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BINOCULAR INSTABILITY / CONVERGENCE INSUFFICIENCY

Clear and Single Vision for Efficient Prolonged Near Point Performance

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Alan P Pearson OD PhD FCOVD

August 15, 2021


AT-A-GLANCE

  • Binocular instability negatively impacts at least 5% of the population.  It causes symptoms such as visual fatigue, eye strain, headaches, double vision, blurry vision, moving words, and loss of place when reading, doing computer work, or other near point visual tasks.  The condition is present in more than 30% of children who are struggling in school or reading.  The condition impacts many adults who have had a concussion or acquired brain injury.
  • Binocular instability is defined as difficulties establishing and maintaining clear and single vision during prolonged visual tasks.  There are many different types such as convergence insufficiency/excess (involving two eye coordination) or accommodative insufficiency/excess (involving eye focusing), but the symptoms and treatment are similar.
  • To diagnose a binocular instability takes testing that usually goes beyond a standard regular eye exam.   A Functional Vision Evaluation involves more involved functional testing of near point visual performance.   Most patients with a binocular instability can pass a regular eye exam with good eye health and no need for eyeglasses, but they may still have a functional problem in coordination of their two eyes together with eye focusing in prolonged near point tasks such as reading or working on a computer.
  • Treatment of straightforward binocular instability (not involving other significant vision issues) can usually be completed over a 4 to 5 month period using a combination of weekly clinic visits combined with home assignments completed 5 times per week.  At Vision Clinics of Development & Learning we use software that assists in the motivation and compliance with the home prescription.
  • While not all insurance plans cover vision therapy, if your insurance plan does then binocular instabilities such as convergence insufficiency are the most likely diagnosis that qualifies for coverage.  No insurance plan covers all of the costs, and copays, deductibles, and coinsurance apply.

WHAT IS BINOCULAR INSTABILITY?

Binocular stability is the skill by which binocular vision and eye focusing are coordinated, maintained, and adapt to stress. Good binocular stability results in continuously clear and single vision during a visually demanding task such as reading. Binocular instability refers to problems in maintaining visual clarity and/or single vision in response to visual demands.

Binocular vision involves precise fine-motor alignment of the eye muscles so that the line of sight of each eye points at the same object. With precise alignment the brain can then fuse the images from each eye into a single image. Binocular vision allows us to appreciate 3D depth. When the two eyes are not aligned, we may experience double vision.

binocular vision

Eye focus, also called accommodation, involves a fine-motor muscle surrounding a lens right behind the pupil. The muscle is relaxed and the lens flat when looking in the distance. The muscle contracts and the lens bulges when focusing up close. Without the proper muscle and lens accommodation, we experience visual blur.  

When involved in a complex visual task such as reading, we have to coordinate both binocular vision and eye focus over a long period of time while the eyes are dynamically moving across the pages. A book is a flat two dimensional surface with high contrast black and white symbols bunched close together. When looking at a word chunk, the line of sight of each eye has to point at the same word chunk, and the eyes need to simultaneously focus for the precise distance of the word chunk. Then, the eyes make small jumps called saccades from one word chunk to the next word chunk while continually maintaining the eye pointing and eye focusing appropriately.  

In binocular instability, there are moments when binocular vision and/or eye focusing are inaccurate, inefficient, or uncoordinated. Because there are neurological connections between binocular vision and eye focusing, sometimes there occurs a viscous cycle between the tasks of single vision and clear vision. For example, trying to make the words clear by focusing the eye can send signals to the eye muscles that cross the eyes, but if this is allowed to happen it will lead to double vision, so eye pointing needs to be relaxed which then sends signals to relax eye focusing which makes the words blurry.  Binocular instability is the condition where the person cannot simultaneously maintain the eye pointing and the eye focusing so the word chunks are almost double or almost blurry rather than solidly single and clear for the duration of the task.   This is frustrating, and can be the root of symptoms such as visual fatigue, headaches, words jumping and moving, words going double at times, words going in and out of focus, losing place, skipping words, poor attention, avoidance behaviors, and poor comprehension.

DIAGNOSING BINOCULAR INSTABILITY

Binocular Instability is difficulty establishing and maintaining clear and single vision in a sustained near point task.  It is therefore more frequently a problem in cultures that value and stress reading, academic learning, and occupations that involve paper work or looking at computer screens for most of the day.   Some children or adults do not report a lot of problems or symptoms because they have learned to avoid near point vision tasks.  But avoidance can lead to poor academic achievement or a different career path compared to finding and addressing the issue early.   

A Functional Vision Evaluation is necessary to diagnose binocular instability. Regular routine eye exams emphasize eye health and eye optics and often do not delve deep enough into functional vision and symptoms unless the patient specifically expresses problems, asks questions or has concerns.  And for those children and adults that have just learned to avoid a lot of near point activities such as reading they may not have many symptoms or concerns but still be falling behind in their achievement potential due to the problem.  While being able to clearly identify small letters on a card means eye focus is happening at that moment, it doesn't mean that eye focusing is working well over an extended reading task.  In order to function well, the eyes need  to be healthy and any need for eyeglasses should be taken care of.  Next, a Functional Vision Evaluation will take an in-depth assessment of binocular vision, eye focusing, and eye tracking in the context of the visual challenges the individual faces in development, school, work, or recreation. A Functional Vision Evaluation looks at abilities to maintain single and clear vision over time when involved in a dynamic vision task like reading.

Binocular instability comes in a variety of types that identify one part of the visual system that is dysfunctional. But in the end most cases involve aspects of all parts of the visual system, such as two eye coordination, eye focusing, and eye tracking working together in an integrated and efficient manner.   The various types are:

  • Convergence Insufficiency:  More problems converging the eyes when viewing near point objects.
  • Convergence Excess:  Too much stress and tension in the convergence system
  • Exophoria:  A natural resting state of the eyes in a more outward posture, requiring more convergence effort to overcome
  • Esophoria: A natural resting state of the eyes in a more inward posture, requiring more divergence effort to overcome
  • Vergence Infacility: Difficulties jumping two eye coordination between distance and near
  • Accommodative Insufficiency: More problems with maintaining eye focus when viewing near objects.
  • Accommodative Spasm:  Too much stress and tension in the eye focusing system
  • Accommodative Infacility: Difficulties jumping eye focusing between distance and near

Only an eye doctor (Optometrist or Ophthalmologist) has the tools to perform a Functional Vision Evaluation and diagnose binocular instability. Not all eye doctors have the interest or training to perform a Functional Vision Evaluation. 

If you are living in Washington State, USA near the Bellevue or Bothell area, you can schedule a Functional Vision Evaluation at the Vision Clinics of Development & Learning
[Schedule Appointmment].

If you are reading this from afar, then the following directories can be helpful in locating a doctor who can perform a Functional Vision Evaluation:

College of Optometrists in Vision Development:  www.covd.org

Optometric Extension Program Foundation:  www.oepf.org

Neuro-Optometric Rehabilitation Association:  www.nora.cc

TREATMENT OF BINOCULAR INSTABILITY

The long range goal for treating binocular instability is:  Patient will be able to maintain single and clear binocular vision in a sustained near point visual task. Patient will demonstrate quick and precise adjustments to varied fixation distances such as distance, intermediate, and near. Patient will eliminate or minimize symptoms of visual fatigue and vision based performance deficits. 

To get to this goal, we first have to help the two eye coordination system converge the eyes and diverge the eyes appropriately and precisely to various distances.  We do the same in helping the eye focusing system (accommodation) focus and relax precisely to various distance.  Finally, we have put both eye coordination and eye focusing together simultaneously.   In the end we have therapeutically developed the ability to dynamically adjust and sustain two eye coordination and eye focusing during various stresses and eye movements that are encountered in a prolonged near point task (especially the left to right top to bottom eye tracking needed in fluent reading). 

Different vision clinics may have different protocols and some cases are more complex involving other issues than only binocular instability.  The following are only typical guidelines at our clinic, and every case has to be considered individually.  Straightforward binocular instability usually responds well to a 4 to 5 month protocol that combines clinic visits once per week and prescribed home activities that take about 30 minutes per day five days per week.  At our clinic we use computer programs that send us data over the internet to coach and monitor the prescribed home activities.   The home activities are essential in our opinion for the successful treatment of this condition.   It is much like going to the gym for physical conditioning.  If you only go to the gym one day per week, you make minimal gains, but if you go to the gym 5 days per week you make tremendous gains.  Without appropriate home activities, vision therapy will take a lot longer to complete.  In some instances where a patient or family lives excessively distant from our clinic, we can get good results facilitating a home based treatment approach with only 1x per month clinic visits, but such an at-a-distance protocol has to be appropriate and is considered on a case by case basis.

In the first appointment you get your software and start working on the program at home.  Depending upon your situation the clinic visits are either half hour or one hour in length and occur one time per week.  A 4 to 5 month program will take about 16 in-clinic sessions to complete.  In addition to the treatment sessions there are three additional appointments called progress evaluations.  These occur about midway through the treatment, at the end of the treatment, and 3 months after finishing the treatment to make sure there are no regressions.

INSURANCE COVERAGE

Binocular Instability, and more specifically the convergence insufficiency type,  is a condition that is increasingly covered by many insurance plans as there is a good research evidence concerning its identification and treatment.   This does not mean, however, that insurance coverage can be guaranteed.  Even with an insurance plan that says they "cover" treatment, you may still find there are large copays, deductibles, and coinsurance to deal with before you realize any benefit.  Almost no insurance plan will cover the entire costs for a treatment plan even if they say you have coverage.  For example, the software and other prescribed home therapy items and monitoring is usually paid privately or through a flexible spending account.   Also, even when an insurance plan covers the treatment sessions they typically only cover a 30 minute appointment.   Progress visits are medical doctor visits in general so they are more frequently covered with less problems.  

Some insurance plans have specific exclusions for "Vision Therapy" in which case they may cover once per month doctor's visits for an at-a-distance program, but they will not cover the in clinic treatment sessions.  You will have to look up the details of your insurance plan to determine if there are such exclusions.  Sometimes it is hard to find such information and it becomes necessary to call your insurance plan to ask them specifically.   Here is the question you can ask them that has the proper language and codes:  "Does my insurance plan cover vision therapy or orthoptics  92065 for a diagnosis of convergence insufficiency H51.11?"  and then ask "are there any exclusions of vision therapy for my plan?"  and finally ask:  "are there any prior authorization requirements?".   Remember, you have to first complete a Functional Vision Evaluation to reach an official diagnosis and prescribed treatment plan, and even if seems like it should be covered there can still be obstacles and coverage is never guaranteed.

NOTES

There are many other visual dysfunctions that can occur simultaneously with binocular instability.   For example, reflex problems, visual-vestibular problems, fixation and orientation problems, rhythm and timing problems, body knowledge/coordination problems, and visual perception and processing problems. Treatment of binocular instability alone is not meant to address these problems. Some of these problems will need to be addressed before the binocular instability treatment can begin. Some of the problems can be addressed simultaneously with treatment for binocular instability.   The eye doctor will determine the best strategy, sequence, and emphasis in treatment plan selection.

www.visioncdl.com   info@visioncdl.com   425-213-1016

©2018 Vision Clinics of Development & Learning


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