Volume-rendered optical coherence tomography (OCT) imaging allows new insight into retinal vascular flow and morphological changes in eyes with macular edema (ME), and the information obtained is the basis for new ideas about the pathogenesis of ME and therapeutic intervention, according to Richard F. Spaide, MD, Vitreous Retina Macula Consultants of New York.
Dr. Spaide presented images from eyes with ME related to different retinal vascular diseases. The examples included serial images taken pre- and post-treatment with anti-VEGF injections and cases with recurrent ME. The imaging was done using split-spectrum amplitude decorrelation, and volume rendering was achieved by integrating structural OCT data into angiographic data.
The studies revealed abnormalities in the inner layer of retinal vessels, decreased or absent flow in the deep vascular plexus, and co-localization of cystoid spaces with flow voids in the deep vascular layer.
Although cystoid spaces resolved with anti-VEGF treatment, there was persistence of flow void in the deep vessels, and in fluid accumulation in eyes with recurrent ME occurred in the same areas where altered inner and absent deep vascular plexus flow signal was noted previously.
Based on these observations, Dr. Spaide proposed that the deep vascular plexus plays an important role in the development of ME.
“ME is a common cause of vision loss in many blinding diseases, and better understanding of its mechanism of development can lead to identification of novel targets for intervention,” Dr. Spaide said.
“Previous theories on ME development did not consider the deep vascular plexus because only the inner vascular layer could be visualized using available techniques,” he said. “Although further study is needed, the early findings from volume rendered OCT suggest that effective control of fluid fluxes in the retina may require management of both main vascular layers.”
Dr. Spaide observed that study of the mechanism of ME development has also been limited by the absence of good animal models. In order to gain a better understanding, he applied recent discoveries from research involving the brain showing there is convective flow of fluid that is mediated by aquaporin-4 channels in astrocytes.