What causes your vision to fluctuate?

Posted in Eye Blog, Fluctuating Vision, Medical

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Fluctuating vision can be a warning of other health issues such as diabetic retinopathy or fluctuating blood sugar levels, high blood pressure, dry eyes, or hormone fluctuation.

I recently heard a new patient express her frustration that no one had ever warned her that uncontrolled diabetes would affect her vision. It meant she would have to come back for a re-refraction – but only after waiting for her blood sugars to stabilize – in order for her to get new lenses for her glasses. Her story got me thinking. While “What might cause my vision to fluctuate or be inaccurate?” may not be a question frequently asked by patients, maybe it should be – before they even come in for their exams!

At Cascadia Eye, we train our technicians to perform the refractometry (where we measure your visual acuity, a.k.a. your lens prescription). Our doctors also review the findings and confirm your prescription during your comprehensive eye exam. So you get the most careful refraction we can give you.

But there are cases when your vision could actually be inconsistent. One day it appears to be one prescription, but if we performed the same refraction a week later it might be something else. That can be a disappointment for you and for us – of course we want to give you the perfect prescription the first time! We do our best to catch instances where this might happen before you order new glasses or contact lenses, and we know a second visit can be inconvenient either way.

So in the interest of arming you with knowledge for the future, let’s talk about the most common factors that might cause inconsistency in your visual acuity, and what you can do to minimize the likelihood of needing a repeat refraction.


If you have diabetes, you most likely already know that doctors stress the importance of yearly comprehensive medical eye exams (dilated exams), to make sure you don’t develop diabetic retinopathy, a diabetes-caused eye diseases that damage the retina) and suffer permanent vision loss.

But even without diabetic retinopathy, uncontrolled blood sugar can have more immediate effects on your vision: during blood sugar spikes, your lens is affected and actually grows larger, causing your distance vision to blur more. When your levels are more normal, the lens also goes back to normal. So the more your blood sugar levels fluctuate, the more your vision does as well! Making sure you have things well under control before your eye exam minimizes the risk of your doctor getting an inaccurate refraction, although of course there are no guarantees.

Dry Eyes

Woman rubbing her dry eyes

I have actually experienced dry eyes firsthand – it is amazing how low tear production can blur your vision. This one can be tricky to prevent if you are unaware of how dry your eyes actually are, like I was. If you don’t have regular eye exams, you might not learn you have a problem until your actual appointment. But if you feel like you might have dry eyes, it doesn’t hurt to purchase over-the-counter artificial tears (any brand) and use them periodically throughout the day. If you’re using them regularly by the time you have our eye appointment, you increase your chances of having a more accurate refraction, and better vision overall.

I found at my last eye exam that my vision had actually improved once I started using artificial tears regularly. Keep in mind that if your dryness is severe, the doctor may discuss other options, like our iLUX treatment and others, with you. Just remember that you may want to come back for new measurements once your dry eye is under control!

Hormone Fluctuation

Ladies, this one is for you in particular. It turns out that during pregnancy, changes in your hormones can actually change your vision too! It can get better or worse, but it doesn’t stabilize until you are through with your pregnancy. Our patients who are pregnant will often still come in for their annual eye exams to make sure their eye health is good, but they may hold off on getting new glasses or contact lenses until it is over.


Cataracts don’t cause a fluctuation in your vision from day to day, but sometimes they can change your prescription over as short a period as a few months. So those new glasses you got in January might not be working so well…in April!

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We usually expect cataracts to take a longer time – say, between yearly eye exams – to develop enough that your vision is drastically affected, but there are definitely cases where the cloudiness progresses rapidly. This is especially true for people who smoke. (For more information, click here: Smoking and Eye Disease) But even if you don’t smoke, if you notice that your glasses don’t seem to be working anymore and you have already been diagnosed with beginning cataracts, rapid cataract progression might be your culprit. And since that kind of vision loss can’t be fixed with a higher prescription, you just might be ready for surgery!

Sleep Deprivation

We all know how a lack of sleep can make us feel terrible. This is because a healthy amount of sleep is required in order for our bodies (and eyes) to recover and function properly. Just one side effect of a lack of sleep is the reduction of tear production, which, when compounded with tired eyes and a fuzzy brain, can certainly effect vision acuity.


Be aware of all of the side effects of any drugs or medications you may be taking. Even if vision distortion isn’t specifically listed among possible side effects, changes to blood sugar or psychological functions may first become noticeable in your visual perception.

The Takeaway

As I said before, sometimes you won’t know you have a problem until your come in for your eye exam (pregnancy excluded, of course.) Coming back for a repeat refraction might be unavoidable. But knowing about these factors in advance, and doing what you can to prepare before your exam, should increase the chances of accuracy when we measure your vision.

Contact Cascadia Eye

If you would like to learn more, or if you would like to schedule an appointment or consultation with our talented doctors at Cascadia Eye, please contact us today or use our online scheduler. You may also pre-shop for glasses at our online pre-shopping page any time. Our entire team is committed to protecting and improving your vision and the health of your eyes. We are happy to answer any questions you might have!

In addition, join us on FacebookInstagram or YouTube to ask your questions about eyes, exams, and our practice. We’d love to hear from you – and there might be a blog to address your questions in the future.

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