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.
Sinusoidal capillaries are leaky capillaries that allow large molecules to pass between the blood and surrounding tissues. Capillary beds are microcirculatory networks consisting of a vascular shunt and true capillaries, which function as the exchange vessels.asomotion, the slow, intermittent flow of blood through the capillaries, reflects the action of the precapillary sphincters in response to local autoregulatory controls. Capillary exchange of nutrients, gases, and metabolic wastes occurs between the blood and interstitial space through diffusion.