Wednesday 30 November 2011

How do I know if my child has a cortical visual impairment? Part One

CVI is not easy to diagnose and it may not even be diagnosed initially in the hospital. Nevertheless it is now as widespread a problem as visual impairment is amongst babies and children. What is often confusing to people is that if the child’s eyes are normal how is it the child cannot see? Why does the child not smile back for instance?  

How can you tell whether a child is visually impaired, cognitively delayed, or if there is something else that is not so easily diagnosable: cerebral or cortical visually impairment?  Often a brain scan (MRI) may help to pinpoint areas of damage in the cortex.  

The region called the parietal lobes is the attention command centre of the brain. This is the area that controls a person’s ability to pay selective attention. Damaged brain cells in this area can be why children have difficulty with attention and are easily distracted. If there is damage in the flow of information from the occipital lobes to the parietal lobes ( an area called the ‘dorsal stream’ ) it can have a significant effect on the child’s ability to isolate and make sense of sensory information, move about and use their vision to guide movements. 

The visually evoked potential assessment refers to the measurement of a visual signal from the eyes to the brain. Flashing black and white squares appear on a monitor and the child’s response recorded. 

Observation of the child’s visual behaviour is important and a history taking with the parents is another essential aspect of the diagnosis. 

CVI is different from ocular visual impairment. Visual impairment is an eye globe issue. It concerns something malfunctioning within the eye itself or the optic nerve leading from the eye to the brain. CVI is an impairment of vision that is caused by damage to the brain tissues. Much of the brain is concerned with some aspect of seeing. Whereas a visual impairment can be measured fairly accurately, CVI is less easy to quantify precisely. It is also quite difficult to manage compared with a ‘malfunction’ of the eye mechanism. An optical aid can give a short sighted person good vision but there is no gadget or device that fixes CVI. 

A common cause is lack of oxygen to the brain or hypoxia, which can happen during birth or at any point during gestation. The result of poor blood supply to the brain and resultant lack of oxygen is that cells in the brain die. CVI is commonly associated with certain other conditions such as cerebral palsy, microcephalus or epilepsy. Wherever there is brain damage it is possible that some visual difficulties may ensue by the very nature of the functioning of the brain.

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