ADCYAP1 and diabetes mellitus: As compared to the diabetes group, the diabetes + PACAP group presented a different phenomenon: it was 50% thicker in TRT (127.05 ± 6.94 μm (diabetes) vs. 182.97 ± 4.15 μm (diabetes + PACAP)); there were also significantly higher values in the majority of nuclear layers, such as the INL thickness (13.95 ± 1.3 μm (diabetes) vs. 24.03 ± 2.22 μm (diabetes + PACAP)), ONL thickness (9.65 ± 0.52 μm (diabetes) vs. 37.67 ± 3.43 μm (diabetes + PACAP)), and OS thickness (9.22 ± 1.95 μm (diabetes) vs. 22.91 ± 0.65 μm (diabetes + PACAP)).