the eye

• to see distant objects the ciliary muscles relax causing the suspensory ligaments to tighten making the lens pull thin and less curved so the light doesn't bend as much so light is focused on the retina.
• to look at near objects the ciliary muscles contract which slackens the suspensory ligaments causing the lens to go fat and more curved, which bends the light more
• Long sighted people are unable to focus on objects near them
• short sighted people are unable to focus on objects far away from them
• myopia can be corrected using a concave lens which causes the light to refract out,
• hyperopia can be corrected using a convex lens which refracts light inwards
• concave lenses are lenses that have a thicker rim and a thinner middle. it refracts light outwards for people who rays converge before the retina
• convex lenses are lenses that have a thicker middle and a thinner rim. They refract light inwards for people who light converges after the retina
• contact lenses are a way to correct vision without surgery, they are placed on the eye. and compensate for the fault in focusing. However they can get infected and cause discomfort. They are good because they are almost invisible and are more convenient than glasses.
• laser eye surgery is a way to correct myopia and hyperopia. It uses a laser to change the shape of the cornea. Its good because the surgeons can see exactly what they are doing and it is very precise. It can completely correct vision. However there are risks of complications such as infection
• replacement eye surgery is a way to treat hyperopia. The natural lens is removed and plastic lens is inserted in its place. However it carries higher risk as it involves working inside the eye. Can cause damage to the retina, could lead to loss of sight.
• what is the eye?

  a sense organ containing receptors sensitive to light intensity and colour
• label this diagram of the eye:

  A) sclera

  B) retina

  C) optic nerve

  D) suspensory ligaments

  E) ciliary muscles

  F) iris

  G) cornea

  H) lens

  I) pupil

  
• what is the sclera?

  tough white supporting wall of the eye
• what is the function of the sclera?

  Protection and support for the eyeball.
• what is the cornea?

  the transparent outer layer found at the front of the eye
• what is the function of the cornea?

  To refract light when it enters the eye
• what is the iris?

  The colored part of the eye that controls the size of the pupil.
• what is the function of the iris and how is it adapted to this function?

  to control the diameter of the pupil so controlling how much light can enter the eye - contains muscles which allow this to happen
• what is the function of the lens?

  focus light onto the retina
• what is the shape of the lens controlled by?

  ciliary muscles and suspensory ligaments
• what is the function of the optic nerve?

  carry impulses from the receptors on the retina to the brain via sensory neurones
• what is accommodation?

  the process of changing the shape of the lens to focus on near or distant objects
• what is the pupil?

  the hole through which light enters the eye
• what two type of receptor cells are there on the retina?

  rods which are sensitive to light intensity and cones which are sensitive to colour
• why must the iris reflex work?

  To regulate the amount of light entering the eye as very bright light can damage the eye
• how does the iris reflex decrease the size of the pupil?

  light receptors (rods) in the retina detect bright light which triggers a reflex that makes the pupil smaller, the circular muscles in the iris contract and the radial muscles relax reducing the amount of light that can enter the eye
• how does the iris reflex increase the size of the pupil?

  when light receptors (rods) in the retina detect low levels of light they trigger a reflex which widens the diameter of the pupil allowing more light in the eye, this happens by the radial muscles contracting and the circular muscles relaxing
• label this diagram:

  A) circular muscles

  B) radial muscles

  C) pupil

  D) iris

  
• this is the iris reflex - label what is happening:

  A) dim light

  B) bright light

  C) radial muscles contract

  D) circular muscles contract

  E) dilation

  F) contraction

  
• which type of lenses are these

  A) convex

  B) concave

  
• why do older people often have eye defects - mainly myopia ?

  your eye lens loses flexibility so it cannot easily spring back to its round shape so light often cannot be focused for near viewing
• what is the scientific word for long sightedness?

  Hyperopia
• what is the scientific word for short sightedness?

  myopia
• what are some causes of hyperopia?

  eyeball being too short or the lens being the wrong shape resulting in the images of near objects being brought into focus behind the retina resulting in a blurry image
• what are some causes of myopia?

  lens being the wrong shape or the eyeball being too long meaning the image of distant objects is brought into focus in front of the retina resulting in a blurry image
• 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 are pulled tight • the lens is then pulled thin and only slightly refracts light rays.
• How are myopia and hyperopia generally treated?

  spectacle lenses
• why does the cornea not have any blood vessels?


  so it is transparent and all the light can pass through, so all the oxygen it needs has to diffuse into it from the outside air rather than the blood like the rest of the body, the cornea refracts the light