There are several factors which affect normal vision and eyesight. These factors include diet, heredity, environmental factors including exposure to artificial light, age, etc. Hormones can also affect our vision considerably.
The flow of blood in the capillaries is controlled by structures called precapillary sphincters. These structures are located between arterioles and capillaries and contain muscle fibers that allow them to contract. When the sphincters are open, blood flows freely to the capillary beds of body tissue.When the sphincters are closed, blood is not allowed to flow through the capillary beds. Fluid exchange between the capillaries and the body tissues takes place at the capillary bed.hen the sphincters are open, blood flows freely to the capillary beds of body tissue. When the sphincters are closed, blood is not allowed to flow through the capillary beds. Fluid exchange between the capillaries and the body tissues takes place at the capillary bed.
Blood flows continuously through the capillaries, it does not squirt and pause as your heart beats. This continuous flow is necessary because there is a constant exchange of oxygen and nutrients happening in the capillary walls. No cell in the body is far from a capillary.