And Altered Tear / Lid Function
Our eyelids work much like the windshield wipers on our cars. The lids wipe across our cornea cleaning it and constantly restoring a new layer of tear film. If the cornea is not kept moist, a dry eye or exposure keratitis may develop. It is much like chapped lips and leads to dry, burning, gritty eyes.
After brain injury, the rate of blinking may slow and the completeness of the blinks may decline. The patient may be making only occasional partial blinks. This leaves the lower portion of the cornea to dry and become uncomfortable.
The simple addition of artificial tears and reminders to the patient to blink fully and frequently can manage this problem. In severe cases, silicone tear duct plugs may inserted to reduce the loss of tears from the eye down the normal draining tubes. This is equivalent to placing a stopper in the bathtub.The result is more tears in the eye.
Balance & Illusions of Movement
Thomas Politzer, O.D.Dizziness and Balance Problems Related to Vision
Vision plays a significant role in balance. Approximately twenty percent of the nerve fibers from the eyes interact with the vestibular system. There are a variety of visual dysfunctions that can cause, or associate with dizziness and balance problems. Sometimes these are purely visual problems, and sometimes they are caused from other disorders such as stroke, head injury, vestibular dysfunction, deconditioning, and decompensation.
Visual Dysfunctions Causing Dizziness and Balance Problems
Aneisokonia
Aneisokonia is a condition where an excessive difference in prescription between the eyes causes a significant difference in magnification of images seen between the eyes. When this magnification difference becomes excessive the effect can cause disorientation, eyestrain, headache, and dizziness and balance disorders. Treatment is with contact lenses, or special magnification size matched lenses called isokonic lenses.
Vertical Imbalance
Normally the eyes work in perfect synchrony. However, following trauma, fever, stroke, deconditioning, or sometimes for no apparent reason, one eye will aim higher than the other will. When mild and not enough to cause double vision this is called hyperphoria. If excessive to the point of causing double vision, it is termed hypertropia. In an effort to adjust to the vertical misalignment of the eyes, the person will frequently tip their head to mechanically help align the eyes. This in turn can cause disorders in the fluid of the inner ear and resultant dizziness and balance disorders. Treatment is with therapy to correct the muscle imbalance and prisms.
Binocular Vision Dysfunction
Binocular vision refers to how the eyes work together as a team. It is the coordination of convergence and divergence (eye teaming and alignment) with accommodation (focusing). Following trauma, fever, stroke, deconditioning, or sometimes for no apparent reason dysfunctions can occur causing the eyes to be weak or overactive. When this occurs, the eyes will manifest a tendency to drift outwards or inwards. This in turn can cause eyestrain, double vision, muscle spasm and excessive peripheral visual stimulation, which in turn can trigger dizziness and balance problems. Treatment is with lenses, prisms and therapy.
Double Vision
Double vision is among the most disorienting and devastating vision disorders. People suffering from double vision will often times go to great lengths to alleviate the double image because it is so bothersome. Many will actually even patch, or cover an eye, thereby eliminating the vision from one eye just to get rid of their double vision. Double vision is caused when the two eyes do not align, or work together and one eye actually turns out, in, up, or down compared to the fellow eye. The overall encompassing term for this is strabismus. The disorientation from double vision will frequently trigger dizziness and balance problems. Treatment is with lenses, prisms, therapy, partial selective occlusion and rarely surgery.
Ambient Visual Disorder
The ambient visual process frequently becomes dysfunctional after a neurological event such as a Traumatic Brain Injury (TBI) or Cerebral Vascular Accident (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 oneself in space for balance and movement, as well as to focalize on detail such as looking at a traffic light. Distortions of the spatial system may cause an individual to misperceive their position in the environment. This in turn can cause dizziness and balance problems with the person showing a tendency to lean to one side, forward and/or backward. Treatment is with specially designed prisms and partial selective occlusion. These techniques work effectively in conjunction with physical and occupational therapy attempting to rehabilitate weight bearing for ambulation.
Eye Movement Disorders
Eye movement disorders typically show up as instability of visual gaze (nystagmus), jerkiness of pursuits (eye tracking), or jerkiness of saccades (visual scanning). Eye movement disorders may be congenital, or acquired. When acquired, some of the typical causes are brain injury, stroke, vestibular dysfunction, multiple sclerosis, and other neurological disease or disorder.
When there is an acute adult onset of nystagmus the brain does not register that it is the eyes that are shaking. Rather, the brain interprets that it is the world and objects in it that are moving. This is called oscillopsia and will frequently cause dizziness and balance problems.
As always, treatment is first aimed at correcting (if possible) the underlying cause for the nystagmus, or other eye movement disorder. Concurrently, the following neuro-optometric rehabilitation approaches may be helpful.
If there is diplopia, prism, and/or partial selective occlusion is indicated. Visual exercises may also help expand the range of single binocular vision. Head position and direction of gaze may help compensate for the oscillopsia by finding a null point where the nystagmus is decreased. Partial selective occlusion can be helpful where (typically) the nasal or temporal aspect of the lenses in eyeglasses are partially occluded with tape. A centimeter or less is usually sufficient. Nasal occlusion helps improve peripheral ambient vision, and temporal occlusion helps block peripheral stimulation. Low amounts of base-in prism can also help stabilize peripheral vision and thereby help the oscillopsia.
Accommodative (Focusing) Problems
To change our focus from distance viewing to near for reading, our brain must interpret how far away the object in space is located and then send a signal to the ciliary muscle inside our eye causing it to change the shape of the crystalline lens to exactly focus for that distance.
Our focusing ability is greatest in childhood and progressively declines throughout most of our life until after age forty, the focus has declined to require reading lenses or bifocals. Trauma to the brain may reduce the ability to focus accurately in young people and may lead to the need for reading correction or bifocals. Spasms of accommodation may occur causing over focusing and may present as a temporary increase in myopia.
Post Trauma Vision Syndrome may impair our ability to interpret spatial relationships and accurately coordinate the focus and convergence mechanism.
Introduction to Vision & Brain Injury
Thomas Politzer, O.D. Former NORA PresidentVision is our dominant sense
More than just sight is measured in terms of visual acuity, vision is the process of deriving meaning from what is seen. It is a complex, learned and developed set of functions that involve a multitude of skills. Research estimates that eighty to eighty five percent of our perception, learning, cognition and activities are mediated through vision.
The ultimate purpose of the visual process is to arrive at an appropriate motor, and/or cognitive response.
There is an extremely high incidence (greater than 50%) of visual and visual-cognitive disorders in neurologically impaired patients (traumatic brain injury, cerebral vascular accidents, multiple sclerosis etc.) Rosalind Gianutsos, Ph.D.
"Visual-perceptual dysfunction is one of the most common devastating residual impairments of head injury". Barbara Zoltan, M.A., O.T.R.
"The majority of individuals that recover from a traumatic brain injury will have binocular function difficulties in the form of strabismus, phoria, oculomotor dysfunction, convergence and accommodative abnormalities". William Padula, O.D.
The process of vision can be broken down into three general categories; 1) visual acuity and visual field, 2) visual motor abilities and 3) visual perception.
VISUAL ACUITY and VISUAL FIELD
Visual Acuity - This refers to clarity of sight. It is commonly measured using the Snellen chart and noted, for example, as 20/20, 20/50, 20/200 etc. Visual acuity becomes blurred in various refractive conditions, for example, myopia (nearsighted), hyperopia (far-sighted), astigmatism (mixed), and presbyopia (age related loss of focusing).
Visual Field - This is the complete central and peripheral range, or paNORAma of vision. Various neurologic conditions, such as stroke, cause characteristic losses of the visual field, for example hemianopsia. The person may, or may not, concurrently demonstrate a visual neglect which is a perceptual loss of vision and visual motor integration to the side of the visual field loss.
VISUAL MOTOR ABILITIES
Alignment - This refers to eye posture. If the eyes are straight and aligned the eye posture is termed phoric. If an eye turns in, out, up or down compared to the other eye then the eyes are not straight or aligned and the condition is termed strabismus. Exotropia is a form of strabismus where an eye turns out, esotropia is where an eye turns in, hypertropia is where an eye turns up, and hypotropia is where an eye turns down. These can also occur in combination, such as hyper- exotropia, or hypo-esotropia.
Fixation - The ability to steadily and accurately gaze at an object of regard. This is most dysfunctional in nystagmus which is an uncontrollable shaking of the eyes.
Pursuits - The ability to smoothly and accurately track, or follow, a moving object
Saccades - The ability to quickly and accurately look, or scan, from one object to another
Accommodation - The ability to accurately focus on an object of regard, sustain that focusing of the eyes, and to change focusing when looking at different distances
Convergence - The ability to accurately aim the eyes at an object of regard and to track an object as it moves towards and away from the person
Binocularity - The integration of accommodation and convergence
Stereopsis - Depth perception
VISUAL PERCEPTION
Visual-Motor Integration - Eye-hand, eye-foot, and eye-body coordination
Visual-Auditory Integration - The ability to relate and associate what is seen and heard
Visual Memory - The ability to remember and recall information that is seen
Visual Closure - The ability "to fill in the gaps", or complete a visual picture based on seeing only some of the parts
Spatial Relationships - The ability to know "where I am" in relation to objects and space around me and to know where objects are in relation to one another
Figure-Ground Discrimination - The ability to discern form and object from background
THE THREE MOST DEVASTATING AND INTOLERABLE VISUAL PROBLEMS RESULTING FROM BRAIN INJURY AND STROKE
Although there are many visual problems that arise from brain injury and stroke, three are more devastating and impairing than the rest. These are visual field loss, intractable double vision, and visual / balance disorders.
Visual Field Loss
With a visual field loss the patient is literally blind to half of their field of vision. This places the person at increased risk of further injury and harm from bumping into objects, being struck by approaching objects, and falls.
A two fold approach is used to treat visual field loss. Visual rehabilitation activities are prescribed by the doctor and administered by the therapist to teach scanning of the hemianopic field loss. This is a difficult task. It is the act of seeing something that brings our visual attention and scanning to bear. However, these patients do not see to the field they are being trained to scan and attend. Therapy is aimed at teaching that and several approaches have been developed to assist in this, but remediation still requires a lot of effort and patience.
Special visual field awareness prism lenses are used in treating visual field loss. As the patient scans into the prism the optics are shifted so as to perceptually gain about 15 to 20 degrees of visual field recognition. Since diplopia is perceived when scanning into the prism, fixation in the prism must be brief. These are used as spotting devices only to determine if there is an object in the periphery that deserves further visual attention. When such an object is spotted, the patient turns their head to view it in detail with their intact central vision.
Double Vision ( Diplopia)
Double vision (diplopia) is a serious and intolerable condition that can be caused by strabismus, ophthalmoplegia, gaze palsy, and decompensated binocular skills in patients with brain injury, stroke and other neurologically compromising conditions. Prisms, lenses and / or vision therapy can oftentimes help the patient achieve fusion (alignment of the eyes) and alleviate the diplopia. If and when these means are not employed, the patient may adapt by suppressing the vision of one eye to eliminate the diplopia. If lenses, prisms, and / or therapy are not successful and the patient does not suppress, intractable diplopia ensues.
In this population of patients, patching has frequently been used to eliminate the diplopia. Although patching is effective in eliminating diplopia it causes the patient to become monocular. Monocular as opposed to binocular vision will affect the individual primarily in two ways; absence of stereopsis and reduction of the peripheral field of vision. These limitations will directly cause problems in eye hand coordination, depth judgments, orientation, balance, mobility, and activities of daily living such as playing sports, driving, climbing stairs, crossing the street, threading a needle etc.
A new method of treating diplopia that does not have these limitations has been successfully evaluated. It is called the "spot patch" (invented and named by this author) and is a method to eliminate intractable diplopia without compromising peripheral vision. It is a small, usually round or oval, patch made of dermacil tape, 3-M blurring film (or another such translucent tape). It is placed on the inside of the lenses of glasses and directly in the line of sight contributing to the diplopia. The diameter is generally about one centimeter, but will vary on the individual angular subtense required for the particular strabismus, or gaze palsy.
Visual Balance Disorders
Visual balance disorders can be caused by a Visual Midline Shift Syndrome (VMSS), oculo-motor dysfunction in fixations, nystagmus, and disruptions of central and peripheral visual processing. A full description of these disorders is beyond the scope of this paper. The treatment will depend on the visual diagnosis and etiology. Lenses, prisms and visual rehabilitation activities are used in the remediation of these disorders.
Overview of the Pathophysiology of Vision Problems following Brain Injury or Stroke