What is Farsightedness and Nearsightedness?
Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects can be seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature. In these cases, your eye can’t correctly focus the light that enters it.
Common signs of hyperopia include difficulty concentrating and maintaining a clear focus on near objects, eye strain, fatigue and/or headaches after close work, aching or burning eyes, and irritability or nervousness after sustained concentration.
Common vision screenings, like the ones done in schools, often don’t detect hyperopia. However, a comprehensive optometric examination will include the necessary testing to diagnose hyperopia. If needed, your optometrist can offer treatment options.
In mild cases of farsightedness, your eyes may be able to compensate without corrective lenses. In other cases, your optometrist can prescribe eyeglasses or contact lenses that alter the way the light enters your eyes, allowing you to clearly see close objects.
Why does hyperopia occur?
If the length of the eyeball is too short or the cornea has too little curvature, it is difficult to focus on near objects. Hereditary factors often control the growth and development of the eye. However, environmental factors may also contribute to the development of hyperopia.
How common is hyperopia?
Many people have some degree of hyperopia. The condition is only a problem if it significantly affects a person’s ability to see. It is estimated that over half the people who wear glasses are wearing them due to farsightedness or presbyopia (a naturally occurring decrease in focusing ability at near distance).
What are signs/symptoms of hyperopia?
Common signs and symptoms of hyperopia include difficulty concentrating and maintaining a clear focus on near objects, blurred vision, eyestrain, fatigue and/or headaches after close work.
How is hyperopia diagnosed?
Hyperopia can be effectively diagnosed in a comprehensive optometric examination. Common vision screenings, often done in schools, generally don’t detect farsighted people. This is because these individuals can identify the letters on a distance eye chart with little difficulty, but they are not often effectively tested at near distance.
How does hyperopia affect vision?
If you are hyperopic, you involuntarily exert extra effort to maintain clear distance vision and even greater effort to see clearly at close range. This extra effort can cause fatigue, tension and discomfort. If the crystalline lens of the eye cannot bring the viewed object into focus, blurred vision results.
How is hyperopia treated?
In mild cases, your eyes may be able to compensate adequately without corrective lenses. In moderate or severe cases, your optometrist may recommend glasses or contact lenses. Most individuals adapt well to wearing glasses or contact lenses, and farsightedness does not significantly affect their lifestyle.
Myopia – Nearsightedness
Nearsightedness, or myopia, as it is medically termed, is a vision condition in which people can see close objects clearly, but objects farther away appear blurred. People with myopia can have difficulty clearly seeing a movie or TV screen or the whiteboard in school.
Myopia occurs if the eyeball is too long or the cornea (the clear front cover of the eye) is too curved. As a result, the light entering the eye isn’t focused correctly, and distant objects look blurred.
Myopia affects nearly 30 percent of the U.S. population. While the exact cause of myopia is unknown, there is significant evidence that many people inherit myopia, or at least the tendency to develop myopia. If one or both parents are nearsighted, there is an increased chance their children will be nearsighted.
Even though the tendency to develop myopia may be inherited, its actual development may be affected by how a person uses his or her eyes. Individuals who spend considerable time reading, working at a computer, or doing other intense close visual work may be more likely to develop myopia.
Generally, myopia first occurs in school-age children. Because the eye continues to grow during childhood, it typically progresses until about age 20. However, myopia may also develop in adults due to visual stress or health conditions such as diabetes.
Myopia may also occur due to environmental factors or other health problems:
- Some people may experience blurred distance vision only at night. With “night myopia,” low light makes it difficult for the eyes to focus properly. Or the increased pupil size during dark conditions allows more peripheral, unfocused light rays to enter the eye.
- People who do an excessive amount of near-vision work may experience a false or “pseudo” myopia. Their blurred distance vision is caused by overuse of the eyes’ focusing mechanism. After long periods of near work, their eyes are unable to refocus to see clearly in the distance. Clear distance vision usually returns after resting the eyes. However, constant visual stress may lead to a permanent reduction in distance vision over time.
- Symptoms of myopia may also be a sign of variations in blood sugar levels in people with diabetes or may be an early indication of a developing cataract.
An optometrist can determine the cause of the vision problems through a comprehensive eye exam.
How is myopia diagnosed?
Testing for myopia may use several procedures to measure how the eyes focus light and to determine the power of any optical lenses needed to correct the reduced vision.
As part of the testing, you will identify letters on a distance chart. This test measures visual acuity, which is written as a fraction, such as 20/40. The top number of the fraction is the standard distance at which testing is performed (20 feet). The bottom number is the smallest letter size read. A person with 20/40 visual acuity would have to get within 20 feet to identify a letter that could be seen clearly at 40 feet in a “normal” eye. Normal distance visual acuity is 20/20, although many people have 20/15 (better) vision.
Using an instrument called a phoropter, an optometrist places a series of lenses in front of your eyes and measures how they focus light using a handheld lighted instrument called a retinoscope. Or the doctor may choose to use an automated instrument that evaluates the focusing power of the eye. The power is then refined based on your responses to determine the lenses that allow the clearest vision.
Your optometrist can conduct this testing without using eye drops to determine how the eyes respond under normal seeing conditions. In some cases, such as for patients who can’t respond verbally or when some of the eye’s focusing power may be hidden, an optometrist may use eye drops. The eye drops temporarily keep the eyes from changing focus during testing.
Using the information from these tests, along with the results of other tests of eye focusing and eye teaming, your optometrist can determine if you have myopia. He or she will also determine the power of any lens correction needed to provide clear vision. Once testing is complete, your optometrist can discuss treatment options.
If you have myopia, you have a variety of options to correct your vision problem. In consultation with your optometrist, you can select the treatment that best meets your visual and lifestyle needs.www.aao.org