Cortical Vision Impairment (CVI)
Annette Godfrey-Magee, 2013
An increasing number of children with a diagnosis of cortical vision impairment (CVI) are entering the educational system. These children pose many difficulties in identifying their educational and visual needs and in planning for their programs. There is a difference between children who have true cortical vision impairment and those children who have reduced visual functioning due to more widespread, global damage. In the literature, this global damage is often referred to as cerebral blindness. It is widely believed that CVI is now the single leading cause of vision impairment in children in developed countries. However, it is far too easy to label all children who have chronic developmental disability as being cortical vision impaired or blind.
Vision is a complex process involving intact anterior visual pathways (eyes, optic nerves, and chiasm) and preserved geniculo-straite pathways (the pathways the optic nerves take through the brain to the back of the brain, the occipital lobe), including the lateral geniculate body (located approximately mid brain), optic radiations (approximately mid brain) and the primary visual cortex (areas 17, 18 & 21).
Cortical Visual Impairment is reduced vision that is associated with normal or minimal ocular abnormalities, lesions involving the visual cortex, widespread neurological disease and frequently visual field and visual perceptual abnormalities. Any disease that affects the areas corresponding to the geniculated and extrageniculated pathways can cause CVI.
The disease or accidents that cause CVI can also damage other areas of the brain or the visual pathways. Consequently, children with CVI often have additional disabilities.
Causes of CVI
- anoxia, hypoxia, ischaemia, asphyxia: lack or insufficiency of oxygen (the visual cortex can only survive for approximately 4 minutes without oxygen)
- cerebral haemorrhage/cortical thrombosis
- dysgenesis: malformation of the brain during prenatal development
- trauma: car accidents, shaken baby syndrome
- near-miss and/or sudden infant death syndrome
- severe central nervous system infections: meningitis, encephalitis
- shunt malfunction in children with hydrocephalus
Recovery of vision depends on many factors, however the vast majority of children show some degree of improvement, though often remaining vision impaired.
A number of clinical tests can be used to determine CVI. These include Electroretinogram (ERG), Electroretinogram (EOG), Visual Evoked Response (VER), Visual Evoked Potential (VEPM), Electroencephalogram (EEG), Computer Tomography (CT Scan), Magnetic Resonance Imaging (MRI), Position Emission Tomography. The Ophthalmological clinical assessment generally includes history, assessment of eye movement and head, fixation to light, optokinetic nystagmus, response to a threatening gesture, blink reaction to a bright light, pupil reaction, ophthalmoscopy.
Evaluation and assessment of visual function is often more relevant than attempts at acuity measurements. Functional assessment has an emphasis in two areas, the first being visual responses and the second being observed response to the environment. This assessment includes mobility, responses to light, colour, threat, checkerboard patterns, zig zag patterns, responses to people and stylised faces, noting when is the child most alert and assessing preferred sensory modality for learning.
Characteristic features of children with CVI
- children do not look “blind”
- expressionless faces
- eye movement smooth, slow but aimless
- visual self-stimulation is rare
- visual inattention
- tendency to look away from people and events
- diminished visual communication
- normally reacting pupils
- normal blink reflexes e.g. blind to a threat
- no optical/sensory nystagmus present
- additional neurological impairment always present
Visual characteristics of children with CVI
- visual abilities fluctuate
- peripheral vision appears to be more functional
- attends to moving objects: children tend to “see” better when, for example, travelling in a car
- “sees” better in familiar environments
- lacks visual curiosity/attention
- spontaneously use reduced vision for short periods of time only
- tires easily during visual learning
- may move head from side to side when looking
- may turn head when reaching
- visual fields restrictions may be apparent
- some children respond selectively to visual stimuli
- colour can be important
- some children engage in light gazing while some are light sensitive (1 in 4 are photophobic)
Perceptual characteristics of children with CVI
- appears unable to recognise stationary objects
- may not recognise faces
- needs wide spaces between objects and visual stimuli
- focuses on only one toy among several
- reach is often inaccurate
- identifies colour more easily than objects or shapes
- familiarity of environment or object can aid recognition
- little generalisation
- difficulty seeing objects or pictures placed close together – “crowding effect”
- uses hand searching movements when locating objects
- supplements vision with touch
- appears to hear better, when eyes are closed
- many children with CVI are not capable of filtering out sensory information
- rarely bump into objects during travel – often have good mobility
- balance also appears better when eyes are closed
Given these characteristic features of this population of children and young people, their educational program generally requires specific intervention. Since the 1970’s leading vision educators including Natalie Barraga have identified “that a child’s visual skill can never be greater than his/her cognitive ability.” Keeping this in mind, children with CVI present particular challenges to educators.
Management of children with CVI requires careful consideration, the literature suggesting the use of a functional curriculum embedded in routines. One of the most significant educational considerations is the construction of a “user friendly” environment when working with these children. Sensory bombardment may cause the child with CVI to shut down to block out an overload of input. Creating a quiet, stimuli-restricted environment – sensory filtering – will support the students’ learning. Control needs to be placed on the type, intensity and duration of sensory input.
Considerations for teaching and learning
- well-lit area for working
- indirect light source
- work in familiar area or setting
- provide optimum positioning of the child – head upright and in the midline
- position of stimuli is critical
- distance: up to 3 months, the child sees no further than approximately 75cm from himself, bigger objects 150cm
- field: offer stimuli in every part of normal field, determine best area, then expand field of visual attention
- background: simple stimuli against neutral but contrasting background
- short periods of structured activities – frequent rest breaks may be required
- repetition is helpful
- use real, familiar objects
- present objects in dominant field
- allow time for the child to respond
- colour is significant – there may be a preference for yellow, red and orange stimuli
- requires verbal and tactile cueing
- visual responses may need confirmation from tactile sense
- maximise the use of moving objects as this may enhance visual performance
- minimise crowding
- adopting a shortened focal length – hold stimuli close to child, for example, use tilt board to place work close and cut out background information
- widely separate objects/pictures
- point to objects/pictures cue with verbal and auditory prompts
CVI is complex and poorly understood. Ambiguity within the literature makes it very difficult for educators to have confidence in the strategies they employ when working with these children. Research, however, suggests that it is essential to present visual information before introducing additional sensory information. Further, it is suggested that an object be presented first for tactual exploration and before identifying the visual characteristics. There appears to be little evidence that vision training is effective with children with CVI, but the use of routine coupled with a functional curriculum that maximises environmental considerations appears to be the most effective way to teach these children and young people.
Barraga, N. (Ed). (1980). Program to develop efficiency in visual functioning. American Printing House for the Blind, Louisville.
See also: about vision and vision impairment