What causes different results in eyesight tests?

If you’ve ever had your eyes tested, you may have noticed that there are slight differences in the results. Even if two exams are taken just a few hours apart, the eyesight test results may differ from one another. There are several factors that may cause these different results, and we’re going to explain some of the most common culprits; and we’ll also give you some essential tips for ensuring your next eye test results are as accurate as possible.

What factors can lead to different eye test results?

To understand exactly what can impact an eyesight test result, we’ve rounded up some key factors below:

The state of your eyes varies throughout the day

The performance of the human eye varies ever so slightly during the course of the day. This is caused by the fact that our bodies do not remain in the same condition throughout the day, and we can be impacted by a mixture of both internal and external factors – from doing strenuous exercise, to changes in our sugar level and hormones. These circumstances can change our vision quality, leading to differences in eyesight test results.

While there’s no golden rule for choosing the best time of day for an eye test, there are some helpful principles that you can follow to ensure your results paint a clear picture of your sight. Make sure that you’re not hungry or thirsty before the test, and consider arranging your appointment in the morning before your work day begins if possible/before you’ve had a lot of screen exposure.


Certain health conditions can impact your eyesight test results. As alluded to above, blood sugar levels can impact the quality of your vision, and this is prevalent in those with diabetes.

If you have diabetes, your visual performance may fluctuate throughout the day in line with changes to your sugar levels. We’d suggest trying to get eyesight tests at different times of the day to counteract this.

Dry eyes

Dry eyes can have some uncomfortable effects on our sight, and the condition can also impact the results of your vision exam. If you’ve already been diagnosed with dry eyes, you’ll be aware of the symptoms that it can cause – but we’ve outlined them below in case you haven’t had a diagnosis yet:

  • Light sensitivity.
  • Stinging, burning or scratching sensation in your eyes.
  • Redness.
  • Persistent feeling of having something in your eyes.
  • Stringy mucus in or around your eyes.

These symptoms alone can be bothersome, but they can be managed with targeted treatments such as eye drops. We’d always advise notifying your optician if you know that you have dry eyes – but our highly trained team will be able to pick up on it if you aren’t already aware.

How well rested your eyes are

Our vision system needs a sufficient amount of sleep every night to replenish – so booking your eye exam bright and early when you’ve had a short, disturbed rest the night prior could also impact your results.

Try to get plenty of rest before you go for your eyesight test – in general, between 7-9 hours is considered optimal, but this will vary depending on your age and lifestyle.

Certain prescription medications

Some prescription medications have been shown to have a negative impact on sight quality, and when their long-term/frequent usage coincides with an eye exam, it can lead to inaccuracies. Some of the medications that have been linked to vision-related side effects include:

  • Non-steroid anti-inflammatory drugs (NSAIDs).
  • Plaquenil (often prescribed for rheumatoid arthritis).
  • Cortisone steroids
  • Antidepressants
  • Accutane
  • Oral contraceptives

As a rule of thumb, it is best to let your optician know about your medication history before your eyesight test begins; and this is a crucial starting point for us in our bespoke 3d OCT eye exam.

Your optician of choice

The opticians that you choose for your test can have a major influence on your result. An eyesight test that is done quickly will not give you the same result as the test that is done carefully, taking as much time as needed.

The test environment can also impact the accuracy of your eyesight test results. Exposure to sunlight will make it harder to assess your eyes, so ensure that you choose an optician where the exam takes place in a dark room.

During a quality eyesight test at your local Optical Revolution store, you won’t feel rushed, and the appointment will involve an in-depth exploration of your vision.

Contact lenses

Contact lenses tend to modify the geometry of the cornea, which may lead to inconsistent test results. If you wear contact lenses, we’d suggest switching back to your spectacles 24 hours before going in for the test; as this will give us the most accurate understanding of your vision.

Why is it important to get accurate eyesight test results?

Precision is key when it comes to an eye exam, and this factor will enhance the investment you’ve made in maintaining and improving your vision. A comprehensive eye exam will tell you exactly what you need from your next pair of prescription glasses; and if you choose our 3D OCT eye exam, it can also give you an early diagnosis of certain eye conditions. This kind of thorough eye exam can help you to understand why your eyesight has declined.

To get the best eyesight test results, always make sure that you are going to a trusted optician for a consistent eyesight test. By doing so, your resultant prescription will be perfectly tailored to correct and enhance your vision. Ready to invest in better vision? Use our online system to book an appointment now, or call your local practice to speak to a member of our team.


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