I have previously discussed the difficulty patients often have in reading after head injuries. I have also blogged on the importance of Accommodative Insufficiency, (the inability of an eye to focus up close) after a traumatic brain injury (TBI).
There is one other major factor which can impact a person’s near vision after head trauma that is termed Convergence Insufficiency.
Without getting too technical, to have your eyes focus up both eyes need to turn inwards slightly (converge). If the eyes remain perfectly aligned- like looking at a distant road sign- they would be unable to focus on a fingertip. Thus, the brain unconsciously pulls the eyes in to focus on the near target.
Now, what happens if the eyes are unable to make this adjustment and turn in slightly? There are several possibilities:
1. The object up close may appear double (side by side).
2. The object may appear blurred.
3. The person may begin to close the less dominant eye.
4. The brain may begin to ignore the vision from one eye.
All of these adjustments have consequences, and the consequences are not good.
It is important to understand the optometric and ophthalmic literature estimates the frequency of Convergence Insufficiency after TBI is between 10-20% – that’s frequent. But in basic eye exams measuring just visual acuity (reading the letters on the E chart), Convergence Insufficiency will not be detected. What does the eye doctor need to do to assess for Convergence Insufficiency? The most important thing is to take a careful history. These patients will complain of early fatigue after reading, the letters may begin to swim around.
As already mentioned, the patient may experience double vision while reading, but single vision at distance. A patient may also state that he/she starts to close one eye after reading for a half hour. All of these secondary activities tend to cause headaches, eye aches, and visual fatigue.
An outside observer might notice one eye begins to drift outward while watching the patient read. The clues are usually there, but the doctor needs to ask and measure. During the exam, the doctor may ask the patient to focus on the tip of a pencil while moving it slowly towards the patient’s nose. A normal young person can do this until the pencil tip is fairly close (everybody breaks down if you get it too close), older patients can still do it but may require reading glasses. Individuals with Convergence Insufficiency can’t perform the task. The eyes quickly break down and normal fusion is lost (like a runner who suddenly gets leg cramps).
The consequences can be enormous. Students cannot finish their homework, professionals will turn off the computer and needed work is neglected. If the person pushes on (and most do) he/she gets severe eye strain and headaches and that person eventually quits and the eyes close. Sleep is the best cure, but sleep doesn’t pay the bills.
What else can be done?
Vision Therapy (as discussed in a previous blog) has been shown to be effective in treating Convergence Insufficiency. Trained eye care professionals can help the individual retrain the eye muscles to allow the eyes to turn in. This often requires multiple sessions and may be expensive, but should be included in the patient’s long-term life plan and compensated in any settlement agreement. The expense of doing appropriate supervised Vision Therapy along with home exercises is often only a small fraction of the cost of lost worker productivity and the burden of chronic discomfort. Glasses may help, but are usually more beneficial in Accommodative Insufficiency, and can sometimes make Convergence Insufficiency worse.
The worst treatment of all is neglect, and most adult TBI patients with Convergence Insufficiency are ignored by regular doctors and eye doctors. Younger children and students often are diagnosed and treated- teachers notice these kids having trouble in school. Healthy adults don’t get the careful observation of a teacher, and after a head injury they rarely see an eye doctor.
Convergence Insufficiency is real, can be diagnosed, and can often be treated. That is one reason I firmly believe all TBI patients should be examined at least once after an injury by a trained ophthalmologist who specializes in TBI. I am proud to provide that service to the general community. Patients are evaluated, treated, and no longer told it is just their imagination.
