Mystery of Retinal Vein Occlusion: Vasoactivity of the Vein and Possible Involvement of Endothelin-1

Received May 31, 2017; Accepted Jul 13, 2017

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1. Introduction

Retinal vein occlusion (RVO) is common vascular disease of retina. Some well-known studies in large populations indicate that RVO is the second most frequent retinal vascular disease behind only diabetic retinopathy and that RVO is the fifth leading cause of blindness [1–4]; however, the pathomechanism leading to RVO is not yet clear. In general, RVO can be classified into branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO), depending on the affected vein lesion. Both RVO commonly occur unilaterally and show different variations on the degrees of severity. Some RVO are resolved without any treatment and others develop the vision-threatening complications [4–6], such as macular edema, combined retinal artery occlusion [7, 8], vitreous hemorrhage [9], and glaucoma [10, 11].

Despite taking numerous clinical courses of RVO, these complications are decreasing due to the development of various therapeutic approaches in addition to early alert and treatment by internal medicine doctors for cardiovascular diseases like systemic hypertension and dyslipidemia, which are well-known risk factors of RVO [6, 12–14]. Vein congestion can lead to local hypoxia, thereby increasing vascular endothelial growth factor (VEGF) [15]. Anti-VEGF therapy is the standard treatment for RVO-related macular edema at present, and it is effective in achieving a relatively rapid resolution of macular edema in most RVO patients [16–19]. In addition, it has been reported that not only VEGF but also inflammatory cytokines are associated with RVO-related macular edema [20–22].

Interestingly, the prevalence of RVO in Japan is higher than in other countries [3, 23–27]. The Hisayama study of the general Japanese population aged 40 years or older found that the prevalence of RVO is higher in Japanese patients than in other Asians or Caucasian individuals [3]. In this situation, repeated injections are often required due to a recurrence of macular edema, and the number of injections continues to increase. Thus, it is imperative that we gain a much better understanding of the clinical...