April 2, 2023 | Basecamp

Visual Reasons For Dizzy And Trouble Focusing Eyes

By Barrett Eubanks, M.D.

Visual Reasons For Dizzy And Trouble Focusing Eyes

You’re not crazy, your vision can be making you dizzy.

Specifically, this can occur when you are having trouble using both eyes together.

The biggest reason for this is when the eyes are seeing “different" pictures. The vision is out of balance between the two eyes and the brain just simply has a hard time processing those two images together. This can create a whole host of symptoms including eye strain, trouble focusing the eyes as well as dizziness.

While our brain is capable of doing a lot, there are some things it just has a harder time handling. Let’s see what’s causing the problem and what can be done about it.

First, Not ALL Dizziness Is From Eyes

The dizziness and blurred vision you are experiencing may not be due to your eyes. This is important to know. There are other medical reasons that can cause dizziness and blurred vision; some being serious.

Dizziness can be a symptom of many things. It can be a sign that the brain isn’t getting enough blood flow. This can be due to changes in medication or other heart or blood pressure related cause. Especially if the dizziness and blurred vision occur right after standing up.

This can also be due to stroke. Especially if you are having other neurologic symptoms such as weakness or trouble speaking going along with the dizziness.

Trouble with inner ear also will cause a severe amount of dizziness called vertigo. This can make it seem like the room is spinning.

So, any sudden onset of dizziness and / or blurred vision NEEDS to be followed up by a medical evaluation to determine if there are any other causes.

Why Can Vision Be Out Of Balance

When light enters our eyes, if focuses on the retina in the back of our eye. Our retina then sends this information to the brain and the brain tells us what we see.

This works exactly like a digital camera. You can think of the retina as the photoreceptor chip of the camera. It just absorbs light and passes on that information to the brain. Like a camera, a tiny picture is formed on the retina and sent to the brain.

The shape of the eye determines the size of that picture. For most people, this size is not important. When both eyes are about the same shape, the size of the picture is the same and we just simply “see".

The trouble comes when both eyes aren’t the same shape. The size of the picture can differ between the two eyes. This is problematic for the brain.

When the size of the pictures differs too much, the brain can’t merge things together.

This can cause:

  • Eye Strain
  • Headache
  • Trouble with glasses
  • Impaired Depth Perception
  • Dizziness and Imbalance
  • Nausea
  • Double Vision

All just simply due to the fact that eyes see things slightly different!

Different Prescriptions Causes Different Image Sizes

One of the biggest causes is a significantly different prescription between the two eyes.

Let’s say that your right eye can see well without any prescription. Your left eye on the other hand, needs -6.00 of prescription to correct vision.

When correcting your eyes with a pair of glasses, that left eye will see a different size of image than the right eye. The necessary prescription of the glasses changes the size of the image between the two eyes.

Combing two different size of images into one
Having two different size images can stress the brain; image by The Lucky Neko on Unsplash / modified from original

Now, there are small amounts of image size that the brain can tolerate. A rough rule of thumb is that the brain can tolerate approximately a 3% difference in the size of images. Very roughly, this corresponds to about 3.00 difference in prescription.

So because your left eye has 6.00 difference in prescription compared to the right, this can cause the vision to be out of balance and cause you to be dizzy with trouble focusing the eyes.

This applies not only to large differences in prescription, it also applies to large differences in astigmatism between the two eyes. If one eye has much more astigmatism than the other, the size AND shape of the image will be different and can cause issues.

From birth

If the eyes have different prescription from birth, this is much more “tolerated" than if different prescriptions develop later in life.

During the first decade of our life, our eyes are developing. If anything prevents us from being able to see during this time frame, vision just simply doesn’t develop. This is known as amblyopia (also known as a lazy eye). Having a large difference between the two eyes is one common way a lazy eye develops.

But let’s say we correct the eyes but a large image size difference exists. Rather than fight it, the brain simply suppresses one eye. While this prevents symptoms, it also prevents the ability to use both eyes together and reduces depth perception.

A similar concept occurs in children who have eyes that are misaligned. Instead of having double vision, one eye is suppressed and prevents the ability to use both eyes together.

So if you’ve always had a large difference in prescription or astigmatism between eyes, you may not really be bothered by it.

Prescription change after birth

The bigger issue comes when there is a change from the norm of what you are used to.

Some of this comes from certain eye conditions: (However if one eye is significantly more blurry than the other, symptoms are less likely)

  • Keratoconus will change the shape of the cornea and can significantly increase the prescription of one eye more than the other.
  • Cataracts can cause a large shift in prescription
  • Issues with the macula such as swelling or the development of a membrane or film can distort one eye over the other (technically not a prescription change but can still cause vision imbalance).

But a large amount of changes in prescription occur because of surgery.

Cataract surgery

For many, cataracts occur in both eyes. But not all. Some people get cataracts in one eye only and only need cataract surgery on one eye.

However, cataract surgery will change the prescription of the eye. For many, this means better distance vision without glasses.

But problems can arise if you go into cataract with a large prescription. The eye that just had surgery may have a very different prescription than the eye that doesn’t need surgery.

Also check out Resolving Vision Imbalance After Cataract Surgery

Laser eye surgery & monovision

It’s uncommon to only correct one eye with laser eye surgery. So this doesn’t come up quite as often with laser eye surgeries such as lasik than with cataract surgery. But a different situation comes up more frequently.

Within our 40s, we start to lose our reading vision. This requires reading glasses or progressive glasses in order to see up close. But what some contact lens wearers decide to do instead is a technique known as monovision. One eye is corrected for distance while the other is corrected for reading vision. In short, an intentional prescription difference is created between the two eyes.

The same is often done with lasik in this age group to get out of reading glasses. One eye is corrected for distance while the other is focused for reading vision.

While monovision does create an imbalance between the two eyes, it does fall into a slightly different category (unless you are using glasses to correct through the monovision).

Because the two eyes are focusing at different things, one image being sent to the brain is more blurry than the other one. While this is something else the brain needs to adjust to, there is less difference in the size of the images.

Everyone Is Different

The 3% difference is a very rough guideline. In reality, there is a huge range of what people can tolerate. For some, they may only be able to tolerate a 1% difference, others may adjust to 5% difference or more!

A lot of this has to do how well the brain is capable of adjusting. And the brain is capable of adjusting to quite a lot!

And so, if your new glasses are causing you to develop some vision imbalance and cause you to be a little dizzy and have trouble focusing your eyes, often the best initial course is give it time for the brain to adjust to the new glasses prescription. A week is a good, a month is great, but a few months really gives a good idea of how much your brain can do.

But if the difference between the eyes is too much or intolerable, there are other effective ways to treat it.

Treating The Difference Between Eyes

Glasses change the size of the image that we see. That’s a lot of the problem between having different prescriptions in the eye. And the further the way the glasses are from the eye, the more it changes the size of what we see.

So, some very effective ways to solve the issue of having two different eye prescriptions is to get the prescription as physically close as possible to the eye.

But try as you may to push your glasses against your head, there is a better way.

While sometimes the glasses may be modified to reduce the size difference, the best way this is achieved is through either contact lenses or surgery.

  • Contact lenses sit on the surface of the eye. Because of this, they have very little effect on the size of the image that we see. This makes contact lenses a great solution to correct large differences in prescription between the eyes.
  • As an alternative to contact lenses, laser eye surgery can achieve a similar function. By placing the prescription of the eye directly on the eye, it dramatically reduces image size differences between the eyes.
  • If the imbalance was caused by cataract surgery and can’t be fixed by either of the other two methods, this may be a good reason to do cataract surgery on the good eye so that both of the eyes match.

It is good to note that it may still take some time to adjust even after correcting the imbalance with contact lenses or surgery. Even if objectively things are better, the brain still has to adjust to those changes.


Being dizzy and having trouble focusing eyes can be caused by an imbalance between the two eyes. Specifically, if one eye has a higher amount of prescription or astigmatism, the image it sees won’t match the other eye and this will bother the brain. There are certain eye conditions that will cause this but another large cause is through surgery. Fortunately, this can be corrected quite effectively with contact lenses or through other surgeries.

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