Optical coherence tomography angiography

Optical coherence tomography angiography (OCTA) can delineate neovascularisation and areas of capillary nonperfusion in eyes with diabetic retinopathy (DR). However, more research is needed to determine what role this newer imaging technique might have in patient care. Noting that the capabilities of OCTA for studying the blood vessel patterns in eyes with DR had not yet been established, Yasuki Ito MD, and colleagues from the department of ophthalmology, Nagoya University School of Medicine, Japan, undertook a study comparing OCTA and fluorescein angiography (FA) in 34 eyes of 23 patients. Images obtained with each method were analysed to determine the number of neovascularisations, number of local capillary nonperfused areas, and size of the areas of nonperfusion. There was no difference in the mean number of neovascularisations counted in the OCTA and FA images, and the vessels detected with the two techniques were similar as well. However, the mean number of local capillary nonperfused areas and their mean area was greater using OCTA compared with FA. “Although we have shown that OCTA can be used to study the vasculature in eyes with DR, we found that the information obtained is different than with FA. Therefore, we believe some caution is needed when using OCTA, and that perhaps combining it with FA may allow for a more accurate evaluation,” Dr Ito said. He offered explanations to account for the differences between OCTA and FA in characterising areas of nonperfusion. One possibility is that OCTA may falsely identify areas of low perfusion as being nonperfused. Alternatively, the discrepancy may reflect an artefact of the FA technique, i.e., areas of dye leakage may create a false signal so that areas of nonperfusion appear smaller than they actually are. For this study, FA was performed using the Optos 200Tx (Optos). OCTA was performed with the Cirrus 5000 HD-OCT platform (Carl Zeiss Meditec) using a 6x6 mm scanning program and moving the fixation point to nine sites across the entire posterior pole. Evaluation of the retinal vasculature was done by adjusting the segmentation to be between the retinal pigment epithelium and the internal limiting membrane (ILM) for retinal en face maps. Neovascularisation was evaluated by adjusting the segmentation to be between the ILM and vitreous cavity for vitreoretinal interface en face maps.