Why do Some People Need Glasses?
Chances are you know someone who wears glasses or contact lenses. About 79% of the United States population wears corrective lenses to improve the quality of their eyesight.
How does the eye work?
There must first be a foundational understanding of how the human eye works to understand how corrective lenses work. We have a layer of cells in the back of our eyes that react to incoming light called the retina. The light information from the retina is sent to the brain via our optic nerve. Light rays entering the eyes are scattered. To see clearly, three things must happen to the light:
1. The size of the image needs to be reduced to fit onto the retina
2. The light must focus exactly on the retina
3. The curve of the image must match the curvature of the retina
The eye’s lens and cornea are used to accomplish these three things. The lens lies between the retina and the pupil. The cornea is a transparent covering on the front of the eye.
Numerous factors can cause the eye to be unable to focus quite right. Some of the reasons include the lens or corneal surface may not be smooth, the lens may be unable to adjust its curvature to match the image, or the cornea may be misshapen.
Most vision issues often result from the eye’s inability to focus the image onto the retina. This is the case for three common vision problems: myopia, hyperopia, and astigmatism. Myopia, commonly known as nearsightedness, results from the incoming image being focused in front of the retina. Hyperopia, commonly known as farsightedness, results from the incoming image being focused behind the retina. Astigmatism is caused by a distortion (likely from an unsmooth lens and/or corneal surface) that creates a second focal point. This is where corrective lenses come in!
Lenses for Nearsightedness, Farsightedness, Astigmatism, and “My arms are too short!”
Myopia (nearsightedness) requires the use of eyeglasses to see far away. A minus lens is used to correct myopia by pushing the focus farther back. Someone with myopia sees more clearly because the image in the distance is moved closer with the corrective lens, allowing them to see clearly. Myopia is a growing epidemic in the world, and there are many treatment protocols to slow/stop the progression of myopia in children.
In the case of hyperopia (farsightedness), eyeglasses are used predominantly to see things up close. Depending on the severity of hyperopia, vision can also be blurry for objects in the distance. A plus lens is used to correct for hyperopia by moving the focal point forward. These lenses take the effort of focusing away from the person by pushing the image further back to relax the eyes.
Astigmatism causes vision becomes out of focus at any distance. It often occurs concurrently with myopia (nearsightedness) and hyperopia (farsightedness). Astigmatism lenses have two focal points to compensate for the uneven curves in your cornea or lens.
Presbyopia occurs in everyone around 40-45 years of age. A person typically notices when they need to start holding objects at a further distance to see them clearly and comfortably. Over time, the lens of your eye can’t focus light as well due to its thickness and inelasticity. Presbyopia is a normal and natural age-related change in the function of the eye, not a disease. Similar to hyperopia, plus lenses push the image back further and allow the person to see the image clearly.
When glasses are not enough
About one in five children still complain of visual symptoms despite being told they have perfect vision with or without requiring lens correction. An often overlooked piece to the puzzle is our visual efficiency skills. Once the eyes take in information, the brain must interpret what is being seen. Many kids suffer from intermittent blurry vision, double vision, eyestrain, reading fatigue, poor reading comprehension, or words jumping around the page. In addition to the annoyance of headaches and the confusion of double vision, these conditions may prevent the person from seeing 3D or negatively impact school performance. The coordination of both eyes and the brain is required for clear, comfortable vision.
If your child is having difficulty reading, is diagnosed with ADD/ADHD, or is having other learning problems, get a comprehensive developmental vision exam — not just a traditional chart eye exam. While many schools and pediatricians perform eye checkups, those screenings check for visual acuity, not visual skills such as tracking or focusing.