What Does It Mean to be Nearsighted vs. Farsighted?
People who wear eyeglasses or contact lenses are familiar with the terms that describe their vision, and two of the most common are nearsighted and farsighted. You may know what these words mean, but you might still be surprised by how they are caused.
Both nearsightedness and farsightedness are what we call refractive issues. But what does that mean – and how does your prescription correct these issues?
The Facts About Nearsightedness
People who are nearsighted have an issue with the way light bends when it reaches the eye. A person with perfect eyesight would have eyes that captured light without bending it, sending it directly from the cornea to the retina.
Nearsightedness, which is also known as myopia, causes images to focus in front of the retina instead of on it, resulting in blurry vision. People who have myopia can typically see items that are close to them clearly, but they struggle to see at a distance. Several things can cause myopia:
The eyeball itself is too long, and the distance between the cornea and the retina results in refraction
The cornea is abnormally shaped
The lens of the eye is unusually shaped
People who have nearsightedness may be able to read or do close work without corrective lenses. However, they will require vision correction for driving, since they are likely to have a hard time reading signs and seeing clearly on the road. Approximately 25% of all Americans have myopia.
According to the National Eye Institute, nearsightedness is most commonly diagnosed between the ages of 8 and 12. There may be a genetic component to nearsightedness.
The Facts About Farsightedness
As you might expect, farsightedness is the opposite of nearsightedness. The medical term for farsightedness is hyperopia. When images reach the eyes of someone who is farsighted, the focal point is behind the retina. People who are farsighted can usually see very well at a distance. However, they are likely to struggle seeing things that are close to them.
Farsightedness is not as common as nearsightedness. The National Eye Institute estimates that between 5% and 10% of Americans are farsighted. Like nearsightedness, there appears to be a genetic component. If one or both of your parents were farsighted, you are more likely to experience the same problem than someone who didn’t have a family history of hyperopia.
While nearsightedness tends to be diagnosed in childhood, the same is not true of farsightedness. People who have it may not notice any issues with their vision when they are young. In some cases, the problem may not be diagnosed until the person starts learning to drive. People who have hyperopia are very likely to need corrective lenses for driving.
The causes of farsightedness are as follows:
The eyeball may be too short, which causes the focal point to be behind the retina
The cornea has an abnormal shape that causes the refraction
The lens has an irregular shape
Like nearsightedness, farsightedness may be corrected with glasses or contact lenses. In severe cases, refractive surgery may be required.
The first two sets of letters are an indication of which eye the number refers to:
OD stands for Oculus Dexter, which is Latin for right eye
OS stands for Oculus Sinister, which is Latin for left eye
In addition to the abbreviations for your eyes, you will see some other letters on your eyeglass prescription. Here’s what you should know to understand them:
SPH is short for ‘sphere’ and refers to the strength of your prescription for nearsightedness or farsightedness
CYL & AXIS is short for “cylinder and axis” and refers to correction for astigmatism
ADD is a reference to magnifying power, something that is commonly included in bifocal and progressive lenses
PD is short for ‘pupillary distance’ and refers to the distance, typically in millimeters, between the middle of one pupil to the middle of the other
Next to these letters, you will see numbers. If your prescription does not have a number next to one of these items, it merely means that your eyes do not require correction for that issue. Someone who did not have astigmatism, for example, would not have anything written next to CYL & AXIS.
The numbers that appear next to OD and OS indicate how strong your nearsightedness or farsightedness is. A negative number in either spot suggests that you are nearsighted, while a positive number shows that you are farsighted. The more negative (or positive) the number is, the more serious a refractive error you have.
Contact lens prescriptions have OD and OS on them as well, but they include two other abbreviations. The first is BC, which stands for base curve. The second is Dia, which is short for diameter. These indicators are what ensures that your contact lenses will conform to the exact curvature of your eyes.
Which Treatments Are Best for Nearsightedness and Farsightedness?
Fortunately, unlike colorblindness, treatments are available for both of these conditions. An examination by an ophthalmologist will determine whether your vision requires the use of corrective lenses.
Eyeglasses, by far, are still the most common way of correcting vision. If you decide to go this route, you may choose to buy more than one pair of glasses. Some people, for example, opt for one pair of regular glasses as well as a pair of prescription sunglasses. If you are farsighted and require glasses for driving, it may be worth the expense to buy prescription sunglasses.
Contact lenses are the next most common method people choose to correct their eyesight. Because contact lenses sit directly on your eye, their corrective power may be stronger than eyeglasses. However, some people do not like the feeling of contact lenses on their eyes. Contact lenses also require special fittings to ensure they conform to your eyes.
Of course, some people who require corrective lenses choose to have both eyeglasses and contact lenses. This combination offers you a choice. If you are doing something where eyeglasses might be a problem (for example, if you’re running a marathon and you’re worried about your glasses fogging up), you might choose to wear your contact lenses. On a regular day at the office, glasses might prove to be the more comfortable choice of the two.
The final option is to have elective surgery to correct your vision. Most commonly known as LASIK, this laser surgery reshapes your corneas, so that the refraction issues you are experiencing are fixed without the need for glasses or contacts. Not everyone is a candidate for LASIK. You will need to undergo an examination to determine if it will work for you.
If you choose eyeglasses or contact lenses, you should plan on having your eyes examined once a year. Refractive errors may worsen over time. Keeping your prescription up to date will ensure that you can see properly at all times.
Refractive issues like nearsightedness and farsightedness are quite common. Understanding your vision and how it works can help you have a greater appreciation for the corrective lenses you wear and how they allow you to see the world clearly.