Nevertheless, anterior segment OCT does have the advantage of being noncontact. Tumor vasculature is very sensitive to radiation treatment, making OCT angiography a useful measure of treatment effectiveness.”, “The added benefit of using OCTA in the anterior segment is still being investigated,” says Dr. Schuman. Gonioscopy is critical when deciding whether or not an iridotomy should be performed. Optovue uses optical coherence tomography (OCT) to perform SCODI-A with iVue ®, iScan™ and Avanti™. I explain why we do an iridotomy and how it works. “Anterior segment OCT can be very helpful if you want to know whether an angle is going to close in the dark,” Dr. Schuman points out. Not surprisingly, many optometrists now use it to help them … 25 Ways to Maximize Your Cataract Outcomes, 37 Ways to Get Great Outcomes with Torics, Antibiotics & Cataract Surgery: New Frontiers. Areas in which anterior segment OCT is showing promise include evaluation of the angle in glaucoma patients; evaluation of the cornea in refractive surgery patients—particularly LASIK patients; measuring the anterior chamber for certain phakic intraocular lenses; and as an adjunct in other operations involving the cornea, such as PTK and corneal transplants. If an angle looks occludable to me by gonioscopy, I do the Visante as a confirmation. Part of the Essentials in Ophthalmology series, this atlas is designed to comprehensively cover optical coherence tomography of the anterior segment of the eye.The aim is to improve knowledge of the fundamentals of OCT technology for anterior segment, clarify the differences with posterior segment OCT and emphasize the immense relevance and usefulness that anterior segment OCT … Anterior segment OCT is rapidly becoming a valuable tool for managing some glaucoma patients. Anterior segment optical coherence tomography has become an important tool for evaluating the cornea and anterior segment or front portion of the eye. An anterior segment OCT is exactly what it sounds like. However, surgeons can’t use AS-OCT to perform indentation to try to open narrow angles to assess for peripheral anterior synechiae. Here, three experts share their advice on making the most of this technology in the clinic, and offer a glimpse into other uses for anterior chamber OCT that are being developed. (We think that area will be important going forward, in terms of making clinical decisions regarding a patient’s stem cell capacity, which will have implications for corneal transplants and other procedures.) Cross-sectional tissue images of these ocular structures can be generated in vivo, for detailed analysis. “Anterior chamber OCT scans spot-by-spot, so until you have a very fast system, or a parallel system, it doesn’t cover as much area as quickly as some of the other technologies,” says Dr. Huang. “It also has a wide field of view; some systems can scan a 20-mm area. “I think UBM should be limited to situations where you really need penetration, such as when you want to look through a uveal or iris tumor or evaluate a ciliary body problem. Furthermore, OCT usually shows more angle closure than gonioscopy, so treatment decisions can’t be based on imaging alone. Of course, it only provides a structural assessment, not a functional assessment—it doesn’t tell you anything about the consequences of an angle narrowing, such as how much the IOP rises as a result. Another general area of potential use is as a pre- and postsurgical evaluation tool for of AC procedures. “I consider Visante to be an adjunct. A lot of the value of gonioscopy at this point lies in revealing things that imaging can’t reveal. Ptosis or a Different Diagnosis: Asking the Right Questions Before Treatment. It’s just that the utility of this technology hasn’t yet been fully exploited. You can do an anterior segment-OCT with the lights off, if your environment will permit that, and determine how much the angle closes. I also think—and this is anecdotal—that it provides a more physiologic assessment of the angle structure.”, Dr. Radhakrishnan agrees. “Currently, the images tend to be filled with artifacts because the vasculature is in so many planes,” he says. Anterior segment OCT is a relatively new technology, and hardware and software updates continue to be unveiled. Figure 2: … “I see a lot of people measuring depths such as opacity depth on OCT cross-sections incorrectly,” notes Dr. Huang. Now, it’s proving its usefulness as a tool for evaluating the anterior segment as well. This form of OCT eye test is performed to … “When you combine anterior topography, posterior topography, the epithelial map and the pachymetry map, corneal OCT provides comprehensive information about the cornea, and it can pick up very subtle changes,” says Dr. Huang. I do think there will eventually be a paradigm shift. “In my opinion, all patients deserve to have gonioscopy done at least once in their lives,” he says. “Studies have shown that about 25 percent of angles still look narrow after an iridotomy. “However, this is now changing. “Those capabilities have to do with what you can see, rather than the openness or closedness of the angle,” he explains. For example, if you want to diagnose forme fruste keratoconus with the existing corneal mapping software that’s available in the United States, you’ll be looking for epithelial and pachymetric thinning patterns that are different from the patterns you see on topography. Purpose. Its capabilities allow for non-contact imaging, detailed visualization and analytics of anterior segment structures of … As clinicians and scientists explore new and expanded applications for this technology, it will likely become a mainstay of clinical practice. Reproduction in whole or in part without permission is prohibited. ASOCT uses a higher wavelength 1310 nm 5. “I use it both before and after surgery,” he explains. So you’ll have to take a course or read up on it to learn to do that.”. At the practical level, the important factor is simply whether the angle is open, closed or occludable.”, However, Dr. Radhakrishnan admits that she uses the quantitative tools with a few patients. Obviously it can be done, since it’s already possible using instruments available outside the United States.”, Dr. Huang notes that anterior segment OCT angiography is still embryonic, with only a few publications relating to it. “That’s a big advantage of anterior segment OCT: It gives you a more objective measure of the structure of the front of the eye. Posterior segment OCT uses a lower wavelength of light at 830 nm 3. Dr. Huang says this is especially valuable in a patient who has had a lot of regression. Anterior segment optical coherence tomography (AS-OCT) is a form of OCT technology that has been adapted for clinical care and scientific research of ocular surface and anterior segment diseases. I think it’s in a sweet spot in terms of resolution and field of view.”, Vikas Chopra, MD, medical director of the Doheny Eye Centers Pasadena, and an associate professor of ophthalmology at the David Geffen School of Medicine at UCLA, notes other advantages. It will just take a little longer to catch on.”. Dr. Schuman makes a related point. “I also use it before any retreatment to look at the flap thickness and rule out ectasia,” he says. “Most surgeons just scan right across the eye, with the eye looking straight ahead,” he says. It also requires some light to visualize the angle.”, Drs. Ever since it first appeared, optical coherence tomography has been evolving. “There are various mathematical formulas to determine the actual space between the iris and the trabecular meshwork and the shape of that space,” he says. Try different positions, so you can get the best possible image.”, • Remember to apply the de-warping software correction to depth measurements. • When performing cataract surgery. “UBM allows visualization of the ciliary body and structures posterior to the iris, which anterior segment OCT typically hasn’t been able to image well,” notes Dr. Chopra. Background Optical coherence tomography (OCT) is a widely used imaging device in ophthalmology and has been evolving since its first publication in 1991 by Huang et al . However, there may be cases where you won’t be able to get an adequate view using AS-OCT.”. Anterior segment OCT has multiple potential uses relating to managing glaucoma: • Evaluating potential angle closure. In particular, the scanning speed of commercially available OCT units has steadily increased, allowing the technology to be used for an ever-longer list of clinical tasks. “However, I don’t find any of the quantitative tools offered for measuring the angle clinically useful. Sunita Radhakrishnan, MD, research director of the Glaucoma Research and Education Group at the Glaucoma Center of San Francisco, and Joel S. Schuman, MD, Eye and Ear Foundation Professor and chairman of the department of ophthalmology at the University of Pittsburgh School of Medicine, and co-inventor of OCT, note that this technology can be useful in multiple ways: Dr. Schuman notes that in addition to the Visante, a number of spectral domain OCT devices currently avail-
able in the United States, including the Cirrus and RTVue, can be used to image the anterior segment. “But by itself, that’s not enough. “UBM is more cumbersome to perform,” she says. But I think eventually these useful applications will be developed. “For example, it can measure the thickness of the epithelium—in some systems also the endothelium—which would be beyond the capability of other technologies,” he says. Dr. Chopra says he routinely uses AS-OCT when patients are undergoing angle-based minimally invasive glaucoma surgery. “I’m not sure that most comprehensive ophthalmologists would have enough of a call for anterior segment OCT to make it a useful investment for them,” says Dr. Schuman. Alternatives to topical drops appear to be effective—and they’re becoming more popular. One proposed use of anterior segment OCT is to determine whether there is a narrowing of the AC angle, which could lead to angle-closure glaucoma. “This is very helpful for eyes that have previously had LASIK,” says Dr. Huang. “This is one of the real advantages of AS-OCT technology. Anterior segment optical coherence tomography angiography technology. Use of anterior segment OCT growing With this easy non-contact technique, the images are taken quickly, and the technician decides which axis to explore. Of course, AS-OCT has other noteworthy limitations. It can also evaluate iris vessels to some extent, unless the eye is heavily pigmented. Dr. Chopra says he also uses AS-OCT to monitor corneal thinning in keratoconus patients. If anything doesn’t look wide open, you can decide to perform gonioscopy, or if you see apposition and don’t do iridotomies, you can refer the patient to a specialist.“, However, Dr. Schuman believes economic realities might make adding anterior segment OCT too much of a burden. That will help the surgeon perfect the techniques that can then be used easily and reliably in more challenging patients with angle narrowing or other angle abnormalities.”, • Expect a learning curve. “If you really want to see the angle structure, the ciliary processes and the relationship of the ciliary process to the iris, UBM is a better technology in most cases. The aim of this study was to determine whether AS-OCT … Q What are the indications for SCODI of the anterior segment? “Many regression-based formulas are specialized for that, and they work pretty well. “If you section the cornea at an oblique angle, you can’t measure the depth accurately. In many cases anterior segment OCT will provide you with sufficient information to be able to make a clinical decision, so it’s worth trying. With the Visante you can look for signs of plateau iris or a high crystalline lens rise. Unfortunately, anterior segment OCT doesn’t show the ciliary body.”, Dr. Schuman advises caution when considering the possible mechanism, however. “Sometimes you can see almost the whole angle, but you lose the most posterior portion that’s really of interest,” he explains. “They have other expenses that would show more return on investment.”, Because anterior segment OCT provides a detailed look at the. Schuman and Chopra report no financial ties to any product discussed. When reviewing the scans, I look at the overall anterior segment anatomy, the iris configuration and whether iridotrabecular apposition is present or not.”, Dr. Radhakrishnan adds that she seldom uses ultrasonic biomicroscopy as the first imaging method in patients with occludable angles. “At the same time, it’s a subjective assessment,” he notes. • Measuring astigmatism for toric IOLs. “You have to learn what to look for in order to evaluate different things. “However, that will give you a distorted view of the angle. “That means scanning with the lights on, turning the lights off, waiting a couple of minutes and scanning again,” says Dr. Schuman. Background/Objective Anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) are two non-invasive imaging techniques used for the measurement of tumour thickness in corneal and bulbar conjunctival tumours. Optometrists will have an enhanced understanding of the use of OCT for anterior chamber assessment in glaucoma monitoring and refractive surgical pathways Optometrists will have an evidence-based understanding of assessment of the dimensions and curvature of the cornea and other anterior chamber structures using OCT Several studies , , , , have described the use of anterior segment optical coherence tomography (AS-OCT) in evaluating punctal stenosis. Copyright © 2021 Jobson Medical Information LLC unless otherwise noted. “The problem is that the topography capability hasn’t been FDA-approved and people aren’t familiar with the other maps, so there’s an educational process that needs to take place for clinicians to be comfortable using this relatively new technology. The Heidelberg Anterion can provide stunning 360-degree anterior segment images, along with good imaging of the ciliary body.” Dr. Chopra says that he and his colleagues presented a poster at the recent virtual AAO meeting showing how this technology can visualize ciliary muscles and how they behave during active accommodation. using light with a wavelength of 830 nm 4. principle of OCT 1. “Angles can be assessed before and after laser procedures such as iridotomy and iridoplasty, and [the technology can] even confirm the patency of a laser PI,” notes Dr. Chopra. Chopra and Huang note the pros and cons of AS-OCT compared to ultrasound biomicroscopy. “This has been approved outside the United States for several years, but it’s more of a research application in the United States right now. In plateau iris, you see a flat iris plane. 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