Circulating MMP1, MMP7 and MMP9 have also been found to be elevated in patients with diabetes, alongside the MMP/TIMP1 ratio, and these circulating factors are further increased in patients with DR (Jacqueminet et al., 2006) (Maxwell et al., 2001) (Abu El‐Asrar et al., 2014). Here, TIMP1 is linked to diabetes mellitus.