Dr. Shroff Rahul Ashok, S05342, Dr. Shroff Ashok C, Dr. Anand A Shroff
Introduction – Diabetic macular oedema(DME) occurs when high glucose levels cause capillary damage characterised by pericyte loss andendothelial cell breakdown. Fluorescein angiography is currently the gold standard in the analysis of diabetic retinopathy and and the evaluation of treatment. However, it requires the intravenous injection of a dye. OCT angiography permits non-invasive imaging of the superficial capillary plexus and deep capillary plexus and can be used to increase the understanding of ischemic conditions that affect different layers of the retinal microcirculation. Further, OCT angiography gives automated quantification ofcapillary non-perfusion which is reproducible and reliable, and helps evaluating progressive changes in capillary perfusion.
Purpose – To evaluate changes in Foveal Avascular Zone (FAZ) and capillary density following Intravitreal Anti-VEGF injection of Bevacizumab / Ranibizumab for Diabetic Macular Oedema (DME)
Method – Retrospective analyses of 8 eyes of 5 patients with diabetic macular oedema (DME). All patients underwent Best corrected visual acuity (BCVA), IOP check, dilated 78D fundus biomicroscopy, SD-OCT, OCT angiography (OCTA). OCT angiography was done using 6X6 mm macula scans. Repeat examination was done by the same examiner. Calculation of vascular density was done of superficial plexus using the Zeiss software macular grid,prior to Anti-VEGF injection and at each visit. Eyes with age-related macular degeneration, macular pucker, venous occlusion and eyes which had undergone vitrectomy were excluded. Vessel density was calculated as percentage of pixels with flow signal greater than threshold. Parafoveal vessel density was calculated between 0.3 and 1.25mm from centre of the fovea and perifoveal vessel density was calculated between 1.25 and 2.75 mm from fovealcenter. Perfusion density was calculated as vessel count divided by total pixel count.
Results and Discussion – 8 eyes of 5 patients with DME were studied. 5 eyes had non-proliferative diabetic retinopathy and 3 eyes had proliferative diabetic retinopathy. The mean followup time was 4 monthspost Anti-VEGF injection.The mean age was 64.12 yrs. Baseline vision was 6/18 (logmar 0.5+/-0.3). The baseline central macular thickness (CMT) on OCT was 431 microns( +/-46). The mean FAZ was 0.298mm2 at baselineand vessel density was 12.43%. Perfusion was 0.2822. Other studies have shown mean vessel density of 15% in diabetic maculopathy with reduction of vessel density in both superficial and deep retinal plexus in proliferative diabetic retinopathy.
At 1 mthfollowup post injection, BCVA was 6/18 (logmar0.45). CMT had reduced to 295 microns. The FAZ was 0.23mm2 and vessel density improved to 10.45% and perfusion was 0.25.
At 3 months post injection, the BCVA had improved to 6/18 (logmar 0.41). The CMT was 313 microns. The FAZ had improved to 0.255mm2, and the vessel density had improved to 12.58%and capillary perfusion had improved to 0.3395.
Similar studies have shown a significant reduction in parafoveal and perifoveal vessel density and enlargement of the FAZ in diabetic maculopathy. Studies have found that areas of capillary non-perfusion and the FAZ are better delineated on OCT angiography than on fluorescein angiography. Severity of capillary non-perfusion on OCT angiography correlated well with fluorescein angiography. They also found repeatability was good in successive scans with a coefficient of variation of less than 7%. However visual acuity and vessel density were not well correlated.
Conclusion – OCT angiography demonstrated a decrease in capillary dilatation corresponding with reduction in macular thickness at 1 mth post injection which with increase in macular thickness at 3 mths. There was no significant change in FAZ at 3 mths post injection following Anti-VEGFtreatment. OCT angiography was able to visualise and quantitate capillary non-perfusion in the individual layers and in FAZ with good repeatability. The limitation of this study is the small sample size and the short duration of followup.
References
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