Eye movements in congenital nystagmus and oculomotor systems alterations

Congenital Nystagmus (CN) is one of the diseases that can affect binocular vision, reducingthe 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, itspathogenesis is still under investigation. This kind of nystagmus is termed congenital (orinfantile) since it could be present at birth or it can arise in the first months of life. Themajority of patients affected by CN show a considerable decrease of their visual acuity: imagefixation 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 velocityslows down while the target image is placed onto the fovea (called foveation intervals). CNetiology has been related to deficiencies in saccadic, optokinetic, smooth pursuit, and fixationsystems as well as in the neural integrator for conjugate horizontal gaze. Although numerousstudies have described CN pathophysiology and its relation to the visual system, actually, CNetiology still remains unclear. In recent years, a number of control system models has beendeveloped in order to reproduce CN; results don't fully agree on the origin of theseinvoluntary oscillations, but it seems that they are related to an error in 'calibration' of the eyemovement system during fixation.This study aims to present some of the different models of the oculomotor system anddiscuss their ability in describing CN features extracted by eye movement recordings. Use ofthose models can improve the knowledge of CN pathogenesis and then could be a support fortreatments planning or therapy monitoring.