If reading, looking at your phone, or working on a computer causes eye strain, headaches, blurry vision, or difficulty concentrating after a concussion, the problem may involve more than your eyesight.
One possible cause is convergence insufficiency, often shortened to CI.
Convergence insufficiency is a problem with the way the two eyes coordinate when looking at something close. It can occur following concussion and other forms of traumatic brain injury, and it can make everyday activities such as reading surprisingly uncomfortable and exhausting.
What Is Convergence?
Hold one finger at arm’s length and slowly bring it toward your nose while looking at it.
As the finger gets closer, both of your eyes must gradually turn inward toward your nose. This coordinated inward movement is called convergence.
The purpose of convergence is to keep the image from each eye aligned so that your brain can combine the two images into one clear, single image.
Normally, this happens automatically.
You don’t have to consciously tell your eyes how far to turn inward when you look from something across the room to the words on your phone. Your brain calculates the distance and coordinates both eyes accordingly.
What Is Convergence Insufficiency?
With convergence insufficiency, the eyes have difficulty maintaining the appropriate inward alignment during near vision.
This may become particularly noticeable when someone performs a near task for an extended period of time.
A person may be able to read the first few paragraphs of a page without difficulty, for example, but gradually develop symptoms as the visual system becomes fatigued.
Common symptoms of convergence insufficiency can include:
- •Eye strain or tired eyes
- •Headaches during or after reading
- •Blurry vision
- •Intermittent double vision
- •Difficulty concentrating while reading
- •Losing your place on the page
- •Words appearing to move or become unstable
- •Needing frequent breaks from near work
- •Difficulty tolerating computers or phones
- •Closing or covering one eye
- •Feeling unusually tired after visually demanding work
For someone recovering from a concussion, these symptoms can easily be mistaken for headaches, general “brain fog” or cognitive fatigue. Sometimes there is a significant visual component.
Why Can Convergence Change After a Concussion?
Convergence may look like a simple eye movement, but neurologically it is anything but simple.
Your eyes do not decide independently to turn inward.
Convergence requires coordinated activity between the eyes, eye muscles, cranial nerves, brainstem, visual pathways, and higher brain networks responsible for processing where a target is located and directing the appropriate response.
Convergence is also closely coordinated with accommodation, which changes the shape of the lens to keep a nearby object in focus, and pupil constriction.
Together, these responses form what is often called the near response.
A concussion can disrupt the neurological networks responsible for coordinating these functions.
The result may not be a problem with the health of the eyeball itself. Instead, the problem may be with how efficiently the brain and eyes work together.
Why Does Convergence Insufficiency Cause Headaches and Eye Strain?
Imagine trying to hold a relatively light object with your arm extended.
For a few seconds, it isn’t difficult.
But keep holding it there.
Eventually, the muscles begin to fatigue.
Something similar can happen when the visual system is struggling to maintain alignment during near work.
Reading requires your eyes to sustain convergence while repeatedly moving across the page. Your visual system must simultaneously maintain focus, coordinate the two eyes, process the words, and continually adjust as your gaze moves.
When that system is inefficient, a task that should require relatively little effort can become demanding.
The person may experience increasing eye strain, pressure around the eyes, headache, blurry vision, or difficulty concentrating as the task continues.
This is why someone may say:
“I can read, but I pay for it afterward.”
The ability to perform a visual task does not necessarily mean that the task is being performed comfortably or efficiently.
Why Can My Eyesight Be 20/20 and I Still Have a Problem?
This is an important distinction.
A standard visual-acuity test asks how clearly you can see.
You may have 20/20 vision and still have difficulty with convergence.
Visual acuity and binocular coordination are different functions.
Someone can see every letter clearly on an eye chart across the room while still struggling to coordinate the two eyes during reading or computer work. That is why a routine vision screening may not necessarily identify every post-concussion visual problem.
How Is Convergence Insufficiency Evaluated?
There are several ways to assess convergence and binocular vision.
One commonly used measurement is the near point of convergence, which examines how close a target can move toward the person before the eyes can no longer maintain appropriate binocular alignment.
But we don’t want to rely solely on whether someone says, “Now I see two.”
Whenever possible, objective measurements can provide additional information about how the eyes are actually behaving.
At Healing Response Acupuncture & Functional Neurology, we use the BrightLamp Reflex app as part of our objective screening and assessment of convergence function.
This technology allows us to collect objective information about the pupillary and ocular responses associated with near viewing, providing another piece of information that can help us identify patients who may warrant further evaluation.
Importantly, screening for convergence insufficiency is not a substitute for a comprehensive eye or binocular-vision examination when one is needed.
Convergence Insufficiency Isn’t the Only Cause of Eye Strain After Concussion
This may be the most important point.
If you develop headaches or eye pain while reading, it does not automatically mean you have convergence insufficiency.
Post-concussion visual symptoms can also involve:
- •Accommodation or focusing problems
- •Eye-tracking difficulties
- •Abnormal saccades or smooth pursuits
- •Visual motion sensitivity
- •Vestibular-visual dysfunction
- •Light sensitivity
- •Ocular or orbital pain
- •Gaze-evoked pain
- •Cervical contributions
- •Migraine
- •Trigeminal pain pathways
- •Other binocular vision disorders
Sometimes several of these problems occur together.
This is why the symptom “reading gives me a headache” should be treated as a clue rather than a diagnosis.
The next question is:
Why does reading give you a headache?
Working With Optometrists and Vision Therapists
Concussion recovery often requires collaboration between different healthcare professionals.
When our examination suggests that someone may have a binocular vision disorder such as convergence insufficiency, we work closely with optometrists and vision therapists who can provide more comprehensive binocular-vision evaluation and treatment when appropriate.
Our role is also to look at the larger neurological picture.
Vision does not operate independently from the rest of the nervous system. Eye movements interact extensively with the vestibular system, balance, head movement, cervical proprioception, autonomic nervous system, and sensory processing. For some patients, understanding these interactions is an important part of understanding why their symptoms persist.
When Should You Consider Having Convergence Evaluated?
If you’ve had a concussion and notice that symptoms consistently worsen during near work, it may be worth having your visual function evaluated.
Pay particular attention if:
- •Reading causes headaches.
- •Your eyes become tired or painful while using a computer.
- •Words become blurry after you’ve been reading for a while.
- •You frequently lose your place.
- •You have to take far more breaks than you did before your injury.
- •You can perform near work—but it requires considerably more effort than it used to.
These patterns provide useful information.
At Healing Response Acupuncture & Functional Neurology, we screen for convergence issues as one component of a broader functional evaluation following concussion. Because after a concussion, saying “my visual acuity is fine” and saying “my visual system is functioning normally” aren’t necessarily the same thing.
Understanding that difference may help explain why something as ordinary as reading can suddenly become one of the most difficult parts of the day.