Cortical Visual Impairment
From Holoprosencephaly
CORTICAL VISUAL IMPAIRMENT (CVI)
Cortical visual impairment (CVI) is a neurological visual disorder.
Neurological visual disorders: disturbed or reduced vision due to various brain abnormalities.
Ocular disorders: pathology of the eye(s)
The two types of visual disorders (ocular & neurological) can coexist.
Definition for Medical Purposes:
Cortical visual impairment (CVI) may be defined as bilaterally diminished visual acuity caused by damage to the occipital lobes and or to the geniculostriate visual pathway. CVI is almost invariably associated with an inefficient, disturbed visual sense because of the widespread brain disturbance. See brain diagrams.
Definition for Educational Purposes:
Cortical visual impairment (CVI) is a neurological disorder, which results in unique visual responses to people, educational materials, and to the environment. When students with these visual/behavioral characteristics are shown to have loss of acuity or judged by their performance to be visually impaired, they are considered to have CVI.
Note: A student whose visual functioning is reduced by a brain injury or dysfunction may be considered blind for educational purposes if visual function is equal to or less than the legal definition of ocular blindness.
History
Visual impairment was defined in the past by loss of acuity (how far we see) and also by the severity of visual field loss (blind area). This definition was originally designed for characterizing visually impaired adults who required social assistance and not for children with visual impairment caused by various eye conditions. Even though it did not accurately represent visual abilities, the definition was widely accepted, but it adversely influenced our thinking about visual impairment. Services were developed worldwide for only those people with visual problems fitting this definition while others with obvious visual difficulties who required intervention were excluded.
During the last several decades, our understanding of vision has markedly improved. It is now realized that vision is not a single sense but a combination of complex senses which have evolved over millions of years. Almost the entire brain is involved in the process of seeing. In different locations there are specialized areas for distance vision, recognition of faces, objects, colors, contrast, and movement. There are also areas of the brain that coordinate visually-directed movements, and process visual information to achieve perceptions of directionality and depth. CVI is caused by widespread damage to the brain, which affects most of the specialized visual centers, resulting in a damaged, inefficient visual sense. When only a small visual area is affected, it can result in a specific visual disorder, but not in CVI.
Because in the past everyone who was considered to be visually impaired had to have reduced or absent visual acuity, the medical definition of CVI also emphasized loss of ability to see in the distance (reduced acuity). It was hoped that once the correct diagnosis was made, children with CVI would be appropriately managed by a variety of professionals, including educators.
The medical definition of CVI is not well understood by non-medical professionals. While acuity testing is difficult in the young and disabled for physicians, it is even more difficult for teachers. Also, there are many children with visual problems similar to CVI, except they have normal acuity. This visual condition is called "cortical visual dysfunction" (CVD). The educational management of children with CVI and CVD is similar. It is now known that with time the visual acuity of children with CVI tends to improve. Therefore the diagnosis of CVI could change to CVD over time. Both groups require remedial education, which necessitates an increased number of specialized teachers. Based on the above discussion, it is clear that there is a need for an educational definition of CVI and CVD, which addresses the needs of these children.
CVI is suspected by:
- a normal or close to normal eye examination;
- a medical history which includes neurological problems; and
- the presence of unique visual/behavioral characteristics.
Four major causes of CVI:
- Asphyxia
- Brain maldevelopment
- Head injury
- Infection
Unique visual/behavioral characteristics of CVI:
- Normal or minimally abnormal eye exam (CVI may co-exist with optic nerve atrophy, hypoplasia or dysplasia and ROP.)
- Difficulty with visual novelty (The individual prefers to look at old objects, not new, and lacks visual curiosity.)
- Visually attends in near space only
- Difficulties with visual complexity/crowding (Individual performs best when one sensory input is presented at a time, when the surrounding environment lacks clutter, and the object being presented is simple.)
- Non-purposeful gaze/light gazing behaviors
- Distinct color preference (Preferences are predominantly red and yellow, but could be any color.)
- Visual field deficits (It is not so much the severity of the field loss, but where the field loss is located.)
- Visual latency (The individual's visual responses are slow, often delayed.)
- Attraction to movement, especially rapid movements.
- Absent or atypical visual reflexive responses (The individual fails to blink at threatening motions.)
- Atypical visual motor behaviors (Look and touch occur as separate functions, e.g., child looks, turns head away from item, then reaches for it.)
- Inefficient, highly variable visual sense
source: [aph.org]
Intervention Strategies
Interventions selected for students with CVI will be most effective if they are the result of careful assessment of functional vision. Interventions strategies selected should be based on the unique visual and behavioral characteristics associated with CVI (Jan & Groenveld, 1993). These characteristics include: color preference, visual field preferences, difficulties with visual novelty, attraction to movement, difficulties with visual complexity, non-purposeful gaze, attraction to light, visual latency, difficulties with distance viewing, and the inability to coordinate the visual motor action of looking while reaching (Jan & Groenveld,1993, Roman, 2004). The activities and adaptations ought to be designed to embrace any of the CVI characteristics that are interfering with the student's ability to use vision purposefully.
The following suggestions highlight some guiding principles for the family and educational team in planning interventions for students who have CVI.
It is important to understand the base of information known about CVI must be analyzed to each child as an individual. Each characteristic of CVI may or may not fit an individual child. The information that does “fit” will help parents and teachers to design a home and/or school program that is tailored to each child’s needs. Dr. Jan, a pediatric neurologist in British Columbia, and his colleagues at Children’s Hospital have noted the following behaviors associated with cortical impairment:
- Visual performance can be quite variable, simply put, some days are better than others. Visual functioning can even change from hour to hour with some children. Factors which might influence the fluctuation include: fatigue, noisy environments, illness, medications, seizure activity, and unfamiliarity of environment.
- Visual field defects may also be associated with CVI due to specific neurological damage.
- Movement cues, especially in the peripheral fields can often stimulate a visual response. Visual interpretation of the environment may be improved for some children when they are actually moving as opposed to standing still. Parents of some children with CVI have reported improved visual responsiveness when the child is riding in a car.
- Color vision does not seem to be affected. In fact, some colors appear to be “better received” that others such as red, orange, and purple.
The process of visual habilitation is in many ways different for the child with CVI than for the child who experiences an ocular impairment. The focus is for the CVI child to control visual input to avoid overstimulation. In view of the aforementioned characteristics of CVI, the following guidelines are recommended for consideration in home and/or school programming:
- Reduce extraneous sensory information from the child’s “working/playing environment”. Eliminate unnecessary noise or visual distractions. Present one item at a time as much as possible.
- The use of touch should be a primary means of introducing information. Continue to place the objects of daily care or “learning activities” in the child’s hand when presenting the item.
- Language is very important for information about the object or visual situation. Use labels that include description words. Tell the child what she/he is “seeing”. Voice intonation is important as far as providing meaning to a situation. When disciplining, for example, a firm voice should be used to match the words being used.
Familiarity is also an extremely important consideration. Parent and teacher experience has shown objects that are familiar often result in increased visual attention to that object as opposed to one that is new to the child. Think about what objects the child is involved with during his/her daily care activities. Make these objects part of his/her vocabulary (touch, function, sight). Examples might include:
bottle/cup – drinking bowl/plate/spoon – eating comb – morning grooming washcloth or favorite bath toy – bathing music toy – bedtime diaper – diaper changes “security toy” – time to go somewhere outside of the home
Parents and teachers should decide what objects are typically used with the child during everyday activities or routines. To establish familiarity, the same object(s) should be used each time. The object should be visually, tactually, and verbally presented at the onset of the activity and then talked about as the child experiences their function. The exact style of presentation will vary according to each child’s general learning style and needs.
- The colors red and yellow are thought to be more readily perceived so may be used to enhance a visual target.
- Repetition is important for all children, practice is how they learn to integrate their new knowledge and put it to use. This especially is true for children who experience a sight loss.
- Be aware the child might fatigue easily in situations which require visual/auditory/tactile deciphering of information. Build in breaks and allow for extra response time before giving the child more information.
- Proper positioning is important for the child. If she/he is not in an aligned or supported body posture, the child cannot fully concentrate on the task at hand. *This is true for all children, but especially important for the child with CVI and cerebral palsy. Consultation with a therapist should be utilized to promote optimal positioning.
- Each child’s family knows their child the best, their knowledge of what he/she likes, dislikes, etc. should be built into his/her learning activities.
source: [tsbvi]
Prognosis
There is no cure for CVI but consistent and frequent therapy has shown to improve visual ability, sometimes there is a significant improvement.
For more information about Cortical Visual Impairment, please visit this resource: [APH/CVI website]
For more information about vision therapy, visit this section: [Vision Therapy]
