Purpose: To investigate the effect(s) of intravitreally injected ranibizumab on retinal vessel diameter in patients with diabetic macular edema.
Methods: Participants of this prospective study were 14 men and 16 women (30 eyes) aged 60 ± 11 years (mean ± standard deviation), all with clinically significant diabetic macular edema. Treatment comprised 3 intravitreal injections of ranibizumab given at 4-week intervals. Examinations were conducted before the first (baseline), before the second (Month 1), before the third (Month 2) injections, and 3 months after baseline (Month 3). Measured parameters included systemic blood pressure, static retinal vessel analysis (central retinal artery equivalent and central retinal vein equivalent), and dynamic retinal vessel analysis, as measured by the change in vessel diameter in response to flicker stimulation during three measurement cycles. Flicker stimulation was accomplished using a 50-second baseline recording, followed by an online measurement during 20-second flicker stimulation and 80-second online measurements in both arteriolar and venular vessel segments.
Results: Static retinal vessel analysis showed a reduction of central retinal artery equivalent from 186.25 ± 51.40 μm (baseline) to 173.20 ± 22.2 μm (Month 1), to 174.30 ± 27.30 μm (Month 2), and to 170.56 ± 22.89 μm (Month 3), none of which was statistically significant (P = 0.23, 0.12, and 0.14, respectively). Central retinal vein equivalent was reduced from 216.21 ± 25.0 μm (baseline) to 214.48 ± 25.4 μm (Month 1), to 214.80 ± 24.30 μm (Month 2), and to 211.41 ± 24.30 μm (Month 3), revealing no statistically significant differences between examination time points (P = 0.54, 0.06, and 0.24, respectively). Dynamic vessel analysis yielded a mean retinal arterial diameter change of +1.47% ± 2.3 (baseline), +1.91% ± 2.5 (Month 1), +1.76% ± 2.2 (Month 2), and +1.66% ± 2.1 (Month 3), none of which showed statistically significant differences (P = 0.32, 0.49, and 0.70, respectively). Mean retinal venous diameter changes were +3.15% ± 1.7 (baseline), +3.7% ± 2.3 (Month 1), +4.0% ± 2.0 (Month 2), and +4.95% ± 1.9 (Month 3), none of which showed statistically significant differences (P = 0.12, 0.17, and 0.14, respectively). Central retinal thickness, as measured by spectral domain optical coherence tomography, decreased significantly from 435.2 ± 131.8 μm (baseline) to 372.3 ± 142.8 μm (Month 3), P = 0.01. Regression analysis of arteriolar and venular diameters indicated that there was no significant correlation between these 2 parameters (r = 0.053; P = 0.835 and r = 0.06; P = 0.817, respectively). Also, no significant correlation was observed between the difference in the central retinal thickness and change in arteriolar or venular dilatation (r = 0.291, P = 0.241 and r = 0.06, P = 0.435, respectively).
Conclusion: Intravitreally applied ranibizumab did not significantly affect retinal vessel diameter in patients with diabetic macular edema. Decline in the central foveal thickness after ranibizumab therapy, as measured by spectral domain optical coherence tomography, was not linked to any change in retinal vessel diameter or dilatatory response, neither for arterioles nor venules.