Hypertension Likely Drives Arteriolar Wall Thickening in Preclinical Diabetic Retinopathy While Diabetes Drives Wall Thickness in Clinical Retinopathy

Abstract

Purpose: Both hypertension and diabetes are known to increase the wall-to-lumen ratio (WLR) of retinal arterioles, but the differential effects are unknown. Here, we study the timing and relative impact of hypertension versus diabetes on the WLR in diabetic retinopathy (DR) to address this unresolved question.

Methods: This prospective cross-sectional study compared the retinal arteriolar WLR in 17 healthy eyes, 15 with diabetes but no apparent DR (DM no DR), and 8 with diabetic macular edema (DME) and either nonproliferative or proliferative DR. We imaged each arteriole using adaptive optics scanning laser ophthalmoscopy and measured the WLR using ImageJ. Multiple linear regression (MLR) was performed to estimate the effects of hypertension, diabetes, and age on the WLR.

Results: Both subjects with DM no DR and subjects with DME had significantly higher WLR than healthy subjects (0.36 ± 0.08 and 0.42 ± 0.08 vs. 0.29 ± 0.07, 1-way ANOVA P = 0.0009). MLR in healthy subjects and subjects with DM no DR showed hypertension had the strongest effect (regression coefficient = 0.08, P = 0.009), whereas age and diabetes were not significantly correlated with WLR. MLR in all three groups together (healthy, DM no DR, and DME) showed diabetes had the strongest effect (regression coefficient = 0.05, P = 0.02), whereas age and hypertension were not significantly correlated with WLR.

Conclusions: Hypertension may be an early driver of retinal arteriolar wall thickening in preclinical DR, independent of age or diabetes, whereas changes specific to DR may drive wall thickening in DME and later DR stages.

Translational relevance: We offer a framework for understanding the relative contributions of hypertension and diabetes on the vascular wall, and emphasize the importance of hypertension control early in diabetes even before DR onset.

Figure 1.

Example adaptive optics scanning laser ophthalmoscopy images of retinal arterioles. Example arterioles with annotated wall thicknesses and external and lumen diameters. (A) Depicts an example arteriole from a healthy eye with a low wall to lumen ratio (WLR) of 0.27. (B) Shows an example vessel from a patient with diabetes mellitus without retinopathy (DM no DR) with a higher WLR of 0.38. (C) Depicts an example arteriole from a diabetic macular edema (DME) eye with a WLR of 0.45. The top row displays a magnified view of the inset regions from the bottom row. Contrast was adjusted for clarity.

Figure 2.

The inner vessel wall layer as the endothelial cell layer. For AOSLO images with two visible vessel wall layers (left image, indicated by the blue lines), we found that the inner layer is the endothelial cell layer rather than the basement membrane. We used the corresponding XT image (middle image), where the vertical scan is momentarily stopped and thus diagonal streaks represent moving cells, to find the lumen diameter. Here, the lumen diameter is 58.2 um. The inner diameter of the offset confocal aperture image on the left is 57.8 um, highlighting that the inner layer is indeed the endothelial cell layer. The image on the right illustrates a vessel with three clear interfaces in the vessel wall indicated by the three blue lines. These layers are presumably the luminal surface of the endothelial cell layer, basement membrane, and outer vessel wall. Contrast was adjusted for clarity.

Figure 3.

Impact of diabetes, age, and hypertension on the wall to lumen ratio. (A) Boxplot comparing wall to lumen ratio (WLR) in three groups: healthy subjects, those with diabetes without diabetic retinopathy (DM no DR), and subjects with diabetic macular edema (DME). Although DM no DR subjects and DME subjects have a higher WLR than healthy subjects (P = 0.009 and 0.0005 respectively), there is no significant difference in WLR for subjects with DME compared with subjects with DM no DR (P = 0.13). The asterisk symbol (*) indicates statistical significance from Student's t-test (P < 0.05). N.S. stands for not significant. (B) Linear regression shows that WLR is significantly correlated with age (Pearson correlation R² = 0.209, P = 0.003). (C) T-test shows that hypertension is significantly associated with WLR (P = 0.003).

Figure 4.

Regression coefficient plot of the contributions of diabetes, age, and hypertension on the wall to lumen ratio. Regression coefficient plot from multiple linear regression (MLR). MLR on healthy subjects versus subjects with DM no DR only (red) show that hypertension has the strongest effect on WLR with a coefficient term of 0.075 (95% confidence interval [CI] = 0.021-0.129) and P value of 0.009, whereas age and diabetes were not significantly correlated with the WLR (P value of 0.15 for both). MLR on all three groups together (black) shows that DR status has the strongest effect on WLR with a coefficient term of 0.047 (95% CI = 0.009-0.085) and P value of 0.02, whereas age and hypertension were not significantly correlated with the WLR (P value of 0.46 and 0.21, respectively). Three parameters were included in the MLR model: hypertension (yes or no), DR status (healthy versus DM no DR versus DME), and age.