Extracellular modulating factors and the control of intraocular neovascularization: an overview

The process of neovascularization or new blood vessel formation is extraordinarily complex, requiring the successful coordination of numerous cellular and extracellular events. The ever increasing number of factors that can modulate events involved in neovascularization and the ability of some and possibly all of these factors to have different effects, depending upon the presence or absence of co-factors, require new hypotheses regarding the initiation and control of neovascularization. Each factor by itself is probably relatively meaningless, just as an individual number is in a combination used to open a lock. However, several factors occurring in a specific combination can unlock neovascularization. Different combinations may play a role in different disease states. Therefore, rather than classifying these substances as growth factors it may be more accurate to call them "extracellular modulating factors," or EMFs. The balance among these EMFs most likely varies during health and disease and in response to therapeutic intervention.