MMP9 and obstructive sleep apnea syndrome: Several contributory mechanisms to the ocular complications of OSA have been reported, including intermittent hypoxia, oxidative stress, systemic inflammatory responses (such as interleukin-6 (IL-6), IL-8,tumor necrosis factor-alpha (TNF-α), C-Reactive protein (CRP), matrix metalloproteinase 9 (MMP-9), vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), selectins), sympathetic system overaction, damage effects of endothelin-1, and disruption of the blood–retinal barrier (BRB) (Table 1) [11,12,13,14,15,16,18,19,24,25,26].