It is well recognized that a healthy foveal avascular zone (FAZ), containing metabolically active photoreceptors, is essential for central vision. However, diabetic eyes have enlarged FAZ – which has been shown to correlate with reduced visual acuity.
Early microvascular damage in diabetes can now be quantified with OCT angiography (OCTA). Studies have also correlated FAZ size and vessel density with severity of diabetic macular ischemia. In addition, the ganglion cell layer-inner plexiform layer complex (GC-IPL) and retinal nerve fiber layer (RNFL) thinning, indicating retinal neurodegeneration, have been shown to be associated with diabetic retinopathy (DR). This neurodegeneration could be the earliest indicator of functional damage in diabetic eye disease preceding vascular changes.
With this background, Dr. Dilraj S. Grewal, from Duke Eye Center in Durham, North Carolina, USA, and Drs. Manpreet Brar and S.P.S. Grewal, from the Grewal Eye Institute in Chandigarh, India, conducted an investigation to evaluate the correlation between diabetic macular ischemia and retinal neurodegeneration. They used OCTA to examine 195 eyes of 105 diabetic patients and acquired 3×3 mm scans using Zeiss Angioplex OCTA (Carl Zeiss Meditec, Dublin, CA,USA) centered on the fovea. Superficial (SCP) and deep capillary plexus (DCP) FAZ horizontal (H) and vertical (V) greatest linear diameter were calculated using ImageJ (NIH, Bethesda, MD, USA). The GCL thickness was generated from the Macular Cube 512×128 scan protocol centered on the fovea.
OCTA facilitates study of the link between microangiopathy and neurodegeneration in DR as it can allow simultaneous visualization of microvascular abnormalities and quantitative analysis of the inner retinal layers. In diabetic patients without DME, there is a significant correlation between the neurodegenerative component in the inner retinal layers measured using GCL thickness and diabetic macular ischemia in the SCP and DCP FAZ, and these are both significantly correlated with VA. These results confirm the relationship between retinal neurodegeneration and microvasculopathy in diabetic eyes and also demonstrate that neurodegeneration may precede microvasculopathic changes in such eyes.
In conclusion, using OCTA to quantify early microvascular and neurodegenerative changes in diabetic eyes may help optimize patient management – both for evaluation of future neuroprotection and microvascular network reconstitution therapeutic strategies where these changes may serve as a biomarker. However, further work is needed on this topic and assessment of the relationship between the capillary network and retinal neurodegeneration in diabetes is the subject of an ongoing investigation.
Reference:
ASRS 2017 and AAO 2017 Meeting Presentation by Dr. Dilraj S. Grewal, Duke Eye Center, Department of Ophthalmology, Duke University School of Medicine, Durham, North Carolina, USA.
