The Hart Chart

Accommodation

Accommodation is one of the mechanisms that allow us to see up close. Accommodation is the focusing of the lenses in each eye. This action, combined with the convergence, allows for us to see clearly up close. 

Accommodation is the result of the contraction of the ciliary bodies in the eye which allow for the lens to get thicker thereby focusing the image better in the fovea. This action also includes the constriction of the pupil which more precisely focuses the light on fovea making the image sharper. Here is video of this in action

 

“Its blurry up close”

When accommodation does not work, one may see blurry up close, get headaches or rub the eyes due to eye strain. The ciliary muscles attempting to make the image clear, causes this discomfort discomfort. Accommodation can be exercised to strengthen it to improve near vision. This is generally performed in conjunction with convergence exercises to improve near vision  when one treats convergence insufficiency.

The Hart Chart

A simple way to improve convergence is using a Hart chart. With this activity, a grid of letters is placed at distance and one is held by the patient, near. The patient then reads a line close (or letter) then a line at distance. This is done with one eye occluded so the accommodative action is exercised as the eye focuses near then far. In my clinic, this performed while standing on balance board to further challenge the patient. This simple activity is quite effective at strengthening accommodation. A Hart chart can be purchased from Bernell, found on the internet and is included on the Vision Rehabilitation for Pediatrics Course Companion flash drive. Heres a video.

The Hart chart is one way accommodation can be strengthened. In optometric vision therapy, lenses can be used to strengthen accommodation using an activity called Accommodative Rock.

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A complete binocular vision assessment should be conducted before performing these tasks to make sure that are appropriate. Only an ophthalmologist or optometrist can accurately diagnose an accommodative problem.

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ADHD and Eye Movements

ADHD and Eye Movements

There is much research concerning the link between eye movements and ADHD. Researchers consistently find specific eye movement behaviors associated with ADHD. But how does this research help in the clinic?

ADHD and Saccades

Much of the ADHD/Eye movement research has focused on the quick, exploratory eye movements called saccades. Children diagnosed with ADHD show saccade accuracy consistent with their peers. They are able to quickly and accurately look to a new target in the environment. When instructed not to look a target (anti-saccades), children with ADHD have a more difficult time NOT looking at the stimulus (1). Reading is a series of quick fixations and saccades that affects reading speed. These saccades improves reading fluency in children(2) . Children with ADHD also show reduced tracking ability which further affects reading fluency (3)  (4).

Near Vision and ADHD

Convergence Insufficiency, an eye movement disorder affecting one’s ability to maintain clear near vision, is found at three times the rate in ADHD children compared to those not diagnosed with ADHD(5).  A study also shows that children with symptomatic convergence insufficiency score higher (more negative behaviors) on an academic behavior scale then those children diagnosed with ADHD (7). So convergence problems can be associated with ADHD-like behavior problems.

ADHD and Optometry

Optometry is aware of the link between eye movements, behavior and academic performance. ADHD symptoms can mimic the behavioral signs of eye movement problems, even when a child is unable to vocalize the vision problems he is has having. Treatment of convergence problems is also known to reduce the symptoms of ADHD reported by parents (6). Treating saccade and tracking problems also helps to improve reading fluency and improve academic performance.

Only a complete evaluation by an optometrist that specializes in eye movement problems can help identify these problems that could be limiting performance in a child with ADHD. Treatment of these problems with in-office vision therapy can help improve a child’s academic performance.

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How do we see up close?

The Near Vision System

“I can’t see the board” is a common reason children come for their first eye exam. But problems seeing close are more closely related to academic success then distance vision problems. With more computer use, and frequent changes from looking at the board to a notebook, school can be a workout for the near vision focusing system.

Watering eyes, rubbing eyes, and headaches are early signs of discomfort with near vision. These soon lead to difficulty reading and falling grades. The child may also show avoidance behaviors when trying to do school work as it is physically painful to see up close. But worst of all, the child may not say anything at all, as they do not know that their vision is not working right. Typical school vision screenings may miss the problem also.

The near vision system is a balance of several processes…

So what are the mechanisms involved in near vision focusing??

There are 3 processes involved in near vision focusing. Optometrists call it the near vision triad.

1) Pupil constriction- as an object moves closer, the pupils constrict to improve focusing of incoming light to the fovea. The fovea is an area on the retina with the highest density of light receptors. This area gives us our most acute vision.

2) Accommodative Convergence– as an object moves closer, the eyes move nasally to keep the object on the fovea. Both eyes should smoothly convergence together as the target moves closer.

3) Accommodation– lens of the eye focuses- In humans under 40 years old, the lens of the eye changes focus as objects move closer. This is much like a camera lens. As children, the lens is very flexible allowing for a large focusing range. After 40, the lens tends to become less flexible, so we end up wearing bifocals.

Here is a great example of it all working together:

As something moves toward us, the brain adjusts with the right amount of accommodation and convergence, in addition to the pupil constriction. The amount of both convergence and accommodation can be calculated by the the optometrist to come up with the AC/A ratio. This number gives the optometrist clues to the efficiency of the system.

What does it look like when it does not work right??

 

In some children, both of the lenses tend to over focus making them work very hard to maintain focus of near vision objects. The optometrist can assess this and improve it with glasses also. The child with accommodation problems will be rubbing his eyes during close work. He might complain of headaches when reading. He may show poor comprehension and poor reading skills. Or he may not show any of these signs. He may have a short reading span, or have a difficult time hold still, perhaps mis-identified as ADD.

Without enough convergence, the muscles that focus the lens tire as they work to keep near things in focus. They cause similar problems as poor accommodation and frequently a child will has both. This multi-process system is very flexible in children. Therefore, some children have problems coordinating the system. The condition is called convergence insufficiency and is a common vision problem in children. There will be a separate discussion of CI later.

This is easy to screen using the Near Point Convergence test .  

Only the optometrist can identify these problems, but as therapists, teachers and parents, we need to be aware of the signs of near focusing problems. The Convergence Insufficiency Symptom Survey  is a well researched tool that is very effective in identifying patients with possible CI.

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Assessing Eye Movements

Assessing Eye Movements

As therapists, we should assess EOM or extra ocular movements, the optometry term for eye range of motion. Looking at these movements can give information about brain and cranial nerve function as well as help identify limitations on functional tasks like reading .

Eye movements use similar names as other movements with inferior being downward, superior being upward, lateral movements described as duction with adduction  moving toward the nose (nasal)and abduction away from the nose (temporal). Optometry also has vergence, which is the movement of both eyes toward the nose (convergence) or away from the nose (divergence). Smooth convergence and divergence is important in the near focusing system.

With the patient seated and focused on a point about 40 cm away, the eyes should be still. This is called fixation.  A small rhythmic movement, called nystagmus, is a sign of a central nervous system problem. It is often associated central nervous system problems like Multiple Sclerosis.  It is a frequent early sign of the disorder. It is also closely linked to the vestibular system and the patient might report dizziness. When congenital, the brain adjusts to movements as in the video below.

Congenital Nystagmus

9 points of primary gaze are assessed having the patient follow a point to left/right/up/down/up left/low left/upright/low right. The eyes should move together through all of these points.

9points of gaze_normal_540

Assessing Cardinal Gaze

Each of these movements is control by cranial nerves and failure of an orbit to move in a direction could be a sign of cranial nerve problem or a muscle problem. This occurs frequently as a result of brain injury or trauma to the eye or orbit. This can also be congenital. This eye turn is referred to as a strabismus.  Strabismus causes diplopia or double vision. They can be improved with prism by an optometrist or possible surgery to shorten or lengthen the muscle by an ophthalmologist.

To assess convergence use the near point convergence test. In this assessment, a target held about 1 meter from the patient’s nose and slowly brought toward the nose. The patient is instructed to tell the tester when they see two of the targets. The target should get to within 6cm to be considered “normal”. The test should be done 5 times with the final result be the distance at which the child saw double on this final trial. Reduced convergence is not uncommon following brain injury and stroke and is linked to reading difficulty in children. Reduced convergence makes near vision tasks more difficult as the brain has work harder to see clear. This is called convergence insufficiency. The condition even has its own  website.  This has also become more common in adults we put demands on our near vision system with increased use of smart phones.

Near Point Convergence test

In tracking, the patient follows a target in a circular pattern, both clockwise and counter-clockwise making 2 revolutions each direction. Tester notes the number of fixation loses, the smoothness of the movements and the ability of the eyes to move together.

Eye Pursuits or Tracking

Saccades are very quick eye movements of very short duration. It is a series of fixations and saccades that allows one to read efficiently. Inaccurate saccades are frequently associated with poor reading skills. Optometry can improve saccade accuracy and improve reading .  Saccades testing has the patient fixate from one point to another with the tester noting adjustments following the fixation and if the eyes move together. We can perform the Developmental Test of Eye Movement  or the King-Devick for objective testing of eye movement.  Saccade accuracy can be an indicator for possible concussion as well.

Saccade testing

Abnormal EOM tests should be referred to optometry for complete assessment. They are often related to central nervous system problems, cranial nerve palsy’s or cerebellar problems. They are common in stroke and brain injury survivors and cause decreased reading ability, balance and depth perception.  Patients frequently suffer with eye movement problems for years following a stroke or brain injury, but with the right tools, they can be improved improving a patient’s functional ability.

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