Assessment of perfused parafoveal capillary density in patients with preclinical diabetic retinopathy using optical coherence tomography angiography

Abstract

Purpose : To assess changes to the parafoveal perfused capillary density (PCD) between healthy control subjects and patients with diabetes mellitus without clinical diabetic retinopathy (DMnoDR).

Methods : Utilizing a commercial spectral domain optical coherence tomography (OCT) system (Avanti RTVue-XR; Optovue, Fremont, CA), a 3x3 mm macular OCT angiography (OCTA) scan from the inner limiting membrane to 70 µm below the posterior boundary of the inner plexiform layer was obtained in each participant. The foveal avascular zone (FAZ) margin was manually traced on each OCTA image. From the FAZ margin, seven consecutive equidistant annuli were created with increasing retinal eccentricity, each with a step size of 200 µm. PCD was computed for each annulus, defined as the percentage of capillary area divided by the corresponding annulus area after subtraction of large blood vessel areas. Two-way analysis of variance (ANOVA) and post hoc Tukey-Kramer testing were used to assess the effect of study group and annulus on PCD. Unpaired two-tailed t testing was used to assess for significant differences in study group PCD at each annulus. P values less than 0.05 were considered to be statistically significant. Results were reported as mean ± standard deviation.

Results : We analyzed 30 healthy controls and 30 DMnoDR patients. ANOVA indicated that the DMnoDR group had a significantly higher PCD compared to the control group (43.15±3.76% vs. 41.53±5.31%; p<0.0001). As expected for both groups, ANOVA showed that PCD increased significantly with increasing retinal distance from the FAZ margin (p<0.0001). There was no significant interaction between group and annulus (p=0.95). T testing showed that only the innermost annulus (FAZ margin to 200-µm out) achieved a statistically significant increase in PCD (DMnoDR 37.2±2.73% vs. control 34.4±3.85%, p=0.0023).

Conclusions : Increased PCD in the DMnoDR group is most likely related to increased blood flow as an autoregulatory response to relative tissue hypoxia in the diabetic retina. This finding is consistent with other studies of early diabetic microvascular changes prior to the onset of clinical diabetic retinopathy, and may have clinical value for earlier detection of diabetic microvascular disease as well as monitoring response to systemic medications.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.