Glasses; How They Work and Why Do Some People Have to Wear Them?

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Updated on: Educator Review By: Michelle Connolly

That’s our topic for today’s article; in the following sections, we talk about the mechanism by which glasses function and why some people have to wear them. This topic is crucially important for anyone since many people suffer from a condition in their eyes that requires glasses. If you are not suffering from these kinds of problems yourself, just think of your family or friends. Chances are at least one of them will have a refractive error that requires wearing glasses. So let’s find out how these small pieces of glass work.

Ready for that journey!

Here we go.

The main items discussed in this article in order:

How Light Travels Inside Our Eyes

Before we get to how glasses work, we need to go through two main things first; these are to revisit some basic physics of light (that is, refraction and how light travels in different media) and to know the components of our eyes. So let’s start off with the main components of our eyes that light travels through.

To better understand how light travels inside our eyes, we need to know first the main components of our eye. We will go through each component briefly, but we’ve already talked about our eyes and their components in much detail in a previous article. So, if you want more information, head off to this one.

Our eye is formed of the following structures from out inward (if you take a vertical cross-section in it):

Light passes through some structures inside your eye in the following order:

  • The cornea: this is the first structure of your eye that light hits. Light undergoes refraction when passing from the atmospheric air into your cornea.
  • The pupil: after light leaves your cornea, it passes through a small hole at the centre of your iris (the coloured portion of your eye) known as the pupil. Since this is just a hole, light moves through it unchanged.
  • The lens: moving on from the pupil, light travels through your lens, where it gets its second refraction.
  • The vitreous body: then the light moves through a jelly-like structure known as the vitreous body before hitting the final structure inside your eye.
  • The retina: now, the final station light stops at, which is your retina (it lies at the very back of your eyeball). That’s because your retina transforms this light into an electrical signal that travels through your optic nerve, which in turn delivers this signal to your brain.

If it’s still unclear to you how light travels through our eyes, here’s an animation video that explains it in just one minute.

How light travels inside our eyes – animated video

How Light Refraction Works

Now we know the main structures light travels through inside our eye, so let’s move on and talk about some basic physics; the basics of light refraction and how lenses affect light rays.

Refraction of Light

We all know that when light moves from one medium to another and these media differ in their density, it changes its speed and direction (it bends). That is why if you look at a straw or a pen that is put in a glass of water, it sounds bent (its lower part that lies in water does not match its upper part that is out of water). That’s because water bends light rays in a specific way that differs from the air or any other media.

This phenomenon also happens inside our eyes when light travels through its structures, which of course, differ from one another in their density. Light gets refracted first at the cornea, which plays a major role in this process, then when it reaches your lens it undergoes a second refraction.

Lenses and Light Rays

Another important thing to know is how different types of lenses bend light rays. We have two types of lenses: concave and convex. Concave lenses disperse light rays, while convex ones collect them.

How Glasses Actually Work

Since the main problem of blurry vision is due to an error of refraction, glasses work by correcting that error of refraction by focusing light exactly on your retina, giving you a clear picture. Glasses do so by bending light before it gets into your eye so that when it reaches your eye and passes through its components, it gets refracted in a more precise way that will allow it to perfectly hit the retina on the right spot. Glasses are composed of different types of lenses that allow them to correct certain refractive errors. There are mainly three types of lenses used in glasses:

  • Convex (plus lenses): these lenses are thick in the middle and thin in the periphery. They are also called “plus lenses” since their power is measured with numerical values that are always preceded by a “plus/ +” sign. Convex lenses look exactly like your magnifying glass. These lenses bend light rays inward (collect light rays). Convex lenses are used in the correction of farsightedness.
  • Concave (minus lenses): these lenses are thin in the centre while thick at the edges. They are sometimes called “minus lenses” since they are marked numerically with a “minus/ – ‘ in any glasses prescription. These lenses bend light rays outward (they disperse light rays). Concave lenses are used in the correction of nearsightedness.
  • Cylindrical lenses: this special type of lens is used to correct astigmatism.

The power of each type of lens is measured in diopters, and to specify the type of lens, we add a “plus or minus” sign before the power. So when you see a plus sign in your eyeglass or contact lens prescription, this means you are farsighted. And when it has a minus in it, this definitely means you are nearsighted. The number next to that minus or plus symbol is the power of the lens measured in diopters. The higher the number in diopters, the more severe your refractive error.

Who Needs Glasses? And Why?

People wear glasses for different reasons ranging from correcting a refractive error in their eye or just for reading. So what is a refractive error, and how does a pair of glasses correct it?

A refractive error happens when your eye isn’t able to bend the light the right way so that it won’t fall exactly on your retina, giving you a blurry image of the world around you.

Remember which structures in your eye are responsible for refracting light when it travels through them?

Yes, these are your cornea and lens. So when you have abnormal curvature or any kind of irregularity in your cornea or lens, you will get some sort of refractive error. This refractive error can result in many conditions. Having abnormal curvature of your cornea or lens will result in focusing light at a point in front of or behind your retina, not just at your retina (which is the normal pathway).

The following sections show you the main refractive errors that might affect your eye.

Near-sightedness (also known as myopia)

Nearsightedness arises from a problem in the curvature of the cornea or lens. The problem here is that they become more curved, which means their power increases (they can bend light more than what is needed in normal cases). Myopia also occurs in people having long eyeballs. This means images will be focused at a point in front of the retina (not exactly at the retina) which leads to blurry vision.

What does it look like to be nearsighted?

Being nearsighted means you can only see near things clearly while far things look blurry.

How can glasses correct this problem?

For nearsighted people, concave lenses are used to correct their error of refraction since those people are having a strong bending power of light rays. So concave lenses will disperse light rays before it gets to their eyes which are able to bend light rays in a severe form, thus allowing these rays to bend the right way before they hit the retina.

Far-sightedness (also known as hypermetropia or hyperopia)

Unlike nearsightedness, farsightedness happens when the curvature of your cornea or lens becomes less than normal (they become less convex). This means their ability to focus light and bend it decreases, and thus, images will be focused behind the retina (not exactly at the retina). Hyperopia could also be seen in people with short eyeballs.

What does it look like to be farsighted?

Being farsighted means you can clearly see far objects, but you find it difficult to focus on near objects.

How can glasses correct this problem?

For farsighted people, convex lenses are used since the main problem here is that light rays can’t be bend enough due to the weak power of their eyes. Convex lenses collect light rays and thus help people with weak bending power eyes to focus light rays just at the retina, not behind it.


People suffering from astigmatism have irregularities on the surface of their cornea, which means they have difficulties bending light at one point on the retina (we end up with more than one focal point). Astigmatism also leads to blurry vision. However, the type of lenses used to correct it differ from those used for near or farsightedness. These lenses are called cylindrical lenses, while those used to correct near and farsightedness are spherical.


Presbyopia is not a disease in itself but rather a part of our natural ageing process. As we age, our lenses become less elastic, and their ability to change their shape when we focus on near objects decreases. That’s why you might need a pair of glasses just for reading since your lens is no longer able to increase its curvature to allow you to read things at a close distance. Presbyopia differs from other types of refractive errors in that it’s exclusively a problem of the lens.

What does it look like to have presbyopia?

Having presbyopia means you are just having a temporary problem with reading, but you can see things around you clearly.

What About Contact Lenses as an Alternative?

Contact lenses are an alternative option if you don’t like wearing glasses. However, they have many problems associated with them. For example, they cause dryness in your eye. They also aren’t comfortable to wear for some people, given that they are worn directly on your cornea.

If you are into contact lenses, here are some tips to help you minimize their side effects:

  • Don’t wash them with tape water; rather, use their washing solution for the purpose of cleaning.
  • Don’t wear them for so long. It’s always a good idea to check the manufacturer’s instructions, for that matter, since contact lenses differ from one brand to another.
  • Don’t ever sleep with your contacts on.
  • Keep them in their sterile solution and make sure they are kept in a closed container.
  • If you experience any abnormal reaction of your eyes towards your contacts, consult your doctor immediately.

A Brief Introduction to LASIK

This is just a short introduction to this minor surgery, but don’t worry we will cover that topic in detail in an upcoming article.

LASIK (an acronym that stands for Laser-Assisted In Situ Keratomileusis) is a term used to describe a procedure that people with errors of refraction undergo to correct this error and maybe to get rid of their glasses. Nowadays, there are many types of these surgeries, and they are still expanding and improving.

This technology works by directing a special beam of laser to the surface of your cornea (after removing a very thin flap of it). This beam of laser is personalized and specified according to each individual’s needs and their error of refraction to make some permanent changes in the shape of their corneas.

Can You Get Rid of Your Glasses Forever?

The short answer is yes. However, you may still need another kind of glasses as you age.

Let me explain; first of all, not all people are the same. Some people might be good candidates for LASIK, and others won’t. But being a good candidate for this surgery does not mean you will never use glasses for the rest of your life since some people need a special type of glasses for reading only as they age.

Although it might seem a bit frustrating not to be able to live freely independent of any device that you have to use to be able to clearly visualize the world around you, you can learn to love your glasses and the way you look when you put them on. You look great anyway.


A very small piece of glass that can markedly improve the quality of life of many people. We have to admit that this piece of glass is able to transform someone’s life by giving them a crystal clear picture of the world around them.

Just ask anyone who wears glasses to compensate for a refractive error in their eye: how do you see the world around you without them? And see what these small pieces of glass have to offer.

To make it easier for you to imagine, let me break the fourth wall and tell you what the world around me looks like without my glasses, given that I am nearsighted. Well, go to youtube and open any video you like and set the quality to 144p (the lowest quality available on youtube). There you go; that’s exactly what a moderately nearsighted person sees without their glasses.

However, it can get much worse in severely-nearsighted people where it gets too much blurry, and they just see the world around them as halos of light merging into one another (they can no longer identify things around them even though they are not blind, but the severity of blurriness makes it difficult for them to see things clearly). Here’s a vision simulator that shows you exactly what it looks like to be nearsighted, starting from mild to moderate and finally to severe nearsightedness.

If you’ve made it so far to this section, you must be really interested in finding out how your body works. That’s why we highly recommend you follow the tag “STEM” on our website, where you find similar articles that talk about science.

By following this tag, you will find similar articles that talk about different body parts like your heart, nose, eyes, urinary system, skeletal system, cardiovascular system, respiratory system, and much more.


Focal point: this is a point at which light rays meet together (converge) after undergoing reflection or refraction.

Diopter: a unit used in the measurement of the refractive power of a lens.

An optometrist: this is a trained professional whose main work revolves around coming up with the right prescription (measures) for eyeglasses and contact lenses.

An ophthalmologist: this is a medical doctor trained to work on eye-related problems. They have a wide range of responsibilities that can range from writing prescriptions for eyeglasses or contact lenses all the way up to doing eye surgery.

An optician: this is the person who sells eyeglasses and contact lenses. You give them your eyeglass or contact lens prescription (that your optometrist or ophthalmologist has previously written for you), and they just put everything together to give you the final product, which is a tailored eyeglass or contact lens made specifically for you.

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