The eye is the window of the soul. Your eyes reflect what you see, what you feel. You can even see the reflections of yourself in someone else’s eyes. They look like tiny mirrors reflecting back everything. When you can not see clearly, glasses aid your vision. But how do glasses work, and how do these seemingly plain-looking glasses help you see clearer and brighter?
How do lenses work?
To answer this question, you will need to know how eyes work. Eyes have parts like the cornea, iris and pupil. The cornea is a lens covering the pupil, the iris is the coloured part of your eye, and the pupil is the black part through which light passes. When you look at any object, the image of the object falls on your cornea, the light bends and passes through the pupil. The image is reduced in size after passing the pupil and falls on the back of the eyes, that is, the retina. The retina is connected to the brain with optic nerves. These nerves carry the information to the brain. The brain then interprets the information and make sense of the image.
Fun fact - the image formed on the retina is inverted. The optic nerves carry the inverted image back to the brain, which then makes them upright.
When the lens does not work properly, you get vision defects. In such cases, an external lens can correct your vision. Glasses does that work. Glasses reflect the images back to the retina, and the optic nerves send the image to the brain.
When you can’t seem to focus
Often you see blurry images or even ghost images. This is because the lenses are out of focus. It’s similar to a camera. When you see blurry images, you adjust the lens of your camera. Your eyes cannot focus on the object to see a clear image.
Why can you not focus properly? There are several reasons for that.
- The curvature of the lens
- The lens or cornea of the eyes is not smooth
- Blocks in your vision
How does the curvature of the lens affect your vision?
The curvature of the lens affects your vision. If your eyeball is elongated or oval-shaped, you have trouble seeing distant objects. The shape of your eyes distorts your vision, making you lose focus. When you look far distance, the lens reflects the image in front of the retina. The optic nerves receive the blurry image as the image is formed ahead of the retina and not on the retina. The image formed out of focus and hence is blurry.
If your eyeballs are too short, you have trouble seeing near distance. When you read any text, your shortened eyeballs reflect the image behind the retina. The image formed on the retina seems out of focus for you to see clearly. The font appears too small for you to see clearly.
How to correct it?
When you are not able to see clearly in the far distance, you have nearsightedness. You can see the objects in the near distance but see blurry images when seeing them at a far distance. Concave lenses solve this vision issue.
The image falls on the glasses with the correct focal length and is reflected on the retina. You are then able to see clearly without any blurs.
When you are not able to see clearly in the near distance, you have farsightedness. You can clearly see things in the far distance but have difficulty with near objects. Convex lenses can solve this. The image is magnified and pass through the pupil. It falls accurately on the retina, which in turn sends the information to the brain.
Reading Glasses have convex lenses. If you have hyperopia, your prescription denotes it with a (+) sign. Your distance glasses have concave lenses and are denoted with a (-) sign.
How the shape of the cornea affects your vision?
If the cornea is not round perfectly, you get distorted vision. You have an eye defect called astigmatism. The distortion causes the formation of a second focal point, causing you to see blurry visions. When the cornea is not perfectly spherical, the light rays falling on the eyes are focussed at a point except for a part of it, where the shape is irregular.
You see blurry images either along the horizontal lines or vertical lines or both. You can have either myopia or hyperopia, and have astigmatism along with it.
In astigmatism, you will have difficulty seeing or reading some letters. For example, you might not be able to see the dash in H. It will appear blurry or appear like I. You face similar issues in many letters.
How to correct it?
Cylindrical lenses can correct astigmatism. These lenses bend the light along the axis to match the axis of the aberration of the cornea. With the cylindrical lenses, all the light rays are bent to pass through the pupil and focused properly over the retina.
What blocks your vision?
After you age, your lens hardens, causing you to see blurry visions in both distances. This condition is called presbyopia. The growth of cloudy patches over the cornea also blurs your vision. This condition is called cataracts. Similarly, because of many other eye diseases, the vision of your eyes is reduced.
Wearing varifocal glasses can correct both your near and far distance. Varifocal glasses are made with both concave and convex lenses. The lower segment of the glasses, from where you see near objects is made from convex lenses. The upper segment is made with concave lenses. The middle portion is made from plain glasses to provide your vision for immediate distance.
Glasses help you see clearer if the natural lenses in your eyes do not work properly. The magnifying and minimising property of various lenses helps you in seeing clearly. The lenses help you in focusing properly to see clear and defined images as they are in reality.