How to Understand Your Glasses Prescription

by Sep 27, 2021

Whether you are a first time glasses wearer or have been wearing glasses for a long time, understanding your glasses prescription can help you to better understand your eyes.


Why Do I Need Glasses?

Glasses are used to correct the eye’s focusing system to allow light to land perfectly centered on a point of the eye called the macula.

The macula is a part of the retina (the very back structure of the eye responsible for detecting light and transmitting it to the brain) that is responsible for your clearest vision.

All of the structures of the eye have 1 major job—stay healthy to properly refract light and focus it onto the retina.

This may sound simple, but it is actually quite complex!

The average size of the human eye is 22 millimeters in length from front to back. There are many layers and complex structures within these 22 millimeters to help take incoming parallel light and bend and shape it so it focuses on the retina.

Think about a using magnifying glass on a hot summer day. If you hold the magnifying glass in just the right spot in front of a piece of paper, the paper will start on fire. The eye functions in a similar way. The eye is the magnifying glass—it’s entire purpose is to focus light right at the retina.

If the eye is misshapen even a tiny bit (remember we’re talking about microns and millimeters here!) light will not focus perfectly on the macula, and therefore the image perceived by the brain will be a little fuzzy.

There are many, many ways that the eye can be misshapen resulting in defocused vision, however we won’t bore you with the specifics of that here. The main point to understand, is that glasses properly fine tune the refraction of light to allow you to see clearly.


What are Different Types of Glasses Prescriptions?

There are 4 main categories of vision correction—emmetropia, myopia, hyperopia, and astigmatism.

Emmetropia is perfect vision. The eye is already perfectly refracting light onto the retina and does not require glasses correction.

Myopia is more commonly known as near-sightedness. It occurs when the eye is a little too long, resulting in light focusing in front of the retina.

In order to correct for myopia, your eye doctor will prescribed minus lenses (-X.XX). These minus lens push the point of focus backwards so that it aligns correctly on the retina.

Myopia is the most common form of refraction error in today’s society. In fact, it is actually thought to be a global epidemic, as more and more of the population is being diagnosed with this problem yearly.

These individuals can see great up close, but things far away seem blurry.

In children, you may notice the child having a hard time reading the board at school, holding reading material (cell phones, books, iPads, etc.) abnormally close to their faces, sitting extra close to the TV because they “can’t see”, or even squinting or rubbing their eyes a lot.

Hyperopia, on the other hand, occurs when a person can see well far away, but may have a hard time with seeing things up close.

Some of the most common complaints with hyperopes is actually not that they cannot see, but instead that they get headaches after reading or doing computer work, or that their eyes frequently feel tired or fatigued.

Hyperopia occurs when the eye is a little too short. Therefore, light focused slightly behind the retina.

To correct hyperopia, eye doctors prescribe plus (+X.XX) lenses to bring the point of focus forward to land correctly on the retina.

Hyperopia is less common than myopia, however it is also more sneaky. Since these individuals often see great far away, many individuals actually do not realize that they could benefit from a glasses prescription—even if it is just for reading.

Astigmatism is a whole other topic. Astigmatism occurs when the front surface of the eye (the cornea) is not perfectly round.

Think about a normal cornea looking like a basketball cut in half. It is perfect round and equal in all directions.

An astigmatic cornea looks more like a boiled egg cut in half. One meridian is longer than the other.

Having two different shaped meridians of the eye results in two different points of focus. Therefore, a glasses lens needs to be made to correct for both meridians. This prescription will have two numbers. For example -1.00 -0.50 X 180.

The first number denotes the power needed to correct one meridian while the second number denotes the power needed to correct the other meridian. The third number (X 180) simply states where the two meridians lie (they can range from 0 to 180).

To make things a little more complicated, an eye can have combined prescriptions, meaning it could be a simple myopic eye, a simply hyperopic eye, or a myopic eye with astigmatism, a hyperopic eye with astigmatism, or an eye with only astigmatism (i.e. emmetropic in one meridian and a prescription in the other).

All of this is why eye doctors spend so much time in school to really master the art of prescribing glasses. It is complicated! Eyes are like finger prints—no two are the exact same. We want you to see your best, so with many tools and measurements we can work together to find a pair of glasses to suit your individual needs.

Common Questions About Your Glasses Prescription

Is it true that wearing glasses all the time will make my eyesight worse in the long run?

No! This is a common misconception, though. Glasses do not alter the structure of your eye, therefore they cannot change your prescription.

Wearing glasses might make you notice how poorly you were seeing prior to receiving a prescription, so you might become more dependent on them because you like to see better, but they will not make your eyes worse.

For example, let’s say Bobby is an 8 year old getting his first eye exam required for school. No one has ever thought anything about his eyesight since he always seemed to be doing things normally—he can read, write, watch movies, ride his bike, and he has never complained about not being able to see before. Makes total sense!

When taking Bobby’s visual acuity at the beginning of the exam (reading the letters off the eye chart), the doctor sees that Bobby can only read as low as 20/40. This is not bad vision per-say, but things are pretty blurry for Bobby and he would likely struggle to read the board at school.

The doctor determines Bobby could benefit from a pair of -1.00 diopter reading glasses. When Bobby puts his glasses on, he goes outside and says “Wow! I never realized the trees had individual leaves! Everything looks so great!”.

Bobby did not know he had blurry vision—how could he have? He had nothing to compare it to. But now that he has his first pair of glasses, when he takes them off, he will notice that things are blurry. This is not because the glasses are making Bobby’s eyes bad, it is just because Bobby now knows what truly great vision looks like.

This is not to say that Bobby’s prescription will not change down the road. Remember that even a little tiny change to the eye can alter the focusing system. Growth spurts and natural aging can alter a prescription—that is completely normal, but a change in prescription is not corelated to whether or not Bobby wears his glasses.

Are Glasses Made from Actual Glass?

They can be, but typically they are no longer actually made from glass. Originally, the very first pair of glasses was indeed made of glass. However glass is heavy and scratches easily. Today most glasses lenses are actually made out of plastic or polycarbonate—this is quite a bit safer, most cost effective, and lighter for enhanced comfort.


Why Are Glasses So Expensive?

This is a great question. Glasses are custom made to your prescription and to your face. There are many measurements taken throughout an eye exam to ensure your glasses will be made perfectly for you.

After obtaining all the information and measurements, your doctor sends an order to an optical lab where the lenses are ground out and shaped specifically to your prescription.

There is a large range in prices for glasses. Typically, in your doctor’s office the frames are of high quality to make them more durable and come with some sort of a warranty. Lenses have a variety of options, you can add on bell’s and whistles to make your lenses more suited to your personal needs for an additional cost.

Some examples are an anti-reflective coating (great for reducing glare from overhead lights, oncoming traffic at night, reducing eyestrain and fatigue from working on computers, etc.), transitions (where the lenses are clear inside and turn dark like sunglasses outside), and changing materials to make the lenses thinner and lighter.

If you have vision insurance, be sure to check whether or not certain places will except your insurance too. Sometimes the base price elsewhere may be cheaper, but they will not take your insurance. It is always good to explore your options and make sure you are getting a pair you really love that is of high quality and up to your personal standards.


If I Scratch My Lenses, Can I Bring Them in to Get the Scratch Buffed Out?

Unfortunately not. Glasses lenses have the prescription ground into the lens. By trying to buff out the scratch, you would be altering the optics of the lens, thus changing the prescription and making them useless for correcting your vision.


My Brother Wears Glasses, Can I Just Borrow His?

The chances of you and your brother (or anyone else) having the exact same prescription are very slim. His prescription might be able to help you see a little better, but it is best to have your actual prescription put into a pair of glasses for you to wear. Plus, he probably needs his own glasses!

By wearing someone else’s glasses with the wrong prescription in them, you could be causing extra eye strain on your eyes, ultimately leading to some pretty painful headaches!

I won’t say you cannot borrow his glasses if you got into a pinch and he had a second pair lying around, but it is not advisable to wear someone else’s prescription glasses.


Are All Prescription Glasses Made for Full-Time Wear?

No! Some people have very small, minor prescriptions where a pair of glasses just sharpens up their vision a little bit. Glasses can be recommended to wear just when studying, reading, working on the computer, driving, etc. Many people do not require glasses for full time wear. If you’re not sure, do not hesitate to ask your eye doctor about their recommendations.


If I am Prescribed Glasses, Will I Have to Wear Them for the Rest of My Life?

Not necessarily. Our eyes change over time. Some people’s prescriptions may get better while other people’s may get worse. It all depends on your individual eyes.

If you do not like wearing glasses but have a larger prescription, there are always other options you can consider to correct your vision such as contact lenses or even refractive surgery in some circumstances.

Your eye doctor would be more than happy to discuss different options for you. In the end, we just want you to see your best and be comfortable!


Our eye doctors at Neal Eye Group in Conshohocken, PA excel in the prescription of contact lenses, glasses and various eye diseases.  Call our optometrists at (610) 828-9701 or schedule an appointment online if you would like to learn more about and obtain a glasses prescription.  Our optometrists provide the highest quality optometry services and eye exams in Conshohocken, Norristown, Plymouth Meeting, Lafayette Hill, and Philadelphia.

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