correcting vision defects

• what is hyperopia?

  long-sightedness
• what is myopia?

  short-sightedness
• people with hyperopia (long-sightedness) are unable to focus on near objects
• people with myopia (short-sightedness) are unable to focus on distant objects
• when does hyperopia occur?

  when the lense is the wrong shape and doesnt refract (bend) light enough, or the eyeball is too short
• when does myopia occur?

  when the lense is the wrong shape and refracts (bends) too much light, or the eyeball is too long
• with hyperopia the images of near objects are brought to focus behind the retina
• with myopia the images of near objects are brought to focus infront of the retina
• what lense is used to treat hyperopia?

  a convex lense (curves outwards) so the light focuses on the retina
• what lense is used to treat myopia?

  a concave lense (curves inwards) so the light focuses on the retina
• what are three treatments for vision defects (besides glasses)?

  contact lenses, laser eye surgery, and replacement lense surgery
• what are contact lenses?

  thin lenses that sit on the eyes surface and are shaped to compensate for the fault in focusing. the two main types are hard lenses (lower risk of eye infection) and soft lenses (more comfortable)
• how does laser eye surgery work?

  a laser is used to vaporise tissue, changing the shape of the cornea (changing how strongly it refracts light into the eye). slimming it makes it less powerfull so its used to improve short sight, changing the shape so its more powerfull will improve long sight, however there is a risk of complications (e.g infection)
• how does replacement lens surgery work?

  the natural lense of the eye is removed and an artificial lense, made of clear plastic, is inserted in its place. there is a higher chance of complications (e.g damage to the retina)
• explain the cause of myopia

  the lense is the wrong shape and refracts the light too much, so images of distant objects are brought into focus infront of the retina
• how do glasses help someone with hyperopia focus on something nearby?

  the lenses refract the light rays so they focus on the retina