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What is hyperopia?
When you are hyperopic (farsighted), your eyes have to work overtime to keep things in focus. Whenever that effort becomes too great, it can cause symptoms, but these can be easily corrected with glasses or contact lenses. Many people think that farsightedness must be the "opposite" of nearsightedness. And since nearsighted individuals have good near-vision and blurry distance vision, being farsighted "should" mean seeing well at a distance and poorly up close. But that isn't exactly the case. Although it is true that most farsighted people can see distant objects clearly, to do so they need to use more focusing effort than other people, and for seeing up close they need to exert an even greater effort.
What causes hyperopia?
Eyeball size and optical power vary among individuals, just like height and weight. Hyperopia (short for hypermetropia) results when the eyeball is too small, creating less optical power than the eye needs for bringing light rays into clear focus on the retina. Fortunately, the normal focusing mechanism can usually supply the additional optical power needed. At birth, nearly everyone is somewhat farsighted, but the amount lessens as the eye grows. Once you have reached adulthood, any hyperopia still present will tend to remain. It is not affected by diet, vitamins, or eye exercises.
What are the symptoms?
Hyperopia can be symptomless. Or it can cause blurring of vision, browaches, eyestrain or other ill-defined eye discomfort, along with restlessness, fatigue, or irritability, especially after prolonged close work. Whether you have symptoms or not depends partly an how farsighted you are and partly on how much accommodation (focusing ability) you have --and that depends on your age; accommodation is maximal at birth and decreases to zero by about age 60.
Children who are very farsighted may have a poor attention span. They may also have crossed eyes because, in attempting to maintain clear vision, their focusing mechanism has to work extra hard. That effort sometimes spills over into the eye muscles, causing the eyes to over-converge, or cross.
What is accommodation?
Accommodation is a flexible focusing mechanism that automatically adds to any eye's optical power. It is this mechanism that enables normal eyes to focus clearly on objects that are up close. When an eye is farsighted, it needs the extra optical power that accommodation provides just to see objects located in the distance, and even more accommodation to see objects that are up close. As long as there is sufficient accommodative power available, it will automatically "correct" your farsightedness, just like an auto-focus camera.
When are glasses necessary?
For your accommodation mechanism to "self-correct" your hyperopia, it takes continuous focusing effort. If that does not cause symptoms or problems, your hyperopia can be left alone; not correcting it will not harm your eyes in any way. But if it does cause symptoms, the additional power can be supplied by eyeglasses or contact lenses. Farsighted children are rarely aware of a vision problem. The amount of accommodative power they have available is usually so great that it can compensate easily and automatically for the reduced optical power of their eyes. If the extra focusing effort does cause symptoms, they can be relieved by prescription glasses. For example, if the child's eyes cross, eyeglasses will be required, not only to keep the eyes properly aligned, but to maintain clear vision in both eyes and prevent "lazy eye" (amblyopia) from developing.
What is the connection between hyperopia and presbyopia?
From birth onward, everyone's accommodation (focusing power) diminishes. By midlife, presbyopia (normal, age-related focusing difficulty for near) will make focusing impossible for some close range activities. Reading glasses or bifocals can almost always supply the power needed. For most people, presbyopia comes on around the age of 45 or so, but far-sighted people can be affected as young as 25 or 30. This difference exists because farsighted eyes that are not corrected with glasses are already using up some of their accommodation to see at all distances. Because there is less accommodation remaining, it tends to "run out" sooner. It is the depleted accommodation that creates the presbyopia. However, if the farsightedness is corrected with glasses, presbyopia will be put off until 45 or so, the time it would normally occur.
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