SS-OCT more accurate in identifying glaucoma defect than SD-OCT
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The swept-source OCT showed better accuracy in identifying glaucomatous defects in myopic eyes compared with other tomography mapping, according to results published in the American Journal of Ophthalmology.
“The public concern for increasing myopia stems from the fact that it can lead to vision-threatening eye diseases. ... In particular, many epidemiological studies have indicated increased risk of primary open-angle glaucoma (POAG) in myopic eyes,” Yong Woo Kim, MD, PhD, department of ophthalmology, Seoul National University Hospital, and colleagues wrote. “In response to the clinical demand for accurate diagnosis of POAG in myopic eyes, there have been many attempts to improve diagnostic power by using spectral-domain OCT (SD-OCT). ... The present study was initiated to confirm whether the wide-field map provided by swept-source OCT (SS-OCT) is useful in detecting glaucomatous changes in myopic eyes.”
In a prospective, case-control study, 150 myopic POAG eyes and 100 healthy myopic eyes were dilated and underwent SD-OCT and SS-OCT mapping. The locations of defect on thickness and deviation maps from each device where compared for accuracy along with the area under receiver operating characteristic of the peripapillary retinal nerve fiber layer (RNFL) and the macular parameters (GCL++: equivalent to ganglion cell-inner plexiform layer [GCIPL] + RNFL; GCL+: equivalent to GCIP).
Study results showed the wide-field RNFL thickness map was more accurate in locating glaucomatous defect in the inferotemporal and superotemporal regions (96.4% vs. 92.4%, respectively); RNFL/GCL++/GCL+ wide-field thickness map also displayed more accuracy compared with the SD-OCT thickness map (P .05). Further, the average macular parameters of GCL++ thickness (87.6%) and GCL+ thickness (87.5%) showed greater area under receiver operating characteristic for myopic POAG than did GCIPL thickness from SD-OCT (83.8%, P < .05).
“The wide-field thickness (thickness surface) and SuperPixel maps from SS-OCT exhibited better accuracy and diagnostic power compared with the conventional maps from SD-OCT for detection of glaucomatous defects in myopic eyes,” Kim and colleagues concluded. “It is certainly worth taking advantage of this new technology for accurate diagnosis of POAG and prevention of unnecessary glaucoma treatment in healthy myopic eyes.”
Perspective
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Derek MacDonald, OD, FAAO
The interplay between myopia and open-angle glaucoma is complex and frustrating.
First, the risk for OAG increases with degree of myopia in a dose-response relationship. Unfortunately, myopic eyes – by virtue of high axial length, tilted optic nerve hypoplasia (ONH), extensive peripapillary atrophy, temporal RNFL bundle shift and macular abnormalities including epiretinal membrane and foveoschisis – complicate and confound objective ONH/RNFL and GCIPL evaluation, making quality image acquisition challenging and rendering many reference databases less than helpful. Moreover, highly myopic patients may also demonstrate structural defects and functional deficits that mimic those of glaucoma which, based on recent research, may progress over time, potentially limiting the utility of longitudinal analysis.
As a result, despite great advancements in structural assessment techniques, many myopic glaucomatous eyes likely still remain undiagnosed, while healthy myopic eyes are unnecessarily treated.
In demonstrating the advantage of three-dimensional widefield (9 x 12 mm) SS-OCT over standard (6 x 6 mm) SD-OCT imaging, Kim and colleagues provide another tool to accurately diagnose myopic glaucoma. OCT angiography also shows promise with myopic glaucomatous eyes appearing to have lower vessel density than both myopic nonglaucomatous and nonmyopic glaucomatous globes. Perhaps we are poised to make long-awaited inroads into one of the most common, critical and challenging differential diagnoses we face.
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