look at the nerve and the nerve fiber layer together. So, if you see a notch and bundle defect, it is really useful.”

Of particular value is the GCC analysis. “This feature helps to detect disease early. There are software upgrades that allow you to have several scans in a row and use a glaucoma progression analysis to detect change,” says Dr. Craven. “This is analogous to the Humphrey Field Analyzer's statistical package (STATPAC) and Guided Progress Analysis (GPA) on the field machines.”

Meanwhile, Dr. Craven says Visante OCT (Carl Zeiss Meditec), with its wide-field scanning capability, “can really help image the anterior segment. They are working on a Visante with spectral domain. This will provide better resolution to see the iris and angle details.”

He believes most of the changes in OCT during the next year will relate to network links and “structure vs. function” options associated with visual fields.

“The other software improvements will align with disease normative data, such as the abnormal image correlation with a specific disease,” he says. “We'll be looking at the likelihood of cup asymmetry being abnormal. The other consideration is the impact of reimbursement reductions for OCT. Practitioners will need to determine if it's better to share a new OCT with other providers to reduce the cost.”

No More One-size-fits-all

On the industry side of the OCT market, manufacturers offer insights worth considering. Rishard Weitz, executive vice president of Opko, says recent innovations compel prospective OCT buyers to ensure they acquire units that are appropriate for their practices. The days of one-size-fits-all OCT are over.

“High-end OCT, with lots of clinical features, will cost more. Low-end OCT, with limited functions, primarily for the OD market, will be very affordable,” says Weitz. “Because of these distinctions, we will see further development of two tiers of the OCT market.”

Many OCT manufacturers are broadening their focus to include the anterior segment. Optovue has the RTVue-CAM (Corneal Adapter Module), which, like other OCT units that have been adapted for corneal exams, can be used for assessment of both corneal flap thickness and residual stromal thickness following LASIK, measurement of corneal thickness, visualization of intraocular lenses and other implants in the anterior segment, evaluation of several anterior segment ocular structures. It's also the only unit to measure anterior chamber angles. Special software from Optovue that can be used to calculate IOL powers for patients with corneas that are irregularly shaped from LASIK, keratoconus or other issues has been submitted for FDA approval.

Optovue marketing director Peter Naismith says more ophthalmologists use OCT for a growing list of tasks in anterior segment, including the documentation of angles before and after iridotomies. “This can help if you are audited,” says Naismith. “The OCT scans can prove the effectiveness of the procedure.”

Maximizing Value

When deciding which OCT to purchase, Robert Gibson of Topcon, Oakland, N.J., recommends looking for a good return on investment. His company is offering a unit that allows higher billing in many states because it combines color fundus photography with an OCT scan. (See “OCT Update,” below)

“Now that OCT reimbursement has been cut in half, doctors should carefully consider if their patient volume is sufficient to justify the purchase of an OCT,” he says.

Marianne Whitby, senior marketing manager at Carl Zeiss Meditec Inc., Dublin, Calif., believes doctors need to be confident that their OCT provides accurate analysis and excellent visualization for detection of disease and tracking of change. “With the 6 mm x 6 mm cube of data captured by Cirrus HD-OCT, the data can be viewed, segmented and measured in various ways to provide visualization and understanding of the retinal condition,” she says. “Efficiency and ease of use are also important. With patient loads increasing, and with possible staff turnover, you need an imaging instrument that does not require a highly skilled operator. You need something easy to learn and easy to use.”

She notes that backward compatibility of new applications should be considered. “Can the newest applications make use of the data that you have already captured?” she asks. “Will the data you are capturing now be used in future analysis applications? Make sure you get these answers before buying.”

In the future, Whitby says new therapies in the research pipeline will increase the need for tools to help doctors identify and monitor early stages of disease. “For example when there are treatments for dry AMD, the comprehensive eye care doctor will want to monitor patients and determine when they need treatment or referral,” she says. “SD-OCT is quickly becoming the standard of care for retina and glaucoma detection and management.”

In addition, she says, cataract/refractive surgeons better understand the benefits of assessing the back of the eye before surgery. “Knowing the condition of the retina helps the doctor set appropriate expectations and allows for fewer post-surgical surprises,” she adds.

Continued Expansion

In the year ahead, Eric L. Buckland, PhD, CEO of Bioptigen, believes the applications of OCT will continue to grow as the clinical utility for diagnosing disease extends to direct support of therapeutic interventions. “Look for more experimentation with OCT-guided surgery, and for more deep-imaging OCT to support the refractive correction and cataract fields,” he says.

He also foresees software becoming easier to use while providing more analytic functionality for the clinician. “Robust mechanical designs and handheld imaging devices will continue to evolve, allowing clinicians to take OCT imaging to the patient. This will prove particularly useful in cases involving the very young, the wounded and the disabled,” he says.

Meeting Comprehensive Needs

Michael Jacobs, MD, owner of Athens Eye Associates of Athens, Ga., uses his Cirrus 4000 from Carl Zeiss Meditec to manage glaucoma and retinal patients. The findings of scans, combined with other aspects of his exams, can also determine whether he refers a patient to a retina specialist.

“I can detect early AMD and also determine if someone will benefit from surgery,” he notes. “The retina physician is happy because he or she is going to see patients who really need help. I can refer with certainty instead of basing my referral on suspicions that may or may not be confirmed.”

In his comprehensive practice, Dr. Jacobs says OCT helps in the treatment of diabetic retinopathy and AMD, among other conditions. He is like many clinicians who are now using OCT to look for structural optic nerve head changes prior to development of visual field loss.

“What helps me the most is the RNFL deviation map, which can detect subtle changes that are not picked up in the clock hours and quadrants of the scans,” says Dr. Jacobs. “If a defect is straddling two clock hours and there is not enough of the defect in either clock hour to trigger a change in color, I won't see any changes. Subtle findings in the RNFL might heighten my suspicions in the setting of previously normal clock hours or normal visual fields, prompting me to follow certain patients more closely. Our goal, of course, is to diagnose and treat glaucoma before the onset of visual field defects.”

Match Made in Heaven

“OCT and the eye are a match made in heaven,” concludes Dr. Huang. “The eye has very thin layers—the retina and cornea—and clear media that allow for the penetrating effects of the high-resolution light of OCT. That is why from the beginning, the retina and cornea have been the primary targets of OCT research and also why this trend will continue with further developments in the future.” OM

References

1. Potsaid B, Baumann B, Huang D, et al. Ultrahigh speed 1050nm swept source/Fourier domain OCT retinal and anterior segment imaging at 100,000 to 400,000 axial scans per second. Opt Express 2010;18:20029-20048.
2. Chen Y, Burnes DL, de Bruin M, Mujat M, de Boer JF. Three-dimensional pointwise comparison of human retinal optical property at 845 and 1060 nm using optical frequency domain imaging. J Biomed Opt 2009;14:024016.
3. Guedes V, Schuman JS, Hertzmark E, et al. Optical coherence tomography measurement of macular and nerve fiber layer thickness in normal and glaucomatous human eyes. Ophthalmology 2003;110:177-189.
4. Medeiros FA, Zangwill LM, Bowd C, Vessani RM, Susanna R, Weinreb RN. Evaluation of retinal nerve fiber layer, optic nerve head, and macular thickness measurements for glaucoma detection using optical coherence tomography. Am J Ophthalmol 2005;139:44-55.
5. Tan O, Chopra V, Lu AT, et al. Detection of macular ganglion cell loss in glaucoma by Fourier-domain optical coherence tomography. Ophthalmology 2009;116:2305-2314.
6. Tan O, Li G, Lu AT, Varma R, Huang D, Advanced Imaging for Glaucoma Study Group. Mapping of macular substructures with optical coherence tomography for glaucoma diagnosis. Ophthalmology 2008;115:949-956.