“When should we see no head movement during visual tracking?”

When should they hold their head still…

The development  of the visual system in children is much discussed. The AOA offers time lines which have development of eye movement continuing to improve at 36 months. This development is dependent upon many factors including the development of the brain as whole and the vestibular, and proprioceptive systems. The development of these systems is inter-dependent. Problems in the visual system will affect development of the vestibular and other systems and impact the developmental movement sequence. This is why the first eye exam is recommended at 6 months of age.

In the birth to 3 three year old, developmental delays would most likely include tracking and saccades problems, particularly when neurological problems (seizures, anoxia, CP, etc) are present. As therapists, our treatments should should stimulate as many sensory systems at possible, including vision.

Eye Movement norms

The best information on the development of eye movement accuracy comes from the NSUCO Ocular motor norms. The NSUCO protocol looks at ability to perform the movement, accuracy of the movement, amount of head movement present and the amount of body movement present during the testing of tracking and saccades. Each of these skills is rated 1-5 with each score defined in the above referenced article. This is the standard way saccades and tracking are quantified by ODs. Each movement would include 4 numbers describing the child ability to perform the movement. This is a somewhat subjective test, much as our manual muscle testing is somewhat subjective. It is most important for the therapist to recognize the errors and refer to the doctor for scoring, then be able to interpret the score as provided by the doctor.

The norms begin at age 5 and support the idea of a constantly improving ocular motor system until full maturity at the age of the 10. The paper further references minimal standards from age 5 to 10 to help identify less than age appropriate eye movement accuracy.

The Therapist’s job

We should be screening these eye movement on all of our patients. Children with developmental delays have a high incidence of ocular motor problems which affect balance, reading, spatial awareness, fine motor and visual motor integration development. These ocular motor problems are influencing the outcomes of our interventions so being testing them should be a part of every OT and PTs evaluation process.

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Visual Processing Disorder

Visual Processing Disorder

Visual Processing disorder is broad term used to describe children that have difficulty with visual tasks. They may have problems with puzzles, mazes, handwriting or reading. The child may be clumsy and have difficulty remembering things like where toys are located. Visual processing problems can be different in each child. Here is a symptom checklist that might help.

Sensory Processing Disorders

Visual processing disorders are part of a larger group of disorders called “sensory processing disorders“. Sensory processing disorders can be linked to any sense (touch or hearing, vision, taste or smell) and are characterized by the brain magnifying or muting sensory information. This magnification or muting of the sensation can appear a child that does not like loud noises, or constantly likes to touch rough surfaces. They may be picky eaters because some foods “feel funny” in their mouths or they only wear their favorite super soft shirt.

These sensory difficulties can cause problems with fine and gross motor development as well as academic performance and cause behavioral issues as well.

Causes of Sensory Processing Disorder

Research continues to identify causes of these disorders but no real conclusions have been found. There are differences in brain structure noted in these children and environmental toxins have been linked to these disorders.

Treating Visual Processing Disorder

Children diagnosed with visual processing disorder should first have complete eye exam including a binocular vision exam. Children with visual processing disorders and other sensory disorders are frequently found to have eye movement and near vision focusing problems that only a binocular vision assessment can uncover. Treatment for the eye movement and near vision focusing problems can frequently reduce the symptoms associated with visual processing disorders.

Following resolution of the eye movement problems, we can ONLY THEN begin successful treatment of visual motor integration and visual perception problems.

Neurological Events and Visual Processing disorders

Recently, I have had several children referred to me recently with “visual processing problems” that also have histories of seizure disorder and concussion. These children also had significant binocular vision problems. Once their binocular vision disorder was correctly diagnosed (both had CI, accommodative dysfunction and saccade dysfunction) and treated, we then able improve visual processing for both of these children.

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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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