OCT-angiography

Fluorescein angiography. Image courtesy of  Richard F Spaide MD OCT angiography (OCT-A) is a valuable and complementary addition to the imaging tools currently available to retinal physicians, according to Richard F Spaide MD. “OCT-A today can give us information that is not visible by other testing methods. It is useful for detection of retinal vascular disease and offers the opportunity to expand our knowledge of the physiology of the retina. It is also good for monitoring age-related macular degeneration and evaluating vision loss,” he told delegates attending the 17th EURETINA Congress in Barcelona. OCT-A visualises vasculature using motion contrast. No dye injection is required, unlike other imaging modalities such as fluorescein angiography. “It is a very quick test, which enables three-dimensional volumetric imaging of the retinal and choroidal vasculature and can provide information that is not visible by other imaging devices. However, there is a learning curve involved in interpreting the images correctly and identifying artefacts. It is not a plug-in replacement for fluorescein angiography (FA), but is really a separate way to learn how to image the eye,” he said. Dr Spaide presented four case studies to illustrate the utility of OCT-A in clinical practice. The first example was a 71-year-old male patient with a central retinal vein occlusion in his right eye who had been treated in another clinic with anti-VEGF agents. Fluorescein angiography of his left eye showed nothing abnormal. An OCT-A exam of the same eye, however, showed multiple areas of non-perfusion in the superficial capillary plexus. “This was very curious, so I ordered a carotid Doppler ultrasound test which showed a huge ulcerated plaque on the left side. The patient underwent emergency surgery to remove the plaque and the vascular surgeon remarked afterwards that the eye examination had probably saved this patient’s life,” said Dr Spaide. The second case study was a 24-year-old patient with type 1 diabetes that had good overall visual acuity of 20/30, but with dark chequerboard disturbances in her field of vision. The structural OCT showed areas of disorganisation of the retinal inner layers, also known as DRIL. OCT-A showed these areas had absent flow in the deep vascular plexus, a feature common in DRIL that is not visible in fluorescein angiography. OCT-A images also showed microaneurysms surrounding areas of capillary non-perfusion could occur in areas where the deep vascular plexus seemed to anastomose with the superficial plexus. “In this case, OCT-A was really an excellent research tool to reassess information that we thought we knew about fluorescein angiography, but which were not giving us the full picture,” he said. The third case highlighted by Dr Spaide showed a patient with geographic atrophy who had loss of central vision because of the atrophy affecting the central part of the macula. Structural OCT imaging showed an increased amount of reflective material in the deep retina, which further OCT-A examination revealed to be areas of neovascularisation wrapped around the areas of atrophy. “The Sarks showed that unsuspected choroidal neovascularisation occurred in about 45% of patients with geographic atrophy. In this case, OCT-A demonstrated neovascularisation skirting around an area of central geographic atrophy and enabled us to make the diagnosis efficiently,” he said. The final case study presented by Dr Spaide was a patient with end-stage glaucoma who had undergone a filtering operation. One month after surgery his visual acuity dropped dramatically to 20/400. While structural OCT scans showed some epiretinal membrane, there was nothing present on either OCT or FA to really explain the vision loss. An OCT-A scan, however, showed an absence of blood flow in the radial peripapillary capillary network, as well as the loss of ganglion cells. “There was absent flow in the right eye and the left eye was not too good either. If you have someone with advanced glaucoma and particularly if the scotoma bisects the point of fixation and you do filtering surgery to reduce their pressure, they may lose their central visual acuity. This ‘snuff out’ phenomenon was first recognised by Von Graefe over 150 years ago. OCT-A and ganglion cell analysis may offer valuable clues to diagnosis as well as etiology,” he concluded. Richard F Spaide: rickspaide@gmail.com