Unhealthy eating habits and aging of society, there has been an increase of lifestyle-related diseases such as hypertension, hyper lipidemia, and diabetes, which are important risk factors for retinal vein occlusion (RVO), including branch RVO (BRVO) and central RVO (CRVO). Affecting an estimated 180,000 eyes per year in the United States, BRVO and CRVO comprise the second mostcommon type of retinal vascular disorder after diabetic retinopathy BRVO accounts for approximately 80% of cases, but both types of RVO contribute to significant loss of vision, mostly as a result of macular edema . The macula is the important part of the retina for detailed vision, especially the fovea that consists entirely of cones . Therefore, BRVO and CRVO are potentially serious retinal diseases that can lead to severe visual impairment. In BRVO and CRVO patients, vascular endothelial growth factor (VEGF) and several inflammatory factors have been reported to have an important role in the development of macular edema . Several major studies, including BRAVO (Ranibizuma B for the treatment of macular edema following Branch Retinal Vein Occlusion), CRUISE (Ranibizumab for the treatment of macular edema after Central Retinal Vein Occlusion Study), and SCORE (Standard Care vs COrticosteriod for REtinal Vein Occlusion study), have shown that anti-VEGF therapy or intravitreal injection of triamcinolone acetonide (IVTA) improves macular edema in patients with BRVO or CRVO. However, most of the subjects of those studies had nonischemic RVO and the above-mentioned therapies are less effective for macular edema in patients with ischemic RVO . This is probably because production of VEGF and inflammatory factors is higher in ischemic RVO, and because both anti-VEGF therapy and IVTA only have a temporary effect and do not improve the underlying retinal ischemia. pars plana vitrectomy (PPV) was recently reported to achieve greater improvement of retinal sensitivity (measured by the Micro Perimeter 1) in ischemic RVO patients compared with nonischemic RVO patients, suggesting that PPV may indirectly alleviate retinal ischemia in patients with ischemic RVO. Elevation of the oxygen tension in the inner retina could be important for the efficacy of PPV. That is, transport of oxygen from well-perfused to ischemic retinal regions by fluid currents might increase after PPV, leading to better oxygenation of the ischemic inner retina and improvement of macular edema because an increase of oxygen tension would reduce VEGF production and decrease vascular permeability. An increase of retinal oxygen tension would also improve autoregulatory arteriolar vasoconstriction and reduces pressure in the retinal capillaries and venules. When water flux from the vascular compartment to the tissue compartment decreases, edema will improve according to Starlingâs law.
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Last date updated on January, 2021