Nearsightedness (myopia)

What is nearsightedness?
Having a hard time seeing across the room? You’re probably nearsighted. Learn more about nearsightedness (also called myopia) here.
Nearsightedness is a vision problem (or refractive error) in which the eye sees near objects clearly, but distant objects are blurred. The medical term for nearsightedness is myopia - which is derived from a Greek word meaning “closed eyes.” It’s believed this is a reference to the primary symptom of nearsightedness, which is squinting.

What causes nearsightedness?
Clear vision requires the cornea and the lens of the eye to focus light perfectly on the retina. For this to happen, the cornea and lens must have exactly the right amount of curvature so they can focus light within the length of the eyeball.
Nearsightedness occurs when the cornea (or lens, or both) is too curved and light from distant objects is focused inside the eye before it reaches the retina. At the retina (beyond the focus point of the nearsighted eye), images of distant objects are blurred.
In some cases, the cornea and lens have a normal amount of curvature, but the eyeball is longer than normal, and therefore the retina is located too far from the normal focusing point.
This is called axial myopia because the distance blur is due to an unusually-long axial (front-to-back) length to the eye.
  Why is near vision unaffected?
In an eye with normal vision, the focusing muscle inside the eye has to change the shape of the crystalline lens in order for near objects to be seen clearly. This focusing process is called accommodation. Accommodation is required for near vision because light reflecting from near objects enters the eye in such a way that a greater amount of lens curvature is required to focus it (compared to light entering the eye that’s reflected from distant objects). 		 
 
Because a nearsighted eye has a cornea or lens (or both) that is too curved for clear distance vision, it can see near objects with less than the normal amount of accommodation. So a nearsighted eye not only sees near objects clearly without corrective lenses, it does so with less effort than a normal eye!
This is why some nearsighted individuals prefer to remove their eyeglasses for sustained reading and other near vision tasks. If they have a mild amount of nearsightedness, their eyes will be less strained and more comfortable for reading and computer work if their nearsightedness is left uncorrected (reducing the need for accommodation). However, individuals with moderate or severe amounts of nearsightedness must hold objects very close to their eyes to see them clearly—these people are more comfortable leaving their corrective lenses on at all times.
A mild amount of nearsightedness is especially beneficial if you are over age 40 and are experiencing the normal age-related loss of accommodative ability called presbyopia. As we get older, the crystalline lens inside the eye becomes hardened and the focusing muscle inside the eye can no longer change its shape. Accommodative ability is lost, and near objects become blurred. It’s this normal age-related change that requires us to wear reading glasses, bifocals, or progressive lenses to restore our near vision when we get older.
Since a mildly nearsighted eye can see clearly up close without accommodation, some nearsighted individuals who wear eyeglasses can avoid bifocals or progressive lenses by simply removing their glasses for reading and other near vision tasks.
If you are nearsighted, over age 40 and you wear contact lenses, ask your eye doctor about adjusting your contact lens prescription for monovision. This involves changing your contact lens prescription to make (or leave) one eye mildly nearsighted. The eye with your current contact lens prescription will see distant objects clearly, and the eye with the modified contact lens prescription (because it’s made mildly nearsighted) will see clearly up close. Thus with both eyes open, monovision contact lenses allow you to see clearly at all distances without reading glasses.
(Not everyone is comfortable wearing monovision contact lenses. Visit your eye doctor for a trial fitting to see if monovision will work for you. Bifocal contact lenses are also available.)

How common is nearsightedness?
Myopia usually occurs during childhood and is almost always diagnosed before age 20. Nearsightedness can worsen throughout the school years, and the earlier a child becomes nearsighted, the more nearsighted they will tend to be as an adult.

What are the symptoms of nearsightedness?
Symptoms of nearsightedness include:
• Squinting (when viewing distant objects)
• Headaches (usually later in the day; caused by squinting)
• Blurred vision (distance only)

Nearsightedness is not associated with poor academic performance. In fact, nearsighted youngsters tend to be better than average students.
How is nearsightedness treated?
Nearsightedness can be corrected with eyeglasses, contact lenses or refractive surgery.

Can nearsightedness be prevented?
At this time, there doesn’t appear to be anything that can be done to prevent nearsightedness. But research shows that fitting some nearsighted youngsters with rigid gas permeable (RGP) contact lenses may slow or halt the progression of their myopia. (This effect is not seen with soft contact lens wear.) Ask your eye doctor for details.
Some eye doctors recommend reading glasses or bifocal lenses for youngsters to reduce their accommodative stress when reading. They believe accommodative stress may be a factor in the development and progression of myopia, and that relieving this stress may decrease the likelihood that a youngster will become nearsighted or that their myopia will progressively worsen. However, this practice remains controversial.

 
 
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