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.
Capillary hydrostatic pressure created due to the pumping action of heart. Role of capillary hydrostatic pressure in movement of fluid between capillaries and the interstitial fluid: The net filtration pressure is the pressure which determines the movement of fluid between capillaries and interstitial fluid. It is the difference between the capillary hydrostatic pressure and the osmotic pressure. If the capillary hydrostatic pressure is greater than osmotic pressure then fluid will leave the capillary and if the capillary hydrostatic pressure is less than that of osmotic pressure fluid will enter into the capillary.