Eyeworld

EW RETINA 74 July 2015 by Michelle Dalton EyeWorld Contributing Writer improve, leaving the retina special- ists to question why. "We were simply missing some of the details that SD-OCT can now capture, especially at the level of the photoreceptors," he said. SD-OCT has been shown to be very sensitive, but not terribly specific, Dr. Khurana said. That leads to questions about the real subtleties in the images, Dr. Ehlers said. "I think you have more ques- tions in spectral-domain because the level of detail is just so fantastic," he said. Reimbursement is another issue, Dr. Khurana said, as both TD- and SD-OCT are reimbursed at the same rate. Unless there is a compelling reason to purchase an SD-OCT device, Dr. Khurana said that most anterior segment specialists would probably be just as well served by their TD-OCT devices. One area SD-OCT imaging is becoming "very important" is in hydroxychloroquine screening or hydroxychloroquine toxicity, Dr. Khurana said. Before the introduc- tion of SD-OCT, this disorder was areas on the OCT that may represent macular edema or subretinal fluid," he said. For glaucoma specialists, Dr. Hsu said SD-OCT and even more advanced technologies are being used to image the nerve fiber layer. "SD-OCT is much more accurate at measuring the thickness of the nerve fiber layer around the optic nerve," he said, and gives practices another billable diagnostic. Nothing's perfect … The ease of using the systems and interpreting the images varies among the devices, Dr. Ehlers said. It is important to remember that, "although it feels like we're looking at a histology slide, we're simply looking at reflection patterns of light coming off tissue and interfaces in these tissues with the OCT images," he said. When Dr. Hsu's practice was still using only TD-OCT, cataract surgery was occasionally recommended as the retinal images didn't elucidate any pathology that could explain visual declines. But post-cataract surgery, the patient's vision didn't retinal fluid," but SD-OCT "is like going from a standard definition TV to high-def," said Jason Hsu, MD, assistant professor of ophthalmol- ogy, Thomas Jefferson University, Philadelphia, and in practice at Mid Atlantic Retina. TD-OCT is limited by the extent to which one can assess pathologies compared to SD-OCT, such as with 3D reconstruction or line-by-line cube review, said Justis P. Ehlers, MD, Cleveland Clinic, Ohio. For anterior segment surgeons, using more advanced OCTs (and even sending the patient with his/ her OCT to a retina specialist for confirmation if necessary) may help differentiate between a cataract causing decreased vision and a reti- nal disorder that's compounded by the cataract, Dr. Hsu said. Cataract surgeons who learn how to read SD-OCTs for these subtle differences can avoid patient dissatisfaction post-cataract surgery when the expectations for improved vision don't materialize because of the underlying retinal disorder, Dr. Hsu said. One key giveaway there's retina disease? "Dark or hyporeflective The ongoing improvements in imaging will help identify treatable diseases earlier, experts say. And it's not just for retina specialists C ompared to the first gener- ation of optical coherence tomography (OCT), the third-generation time-do- main (TD) was considered the gold standard—with a resolution of 10 microns, 400 scans/second, and 6 radial scans, "it was pretty amazing in its time," said Rahul N. Khurana, MD, Northern California Retina Vitreous Associates, Moun- tain View, Calif. But spectral-do- main OCT (SD-OCT) has eclipsed TD-OCT—it's about 100 times faster and produces closer to 40,000 actual scans, taking resolution down to the 5-micron level. For retina specialists, "the standard of care is really using SD-OCT," he said, especially when evaluating retinal pathologies like age-related macular degeneration. TD-OCT is "definitely able to pick up macular edema and sub- Technology advances in optical coherence tomography Adaptive optics image of an eye; the white dots are the eye's photoreceptor cones. Source: Rahul N. Khurana, MD Upper left, a color fundus image of a diabetic eye; upper right, conventional fluorescein angiogram of the same eye; bottom left, OCT angiography of superficial vessels in the same eye; and bottom right, OCT angiography of deep vessels in the same eye Source: Jason Hsu, MD

• Cover