Correcting Vision Defects

• Long-sighted people are unable to focus on near objects
• Long-sightedness occurs when the lens is the wrong shape and doesn't refract the light enough or the eyeball is too short
• Long-sightedness

  the images of near objects are brought into focus behind the retina
• You can use glasses with a convex lens to correct long-sightedness
• Convex lens

  a lens that curves outwards
• The medical term for long-sightedness is hyperopia
• Short-sighted people are unable to focus on distant objects
• Short-sightedness occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long
• Short-sightedness

  the images of distant objects are brought into focus in front of the retina
• You can use glasses with a concave lens to correct short-sightedness
• The medical term for short-sightedness is myopia
• There are several treatments for vision defects:

  • glasses
  • contact lenses
  • laser eye surgery
  • replacement lens surgery
• Contact lenses:

  • contact lenses are thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing
  • they are popular because they're lightweight and are almost invisible, and are more convenient than glasses for activities like sport
  • the two main types of contact lenses are hard lenses and soft lenses
  • soft lenses are generally more comfortable, but carry a higher risk of eye infections than hard lenses
• Laser eye surgery:

  • a laser can be used to vaporise tissue, changing the shape of the cornea (and so how strongly it refracts light into the eye)
  • slimming it down makes it less powerful and can improve short-sightedness
  • changing the shape so that it's more powerful will improve long-sightedness
  • the surgeon can precisely control how much tissue the laser takes off, completely correcting the vision
  • however, there is a risk of complications, such as infection, or the eye reacting in a way that makes your vision worse than before
• Replacement lens surgery:

  • sometimes short-sightedness may be more effectively treated by replacing the lens of the eye
  • the natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place
  • as it involves work inside the eye, replacing a lens carries higher risks than laser eye surgery, including possible damage to the retina (which could lead to loss of sight)