Can eye exam results fluctuate by day and season?

woman and child looking at eye exam results with doctor

Can the results of your eye exam change depending on time of day or year? Absolutely. Eyesight can fluctuate depending on how you feel, the season and even between morning and evening.

For example, you can see 20/20 on an eye exam in the morning and 20/40 in the afternoon. Your vision prescription also can be different if you had your eye exam in the winter or fall. 

The time of day or the time of year can affect the outcome of an eye exam. Let’s look at how daily and seasonal shifts might alter the results of your next eye exam -- and when and why you might want a do-over on your eye exam.

Can the results of my eye exam change depending on the time of day?

Throughout the day, the results on your eye exam can vary. 

For instance, if you’re tired, your eyes might get droopy, causing you to squint (and possibly distorting the outcome of your eye exam). 

Your vision also might vary after you’ve exercised or after you’ve stared at a computer screen for several hours. 

If you suspect circumstances (being tired or having just worked out) aren’t giving an accurate picture of your vision, you might ask your eye doctor to examine your eyes at two different times of day or even on two different days.

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Furthermore, research suggests your vision might peak at certain times of day. 

A study by neuroscientists at Goethe University Frankfurt indicated 8 a.m. and 8 p.m. are the prime times for vision, and eyesight is at its worst at 2 p.m. 

How did they find these peaks and lows for daily vision? Researchers checked men’s reaction to visual cues at six different times over the course of two days. 

The conclusion of their 2018 study: The men’s vision was strongest close to dawn and dusk, and was weakest in the mid-afternoon.

“Driving at dusk and dawn may be easier than it should be because the brain has this mechanism to change our perception of light,” study co-author Christian Kell told The Daily Mail newspaper. “This makes sense because it would have helped us to survive as ancient humans by perceiving, for example, a lion in the savannah.”

In other words, we’ve inherited some basic instincts of our prehistoric ancestors when it comes to eyesight.

Can the results of my eye exam change depending on the time of year?

Seasonal changes can lead to vision changes — and to potential changes in the results of your eye exam. Before an eye exam, be sure to share any seasonal vision issues with your eye doctor.

A 2013 study in Ophthalmology, the journal of the American Academy of Ophthalmology, turned up seasonal differences in what’s known as visual field sensitivity. 

Based on data from 1,636 people enrolled in the Ocular Hypertension Treatment Study, researchers discovered this sensitivity was much higher in the winter than in the summer.

Why does visual field sensitivity matter? As explained in Diabetes, a journal published by the American Diabetes Association, visual field sensitivity refers to the ability to detect a dim white spot at various places on a white background. 

Visual field sensitivity plays a role in walking, driving and other common tasks. Ultimately, a poor field of vision can decrease someone’s quality of life.

“It’s where there is a bigger change in the seasons that you get a bigger seasonal effect,” Stuart Gardiner, co-author of the study and a scientist at the Devers Eye Institute, told EyeWorld News Service. 

Visual field sensitivity “wasn’t very big in California, because the seasons don’t change much in San Diego,” he said. “Around Detroit and the Great Lakes and those areas, there was a much more substantial change between winter and summer.”

Cold weather also can affect your vision (and your eye exam).

During the winter months, complaints about dry, itchy, watery eyes go up, according to the University of Alabama at Birmingham’s Department of Ophthalmology. 

Why? In cold weather, people often are cooped up much of the day in heated places with dry indoor air, decreasing the amount of moisture in their eyes.

If your eyes are dry, itchy and watery, this could blur your vision and increase your sensitivity to light. As such, the outcome of your eye exam could be altered.

Meanwhile, springtime — the height of allergy season for many sufferers — might increase cases of dry eye and trigger changes in the results of your eye exam. Allergy symptoms include burning, irritated and blurry eyes. 

Research published in 2015 in the journal Ophthalmology drew a connection between springtime allergies and dry eye

A review of millions of visits to eye clinics operated by the U.S. Department of Veterans Affairs showed dry eye diagnoses peaked in April, when spring pollen annoys millions of people.

SEE RELATED: Eye allergies: Get relief from itchy, watery eyes

So, when is the best time to get an eye exam?

If you want to get the best results from your eye exam — and the most accurate prescription — research suggests 8 a.m. or 8 p.m. is the best time to book your eye exam.

Practically speaking, though, most eye doctors aren’t likely to be open at 8 a.m or 8 p.m.

The best time to get an eye exam is when you can get in to see your eye doctor. When is your schedule free? When does your eye doctor have open appointments? Some eye doctors even take walk-in patients.

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