Joanne Mitchell, BAppSc (Cumb) DOBA
Heather Crossman, BAppSci (Latrobe) DOBA
Much research has gone into establishing the critical or sensitive period for the development of binocular vision in humans. An understanding of this and the plasticity of the visual system has had implications for the treatment of amblyopia in children. Occlusion therapy is thought to be effective until approximately eight years of age and most effective below the age of four years.
This paper presents a case study of an eleven year old boy who is diagnosed with cortical visual impairment, cerebral palsy and epilepsy. At six months of age no visual responses were evident on both observation and VER testing. At eleven months, responses to light were noted and vision continued to slowly develop. Part time occlusion to decrease right amblyopia began at the age of four years and eight months. Greatest improvement was noted between the ages of nine and ten years when vision improved to approximately 6/45, equalling the vision in the left eye.
Literature in the 80’s, describing experiments on cats, found a lengthening of the “critical period” following an early period of no visual attention. The hypothesis is made that in cases of delayed visual development in children there is the possibility of a lengthening of the sensitive period and thus response time to occlusion therapy.