Eye

• The eye is a sense organ containing receptors sensitive to light intensity and colour
• The retina contains receptors which are sensitive to light intensity and colour
• The optic nerve carries impulses from the retina to the brain
• The sclera is a tough wall supporting the eye
• The cornea is the transparent outer layer found at the front of the eye that refracts light into the eye
• The iris contains muscles that control the diameter of the pupil and how much light enters the eye
• The ciliary muscles and suspensory ligaments control the shape of the lens
• The lens focuses light
• When the eye is in dim light the radial muscles contract and the circular muscles relax which makes the pupil wider
• To focus on a near object

  • The ciliary muscles contract
  • The suspensory ligaments loosen
  • The lens is then thicker and refracts light rays strongly.
• To focus on a distant object

  • The ciliary muscles relax
  • The suspensory ligaments tighten
  • The lens is then pulled thin and only slightly refracts light rays
• Hyperopia (long sighted) is when people cannot focus on near objects. The lens does not reflect light enough or the eyeball is too short
• Hyperopia can be corrected with a convex lens as it refracts light more so it hits the retina
• Myopia (short sighted) is when people cannot focus on distant objects because the lens is too thick or the eye is too long
• Myopia can be corrected with a concave lens which will focus light onto the retina
• Hyperopia

  
• Myopia

  
• Contact lenses compensate the fault in focusing
• Soft contact lenses are more comfortable but carry more risk of infection than hard lenses
• Laser eye surgery can change the shape of the cornea but there is a risk of complications
• Replacement lens surgery removes the natural lens and replaces it with an artificial lens made of plastic
• Replacement lens surgery comes with higher risks than laser eye surgery and could damage the retina
• The eye

  A) Retina

  B) Optic Nerve

  C) Cornea

  D) Iris

  E) Ciliary Muscle

  F) Suspensory Ligament