5 errors of refraction

• Nearsightedness (Myopia)

  Occurs when light entering the eye focuses in front of the retina instead of directly on it. Caused by a cornea that is steeper, or an eye that is longer, than a normal eye. Nearsighted people typically see well up close, but have difficulty seeing far away.

  
• Nearsightedness

  • Often discovered in school-age children who report having trouble seeing the chalkboard
  • Usually becomes progressively worse through adolescence and stabilizes in early adulthood
  • An inherited problem
• Farsightedness (Hyperopia)

  Occurs when light entering the eye focuses behind the retina, instead of directly on it. Caused by a cornea that is flatter, or an eye that is shorter, than a normal eye. Farsighted people usually have trouble seeing up close, but may also have difficulty seeing far away as well.

  
• Farsightedness

  • Young people with mild to moderate hyperopia are often able to see clearly because their natural lens can adjust, or accommodate to increase the eye's focusing ability
  • As the eye gradually loses the ability to accommodate (beginning at about 40 years of age), blurred vision from hyperopia often becomes more apparent

  
• Astigmatism

  Means that the cornea is oval like a football instead of spherical like a basketball. Most astigmatic corneas have two curves – a steeper curve and a flatter curve. This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near.
• Astigmatism

  • Often occurs along with nearsightedness or farsightedness
• Presbyopia

  Also known as the "short arm syndrome", is a term used to describe an eye in which the natural lens can no longer accommodate. Accommodation is the eye's way of changing its focusing distance: the lens thickens, increasing its ability to focus close-up. At about the age of 40, the lens becomes less flexible and accommodation is gradually lost.

  
• Visual acuity

  Measured as a fraction, with the numerator representing the distance in feet the patient is from the eye chart, and the denominator representing the distance an eye with "normal" vision can read the same line. 20/20 vision means the patient can see at 20 feet what a normal eye can see at 20 feet.

  
• Refraction

  A vision test that determines a person's best visual acuity with corrective lenses, using an instrument called a phoropter to adjust the lenses until the eye chart appears the clearest possible.

  
• Astigmatism is a term that relates to the cornea
• Astigmatism causes blurred vision

  
• An astigmatic cornea is shaped most like a football
• Astigmatism can occur along with both nearsightedness and farsightedness
• Astigmatism can be corrected with both surgery and glasses