You’ve had your eyes checked.
You’ve been told your eyesight is normal—or perhaps that your prescription hasn’t changed.
But after several hours on the computer, the words become blurry. Your eyes feel tired. You have trouble keeping things in focus. Maybe you look up from your phone and it takes a few moments before something across the room becomes clear.
So how can your eye exam be normal when your vision doesn’t feel normal?
The answer is that seeing clearly involves much more than visual acuity.
A traditional eye examination provides extremely important information about eye health and vision. But when symptoms are intermittent, brought on by prolonged visual activity, or related to how the two eyes coordinate, additional testing may sometimes be needed to understand what’s happening.
This is particularly relevant after a concussion or traumatic brain injury.
20/20 Vision Is Only One Part of Vision
When most people hear that their vision is “normal,” they assume that every aspect of their visual system has been tested and is functioning normally.
Often, what they remember most clearly is their visual acuity:
“I have 20/20 vision.”
Visual acuity tells us how clearly you can resolve detail at a particular distance.
That’s important.
But your brain and eyes perform many other tasks throughout the day.
Your eyes have to move together. They must point toward the same target. They must change focus as objects move closer or farther away. They must track moving objects, rapidly jump from one target to another, and maintain stable vision while your head is moving.
And they need to do all of this repeatedly for hours.
You can have excellent visual acuity while experiencing difficulty with one or more of these other functions.
Your Two Eyes Have to Work as a Team
Each eye receives its own image.
Your brain must continually coordinate the two eyes so that those images can be combined into a useful, stable visual experience.
One important part of this process is called vergence.
Vergence refers to coordinated eye movements in which the eyes move in opposite directions to maintain alignment on targets at different distances.
When something moves closer, the eyes generally turn inward toward the nose. This is called convergence.
When viewing something farther away, they move outward again. This is called divergence.
Normally, these adjustments happen so effortlessly that we never think about them.
After a concussion, however, coordinating the eyes can sometimes become more difficult.
What If My Eyes Work Fine During the Exam?
This is where things become particularly important for people whose blurry vision is intermittent.
Imagine having your vision examined at 9:00 in the morning after a good night’s sleep.
Your eyes may coordinate reasonably well.
Now compare that with 4:30 in the afternoon after eight hours of reading emails, participating in video calls, looking at spreadsheets, and switching between your phone and computer monitor.
Those are very different demands on the visual system.
Some people can compensate remarkably well for subtle problems with eye alignment or coordination when they are rested.
As the visual system becomes fatigued, however, maintaining that compensation may become more difficult.
That’s when symptoms appear.
A person may notice:
- •Intermittent blurry vision
- •Double vision
- •Eye strain
- •Headaches
- •Difficulty concentrating
- •Words becoming blurry while reading
- •Needing to blink or refocus frequently
- •Closing one eye
- •Difficulty maintaining focus on the computer
- •Symptoms that progressively worsen throughout the day
By the time they stop working and rest their eyes, the symptoms may improve again.
This means the visual problem can be dynamic rather than constant.
Sometimes the Problem Is Hidden Until the System Is Challenged
Some eye alignment problems are obvious and consistently present.
Others are much more subtle.
The eyes may appear properly aligned most of the time because the visual system is actively working to keep them coordinated.
Think of it as the difference between being unable to hold something and being able to hold it—but only until your muscles become tired.
A brief examination may show that the person can perform the task.
A more detailed evaluation asks:
How well can they perform it?
How much effort does it require?
How long can they maintain it?
What happens when the system becomes fatigued?
This is one reason someone can sincerely report intermittent blurry vision even when a brief examination earlier in the day looked relatively normal.
Why Does My Vision Become Blurry When I Look From Near to Far?
Another common complaint after concussion sounds something like this:
“When I look up from my phone, it takes a few seconds before the television becomes clear.”
Or:
“I can eventually focus on something far away. It just takes longer than it used to.”
This brings us to another visual function called accommodation.
Accommodation is the process by which the lens inside the eye changes shape to bring objects at different distances into clear focus.
When you look from something far away to something close, your visual system has to rapidly adjust.
When you look back into the distance, it has to adjust again.
Accommodation also works closely with convergence and other components of what neurologists call the near response.
After a concussion, some people have difficulty making these adjustments as quickly or efficiently as they did before.
The result isn’t necessarily constant blurry vision.
Instead, it may be delayed focus.
The object eventually becomes clear—it simply takes longer than it should.
Changing Depth Requires Multiple Systems to Work Together
Think about how often you change viewing distances throughout a normal day.
You look at your phone.
Then the television.
Back to your phone.
Across the room at another person.
Down at your computer.
Up at a presentation screen.
Back to your notes.
Each transition requires your visual system to rapidly recalculate where the new target is located and adjust both eye alignment and optical focus appropriately.
Your brain also uses information from both eyes and other visual cues to understand depth and spatial relationships.
These processes normally happen almost instantaneously.
When they become less efficient, the patient may simply experience the end result:
“My vision keeps going blurry.”
Why More Detailed Testing May Be Helpful
When blurry vision persists despite a reassuring eye-health examination, it can be useful to look beyond visual acuity alone.
Depending on the symptoms, additional evaluation may examine:
- •Near and distance visual function
- •Convergence
- •Divergence
- •Accommodation
- •Vergence ranges
- •Eye alignment
- •Ability to sustain binocular coordination
- •Eye tracking
- •Rapid eye movements
- •Visual endurance
- •Eye and head coordination
- •Responses to prolonged or repeated visual tasks
The goal isn’t to search for abnormalities simply because someone has symptoms.
It is to reproduce, as much as reasonably possible, the conditions under which those symptoms actually occur.
If your vision only becomes blurry after sustained near work, that history matters.
If it happens primarily when you’re tired, that matters.
If the blur occurs when shifting from near to far, that matters.
If closing one eye makes the problem disappear, that matters.
The pattern provides clues about which parts of the visual system deserve closer investigation.
Blurry Vision Is a Symptom, Not a Diagnosis
There are many possible causes of blurry vision, ranging from relatively simple refractive errors to eye disease, medication effects, migraine, dry eyes, and neurological or binocular-vision problems.
New or unexplained blurry vision therefore deserves appropriate medical and eye evaluation.
But when eye health and visual acuity have been evaluated and someone continues to experience intermittent blurry vision after concussion, the next question may need to be more specific.
Not simply:
“Can you see clearly?”
But:
“How well does your visual system maintain clear, coordinated vision throughout the demands of your actual day?”
At Healing Response Acupuncture & Functional Neurology, we look at visual function as part of the larger neurological picture following concussion. This may include evaluating eye movements, convergence, vergence, accommodation, visual endurance, and the interaction between vision and other systems involved in balance and spatial orientation.
When appropriate, we also work collaboratively with optometrists and vision therapists for more comprehensive binocular-vision evaluation and treatment.
Because sometimes your vision really is clear during the eye exam.
The problem is keeping it clear eight hours later.