Eye movements in Congenital Nystagmus and oculomotor systems alterations.

Congenital Nystagmus (CN) is one of the diseases that can affect binocular vision, reducing the visual quality of a subject. It is an ocular-motor disorder characterised by involuntary, conjugated ocular oscillations and, although identified more than forty years ago, its pathogenesis is still under investigation. This kind of nystagmus is termed congenital (or infantile) since it could be present at birth or it can arise in the first months of life. The majority of patients affected by CN show a considerable decrease of their visual acuity: image fixation on the retina is disturbed by nystagmus continuous oscillations, mainly horizontal. However, the image of a target can still be stable during short periods in which eye velocity slows down while the target image is placed onto the fovea (called foveation intervals). CN etiology has been related to deficiencies in saccadic, optokinetic, smooth pursuit, and fixation systems as well as in the neural integrator for conjugate horizontal gaze. Although numerous studies have described CN pathophysiology and its relation to the visual system, actually, CN etiology remains yet not clear. In recent years, a number of control system models has been developed in order to reproduce CN; results doesn’t fully agree on the origin of these involuntary oscillations, but it seems that they are related to an error in ‘calibration’ of the eye movement system during fixation. This study aims to present some of the different models of the oculomotor system and discuss their ability in describing CN features extracted by eye movement recordings. Use of those models can improve the knowledge of CN pathogenesis and then could be a support for treatments planning or therapy monitoring.