AIM:To evaluate retinal parameters in a sample of healthy young Caucasian adults to define the normal or physiological range of inter-ocular asymmetry in this particular age and ethnic group.METHODS:Study sample consisted of 37 Caucasian children and young adults aged between 12 and 23 years (spherical equivalent from-3.00D to + 4.00D,anisometropia ＜ 0.5D and axial length differences ＜0.3mm).Normal inter-ocular asymmetry values were determined and 95％ inter-ocular difference tolerance values were obtained.RESULTS:Statistically significant inter-ocular differences were found in mean (P=0.003) and superior (P=0.008) retinal nerve fiber layer (RNFL) thickness,as well as in central macular thickness (P=0.039),with larger values in the left eye in all instances,and with tolerance limits of inter-ocular asymmetry of-9.00p m to 6.00μ m,-28.00μ m to 9μ m and-39.00μ m to 29.00μ m,respectively.In addition,statistically significant differences were found between males and females in mean thickness of the RNFL in the right eye (P=0.020).CONCLUSION:The exploration of the normal asymmetries of the retina may be an effective approach to further understand myopia onset and progression,which is particularly relevant in this age group.Differences in instrumentation and sample characteristics compromise direct comparison with published research and warrant the need for further studies.