Continual OCT advancements revolutionize ocular analysis, examination

The invention of optical coherence tomography has had an impact on the eye care world. Ophthalmologists are able to identify and recognize more details than ever before, resulting in fewer errors and more awareness of clinical success.

Multiple platforms have been developed for OCT imaging. Each platform offers its own advantages and capabilities, with new developments under way in laboratories across the world. Continual advances in software and technology help keep OCT relevant to the ever-changing world of ophthalmology.

According to Carmen A. Puliafito, MD, MBA, OSN Retina/Vitreous Section Editor and co-developer of OCT, the development of retinal pharmacotherapy helped explode the widespread use of OCT imaging.

“When OCT started, really there was no retinal pharmacotherapy. Treatment of macular disease was essentially observational or laser photocoagulation,” Puliafito said. “It became apparent to us after the introduction of photodynamic therapy that OCT was ideally suited for monitoring retinal pharmacotherapy. And that’s really the reason why there’s literally tens of thousands of OCT units around the world.”

Platform capabilities, advantages

The first OCT device was conceived in a laboratory more than 20 years ago at the Massachusetts Institute of Technology. Carl Zeiss Meditec initially commercialized OCT technology for ophthalmologists, and since then, several other companies have produced OCT technology for ophthalmologists.

OCT platforms cannot be treated interchangeably because the hardware capabilities and software algorithms of the devices vary, Puliafito said.

Competition among companies has led to the growth of OCT platforms, Peter K. Kaiser, MD, OSN Retina/Vitreous Board Member, told colleagues in a presentation at the Optical Coherence Tomography and Imaging: Panel Experts Review (OCTIPER) in Las Vegas.

“Competition in anything is good because that pushes all the companies to become better and to improve their software, and that’s good for us and good for our patients,” he said.

At OCTIPER, Kaiser presented a comparison of currently available spectral-domain OCT (SD-OCT) hardware, including wavelength, scanning depth, axial resolution, scanning speed and any available ancillary imaging.

The Bioptigen Envisu Spectral Domain Ophthalmic Imaging System (SDOIS) has a wavelength of 840 nm, a scanning depth of 2.5 mm in the retina, an axial resolution of 3 µm, and a scanning and display speed of 32,000 axial scans per second.

An advantage of this platform, Kaiser said, is the ability to change the head of the scanning system.

“You can use the traditional table mount of the device,” he said. “More importantly, you can use a portable mount to image kids. You can take this into the [neonatal intensive care unit]. You can also take this into the operating room and image macular surgery cases.”

The Carl Zeiss Cirrus HD-OCT has a wavelength of 840 nm, a scanning depth of 2 mm, an axial resolution of 5 µm, and a scanning speed of 27,000 axial scans per second.

Kaiser called the Cirrus a ubiquitous device and said that it offers high-resolution noise reduction, the ability to pseudo-register images, and software to look at drusen and atrophy mapping for dry age-related macular degeneration. Ganglion cell layer mapping is also available, as is FastTrac, a retinal tracking system introduced at the American Academy of Ophthalmology meeting in Chicago.

The Heidelberg Spectralis OCT has an OCT wavelength of 870 nm, a scanning depth of 1.9 mm, an axial resolution of 7 µm, and a scanning speed of 40,000 axial scans per second.

The Spectralis is a multi-modal system that offers confocal scanning laser ophthalmoscopy (cSLO) fundus imaging. It can be upgraded to include any combination of fluorescein angiography (FA), indocyanine green (ICG) angiography, blue laser fundus autofluorescence or MultiColor imaging. Because the device allows for multi-imaging with pinpoint registration, Kaiser said he currently uses the Spectralis to explain to his dry AMD patients why they are losing vision.

“If you’re not really sure about what something is, Spectralis allows you to look at things multiple different ways to figure out exactly what it is,” he said. “It also has the ability to do wide-angle shots, in either a montage or with the use of special lenses to get peripheral views.”

Another capability of Spectralis is TruTrack, an active eye tracking system that simultaneously images the eye with two beams of light, according to Heidelberg’s website.

The Optos OCT SLO has a wavelength of 830 nm, a scanning depth of 2 mm and an axial resolution of less than 6 µm, according to the Optos website. Opko sold its ophthalmic instrumentation business to Optos in 2011.

The Optovue RTVue Vtrac Premier device has a wavelength of 840 nm, a scanning depth of nearly 3 mm, an axial resolution of 5 µm, and a scanning speed of 26,000 axial scans per second. The Optovue RTVue XR offers a wavelength of 840 nm, a scanning depth of nearly 3 mm, an axial resolution of 5 µm, and a scanning speed of 70,000 axial scans per second. Both Optovue devices have an anterior segment attachment; both corneal and anterior lenses have an axial resolution of 5 µm.

The Canon platform has a wavelength of 850 nm, a scanning depth of 2 mm, an axial resolution of 3 µm, and a scanning speed of 52,000 axial scans per second.

Kaiser said this platform is a high-resolution device that has not yet been approved by the U.S. Food and Drug Administration. He said new versions of this platform will have dramatic improvements in axial resolution.

Nidek also offers OCT technology that is not available in the United States.

Both the Topcon 3D OCT-2000 and 3D OCT-2000 FA have a wavelength of 840 nm, a scanning depth of 2.3 mm, and an axial resolution of 5 µm to 6 µm. The OCT-2000 FA has a scanning speed of 50,000 axial scans per second, whereas the OCT-2000 has a scanning speed of 27,000 axial scans per second.

The Topcon platforms can also take color fundus images. Kaiser said the system offers drusen and atrophy mapping, as well as an algorithm for conducting drusen analysis.

Before committing to a particular platform, ophthalmologists should consider ease of operation, content of test reports and additional features of the device, such as the capabilities of FA and fundus photography, Joel S. Schuman, MD, FACS, OSN Glaucoma Board Member and another co-developer of OCT, said.

“A glaucoma-based practice that is interested in the most accurate and reproducible measurements might be interested in a certain device, while a retina-based practice that is mostly interested in qualitatively visualizing the macula may find precise quantitation of tissue thickness of lesser importance,” Schuman said.

Evolution of OCT imaging

The first OCT device was a time-domain system that served as the basis for the Stratus OCT (Carl Zeiss Meditec), which, according to Puliafito, was the dominant platform in the first 10 years of widespread use of OCT.

Time-domain OCT uses an interferometric technique with a varying path length reference arm to measure depths in the eye. This technique has rapidly evolved since its debut in the mid-1990s, particularly with the advent of high-speed scanning with Fourier-domain OCT.

“I think we’re moving from an era of qualitative to quantitative assessment,” Puliafito said at OCTIPER. “Most ophthalmologists use OCT in an extraordinarily qualitative way because, really, when we had six images from the Stratus OCT, we were looking at things qualitatively. Right now, most of us don’t use the full potential of the device.”

Advances on the horizon include increased scanning speed, a change in wavelength, the use of OCT as a primary imaging tool, and the potential of combining OCT with angiography, Puliafito said in a subsequent interview.

Increased scanning speed is obtainable through the use of swept-source OCT, a laser system that is smaller than most OCT devices and can have high scan speeds of more than 100,000 axial scans per second. The swept-source OCT platform also has a longer wavelength of approximately 1,000 nm.

Fourier-domain OCT devices have a similar light source and wavelength compared to swept-source OCT.

Faster scanning speeds and a longer wavelength will allow for greater sampling and more averaging of data. Puliafito said the device allows clinicians to look at specific coordinate points in images on subsequent occasions following data collection.

The swept-source platform eliminates the use of the spectrometer and is more straightforward to use than current OCT platforms, he said; however, swept-source lasers are expensive and are not yet readily available.

“You want to have systems that can be manufactured at a relatively low cost so they can be widely dispersed,” he said.

Puliafito said another advancement to expect in future OCT platforms is the ability for panoramic images. He said this will be most beneficial for imaging patients with widespread changes and a wide variety of peripheral diseases, such as diabetic retinopathy.

“Imagine having OCT not only as a cross-sectional study device of the small area of the macula, but OCT as a comprehensive tool for essentially creating a comprehensive both en face and cross-sectional view of the retina,” he said. “That’s really the ideal case for retinal imaging of the future, and the power of that would really alter the dynamic of OCT in the office.”

OCT advances in glaucoma

The ability of SD-OCT to detect glaucoma progression has increased over time, Schuman said, but limited correspondence still exists with visual field progression.

“Disease progression can be detected with SD-OCT in the peripapillary region when sampled along a circle that is centered around the optic nerve head or when comparing the peripapillary retinal nerve fiber layer thickness throughout the scanning region, not confined to the sampling circle, with prior scans,” he said.

The macula is another area where glaucoma progression can be detected, Schuman said, especially when examining ganglion cell layer thickness.

Future improvements in glaucoma detection through OCT imaging will be accomplished through hardware and software advances and the use of enhanced statistical methods, according to Gadi Wollstein, MD.

“True progression needs to exceed the inherent measurement variability of the device in order to be detected,” he said. “Better measurement reproducibility would allow detection of disease-related changes at an early stage.”

Wollstein said possible hardware improvements include a higher resolution and scanning speed, thus resulting in highly detailed information of the scanned area while also “minimizing eye motion artifacts.”

Possible software improvements could include more precise retinal layer segmentation and an improved registration of the scan area, especially when the damage is outside of the circular sampling area.

“The ability to use images acquired from different iterations of OCT or across different models of OCT can allow fuller and more complete use of imaging records available for each patient,” Wollstein said.

Advanced statistical models will better uncover true glaucoma progression that is masked by measurement variability, as well as incorporate additional covariates, such as age and ethnicity, consider changes that appear in different locations of the eye, and combine information from multiple technologies, Wollstein said.

“This is only a small part of the wide range of methods that are currently investigated to further improve disease progression detection,” he said.

Standardizing OCT protocols

Standardization of the OCT protocol, especially for glaucoma, is crucial for the ophthalmic community, Schuman said.

“In the absence of such criteria, many studies use different criteria for progression, and the comparison of their findings is difficult,” he said. “In glaucoma there is a fundamental requirement for the presence of structural or functional abnormalities in order to diagnose the disease.”

Schuman said standardization would be highly beneficial to clinicians and would help provide the best possible care for patients.

Due to the availability of multiple OCT platforms and the possibility of patients or physicians leaving a practice, Schuman said it often becomes necessary to establish a new baseline for patients, thus potentially reducing the relevance of the patient’s prior OCT data.

“It is indeed possible to create software that can read OCT data from any OCT device, and that can compensate for the different units used, so that measurements from one device to another are essentially interchangeable,” he said. “We have developed such software in our laboratory; however, the proprietary nature of the OCT output from different machines makes it impossible to use the software clinically.”

Although manufacturers must have a way to protect their investment, Schuman said, a method must also be developed to access all clinical information across all OCT platforms for a particular patient to help reduce the loss of data from prior testing and the additional cost of potential retesting.

“If our goal is to detect glaucoma progression as early as possible for our patients, then incorporation of all possible past OCT information is critical but currently impossible for the clinician in practice. What a shame for our patients,” Schuman said. “We must demand standardization of scan parameters and access to all patient data in a standardized format that can be analyzed across any OCT platform, both for that given scan and over time across OCT scans acquired by any device.”

Intraoperative, perioperative applications

The potential of intraoperative OCT use is growing and will potentially play a significant role in ophthalmic surgery in the future, according to Justis P. Ehlers, MD.

“I think both from an anterior segment and a posterior segment standpoint, OCT can be an important tool for the surgeon,” he said. “We are in the early stages of understanding what information is particularly important to a surgeon and how we can use this technology to improve surgical outcomes.”

Ehlers said intraoperative OCT imaging may guide surgeons’ surgical maneuvers and provide feedback on the achievement of critical surgical objectives. As intraoperative OCT continues to expand, specific diseases or procedures will likely be identified that will particularly benefit from the technology, Ehlers said.

The use of perioperative OCT imaging, particularly trans-tamponade (eg, OCT in gas-filled eyes) is also being currently studied. Ehlers said research is under way examining how OCT imaging can assess early architectural changes during the healing period after surgery. For example, the ability to achieve high-quality imaging in gas-filled eyes is crucial in definitively determining macular hole closure in the early postoperative period.

“The multiple interfaces in gas-filled eyes provide unique challenges to optimal image acquisition and quality. Improvements in scan protocols can significantly improve scan quality and provide important feedback to the surgeon, even as early as 1 hour after surgery,” Ehlers said.

Future applications

Puliafito said he sees OCT imaging evolving in two directions, as both a ubiquitous device and a comprehensive tool that will someday replace ophthalmoscopy.

“I think that if we come back 50 years from now, an automated examination of the retina will be the dominant technology, and direct ophthalmoscopic examination will indeed fall off as a significant tool,” he said.

According to Ehlers, researchers must answer the following question regarding surgical applications: “What do we need for seamless integration of OCT into our surgical practices that improves functional and anatomic outcomes?”

Some of the currently available commercial OCT platforms have been modified for intraoperative use. Other systems have been adapted for optimal use in the operating room. For example, Ehlers uses a custom microscope mount for the Bioptigen system. He said the microscope mount allows for increased stability and rapid intraoperative OCT imaging.

The success of a microscope-integrated system, Ehlers said, depends on its ability to minimally change the surgeon’s environment in terms of modifying ergonomics and view. It must also maintain patient safety.

“Patient safety is the No. 1 priority. Image acquisition efficiency is also critical so that surgeons are able to get the images quickly, so as to disrupt the surgery as minimally as possible,” he said.

Both Ehlers and Puliafito said that a comprehensive OCT device that is able to analyze patient data from the point of disease conception to the point of postoperative follow-up would be most beneficial for clinicians and patients.

“Another area of interest is OCT as a comprehensive ophthalmic evaluative system,” Puliafito said. “You would use OCT to look at things like ocular alignment, measure corneal thickness, measure the anterior chamber depth and examine the retina.”

A hand-held device that could be used on children, infants or even patients in a waiting room would also be ideal, Puliafito said.

“I believe that with the development of a more advanced computerized analysis system, it’ll actually be able to give the clinician some really practical tools to help make their clinical decisions,” he said. – by Ashley Biro

Under what circumstances would you perform OCT in contemplation of cataract surgery?

Suspected macular disease would warrant OCT

Optical coherence tomography has revolutionized the way we examine the macula, affording us a view of anatomic detail that was never before possible. Its use in evaluating epiretinal membranes, macular edema, macular degeneration and other disorders is unmistakable. In my practice, there are two roles for the use of OCT prior to cataract surgery.

First, for patients with suspected macular disease, OCT scanning can define the extent and configuration of the anatomic defect. This, combined with potential acuity testing, can help us define the visual potential in an eye with comorbidities of macular disease and cataract. In this setting of existing disease, the OCT test is billed to the patient’s insurance company or Medicare with the appropriate diagnostic code.

Second, OCT can be used as a screening tool in patients not expected to have macular disease. This is most useful for patients electing a premium lens implant, where the view of the macula can be compromised by cataract and where we want to know in advance about a subtle epiretinal membrane or other pathology that might be missed on exam.

In these patients, the unexpected presence of macular disease would be an unpleasant surprise after premium surgery. In my practice, part of the “premium package” for which patients pay with refractive cataract surgery is a preoperative OCT. It is important to remember that an OCT scan cannot be billed to insurance or Medicare solely as a screening test for macular disease. The test is only billable when an exam first confirms the presence of disease and the OCT is intended strictly to further define its anatomic extent.

John A. Hovanesian, MD, FACS, is the OSN Cataract Surgery Section Editor. Disclosure: Hovanesian has no relevant financial disclosures.

Preoperative and postoperative OCT scans vital

The use of OCT in the context of modern implant surgery has essentially become indispensable for the progressive cataract surgeon. In fact, it is difficult to imagine practicing without this technology. This is particularly true in light of the unprecedented levels of success expected by today’s cataract patients and especially those who are increasingly undergoing lens-based refractive procedures.

OCT found its way into our armamentarium originally when treating cataract patients who harbored or were suspected to have concomitant retinal disease — this being especially true for age-related macular degeneration and diabetic retinopathy, diseases frequently associated with cataract. Scanning of the macula preoperatively yielded important prognostic information and would often help guide treatment decisions. This tool was also crucial in managing patients through their postoperative courses. Today, its role has vastly expanded both in regard to patients with known retinal pathology and many without established posterior segment disease.

It is now widely accepted that Snellen acuity is but one parameter used to determine the need for cataract intervention, and surgery is increasingly based upon symptoms and interference with activities of daily living. In cases in which the cataract density and subjective complaints do not appear to correlate, OCT testing preoperatively can be extremely useful. Similarly, when postoperative results are not at an expected level, clinical examination and scanning of the macula are indicated.

With improvements in IOL designs and refined refractive outcomes, implant surgery has evolved into a legitimate refractive option, especially for correction of high degrees of ametropia (wherein keratorefractive surgery may not be appropriate) as well as for presbyopia. OCT testing preoperatively in this demanding patient population is important to rule out subtle pre-existing macular pathology and can detect postoperative issues such as cystoid macular edema that may be contributing to less-than-optimal results.

Louis D. "Skip" Nichamin, MD, is an OSN Cataract Surgery Board Member. Disclosure: Nichamin has no relevant financial disclosures.