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What is Cortical Vision Impairment?

Presently, Cortical Visual Impairment (CVI) is the most common cause of permanent visual impairment in children aged 1-3 years. The diagnosis of CVI is indicated for children showing abnormal visual responses that cannot be attributed to the eyes themselves. Brain dysfunction must explain the abnormal visual responses, as abnormal ocular structures, abnormal eye movements, and refractive error do not. Fixation and following, even to intense stimulation, may be poor and the child does not respond normally to people’s faces. Visual regard and reaching (in the child with motor capabilities) toward objects is absent. 

Causes of Cortical Vision Impairment

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. 

Common causes of 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 hypoglycaemia, infections (e.g., viral meningitis) 
  • 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

How Cortical Vision Impairment Affects Children

Behaviours 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 
  • Coloured stimuli elicit better responses than black and white 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

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 utilised in preference to vision. Commonly, the child positively responds to voices and music 

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 behaviours (personal experience). 

Getting Help With Cortical Vision Impairment

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 which may help to improve your child’s vision. 

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 behaviours. 

In all children with cerebral visual impairment, services of trained and experienced teachers are very important for the child’s development, rehabilitation and education. 

Your child’s GP is normally responsible for their general medical care. The GP may refer your child to a Paediatrician or Paediatric Neurologist (a children’s doctor who specialises in the brain and nervous system). An epilepsy specialist nurse may also be involved in their care. 

For more information: https://www.cvicommunityaus.net/lander  

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