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Eye terminology can be very confusing. When your optometrist diagnoses you or your family members with farsighted vision, that is usually the end of the explanation. Farsighted vision can create so many different effects on your eyesight that it may not even seem to be one visual condition. Being farsighted (hyperopia) usually results in good distance vision, with problems induced by near tasks like reading and computer work. It is a somewhat muddled term since farsightedness is actually an optical error of distance vision, while the symptoms are most common when you use your near vision.
To further complicate the situation, if your optometrist finds your eye prescription is extremely farsighted, you will not see clear up close or far away. If you are young and have a low or moderate degree of farsightedness your eyesight may be clear for all distances. There is no wonder people have trouble grasping the concept of farsighted vision, and why eye doctors often avoid trying to explain it. Fortunately there is a muscle referred to as the ciliary muscle that surrounds the lens in the eye, and is attached to the lens with small fibers. Active contraction of this muscle loosens the tension on the lens in the eye and increases the eyes focusing power. In lower amounts of farsightedness if you are under the age of forty, the focusing capacity of the eye can accommodate for farsightedness and clear your vision for both distance and near easily. Eye Doctors use the words focusing and accommodation interchangeably to mean the eye muscle has gone to work to increase the power of the eye for near vision.
Even lower amounts hyperopia have been shown to interfere with reading in some children and adults, but normally between two to three prescription units it starts to create visually related symptoms. Kids and teens have an enormous amount of accommodation, and sometimes very large prescriptions for farsightedness are not noticed because they can clear near and distance vision by focusing. Often they will suffer headaches and an unconscious aversion to reading because of the eyestrain and effort constantly being required to keep their vision clear. As we grow older we gradually lose the ability to focus. This degradation of focusing starts between the age of fifteen to twenty, but effects distances so close at first that we never notice because we do not use our vision one or two inches away.
People who are farsighted have a different type of problem than individuals who are nearsighted. They constantly have to focus to keep their distance vision clear and as objects move closer they have to ramp up their focusing efforts even more. This is not a problem if you are young and have lower amounts of hyperopia, but as you age or with larger amounts of hyperopia the extra effort you exert starts to become noticeable. This occurs with reading and computer use initially, due to the added effort of focusing on top of the amount required for distance. In high tech areas like Northern Colorado there is a larger percentage of the population using computers all day and more symptoms from farsightedness are being seen by optometrists. Farsighted vision that is not corrected can be a significant component of Computer Vision Syndrome. Frequently, eye patients will be prescribed glasses or contact lenses for close work that only correct the distance amount of farsightedness. This lessens the amount of focusing needed for near to normal levels. The remaining normal effort to read or work on a computer rarely creates visual discomfort. This is another reason your optometrist may not communicate much about your farsighted vision. It is tough for them to explain why you are having a distance eye glass prescription being recommended when you are only having problems up close.
As farsighted optometry patients enter their early forties they find they have gradually started wearing glasses all the time. Many people mistakenly believe that wearing the glasses have made their eyes weaker, and sometimes feel their eye doctor has made them dependent on the lenses. This is an incorrect assumption, as the loss of accommodating ability would have occurred without wearing glasses, and would have been a problem at an earlier age in the absence of corrective eye wear. This loss of focusing power is a visual condition specified as presbyopia, which patients often confuse with farsightedness. Although it progresses from an early age as explained before, it is only diagnosed when it reduces your focusing capacity so you cannot see at about sixteen inches, the average reading distance.
Optically, the farsighted eye is usually too short and light focuses behind it instead of on the retina for distance. There may also be individual components of the eye that are too weak to focus vision adequately. The lens could be a little short in power, or the clear cornea tissue on the front of the eye could be curved slightly less than normal. A lens with plus, or positive power is used to correct for hyperopia. This is a lens thicker in the middle and thinner on the edges, like a biconvex lens. Best optical design for clear central and peripheral vision is a lens more curved on the front and still curved forward on the back, just to a lesser degree. This results in a lens with a center that sits relatively far away from the front of the eye, with a bulging appearance.
As you move an ophthalmic lens used for farsightedness away from the eye, the eye appears larger, just like the effect produced from moving a magnifier away from an object. This also magnifies the size of the image seen by the eye. Advanced optical designs have eliminated the resulting type of bug eye appearance by using aspheric lens designs. Aspheric lenses start out with a front lens surface spherical in the center (like the curve on a tennis ball) then the curvature gradually decreases or flattens towards the edge of the lens. This is the traditional design that has an accompanying spherical curvature on the back surface of the lens. Newly emerging free form lens technology allows aspherical lens curves to be ground on the back surface of a lens. These lenses are very sophisticated designs using different degrees of asphericity in different tangential lines to compensate for astigmatism in your prescription.
Either way, the flattened lens design allows the lenses to sit closer to your eyes decreasing the magnification or bug eye effect. The aspherical design by the complex quirks of optics also counters several forms of optical aberrations (blurring of vision) that normally occur when you look to the side of a spherical lens using a flatter lens design. A common misconception is that aspherical lenses improve vision. They do not significantly improve vision but they do allow for a thinner, lighter, more cosmetically appealing lens with less magnification. The aspherical design allows these improvements to be achieved without compromising clear peripheral vision. The lenses available to your eye doctor have been undergoing quantum advances in the last five years, probably equivalent to all of the advances made in the prior fifty years. The improvements in lens design are starting to resemble computer chips which double in capacity every eighteen months. The future for lenses has never looked brighter!
Some Farsighted Eye Facts:
- Some people are farsighted in one eye and nearsighted in the other. If the amounts are just right they can see near and distance without bifocals.
- President James Buchannan was farsighted in one eye and nearsighted in the other (and had an eye twitch).
- President Harry Truman was farsighted.
- Latent farsightedness occurs when a child has compensated by sustained focusing for distance for so long they cannot relax their eyes for a true reading of the prescription. Only checking the eye glass prescription after special eye drops have eliminated the eyes focusing capacity can yield an accurate prescription reading.
- Ohio State University has started a study to see if providing prescriptions that are not strong enough for extremely farsightedness infants will help the eyes self correct themselves.
- The eyes tend to become slightly more farsighted (or less nearsighted) between the age of forty to fifty.
- Young to middle age males can develop fluid swelling in the central retina and become farsighted as a direct result of stress.
- Children that are farsighted tend to have brothers and sisters that are farsighted, but not necessarily parents with the eye condition.
- Approximately one in four people are farsighted, but the number is slowly decreasing as nearsightedness is increasing in prevalence.
Contact lenses can be very useful in correcting farsighted eyes for a number of reasons. Unlike eye glasses which bow away from the eye, contact lenses sit right on the surface of your eye and therefore supply very little magnification effect. When you wear contact lenses you are always looking through the optical center of the lens which is the point maximized for good vision. This is by virtue of the fact that contact lenses move with your eye when you look to the sides. With eye glasses you view though the lens at an angle when you turn your eyes, and this creates optical aberrations that degrade your vision. These benefits often frequently result in contact lenses being the primary choice for corrective eye wear for higher amounts of farsightedness in children and teenagers. This is often an age when their appearance is intensely important to their self esteem. Who does not want to look better, especially when the old alternative was bug eye magnifying lenses that weighed a ton and slipped down your nose constantly.
Vision screenings have value in detecting eye prescription problems, but often miss farsightedness because children have a large capacity to focus and pass the 20/20 test. Only a thorough eye exam by your eye doctor can assure you your children and teens have the correct eye prescription for efficient reading and learning in school. Schedule them for an annual eye check up today. And do not forget the new options you have as a farsighted adult.
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Source by Dr. David Kisling, O.D.
