VISUAL PROBLEMS ASSOCIATED WITH ACQUIRED NEUROLOGICAL EVENTS
Allen H. Cohen, O.D., F.A.A.O., C.O.V.D.

INTRODUCTION

In the United States, approximately one person every sixteen seconds suffers some form of acquired brain injury. Additionally, there are approximately thirty thousand persons per year who are hospitalized for other forms of brain insult such as cerebrovascular accidents (CVA) and diseases such as cerebral palsy, multiple sclerosis, etc.

Following a neurological event, there is often an interruption to thc neurological system which innervate the extraocular muscles controlling eye movement as well as the system that regulates focusing. The common visual symptoms often associated with acquired brain injury are:

• diplopia ( double vision)
• ocular pursuits (eye tracking ability)
• saccadics ( difficulties with shifting gaze quickly from one point to the other),
• accommodative inability ( focusing).
• binocular vision (eye alignment)
• glare sensitivity
• Inability to maintain visual contact

Neuro-optometrists have long recognized symptoms and visual problems associated with trauma that affect the functional visual system and have identified a syndrome, Post Trauma Vision Syndrome (PTVS). The following categorizes the clinical characteristics:

FUNCTIONAL VISION PROBLEMS

• Exotropia (eye turned outward)
• Exophoria (tendency for the eyes to turn out)
• Convergence Insufficiency
• Accommodative Insufficiency
• Oculomotor dysfunction
• Increased myopia
• Common Symptoms
• Diplopia (double vision)
• Blurred near vision
• Perceived movement of print
• Asthenopia
• Headaches
• Photophobia (sensitivity to light)

Additionally, depending on the extent of the injury, there are often deficits in many areas of visual information processing ability. Problems with visual processing may contribute to and or exacerbate symptoms of eye strain, fatigue, headaches, difficulties with balance and posture, depth perception, memory loss, and excessively slow visuomotor performance affecting handwriting.

VISION: AN INFORMATION PROCESSING SYSTEM

Visual processing is organized through two main and separate systems. The one that we are most familiar with is called the focal pathway, which is related to central vision. The eye processes central vision primarily through an area called the macula located in the retina and seeing clearly is mainly through this system. However, one can also see receive visual information with their peripheral vision. For example, when aiming one?s eye at a specific object, one can use peripheral vision to be aware of other objects about the room. Peripheral vision is primarily used as a general spatial orientation system and is mostly a function of the other visual process called the ambient pathway.

The ambient process provides information about where one is in space and contributes to balance, movement, coordination and posture. Nerve fibers from the peripheral retina, part of the ambient visual system, are directed primarily to the midbrain where they become part of the sensory motor pathway. The importance of this system is that it integrates visual information with information from kinesthetic, proprioceptive, vestibular and tactile systems which is important for orientation and movement. Thus, the ambient visual process is important in providing information about where one is in space and where one is looking, while the focal system provides information about what one is looking at.

After a neurological event such as a traumatic brain injury (including whiplash), multiple sclerosis, cerebral vascular accident, etc., the ambient visual process can be compromised and this would affect one’s ability to match information with other components of the sensory ?motor feedback loop.

VISUAL FIELD DEFECTS

Visual field loss following a CVA or TBI causes significant problems for persons when reading or walking, in an unknown environment. Although the field loss is due to nerve damage, often the prescription of yoked prism lenses and optometric visual therapy for ocular scanning, will help patients to identify objects in the affected field and react and process at a more functional level.

VISUAL MIDLINE SHIFT SYNDROME

An unusual phenomenon that often occurs following a neurological event is a change in how the ambient process provides information about orientation relative to the true midline. This syndrome is usually associated with hemiplegia and hemiparesis and often the patient will adjust to this visual mismatch by shifting their weight and will actually walk as if the floor is tilted. The neuro-optometrist can prescribe special prisms called yoked prisms, which helps to re-establish a visuomotor balance and often these lenses in conjunction with physical therapy and optometric visual therapy significantly speed up the overall rehabilitative process.

NEURO-OPTOMETRIC REHABILITATION

Neuro-Optometric Rehabilitation is the blending of the art and science of optometry and vision rehabilitation. Neuro-Optometric Rehabilitation is defined as: An individualized treatment regiment for individuals with visual deficits as a result of physical disabilities, traumatic brain injuries, and other neurological insults. Neuro-optometric therapy is a process for the rehabilitation of functional visual problems as well as visual-perceptua1 motor disorders. It includes, but is not limited to, acquired strabismus, diplopia, binocular dysfunction, convergence and accommodation problems, oculomotor dysfunction, visual-spatial dysfunction, visual perceptual and cognitive deficits and traumatic visual acuity loss.

Individuals of all ages who have experienced neurological insults can benefit from neuro-optometric rehabilitation. Visual problems caused by traumatic brain injury, cerebral vascular accident, cerebral palsy, multiple sclerosis, etc., may interfere with their performance and learning ability. Other problems such as balance and vestibular disorders may be exacerbated by the visual dysfunction.

Often, persons who have a neurological problem will mention these symptoms to their physician and rehabilitative therapists who may recommend a routine eye examination rather than a neuro-optometric exam. This often results in the eye doctor stating that the visual acuity and the health of the eye is normal and that their problems are not related to the eyes. In addition, if there are balance disorders, persons will be referred for physical and occupational therapy and/or vestibular evaluation and treatment. In many cases, if the underlying visual processing problem is not determined and treated, there will be limited progress. A neuro-optometric rehabilitation treatment plan improves and or enhances the specific acquired visual deficits that are identified during the neuro-optometric evaluation. Treatment regimens encompass lenses and prisms, specifically prescribed occlusion and optometric visual therapy.

Conclusion: Persons who have suffered a neurological event often have visual processing problems and functional vision problems that are not adequately managed. These problems cause extreme difficulty, not only with balance and movement, but also could affect the person's perception of space and their ability to process this information. The patient often experiences difficulty functioning in an environment with a lot of visual stimulation such as a grocery store, and will experience difficulty finding a specific object on a shelf. Often movement in a crowded environment becomes quite disturbing and may cause symptoms of vertigo. This can be extremely debilitating to the patient.

The problems associated with Post Traumatic Vision Syndrome can affect higher cognitive levels of function as well, by causing a slowing of responses in general and interference with higher perceptual cognitive function. Therefore, neuro-optometric rehabilitation will often have a positive affect on cognitive therapy.

Motor function deficits associated with neurological problems often can be helped with yoked prism therapeutic lenses which help make significant changes in posture, balance and movement. The use of yoked prisms can be incorporated into existing physical and/or occupational therapy programs.

The neuro-optometrist is an important member of the multi-disciplinary team serving this special population.

About the Author:
Dr. Allen Cohen is a partner of Eye Vision Associates in Lake Ronkonkoma N.Y. Dr. Cohen has been in practice since 1965 and specializes in visual therapy and neuro-optometric rehabilitative services.

Dr. Cohen is Chief, Optometry Service, Northport VA Medical Center and Professor of Clinical Optometry, SUNY State College of Optometry. He has lectured and written extensively on the subject of visual therapy and visual rehabilitation.