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CORTICAL VISUAL IMPAIRMENT

DR. ADITYA GOYAL

Cortical visual impairment (CVI) is a decreased visual response due to a neurological problem affecting the visual part of the brain. Generally, a child who has been diagnosed with CVI has a normal eye exam or has an eye condition that cannot account for abnormal visual behaviour. CVI is one of the most frequent cause of visual impairment in children from developed countries. Brain dysfunction explains the abnormal visual responses. The eyes show no pathological changes which can possibly explain the poor response. 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 CVI:
  • 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)
  • Metabolic disorders
    • Causes of CVI:
  • 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
    • Signs and symptoms of CVI:

    The most common CVI symptoms presenting to the ophthalmic clinician are:

  • Abnormal light response — light gazing or photophobia
  • No response to even strong light
  • Blunted or avoidant social gaze
  • Brief fixations, intermittent following
  • Poor visual acuity
  • Visual field loss — generalized constriction, inferior altitudinal hemianopic defect
    • 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 out
  • 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
  • Statokinetic dissociation (in children)
  • Greater reduction in sensitivity to stationary visual stimuli relative to similar targets in motion. Riddoch phenomenon (adults)
  • Ability to sense movement even though blind… “See” moving objects… but not stationary ones
  • Blindsight (ability to ‘sense’ objects in the way)
  • Movement in the peripheral visual field may elicit a smile in the blind child with quadraplegia and profound intellectual disability
  • Children who are fed with a spoon may intermittently open their mouths to receive food when the spoon is moved in an arc from the peripheral visual fields, but not when it approaches the mouth from straight ahead
    • What do we do in CVI?

    Diagnostic Approaches & Strategies:

  • Case History - All the usual questions AND general / motor / visual / auditory development / daily living skills / skills needed for learning
  • Fixation and following
  • Visual Acuity
  • Refractive Error
  • Ocular Health

    • Vision function assessment:

  • Contrast sensitivity
  • Colour vision
  • Oculomotor ability
  • Field of view

    • Eye health:

  • Biomicroscopy
  • Dilated Fundus Evaluation
  • Special diagnostic tools EOG (electrooculogram) ERG (electroretinogram) VER / VEP (visually evoked response visual evoked potential)
    • DVM – Delayed visual maturation:

    DVM type I

    Visually impaired infants: Improved visual abilities by the age of 6 months, often without treatment.

    DVM type II

    Attention problems, associated with neurological / learning abnormalities. Improvement takes longer

     

    DVM type III

    Children have nystagmus, albinism. Vision improves later, can improve to low-normal levels.

    DVM type IV

    Associated with retinal, optic nerve, macular anomalies

    What type of therapies are incorporated in CVI?

    Protocol to be followed depending upon the visual abilities:

    If there is no perception or very poor perception of light and no fixation, follow the steps below. Decide on the starting stage depending upon the visual ability with which the child comes to you.

    1. Photopic stimulation with light in the form of flashing lights (contraindicated in cases of seizure disorders), LED lights, light emitting toys etc. To continue until some semblance of perception is seen constantly.

    2. Floor rotator with light fixed and rotated at a very low speed. The child needs to follow the light. Look for fixation and initiate the same slowly.

    3. Introduce light emitting toys (no sound). Move them very slowly in front of the child. See that the child is maintaining fixation. Restart once the fixation is lost.

    4. Introduce patterns in black print on white background. Initially the patterns should be very bold. Make the patterns fine as the fixation improves.

    5. Introduce red / green colours. This can be done with red / green filter glasses and the child looking at red / green lighted objects or patterns. Look for the fixation with each eye and continue until constant fixation is achieved.

    6. Introduce rotation of coloured objects seen through red / green anaglyphs. Look for fixation and following movements.

    7. Introduce slow moving videos and look for fixation.

    8. Once the fixation is definite, introduce slow movements followed by slow rotatory movements.

    9. Increase the speed of the movements looking carefully for gaze fixations.

    10. Introduce zig zag movements while fixation is maintained.

    11. Introduce big toys with no light and encourage reaching out to them.

    12. Reduce the size of the toys and look for fixation and reaching out skills.

    13. Introduce movements and look for accuracy of fixation, maintenance of fixation and accuracy of reach.

    14. Make the movements more intricate with the child fixating and reaching accurately.

    15. Introduce rotator and objects on Visuoprime professional / SVI and encourage reach and touch.

    16. Start working on binocularity. Look for tropia.

    17. Introduce binasal patches to initiate peripheral fusion.

    18. Introduce translucent patch in case of tropia.

    19. A good objective refraction is required and prescribe glasses in case of significant errors.

    20. Glasses can be prescribed with binasal patches to encourage peripheral fusion and binocularity.