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.
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.
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.
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.