Eyeworld

EW RETINA 94 by Maxine Lipner EyeWorld Senior Contributing Writer Red light, green light Using certain colors in imaging may help identify cysts in macular edema H ow practitioners view a fundus image in a dia- betic eye may impact the number of cysts they are able to visualize, according to Ann Elsner, PhD, professor of op- tometry, Indiana University School of Optometry, Bloomington, Indi- ana. In a recent study, investigators found that practitioners using red channel images are more likely to visualize cysts than with the green channel, Dr. Elsner reported. 1 The study's aim was to compare how diabetic macular edema cysts could be viewed as red or green images versus full color. "With laboratory data, it has been shown that red light penetrates better into the deeper layers of the retina where there will be some cysts, as well as in the superficial layers," Dr. Elsner said. "The idea was to look in our underserved population to see if we could identify as many cysts in red alone as we could in color." Color screening In practice, some who are doing di- abetic retinopathy screening tend to use green or blue and green images. "They take the red information out," Dr. Elsner said, adding that they may do this to look at the vessels and then may look at the full color image as well. With that in mind, investigators wanted to determine what happens in the underserved population, Dr. Elsner explained. "Most of these people have dark eyes, and that's where there is trou- ble in seeing some of the smaller features," she said. The problem is that dark eyes give dark pictures. In a lighter eye, viewing the image as red-free can show retinal vessels that appear clear cut, unless there is significant cataract. "You see the retinal vessels in higher contrast, and those vessel changes are an important part of diabetic retinopathy," Dr. Elsner said. "That's not always true for the dark eyes in underserved communities." Included in the study were 13 eyes of adult diabetic patients from the underserved community. Color images were acquired by non-mydri- atic camera. Investigators then split the images into red, green, and blue channels using Photoshop-type software, Dr. Elsner noted. "Given the typical full color clinical fundus photograph, we determined how many of the people that we saw cystoid macular edema in were graded as having cysts in red alone or green alone," she said, adding that they didn't bother grading the blue images since these were too dark to distinguish. "We graded the red and green separately," Dr. Elsner said. Investi- gators found that the red channel did just as well as the full-color image, while the green did not. "The green did well on one person who had a fairly light eye," she said, adding that where the green did not do well was in those who had darker eyes, which was virtually everyone else. In five of the 13 individuals, no matter what investigators did with image manipulation, they could not see cysts at all with the green. The fact that more cysts could be identified in the red channel might have to do with where these are located, Dr. Elsner thinks. "I'm guessing that the cysts we see in the red channel are deeper and we couldn't see them in the green," she said. She theorized that these were obscured by the lack of light coming back from the fundus with the green wavelength. Also, the size of the cysts was judged differently in the red and green images, with the cysts appear- ing to cover a smaller area in the green channel. "We might not only miss pathology, but we might also underestimate the extent of it," Dr. Elsner said. In the clinic She encouraged practitioners to consider viewing fundus photos in the red channel when looking for cysts. "Almost everyone who has a color image has some software on their computer, Photoshop or other, where they can take a peek at the red, in addition to the full color or the red-free, which is the green channel," Dr. Elsner said. "If you have a patient in whom there would likely be some edema, I would suggest viewing carefully in the red, particularly in a dark eye." Several ethnic groups in this dark-eyed population have a higher prevalence of diabetes, Dr. Elsner pointed out. She urged practitioners to look carefully at such eyes since this is a population with a higher risk of macular edema, and many have dark eyes that may make spotting cysts difficult. "It's a perfect storm," Dr. Elsner said. Going forward, Dr. Elsner hopes to do more investigations in this population. "We're looking at sex differences," she said, adding that males are known to have thicker maculae but the question is why. Dr. Elsner would like to consider whether upon careful examination with OCT such patients have higher rates of CME. "I think we should obtain better identification of who is at risk and put those patients into that category if we're going to use the high-end instrumentation," she concluded. EW Reference 1. Alhamami MA, et al. Comparison of cysts in red and green images for diabetic macular edema. Optom Vis Sci. 2017;94:137–149. Editors' note: Dr. Elsner has no finan- cial interests related to her comments. Contact information Elsner: aeelsner@indiana.edu August 2017 Research highlight Color fundus image of the retina of a diabetic 53-year-old Caucasian male diagnosed with cystoid macular edema. The small, bright yellow lesions are hard exudates. The central macular thickness on OCT was 398 microns. Source: Ann Elsner, PhD

• Blank Page
• Blank Page (1)