ABSTRACT
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.
ABSTRACT
Numerous research efforts have been directed toward determining the origin of anisotropies of visual space, in contrast to real space. Recent neurophysiological studies have placed the origin in the primary visual cortex (V1) or beyond. The present study sought to provide new psychophysical evidence of the origin of these anisotropies using auto-stereograms as visual stimuli in a relative depth judgment task. The observers were presented with a hidden three-dimensional shape that consisted of two pairs of parallel line segments that were located in different depth planes and oriented at 0º (horizontal line segments), 45º, and 90º (vertical line segments). The influence of orientation on the visual performance of five observers was evaluated. The encountered differences at 45º compared with cardinal orientations revealed a non-conclusive trend toward a negative impact of oblique orientation on the observers' performance. Significant differences were found in accuracy between the horizontal and vertical orientations, and the best scores corresponded to vertical line segments. This finding may be interpreted as the expression of vertical-horizontal anisotropy in depth. The perception of hidden three-dimensional shapes in auto-stereograms occurs beyond the primary visual cortex in the dorsal stream, and the present findings provide psychophysical evidence of the location of vertical-horizontal anisotropy in non-retinotopic areas beyond V1.