Module 3: Vision

Cortical Visual Impairment

Cortical visual impairment (CVI) results from damage to the brain that impairs visual functioning. CVI is the most common form of visual impairment in children in high-income countries including Canada and may occur alone or in conjunction with ocular-based causes of visual impairment.

CVI is increasingly associated with a variety of other conditions. For example, published estimates indicate that approximately 30% of students with cerebral palsy may also have a profile that includes CVI (Salavati et al., 2017). CVI may have wide-ranging implications for the student’s ability to gather and process sensory information through the visual channel, including impacts on cognitive, motor, and social development. Students with CVI may have a diverse functional vision profile that may include the ability to visually detect:

  • Stationary objects but not moving targets
  • Moving objects but not stationary targets
  • Objects against a plain background but not a cluttered one
  • One or two objects but not many objects at once

Pictured above is a spinner on an illuminated lightbox. This is an example of a tool used to support a student with CVI to engage their functional vision.

It is critical to recognize that any reporting on functional vision gives us only a snapshot of how that student engages their visual system to gather information in a particular environment at a particular point in time. There are a diverse range of factors that will impact how effectively a student can engage their visual system at school. The model below provides a framework for understanding how diverse aspects of the student’s profile as an individual learner can interact with environmental factors to impact the use of functional vision.

The Corn Model of Visual Functioning (Corn, 1983) views a student’s engagement of functional vision as being determined at the intersection of visual abilities, environmental cues/conditions, and other individual factors such as cognition, perception, or physical health and well-being.

Two students with the same eye condition and level of vision may use their vision very differently in school and the community. However, if one student has challenges with attention and has not slept well the previous night, they might not be able to engage their functional vision as effectively as the student without attention issues and who is getting enough sleep.

There are many factors that may impact how effectively a student can engage their functional vision in any environment.

Some of these factors include:

  • Visual abilities (visual acuity, visual fields)
  • Stored and available individuality (cognition, physical health)
  • Environmental cues (colour, contrast)
  • Environment (noise, clutter, familiarity)

The Corn Model of Visual Functioning