Anatomy of the Visual System

The Sense of Vision

• The sense of vision consists of three major components: the eyes, the system of nerves, and the visual cortex.
• Blindness results if any one of these parts does not function.

Focusing Elements of the Eye

• The cornea is a fixed focus element that does about two-thirds of focusing light.
• The lens is variable in shape and has the ability to focus objects at various distances.

Anatomy of the Eye

• The cornea focuses by bending (refracting) light rays.
• The amount of bending depends on the curvatures of its surfaces and the speed of light in the lens compared with that in the surrounding material.

Refractive Indices of Eye Components

• The index of refraction is nearly constant for all corneas.
• Refractive indices of different parts of the eye:
  • Cornea: 1.37
  • Aqueous humor: 1.33
  • Lens cover: 1.38
  • Lens center: 1.41
  • Vitreous humor: 1.33

The Iris

• The iris is the colored part of the front of the eye.
• Functions of the iris:
  • Adapts vision from light to dark and vice versa.
  • Aids the eye by increasing or decreasing incident light on the retina until the retina adapts to new lighting conditions.
  • Reduces lens defects under bright light conditions.