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Advances in OCT technology revolutionize ocular analysis, examination
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Continual advances in optical coherence tomography software and technology, specifically in the areas of resolution and scan depth, are helping eye care providers collect more information and ultimately deliver better patient care.
“With OCT today, we can penetrate deeper into the retina and below it, into the choroid, and we can take measurements. We’re now getting information about choroidal structure that we’ve never had before,” Primary Care Optometry News Editorial Board member Jerome Sherman, OD, FAAO, said in an interview. “A thin choroid is often revealed in high myopia and in older patients. A proposed new clinical entity, age-related choroidal degeneration, can explain visual complaints in a patient with a normal retina.”
“We’re moving from an era of qualitative to quantitative assessment,” Carmen A. Puliafito, MD, MBA, co-developer of OCT, said at the Optical Coherence Tomography and Imaging: Panel Experts Review meeting. “Most eye care providers use OCT in an extraordinarily qualitative way, because when we had six images we were looking at things qualitatively. Right now, most of us don’t use the full potential of the device.”
Eye care providers are also able to get information about the ganglion cells. “It is now possible to measure the thickness of ganglion cells, or the ganglion cell complex (GCC or GCA), which is important for glaucoma detection,” Sherman said.
“We can get a cross section of the retina — and with the improvements in resolution and software, we’re able to segment out various layers of the retina,” he continued. “If we can segment out and measure just the ganglion cells, we obtain qualitative data about all optic nerve diseases, including glaucoma, and myriad nonglaucomatous optic neuropathies as well.
With the latest version of spectral-domain OCTs, choroidal measurements are now becoming possible, resulting in identification of previously unrecognized disorders such as age-related choroidal degeneration..
Image: Sherman J
“The hardware and software just keeps improving. Every new version seems to have better resolution, and the better the resolution, the more you see, and the more you see, the more you can detect and diagnose,” Sherman said. “Many retinal disorders are invisible to ophthalmoscopy but not invisible to SD-OCT.”
According to Puliafito, the development of retinal pharmacotherapy helped motivate the widespread use of OCT imaging.
“When OCT [first came out] there was no retinal pharmacotherapy,” he said. “Treatment of macular disease was essentially observational or laser photocoagulation. 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 are literally tens of thousands of OCT units around the world.”
Platform capabilities, advantages
OCT platforms cannot be used interchangeably because the hardware capabilities and software algorithms of the devices vary, Puliafito said.
Before committing to a particular platform, eye care providers should consider ease of operation, content of test reports and additional features of the device, such as the capabilities of fluorescein angiography and fundus photography, Joel S. Schuman, MD, FACS, 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 quantification of tissue thickness of lesser importance,” he said.
Jerome
Sherman
According to Robert W. Dunphy, OD, FAAO, the combined use of confocal scanning laser ophthalmoscopy and OCT allows optometrists to reliably identify a host of clinical findings that greatly enhance their ability to diagnose and manage a wide variety of clinical problems.
“With reliable qualitative image information and quantitative biometric information, optometrists are able to generate more refined diagnoses for their patients and, once diagnosed, to stratify their patients to identify those who need prompt intervention and those who are candidates for surveillance to identify change over time,” Dunphy said.
The image data, he said, can also help to educate patients on their condition, which makes it easier for doctors to present treatment options.
“Patients are happier when they better understand the diagnostic and therapeutic process,” he said.
Also, Dunphy added, during treatment optometrists can use the image data to assess the patient’s response.
Robert W.
Dunphy
Sherman said that optometrists need to recognize that new OCT systems can provide information that ophthalmoscopes cannot, such as direct or indirect information about the photoreceptors.
“When you pick up an ophthalmoscope, you can’t see rods and cones, which are arguably the most important part of the retina,” he said. “Spectral domain OCT allows us to observe the photoreceptor integrity line or PIL (a.k.a. IS/OS junction or ISe), the biomarker for photoreceptor integrity. That’s very important in the diagnosis of a whole series of outer retinal diseases.”
OCT 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 being 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 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.”
Joel S.
Schuman
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.”
Future applications
Advances in OCT 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 an 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, he said. The swept-source OCT platform also has a longer wavelength of approximately 1,000 nm.
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 after 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.
Carmen A.
Puliafito
“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 advance 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 both en face and cross-sectional views 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.”
Color fundus photograph (1) of left macula demonstrating pigment epithelium irregularity. CSLO fundus autofluorescence image (AF) demonstrating characteristic circular regional alteration of the autofluorescence pattern, suggesting outer retinal and pigment epithelial complex abnormality.
Puliafito said he sees OCT imaging evolving in two directions, as both a ubiquitous device and a comprehensive tool that will someday replace ophthalmoscopy.
“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.
On the top spectral domain OCT image, e left macula inferior to the fovea demonstrating atrophic photoreceptor outer segments overlying a region of clear subretinal fluid with the lamellar structure beneath the retinal pigment epithelium consistent with chronic class type 1 choroidal neovascular membrane and consequential serous macular detachment. A detailed of image of the infrared cSLO image demonstrating detachment of the retinal pigment epithelium, revealing Bruch’s membrane with lamellar detail beneath the pigment epithelium and consistent with choroidal neovascular membrane.
Images: Dunphy R
“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 handheld 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 Daniel R. Morgan and Ashley Biro
References
Kotowski J, et al. Ophthalmic Surg Lasers Imaging. 2011;doi:10.3928/15428877-20110627-01.
Nadler Z, et al. Optom Vis Sci. 2012;doi:10.1097/OPX.0b013e31824f164d.
Wang M, et al. J Glaucoma. 2012;doi:10.1097/IJG.0b013e318264b941.
For more information:
Carmen A. Puliafito, MD, MBA, can be reached at Office of the Dean, Keck School of Medicine, University of Southern California, 1975 Zonal Ave., KAM 500, Los Angeles, CA 90033; (323) 442-1900; cpuliafito@usc.edu.
Joel S. Schuman, MD, FACS, can be reached at Department of Ophthalmology, UPMC Eye Center, 203 Lothrop St., Suite 816, Pittsburgh, PA 15213; (412) 647-2205; schumanjs@upmc.edu.
Jerome Sherman, OD, FAAO, can be reached at: SUNY, 33 West 42nd St., New York, NY 10306; (212) 938-5862; j.sherman@sunyopt.edu.
Gadi Wollstein, MD, can be reached at Department of Ophthalmology, UPMC Eye Center, 203 Lothrop St., Suite 834, Pittsburgh, PA 15213; (412) 647-0325; wollsteing@upmc.edu.
Disclosures: Dunphy receives speaker’s honoraria from Heidelberg Engineering and Optos and support in kind from Optos, Optovue and Heidelberg, and is a member of the Optovue advisory panel. Puliafito receives grant and research support from Carl Zeiss Meditec. Schuman receives royalties for intellectual property licensed by MIT and MEEI to Carl Zeiss Meditec. Sherman has received support from Topcon, Zeiss and Optovue. Wollstein is a consultant for Allergan.