If you make an appointment for a routine eye exam, you’ll participate in a series of diagnostic tests. One of the most common is called the Snellen Test Chart – the good ol’ fashioned “Eye Chart” that contains a series of different letters and numbers in varying sizes in descending order.
The results of that and other diagnostic screenings give your optometrist a good indication of whether you have normal vision (congrats!), or whether you are nearsighted vs farsighted or both!
Normal vision (20/20, 20/15, 20/10)
Ever wondered what 20/20 (or normal vision) means?
A diagnosis of 20/20 vision means that you can see exactly what the average “normal sighted” person can see from a distance of 20 feet. To do that, the eye takes light in and focuses the light (and the image) in a single focal point, directly on the retina. According to the CDC, roughly 75% of all adults have “normal” or “better than normal” vision.
If you are one of the lucky 75%, you have normal vision for both near and “far” distances. Even within the “normal vision” range, there are variances. For example, younger people with normal vision may actually have 20/15 or 20/10 vision in one or both eyes. If this is the case for you or your child, it means they can still see clearly at 20 feet what others have to be a closer 15 or 10 feet away from.
Nearsighted vs Farsighted Depends On The Anatomy Of Your Eye
The difference between nearsighted and farsighted has to do with the relationship between the physical length of the eye (the length of the eye’s axis) and the optical length (a more complicated factor). If you are a math or science aficionado, we invite you to visit the Optical Path Length Page, posted by the International Society for Optics and Photonics (SPIE), to learn more about optical lengths and the equations used to assess them.
If you are nearsighted, you see things that are close up just fine but have a problem seeing things that are further away. They look blurry to you and have lost their details, texture, and depth. This can be challenging for athletes, those who drive (can you read that sign??) and can make it more difficult to drive at night.
When you are nearsighted, things aren’t lining up quite as they should when the light enters your eye. Instead of coming to a focal point directly on the retina, the light comes to its focal point in front of the retina instead of on its surface.
This occurs because the physical length of the eye is longer than the optical length of the eye. This is why the large majority of nearsighted diagnoses occur in school children, teens, and young adults. These proportions change as the eye grows, which can make a normally sighted person become a nearsighted one.
It is also a reason why it is so important to have your child’s vision checked on an annual basis. If you don’t catch nearsightedness in time, you can wind up with a child who struggles to read or hates school work, and that might be 100% related to vision struggles rather than lack of ability or a true dislike of learning.
Those who are farsighted have the opposite issue. Their eyeballs may be too small or their focusing power is too weak. When you are farsighted, you can see clearly from a distance, but things that are close (books, for example) are blurry.
Farsightedness is often an issue from birth, but it can take a while to diagnose since the developing brain in a baby – and then a young child – has a remarkable ability to adapt. Also, mild cases may resolve themselves as a child and teen growing up and the eye grows into a more balanced proportion.
People can also develop farsightedness if their eye muscles weaken or as the result of other vision conditions such as astigmatism (see next). Either way, those who are farsighted will need bifocal lenses, or graduated/transitional lenses, that have a non-amended lens at the top and a prescription lens amendment at the bottom so the eyes can see both near and far. Contact lenses can also help.
Nearsighted vs farsighted: astigmatism makes you both
Some people are both near and farsighted. The most common cause (outside of cataracts or something like that) is astigmatism. With astigmatism, the basic shape of the lens and/or cornea is oblong instead of round. When that is the case, the light coming into the eye cannot meet at a single focal point. Instead, it wraps around the “oblong path” and settles in two separate spots.
This results in blurred vision at both near and far distances. The more dramatic the curvature of the eye, the further apart those focal points are, and the more separate the two images become – which increases the experience of blurred vision.
Treatment for nearsightedness, farsightedness, and astigmatism
The first line of treatment for nearsightedness, farsightedness, and astigmatism is glasses and/or contacts. In cases where muscle weakness is an issue, vision therapy may be an option. Just as physical therapy strengthens a weakened part of the body, vision therapy does the same for the muscles and nerves responsible for vision.
You can also speak to your optometrist about whether or not you are a good candidate for LASIK surgery, which can be used to treat a range of vision issues, including nearsightedness, farsightedness, and astigmatism.
The Atlantic Eye Institute is here to help you and your family determine who sees near, who sees far, and who is lucky enough to be “normal”. Contact us to schedule your eye exams for the upcoming year.