Our body is regulated by many basic mechanisms working intricately to maintain the homeostasis. This is true for all major organs and organ systems including the eye. This chapter gives an insight into these basic mechanisms of congestion, hemorrhage, and edema that we see so routinely in clinics. Also discussed are some less common causes of blood clotting, disseminated intravascular coagulation (DIC), and shock, which may also sometimes affect vision and should alert an ophthalmologist to retrospectively look for the systemic danger signals, or vice versa.