Cortical Visual Impairment | Symptoms & Causes
What are the symptoms of cortical visual impairment?
The most common CVI symptoms presenting to the ophthalmic clinician are:
- Abnormal light response — light gazing or photophobia
- Blunted or avoidant social gaze
- Brief fixations, intermittent following
- Poor visual acuity
- Visual field loss — generalized constriction, inferior altitudinal, hemianopic defect
Behaviors reported by parents, teachers, and low vision specialists include:
- Variable or inconsistent visual responses to the same stimuli
- Better responses to familiar than to novel stimuli
- Fatiguing from visual tasks
- Peripheral vision dominates when reaching
- Colored stimuli elicit better responses than B&W stimuli
- Visual attention for moving stimuli is better than for static stimuli
- Vision for navigation is unexpectedly good
- Difficulty seeing an object or image in a "crowded" array or a busy background
- Reduced responses to visual stimuli when music, voices, and other sounds are present, and often, when the child is touched
All or most of these behaviors are not observed in individual children with CVI. Conversely, a child showing only one or two of the behaviors above does not indicate CVI.
Parents are most disturbed by the child's lack of social gaze and direct eye contact. Active avoidance of or withdrawal from unfamiliar visual stimulation, including people's faces, is frequently reported. Tactile stimulation may be avoided by the child, while in others, touch may be utilized in preference to vision. Commonly, the child positively responds to voices and music. Therapists and teachers are rightly concerned about the child's reaching without looking at the object or the hand.
Visual development
Partial recovery of vision in many children with CVI and severe visual impairment occurs. Improvements are seen in visual acuity, orienting to peripheral stimuli, attention to and reaching for objects and for social gaze. Effective management of intractable seizures often results in improved visual behaviors (personal experience).
What causes CVI?
It is now widely accepted that "cortical blindness" is not an appropriate diagnostic term for children with early, acquired visual impairment due to non-ocular causes. The term "cortical" is misleading because the visual impairment is due to abnormality of bilateral, post-chiahydrocephalus shunt failure, se smal visual pathways, including damage to cortical (gray matter), subcortical (white matter), or both. Non-anatomical lesions, for example, seizures, metabolic derangements, also can cause CVI.
Thus, "cerebral visual impairment" is preferred to "cortical blindness."
Common causes CVI in infants and young children include:
- Hypoxic ischemic encephalopathy (HIE) (in the term born infant)
- Periventricular leukomalacia (PVL) (in the preterm infant)
- Traumatic brain injury due to shaken baby syndrome and accidental head injuries
- Neonatal hypoglycemia, infections (e.g. viral meningitis)
- Severe epilepsy
- Metabolic disorders
Other causes include:
- Antenatal drug use by the mother
- Cardiac arrest
- Twin pregnancy
- Central nervous system developmental defects
Accompanying features of CVI include cerebral palsy and developmental delays.
Confusing diagnostic entities include:
- Delayed visual maturation
- Autism spectrum disorders
- Severe bilateral central scotomata (with eccentric fixation)
- Dyskinetic eye movement disorders
- Profound mental retardation
How is CVI diagnosed?
An eye examination may show anomaly of the optic nerves (paleness, large cups) that, however, is not severe enough to result in the visual impairment exhibited by the child. Strabismus is common; nystagmus is less common. Pupillary reactions are usually normal. High refractive error corrected by glasses may improve some visual behaviors and should be tried if present.
In addition to the complete eye examination, objective measures of visual abilities should be done where feasible. Visual acuity is measurable in most children with CVI using large, black and white gratings (stripes) presented using preferential looking tests, or using cortical visually evoked potentials. Acuity may be very poor in infancy and remain so. In others there is gradual improvement in acuity. In most children with CVI, acuity does not reach normal levels. And, when measurable, recognition acuity for pictures, symbols or letters may be much poorer than the acuities previously measured for gratings. Glasses should be given if warranted, as visual abilities may improve, surprisingly so.
Visual field abnormalities are much more common in children with CVI than realized probably because of the difficulties in assessing peripheral vision in children with poor fixation, poor orienting, and visually avoidant behaviors. Certainly, in individuals with diffuse, extensive lesions of the posterior visual pathways, visual field defects would be expected. Inferior field defects, often dense and complete, are seen in patients whose CVI is attributable to HIE or to PVL.
Visually guided responses, especially reaching and environmental scanning, should be interpreted in the context of the child's visual field status. Referral to a pediatric low vision specialist for further evaluation may be helpful.
How is CVI treated?
In all children with cerebral visual impairment, services of trained and experienced teachers are very important for the child's development and education: See the Linda Burkhart's Technology Integration website.
Referral of the child with CVI to state services for visually impaired children should be done promptly after diagnosis. Specific recommendations based upon the clinical measurement of visual abilities, such as visual acuity and visual fields, should be provided to parents, therapists and teachers. Teachers of visually impaired children should assess broader, "functional" visual behaviors and, often in conjunction with other therapists, devise interventions appropriate for the specific needs of the child. Appropriate additional support services for the school aged child, including for non-verbal learning disabilities, will be needed.
In children with visual field defects, visually guided mobility and spatial orientation can be expected to be impaired. Evaluation and instruction by a certified orientation and mobility instructor should be provided when the child is independently mobile.
Conceptual framework for understanding the visual difficulties in CVI
Understanding the basis of complex visual difficulties of children with CVI may be aided by description of the specific problems associated with lesions in specific areas of visual association areas of the brain in adults:
- Visual motor disturbances, as in moving the eyes to direct visual attention to an object, fixating on an object of interest, shifting fixation and gaze to a new visual stimulus, and accomplishing fine motor tasks such as copying a drawing, are associated with posterior parietal (-occipital) lobe lesions. These are considered due to damage to the "dorsal" visual association pathway.
- Visual spatial disturbances, as in localization of objects, judgment of direction and distance of objects, and orienting the body in relation to the physical world (the "Where is it?" aspect of vision), are associated with posterior parietal (-occipital) lobe lesions (also "dorsal" pathway).
- Visual perceptual disturbances, as in discrimination, recognition, and integration of visual images and objects (the "What is it?" aspect of vision), are associated with inferior posterior temporal lobe lesions (due to a different visual pathway, the "ventral").
Brain damage in children with CVI is more diffuse than in adults with the specific difficulties indicated below. Thus, children with CVI may show more than one of the specific domains of visual impairment (for example, both dorsal pathway difficulties — visual motor and visual spatial). During early development, visual motor disturbances are more evident than at later ages. Aspects of abnormal reaching and visual avoidance may be affected by abnormal sensory integration and motor output difficulties. In some children with minimal visual acuity loss, specific difficulties in visual perception or in spatial orientation become more evident as they mature. Specific visual cognitive dysfunctions are common in children with traumatic brain injury (personal experiences).
Cortical Visual Impairment | Helpful Resources
- Flanagan NM, Jackson AJ, Hill AE. Visual impairment in childhood: insights from a community-based survey. Child Care Health Dev 2003;29(6):493-9.
- Good WV, Jan JE, DeSa L, Barkovich AJ, Groenveld M, Hoyt CS. Cortical visual impairment in children. Surv Ophthalmol 1994;38(4):351-64.
- Steinkuller PG, Du L, Gilbert C, Foster A, Collins ML, Coats DK. Childhood blindness. J Aapos 1999;3(1):26-32.
- Hoyt CS. Visual function in the brain-damaged child. Eye 2003;17(3):369-84.
- Good WV, Jan JE, Burden SK , Skoczenski A, Candy R. Recent advances in cortical visual impairment. Dev Med Child Neurol 2001;43(1):56-60.
- Fielder AR, Mayer DL. Delayed visual maturation. Sem Ophthalmol 1991;6(4):182-93.
- Jan JE, Lyons CJ, Heaven RK, Matsuba C. Visual impairment due to a dyskinetic eye movement disorder in children with dyskinetic cerebral palsy. Dev Med Child Neurol 2001;43(2):108-12.
- Huo R, Burden SK, Hoyt CS, Good WV. Chronic cortical visual impairment in children: aetiology, prognosis, and associated neurological deficits. Br J Ophthalmol 1999;83(6):670-5.
- Afshari MA, Afshari NA, Fulton AB. Cortical visual impairment in infants and children. Int Ophthalmol Clin 2001;41(1):159-69.
- Hoyt CS. Neurovisual adaptations to subnormal vision in children. Aust N Z J Ophthalmol 1987;15(1):57-63.
- Baker-Nobles L, Rutherford A. Understanding cortical visual impairment in children. Am J Occup Ther 1995;49(9):899-903.
- Jan JE, Wong PK , Groenveld M, Flodmark O, Hoyt CS. Travel vision: "collicular visual system"? Pediatr Neurol 1986;2(6):359-62.
- Porro G, Dekker EM, Van Nieuwenhuizen O, et al. Visual behaviors of neurologically impaired children with cerebral visual impairment: an ethological study. Br J Ophthalmol 1998;82(11):1231-5.
- Morse M. Visual gaze behaviors: considerations in working with visually impaired multiply handicapped children. RE;view 1991;23(1):5-15.
- Birch EE, Bane MC. Forced-choice preferential looking acuity of children with cortical visual impairment. Dev Med Child Neurol 1991;33(8):722-9.
- Hertz BG, Rosenberg J, Sjo O, Warburg M. Acuity card testing of patients with cerebral visual impairment. Dev Med Child Neurol 1988;30(5):632-7.
- Weiss AH, Kelly JP, Phillips JO. The infant who is visually unresponsive on a cortical basis. Ophthalmology 2001;108(11):2076-87.
- Frank Y, Kurtzberg D, Kreuzer JA, Vaughan HG, Jr. Flash and pattern-reversal visual evoked potential abnormalities in infants and children with cerebral blindness. Dev Med Child Neurol 1992;34(4):305-15.
- Good WV. Development of a quantitative method to measure vision in children with chronic cortical visual impairment. Trans Am Ophthalmol Soc 2001;99:253-69.
- Jacobson L, Hellstrom A, Flodmark O. Large cups in normal-sized optic discs: a variant of optic nerve hypoplasia in children with periventricular leukomalacia. Arch Ophthalmol 1997;115(10):1263-9.
- Dutton GN. Cognitive vision, its disorders and differential diagnosis in adults and children: knowing where and what things are. Eye 2003;17(3):289-304.
- Hyvarinen L. Visual rehabilitation of the infant and child. In: Hartnett WE, ed. Pediatric Retina. Philadelphia : Lippincott, Williams & Wilkins; 2005:493-514. 23. Morse MT. Cortical visual impairment in young children with multiple disabilities. J Visual Impair Blind 1990;84:200-3.
- Girkin CA, Miller NR. Central disorders of vision in humans. Surv Ophthalmol 2001;45(5):379-405.
- Trobe JR, Bauer RM. Seeing but not recognizing. Surv Ophthalmol 1986;30(5):328-36.
