Can Slip of the Retinal Image Cause Amblyopia?

Abstract

One of the main purposes of the oculomotor system is to keep the image projected on the retina stationary in spite of the continuous movement of the head. If the vestibulo-ocular and optokinetic reflexes are defective, the retinal image becomes blurred owing to the uncoordinated movements of the head and the eyes. It is well known that in children retinal blur caused by media opacities or large refraction errors results in amblyopia. In a similar way amblyopia could be caused by slip of the retinal image due to a defective oculomotor system. Our patient was a small for gestational age A-twin. He developed dystonic diplegia with poor head control. At the age of 7 months he was considered to have cortical visual impairment. In a magnetic resonance image of the brain there were diffuse periventricular changes in the white matter and hypoplasia of the corpus callosum and the cerebellar vermis. Binocular optokinetic reflexes to full-field stimuli were horizontally asymmetric and were missing vertically. The reflexes to rotation of the child were asymmetric in the same way. In order to stabilise the retinal image the head of the child was supported always when he was supposed to look at a target with fine details. Increase in visual acuity measured with a Teller acuity card procedure was apparent after head support. This suggests that retinal slip can cause amblyopia. It is usual practice not to support the head of a child who has cerebral palsy and poor head control. In the case of defective head - eye coordination this practice could be harmful to the normal development of vision.