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Vision- Visual Processing

Vision involves more than the eye's ability to detect images in the environment correctly, your brain must also process what the visual information means, remember it, be able to follow it as it moves or you move, know whether you need to respond to it, and if so, determine the best way to respond.

Stimulation of sensory receptors in the eyes generates an impulse to the optic nerve, which sends the sensory messages to various sites in the brain where the information is perceived, sorted out, and linked up with other senses.

Functioning of the eye muscles

Ocular muscles keep the eyes aligned and help them move smoothly and simultaneously. If the eyes don't work together, conflicting visual input can result in confusing misconceptions about the world. Working together with vestibular and visual sensory information, the eye must also be able to:

  • Follow moving objects such as a ball or children running in the playground
  • Visually fixate on objects as you move to keep the visual field stable
  • Control sequential scanning, such as when reading lines of print in a book
  • Fix from one point to another, such as from one word to the next when reading; or from near to far away, such as when taking notes from the board.
  • Children with these difficulties will have trouble looking into someone else's eyes, climbing stairs, navigating obstacles like furniture and other people, playing sports, reading, and writing.

Under-sensitive

  • Objects appear quite dark, or lose some of their features.
  • Central vision is blurred but peripheral vision quite sharp.
  • A central object is magnified but things on the periphery are blurred.
  • Poor depth perception, problems with throwing and catching, clumsiness.

Ways you might help include the use of visual supports or coloured lenses, although there is only very limited research evidence for such lenses.

Over-sensitive

  • Distorted vision – objects and bright lights can appear to jump around.
  • Images may fragment.
  • Easier and more pleasurable to focus on a detail rather than the whole object.
  • Has difficulty getting to sleep as sensitive to the light.

You could make changes to the environment such reducing fluorescent lighting, providing sunglasses, using blackout curtains, creating a workstation in the classroom – a space or desk with high walls or divides on both sides to block out visual distractions, using blackout curtains.

Visual hypersensitivity

Some people with Autistic Spectrum Disorders and other developmental conditions suffer with a visual- perceptual problem caused by hypersensitivity to colour, lights, glare, patterns, and contrast. At its most severe, vision may be so problematic that a child may literally have a visual whiteout and temporarily lose the ability to see.

  • Light sensitivity
    Bright lights, sunlight, glare, and fluorescent lighting bombards the nervous system and can result in fatigue, anxiety, dizziness headaches, and other physical problems. Problems with light flickering can range from excessive eyestrain to seeing a room pulsate on and off. Fluorescent lighting can be a problem in that reflections bounce off everything in a room and can be blinding.
  • Contrast sensitivity
    For some children when reading, the white background competes with the black letters, making letters lose their distinct edges.
  • Impaired print resolution
    Letters appear to be unstable, and shimmer, move, shift, or break apart.
  • Distortions in the environment
    For some people, objects disappear and lose their meaning, for example in a quick moving environment i.e. a busy hall, perceptually the hall may not exist, seeing instead only shapes and colours moving around. The visual system can become completely overloaded with stimuli and all meaning in visual sensation can be lost. A child may therefore resist climbing stairs, avoid eye contact, and prefer to remain relatively still.

Visual skills are closely linked with motor skills. We use our eyes to guide our hands and feet for any new skills. As a child learns to use the computer keyboard for example, they will look at their fingers. As new movement patterns become familiar, as mental maps for doing things get ingrained, your child relies less and less on vision. They will then be able to look at the computer screen as they type. That’s a result of the proprioceptive and vestibular systems taking over.

Signs of vision problems

Does the child:

  • Complain of headaches or tiredness, rubbing eyes often, or squinting
  • Have difficulty concentrating and paying attention
  • Skip words or lines or frequently lose their place when reading unless they use their finger as a guide
  • Have poor handwriting and drawing skills
  • Have trouble copying from the board
  • Seem disinterested in, or overly distracted by, objects in the environment.

Strategies that might help

  • A child with difficulties processing visual stimuli may benefit from a designated area to complete work in order to focus their attention, if necessary.
  • If a child becomes disturbed/ distracted if there is a lot of movement around them then limiting distractions will enable the child to complete tasks.
  • The child may benefit from engaging in tactile, proprioceptive and vestibular activities incorporating visual challenges such as using targets and completing sequencing tasks.

Useful resources

  • Grandin, T. (2006) Thinking in Pictures. Bloomsbury Publishing
  • The National Autistic Society http://www.autism.org.uk/sensory
  • Raising A Sensory Smart Child by Lindsey Biel and Nancy Peske
  • Building Bridges through Sensory Integration by Ellen Yack, Paula Aquilla and Shirley Sutton.
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