Eye

• Sclera

  White layer outside of the eye ball

  Functions

  • Protects eye
  • Maintains shape of eye
• Cornea

  Transparent part of sclera & is more convex than the rest of the eye.

  Function:

  • Allows light to inner parts of the eye.
• Choroid

  Thin, dark pigmented layer(under sclera)

  Function

  • Pigment absorbs excess light, preventing internal reflection.
• Ciliary Body

  Thickened part attached to the lens

  • Contracts and relaxes to change the shape of the lens during accommodation.
• Iris

  Colour part of the eye

  • Regulates the amount of light that enters the eye by controlling the size of the pupil.
• Lens

  Elastic, biconvex

  • Change shape to refract light rays to form clear images.
• Retina

  Has a pigmented layer in contact with choroid.

  • Absorbs light rays, preventing internal reflection.
• Yellow spots

  Form the clearest & most accurate image.
• Optic nerve

  Conducts nerve impulses to cerebrum, giving rise to sight.
• Functioning of eye

  • Light rays enter and are refracted by the cornea & lens to focus a clear image on the yellow spot.
  • Retina contains photoreceptors(rods & cones)
  • Rods are stimulated in low light giving rise to black and white vision
  • Cones are stimulated in high light, giving rise to bright colour vision.
  • When stimulated by light rays, impulses are discharged to the cerebrum.
• Binocular vision

  • The left and right eye form their own seperate images and the brain combines them to form one image.
  • Binocular vision provides wider vision, and depth.
• Accommodation

  The process where the eye adapts for the sight of nearby objects by changing the lens’ shape.

  Distant vision

  • Muscles are relaxed
  • Ciliary body is further away from the lens (lens is pulled)
  • Lens is less convex
  • Less refraction of light due to flat lens.
  • Sharp, focused image falls on the retina.

  Near vision

  • Muscles contract
  • Ciliary body is closer to the lens(lens is curved)
  • Lens becomes more convex
  • More refraction of light due to curved lens.
  • Sharp image falls on the retina.
• Pupil reflex

  Bright light

  • Radial muscles relax
  • Circular muscles contract
  • Pupil becomes smaller
  • Less light enters

  Dim light

  • Radial muscles contract
  • Circular muscles relax
  • Pupil becomes bigger
  • More light enters.