Neuro Optometric Rehabilitation
What is Vision?
Vision is much more than “seeing 20/20. Our brain uses a dynamic process to integrate both motor and sensory functions to provide a cognitive perception called “the visual process”. Although this process has been compared to a camera and a computer delivering information to the brain, the act of “seeing” is much more complex. Body movement, posture, and our motor system are related and coordinated rapidly by the brain. Obviously, we take all of this for granted, and only recently have we begun to learn more about how vision, movement and ultimately, perception are related.
The Process of “Seeing”
To make things more interesting, we talk about two kinds of vision; The FOCAL process and the AMBIENT process. Focal helps us see central detail and ambient deals with information from our peripheral or side vision. These systems must work together properly as they tell us “where we are at” relative to things around us.
We now know the visual process is not a single system but a “bi-model” model as mentioned above. There are more than 1,000,000 visual nerve fibers exiting from each eye. 80% of these go directly to the primary visual cortex.(V1) located at the back of the brain (occipital cortex); this provides the “20/20” or detailed vision (FOCAL).
The remaining 20% of visual fibers will continue to 99% of the remaining cortex. This 2 nd system (AMBIENT) is critically important for “releasing” the FOCAL system to easily scan visual space to make accurate and micro-quick decisions as to “where we are coming from and where are we going to”.
With 12 muscles coordinating eye movement and something called the ciliary body focusing the light, two processes called ACCOMMODATION and CONVERGENCE PLAY A major role in determining our ability to read, drive, and engage in virtually all areas of the visual performance. One system (convergence) aims at the target, and the other system (accommodation) focuses it. When the two systems are not coordinated, the eyes feel easily fatigues, attended by discomfort, possible headaches, and blurred or perhaps even double vision.
Hidden Vision Problems
Of equal importance are the various problems created by lack of visual efficiency and/or deficiencies in visual perception. Even if your vision is “20/20”, you may have some of these deficiencies. Many learning and attention deficits exhibited by children may be the result of these conditions. Poor or inconsistent sports performance may also be a signal of inadequate visual skills. Patients who have suffered brain injuries or strokes often have similar problems with visual skills. Visual skills, including visual perception, can be improved in many cases through visual training.
The “visual system” can no longer be confined to the end organ (eye) optic nerve, and visual cortex nor can we assume that there is a single visual system. Vision is now known to be a “bimodal” process involving two separated Neuropathways, the parvocellular and the magnocellular. These functions are termed the “focal” and “ambient” systems. The Air Force Research Laboratory states in their published paper ( J. Vestib. Res., 2000) that “ambient vision comprises the visual functions that are associated with the maintenance of spatial orientation and depend upon peripheral preconscious visual input…These findings provide further evidence that the ambient visual signal is either processed or transmitted throughout the entire brain as befits a visual function that is fundamental to all other perceptual systems.”
Following a neuro event such as CVA, TBI, encephalitis, and many other possibilities, visual sensory deficit can be caused by damage to other areas of the brain and not just the primary visual cortex (occipital cortex). The number of CNS sites are said to exceed 50, so wide spread changes throughout the brain can be expected from focalized damage.
To better understand the vestibular system, it is necessary to further examine the “visual system”. While 80% of the nerve fibers from the eyes are delivered to the primary visual cortex, (focal), 20% of the fibers from the peripheral retinas move to the midbrain. This sensory-motor feedback loop the organizes visual spatial information about balance, movement and orientation in “visual space” and matches information from the kinesthetic, proprioceptive, tactile, and “vestibular” system. This fee-forward mechanism then directs the information to higher cortical areas including the occipital cortex and 99% of the remaining cortex. This information supports the statement that 90% of the information received by the brain comes from our vision!
Two specific syndromes regarding vision/visual perception frequently occur following neuro event: Post Trauma Vision Syndrome (PTVS) and Visual Mid-Line Shift Syndrome (VMSS). One of the primary functions of the vestibular system is to produce compensating eye movements to correspond with head motion. This is referred to as the Vestibular-Ocular Reflex (VOR).
Remember, the primary function of the vestibular end organ is stabilization of the visual scene while the head is in motion.
If you have any of the following symptoms or unresolved visual difficulties, make an appointment for a neuro-optometric evaluation.
Headaches
|
Poor Visual Memory (difficulty in object recognition) |
| Dizziness, Poor Balance, Coordination |
Visual hallucinations |
| Double Vision |
Formed – objects |
| Discomfort/Fatigue |
Unformed - starts or lightning bolts |
| Decreased Comprehension |
Visual Perceptual Disturbances |
| Attention/Concentration difficulty |
Disturbances in body image |
| Sensitivity to Light |
Disturbances of spatial relationships |
| Reading difficulties such as skipping words or lines |
Learning disabilities |
Neuro-optometric rehabilitation is an individualized treatment regimen for patients with visual deficits as a direct result of physical disabilities, traumatic brain injuries, and other neurological insults. People of all ages who have experienced neurological insults may require neuro-optometric rehabilitation.
Visual problems caused by traumatic brain injury, cerebrovascular accident, (stroke) cerebral palsy, multiple sclerosis, etc., may interfere with performance causing the person to be identified as having a learning disability or as having attention deficit disorder. These visual dysfunctions can also manifest themselves as psychological sequelae such as anxiety and panic disorders, as well as spatial dysfunctions affecting balance and posture.
A neuro-optometric rehabilitation treatment plan improves specific acquired vision dysfunctions determined by standardized diagnostic criteria. Treatment regimens encompass medically necessary non-compensatory lenses and prisms with and without occlusion, and other appropriate medical rehabilitation strategies.
Oculi Vision Rehabilitation offers state-of-the-art neuro-sensory diagnostic evaluations to assist in prescribing lenses for patients with *Visual Midline Shift Syndrome and *Post Trauma Vision Syndrome.
*Visual Midline Shift Syndrome
The patient’s center of vision has shifted up/down/ right/left due to a neurological event. Symptoms include dizziness, nausea, lack of depth perception, consistently moving to one side of the hall way or room, bumping into objects while walking, poor balance or posture (leaning back on heels, leaning forward, leaning to one side when walking, standing or seated in a wheelchair) and sensitivity to bright light.
*Post Trauma Vision Syndrome, Visual Midline Shift Syndrome
Following a neurological event such as a traumatic brain injury, cerebrovascular accident, multiple sclerosis, cerebral palsy, etc., it has been noted by clinicians that persons frequently will report visual problems such as seeing objects appearing to move that are known to be stationary; seeing words in print run together; and experiencing intermittent blurring. More interesting symptoms are sometimes reported, such as attempting to walk on a floor that appears tilted and having significant difficulties with balance and spatial orientation when in crowded moving environments. These types of symptoms are not uncommon. Frequently, persons reporting these symptoms to eye care professionals (optometrists and ophthalmologists) have been told that their problems are not in their eyes and that their eyes appear to be healthy. What is often overlooked is dysfunction of the visual process causing one of two syndromes: Post Trauma Vision Syndrome (PTVS) and/or Visual Midline Shift Syndrome (VMSS).
Recent research has documented PTVS utilizing Visual Evoked Potentials (VEP). This documentation concludes that the ambient visual process frequently becomes dysfunctional after a neurological event such as a TBI or CVA. Persons can often have visual symptoms that are related to dysfunction between one of two visual processes: ambient process and focal process. These two systems are responsible for the ability to organize ourselves in space for balance and movement, as well as to focalize on detail such as looking at a traffic light. Post Trauma Vision Syndrome results when there is dysfunction between the ambient and focal process causing the person to over emphasize the details. Essentially individuals with PTVS begin to look at paragraphs of print almost as isolated letters on a page and have great difficulty organizing their reading ability. It has been found that the use of prisms and binasal occlusion can effectively demonstrate functional improvement, being documented with brain wave studies (visually evoked potential, VEP) by increasing the amplitude (this is like turning up the volume on your radio).
I am an optometrist who practice vision rehabilitation (Low Vision) and neuro-optometry. As such, I regularly deal with the most difficult of vision/visual dysfunctions. Most of these patients have been told “nothing more can be done” by health care providers of all disciplines; my job is to provide “something more can be done”.
We invite your questions and pledge to provide eye/vision care at the highest attainable skill level.
James L. Nedrow, O.D., M.S., F.A.A.O.
Links
Neuro Optometric Rehabilitation Association
Brain Injury Association of America
Defense and Veterans Brain Injury Center
800-870-9244
National Brain Injury Research Treatment and Training Foundation
434-220-4824
North American Brain Injury Society
703-960-6500 |
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