How do prescription glasses work?

Posted at 4:00 • 2 April 2020 • Chelsea from Kraywoods


Do you know why some people use glasses and others don't? Everyone's eyes are different in colour, shape, and size. These characteristics can affect one’s vision and how well they can see or perceive objects. Depending on the shape and size of the eye, the light can be focused directly on the retina, in front or behind it. Only when the light is focused directly on the retina can the person have a clear vision, otherwise a correction is needed in order to bring back the focus directly on the retina. Contact lenses or eyeglasses with corrective lenses can help most people with vision deficiencies see things more clearly.

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The different parts of the eye and how it works

The Sclera, it is the white part of the eye which serves as a protective layer to the eyeball.

The cornea, it is the clear tissue buldging in front of the eye that covers the iris and the pupil and is the main refractive surface that allows visual focus.

The iris, it is the coloured part of the eye that controls the amount of light that enters the eye through the constriction or dilation of the sphincter muscle.

The pupil, it is the opening in the iris which appears as a black circle in the middle of the eye. It allows the light to enter into the eye

The lens, it is a transparent body enclosed in an elastic capsule located behind the pupil. With the contraction of the ciliary muscles, the lens contracts and acts like a camera lens by focusing light onto the retina.

The retina, it is the lining in the back of the eye, made up of ten different layers of cells, that takes in the light focused by the cornea and lens and converts it into signals that can be interpreted by the brain via the optic nerve.

When all the above-mentioned parts of our eyes work together and the light focused directly on the retina, this is what results in clear vision. When looking at objects, the eye captures an image similar to how a camera does. Afterwards, the captured image is sent to our brain through the optic nerve where it is interpreted. For example – if you see an elephant standing in front of you, the image will be sent to your brain and interpreted your brain will then instantly send a signal and say hey, there is an elephant.

 

When an image is captured by our eyes, the different parts of the eye need to bend the light rays so that our retina can focus the image sharply. The process starts with the light reflecting off the object we’re seeing and entering the eye through the cornea. The light rays then enter through the pupil to reach the lens. The lens of our eye then serves as a natural refractive lens by contracting and changing in thickness to bend the light and allow it to be focused directly onto the retina. From there, electrical impulses are sent to the brain through the optic nerve and interpreted into an image of the object that we see in front of us.

Eye with normal vision, showing light from an object reflecting onto the retina

The better the light is focused on our retina, the better our brain interprets the image and the better we can see any image clearly. Refracting is a word that means bending the light rays. If a person is not seeing clear images, then it's most likely due to a refractive error in the eye. Contact lenses or glasses can be used to correct most refractive errors. The correction in the glasses lens or contact lens bends the light rays to be focused directly onto the retina and help see images clearly. Laser surgery can also be an option to help correct refractive errors, although it is not recommended for children at a young age.

Refractive Errors

Nearsighted

Nearsightedness is also called myopia, and it occurs when the image is focused in front of the retina. It’s a term used for any person that can see near objects clearly, such as while reading a book or a newspaper, and far objects blurry, such as while watching television or driving.

Eye with myopic vision, showing light from an object reflecting in front of the retina

Farsighted

Farsightedness is also called hyperopia and it occurs when the image is focused behind the retina. It’s a term used for any person that can see near and intermediate objects blurry, such as while reading a book or working on a computer, and far away objects clearly, such as while watching television or driving. Farsightedness in kids can sometimes be normal because they can focus their eyes to make up the difference. But some kids are more farsighted than others and may need eyeglasses to see clear at all distances.

Eye with hyperopic vision, showing light from an object reflecting behing the retina

Astigmatism

Astigmatism is another common refractive error. It occurs when the cornea is an uneven shape and the light is bends in different directions. This can distort the images seen and make objects look blurry at all distances.

Eye with astigmatism, showing light from an object reflecting behing the retina

Presbyopia

Presbyopia is also a type of visual problem that needs to be corrected with glasses or contact lenses, but not quite categorized as a refractive error. It is a form of farsightedness with the gradual loss of the ability to see things clearly up close, such as reading a book or a newspaper or text messages on the phone. Presbyopia is a normal part of aging and it naturally occurs as of the age of 40 years old and over.

man with presbyopia trying to read a computer screen

Contact lenses or glasses correct blurry vision caused by refractive visual problems because they allow the light entering our eyes to be focused directly onto the retina, which helps produce clear images. Since everyone's eyes are different, each person needs a specific refractive correction for their own eyes. You probably know this if you have ever tried someone else's glasses before.

If you ever happen to experience blurry vision, seek out an optometrist to get a professional diagnostic and obtain the prescription needed for your eyes. Your optometrist will perform a complete eye exam to check your ocular health, as well as evaluate the need for a refractive correction and advise you what is best for you. Your vision can then be corrected with contact lenses or prescription glasses, depending on the recommendation of your eye doctor.

Eye Exams

Eye exams are recommended once every two years or every year depending on your doctor’s recommendation, and that is whether you see clear or blurry. It is very important to seek out an eye doctor and perform regular ocular health check-ups. The eye is one of the most important organs in our bodies. Without healthy eyes and clear vision, you wouldn’t be able to see the world and everything around you. Therefore, it is important to take care of your eyes and seek out an eye specialist for regular ocular health check-ups, just as you would do with a general doctor for general health check-ups.

 

When seeking out specialists for your eyes or your vision, there are different types of eyecare specialists and each of them have a different role. Let's check out the difference between them below:

  • An ophthalmologist is a medical doctor who is specializes in eye and vision care. They are trained to diagnose and treat all ocular diseases and visual problems, this includes prescribing contact lenses and eyeglasses. An ophthalmologist can also perform eye surgery such as laser eye surgery, refractive lens surgery, cataract surgery etc. To learn more about ophtalmology, click here.
  • An optometrist is a licensed ocular health professional that specializes in examining the eyes for defects, abnormalities and refractive errors. They are responsible to provide the corrective prescription needed for glasses or contact lenses. To learn more about optometry, click here.
  • An optician is licensed technician that fabricates, fits and dispenses corrective glasses, contact lenses and other optical aids as per the prescription of an ophthalmologist or an optometrist. To learn more about dispensing opticians, click here.

 

During an eye exam, the eye doctor will ask you to read from an eye chart. In the chart, there will be letters and numbers in different sizes. The doctor might also ask you to look at some text closely, like – reading a few lines from a book. These tests are to measure your visual acuity, meaning how well you can see from close, intermediate and far away. They may perform other tests related to your vision such as colour vision test, visual field text, etc. They will also evaluate your ocular health by looking at different parts of the eye to make sure there are no ocular diseases.

 

Once the eye exam is complete, the eye doctor will be able to inform you if there is a need to have glasses or contact lenses and give you the precise corrective prescription for your eyes.

Performing eye exam by an optometrist

The Fun Part

When you get your prescription, it’s time to visit your optician and choose the frame for your glasses! This is the fun part, because it’s not only about finding the right pair for your eyes but also for your style! When choosing a frame, it’s important to prioritize comfort, durability and style. After all, these are glasses that you will be wearing for long hours every day and they will become part of your daily outfit. As for the lenses, they come in different types, materials, thickness, and can also be equipped with different types of coatings. Depending on the prescription you have, your optician will be able to advise you on the best choice to make for your glasses!


If you get glasses then you will also need to know how to clean them properly. And it would be better if you have a glasses case. It’s always advised to keep your glasses in their case when not in use, that will help prolong their durability. If you get contact lenses, then you will get advice from the ophthalmologist or optometrist about what types of lenses would be best for you. Some contact lenses are disposable daily and some can be worn longer and need to be cleaned between wear. Keeping your contact lenses clean and following the recommendations of your eye specialist will help prevent infections from the eyes.

 

Nevertheless, the best and fun part of a new pair of glasses or contact lenses is how well you can see through these. There’s nothing worth more than being able to enjoy clear vision and see beautiful world around you!

Watch Below: How The Eye Works - Refractive Errors

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