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Is My Glasses Prescription Too Strong?

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Can My Glasses Prescription Be Too Strong?

New glasses, outdated prescriptions, and vision changes can all contribute to feeling like your prescription is wrong. 

When your prescription feels too strong, you might experience headaches, nausea, and eye strain, among other things. It might not be clear why your prescription feels wrong, but it doesn’t take long to notice something’s off.

There are a few things you can do to see if your prescription is too strong. If you’re concerned about your prescription, the best thing you can do is visit your optometrist!

Understanding Your Prescription

Your eyeglasses have 2 prescription lenses: one for your left eye and one for your right eye. On a typical prescription, you should see O.S. and O.D. 

O.S. is short for “oculus sinister” and is for your left eye. O.D. is short for “oculus dexter” and is for your right eye.

Your glasses prescription includes additional measurements to ensure your glasses fit your face and are properly aligned with your eyes. 

Sphere (SPH)

The sphere, or SPH, section of your prescription refers to the lens power needed to achieve clear vision. 

A minus next to your SPH number indicates myopia, or nearsightedness. This means you can see clearly up close, but objects at a distance appear blurry. For example, -1.00 SPH would be a mild case of myopia. 

A plus next to your SPH number indicates hyperopia, or farsightedness. This means you can see clearly far away, but objects in a close range appear blurry. For example, a +1.00 SPH would be a mild case of hyperopia. 

Lens power is measured in diopters. The higher the number, the higher the prescription required to correct vision. 

Cylinder (CYL)

The cylinder, or CYL, measures the degree of astigmatism in an eye (if any). 

Astigmatism occurs when the cornea is irregularly shaped or curved. An eye unaffected by astigmatism would have the same curve on any rotation, like a baseball or tennis ball. Eyes with astigmatism can be more oval- or egg-shaped. 

The CYL number helps correct the difference in the eye’s curvature. 


The axis indicates where your astigmatism is on the cornea. Written in degrees between 1 and 180, this number represents where your astigmatism aligns on the eye. 


The add number allows your optometrist to write an additional prescription. This would be used for multifocal lenses, such as bifocals for patients with presbyopia


The prism field records a special type of correction for patients who see double. The prism number helps combine the 2 images into 1 for the wearer. 

What About Contact Lenses?

Your contact lenses sit directly on your eyeball, which means the prescription will be different from your glasses. You’ll need to schedule a contact lens exam and fitting appointment to get the proper prescription for your contact lenses. 

A pair of glasses sits on top of a printed out prescription paper.

Signs Your Prescription Needs Updating

Blurry Vision

Perhaps the biggest indicator of a prescription that needs updating is blurry vision. If your vision is blurred while wearing your glasses, you definitely need to see your optometrist. 

Test your vision while wearing your glasses by covering one eye at a time. Do you notice a difference in your vision between your eyes? If so, schedule an appointment with your optometrist as soon as possible. 

Frequent Headaches

Another sign that your prescription needs updating is if you experience frequent headaches. Wearing glasses with an incorrect prescription puts undue strain on your eyes and visual system, which can result in headaches. 

If you’ve noticed worsening headaches or recurring headaches, contact your optometrist to schedule an eye exam

Dizziness & Nausea

When your prescription is too strong, you might experience dizziness or nausea more often. If wearing your glasses results in these symptoms, contact your optometrist to schedule an eye exam and refresh your prescription. 

Out of Your Adjustment Period

It takes time to adjust to new glasses, especially frames that are different from a previous style or lenses that have multiple prescriptions. This discomfort is normal, but should subside after a few weeks to a month. 

With new glasses or a new prescription, you may experience headaches, dizziness, and nausea. However, these symptoms should gradually subside as time goes on. If these symptoms don’t subside, or worsen over time, it could be a sign your prescription is incorrect. 

Why Is My Prescription Wrong?

It’s normal for a new prescription to feel too strong at first.

Your prescription changes over time, so it’s possible that your prescription may simply be outdated. Changes in your vision are normal, which is why it’s important to get regular eye exams. 

It’s rare that you’d receive an incorrect prescription from the optical team, but it isn’t impossible. The best thing you can do is talk to our North York optometrist

How Can I Fix It?

The easy-peasy fix is by scheduling an eye exam! Your optometrist can perform a comprehensive evaluation of your eyes and help you get the right prescription for your eyes. 

Our team is always here to help you. Contact us today to book your next eye exam. 

Dr. Shaina Nensi, OD and owner of Avenue Optometry

Written by Dr. Shaina Nensi, OD, FCOVD

Dr. Shaina Nensi, owner of Avenue Optometry & Vision Therapy, received her Doctor of Optometry degree from the University of Waterloo. Dr. Nensi went on to complete a residency in Pediatrics and Vision Therapy where she received additional training in the areas of pediatrics, neuro-rehabilitation, vision therapy and eyecare for special-needs populations. Upon completion, she received The Canadian Association of Optometrist’s Award of Merit and the COVD Award for Excellence in Vision Therapy. Dr. Nensi is also a board-certified Fellow in developmental vision and vision therapy by the College of Optometrists in Vision Development (FCOVD).

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