Glasses have been correcting vision for hundreds of years- since 1268 by many estimates- but have you ever stopped to consider the science behind how some curved pieces of glass can correct your vision? Three quarters of Americans wear glasses to correct their vision at some point in their lives, but very few people ever stop to consider the scientific reason behind why they work in the first place.
Poor vision is caused by a having a misshapen lens in your eye, or sometimes by multiple misshapen areas on your lens that can cause multiple focal lengths. Depending on how it is misshapen it can change the focal length of the light waves entering the eye, either making them fall long or short of the focal point and distorting the image the viewer sees. Astigmatism causes multiple focal points, causing visual blurring at multiple distances.
Glasses are cut to change the focal length of the light entering the eye so it hits the focal point properly and the wearer can see without blurring. Convex lenses correct nearsightedness by refracting the light toward the bottom and the top of the lens so it pushes the light farther back into the retina. Concave lenses correct farsightedness by spreading the light away from the center of the lens, moving the focal point farther forward.
The numbers in your glasses prescription mean a few different things. First, the numbers on your frames indicate the frame size- from the width of your face to the length of the arms to comfortably fit over your ears. The lens correctivity is measured in diopters- positive diopters mean convex lenses, while negative diopters mean concave lenses. Different shapes of lenses can be combined to treat multiple vision maladies simultaneously. Even two different eyes on the same person can have dramatically different prescriptions, but they can often be corrected by a single pair of corrective lenses.
Even if you are born with vision problems, glasses can help you have 20/20 vision. Many people experience decreased visual acuity as they age, and glasses can help them regain the vision of their youth. Learn more about how corrective lenses work from this infographic. You might be surprised how simple this concept is, but after all corrective lenses have been around in some form or fashion for nearly 900 years so it stands to reason there is some pretty solid science behind them.