The retinal vessel changes are the primary and major features of retinal vascular diseases.The retinal vessel is part of systemic vessels with its own characteristics to sustain normal retinal function.These basic characteristics are important to the correct understanding and proper treatment of retinal vascular diseases.Always keep in mind that the retinal vessels is one part of the systemic vascular system,thus retinal vascular diseases may have systemic etiology,and systemic drug administration may have a profound effects to the whole body.However retinal vascular system also has its own structural and functional characteristics,thus retinal vascular diseases are also different from the systemic diseases.Finally the main function of retinal vascular network is to maintain the neuro-retinal function,thus we should balance the vision protection and treatments against abnormal retinal blood vessels.Over-treatments may damage the retinal vision.