In an eye with normal vision, focusing ability of the cornea and lens is matched to the length of the eye. Your eyes are therefore able to focus an image precisely on the retina.
In nearsightedness, or myopia, vision is better up close than at a distance.
In farsightedness, or hyperopia, vision is often better at a distance than up close (although it may be blurry both at a distance and up close).
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Both of these conditions are caused by structural distortions within the eye.
In myopia, your eyes focus the image ahead of the retina. This usually occurs with an eyeball that is longer or a cornea that is steeper than normal.
In hyperopia, your eye focuses the image behind the retina. This usually occurs if your eyeball is too short or the cornea has too little curvature. With aging, the lens of the eye becomes less flexible and cannot focus as well on close objects. This condition, called presbyopia, accounts for the development of difficulty seeing near objects in most people after the age of 40.
A risk factor is something that increases your chance of getting a disease or condition. Risk factors are slightly different for the two types of vision disorders.
Having a family member with myopia increases your risk for the disorder. Also, although the evidence is conflicting, some specialists believe that chronic near work, such as iprolonged periods of reading or the daily use of a computer can increase the risk of developing myopia.
There are two main risk factors for hyperopia:
Age: 40 or older (hyperopia due to
- Family member with hyperopia