Diabetic Changes Linked to Reduced Retinal Sensitivity

Retinal vasculature in patients with diabetes are correlated with  reduced retinal sensitivity, according to a prospective, observational study published in Retina.

Previous studies using optical coherence tomography angiography (OCT-A) have concluded that quantitative changes can occur in the foveal avascular zone (FAZ) of people with diabetes without diabetic retinopathy (DR). However, these findings were not linked to visual acuity and related functional parameters. In this current study, researchers examined the relationship between macular microvasculature parameters and functional changes in patients with DR.

For the study, participants with type 2 diabetes mellitus and varying levels of DR were recruited from Singapore National Eye Centre clinics. Excluded from the study were those with media opacity affecting OCT capture, coexisting or previous ocular disease, or intraretinal fluid seen on OCT b-scans or structural en face images, and any eyes that had a previous focal laser. In total, 76 eyes from 39 participants with a mean age of 64 years were included in the study.

OCT-A was used to image superficial and deep perifoveal vessel densities, and FAZ areas. Retinal sensitivity was measured using microperimetry. Investigators found that, as the severity of DR increased, patients experienced a decreasing trend for deep perifoveal vessel density and an increase in FAZ areas. However, none of these metrics correlated with best corrected visual acuity, according to the findings. Instead, retinal sensitivity was linked to increasing superficial FAZ area as well as decreasing deep visual density.

Specifically, deep perifoveal vessel density decreased with increasing severity of DR (adjusted mean 51.93 vs 49.89 vs. 47.96, P =.005). Superficial and deep FAZ area increased with increasing DR severity (adjusted mean: 235.0 mm² vs 303.4 mm² vs. 400.9 mm², P =.003 [superficial]; 333.1 mm² vs. 513.3 mm² vs 530.2 mm², P =.001 [deep]). Retinal sensitivity decreased with increasing DR severity (adjusted mean: 25.12 dB vs 22.34 dB vs 20.67 dB, P =.003). Retinal sensitivity correlated positively with deep perifoveal vessel density (P =.020) and inversely with superficial foveal avascular zone area (P =.010).

“Our findings are important and novel because a significant correlation between retinal microvasculature changes detectable in diabetic patients on OCT-A is now demonstrated with functional loss quantified by retinal sensitivity,” the study explains.

The investigators acknowledge the exclusion of patients with diabetic macular edema as a limitation of this study. Additionally, FAZ size and perifoveal visual density were assessed using commercially available automated software despite the varied approaches to quantification used by OCT-A instruments. Also, the team used a specific protocol for microperimetry that covered an area of 1500 mm x 1500 mm centered on the fovea. However, these dimensions are smaller than the OCT-A scan area, which could only image a minimum area of 3 mm x 3 mm. Lastly, because this is a cross-sectional study, the researchers’ ability to draw conclusions about causation is limited.

Reference

Tsai A, Gan A, Ting D, et al. Diabetic macular ischemia: correlation of retinal vasculature changes by optical coherence tomography angiography and functional deficit. Retina. 2020;40(11):2184-2190. doi: 10.1097/IAE.0000000000002721.