RESEARCH ARTICLE


Evaluation of Spatial Anisotropy by Curvature Analysis of Elliptical Targets



Carlo Aleci*, Giulio Piana, Franco Anselmino
Department of Ophthalmology, Gradenigo Hospital, C.so R. Margherita 8, 10153 Turin, Italy


© Aleci et al.; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http: //creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Department of Ophthalmology, Gradenigo Hospital, C.so R. Margherita 810153 Turin, Italy, Tel: +39 (0)11 8151401, Mobile: +39 340 000 3523; Fax: +39 (0)118151575; E-mail: carlo.aleci@gradenigo.it


Abstract

Spatial relationship perception (SRP), defined as the function able to detect the difference between the perceived extent of a shape along the x/y cardinal coordinates, has been investigated in 42 eyes of 21 emmetropic subjects by means of a psychophysical test conceived on purpose. Aiming to the highest sensibility and since curvature detection is reckoned as an hyperacuity, elliptical stimuli have been chosen to measure the spatial relationship anisotropy (SRA) in the visual system. Observers turned out to be able to detect curvature differences along the elliptical contour as low as 33.6 sec arc, which in terms of SRP means an aspect ratio (i.e. the ratio between the height and the width of the ellipse) as low as 1.0022-1.0035. By comparing these results with those obtained in previous investigations from other curvature discrimination tasks, it is argued that recognition threshold is conditioned by the amount of space anisotropy of the visual system. Indeed, in about half of the recruited subjects, vertical/horizontal anisotropy is found to a certain extent and such SRA correlates with the recognition threshold (r= 0.69, p<0.01). There is direct evidence of visual spatial distortion and in particular increased anisotropy in neuro-ophtalmological diseases such as hemianopia and around scotomatous regions in the visual field. Thence, apart from theoretical considerations in physiological field, results collected in this study may be regarded as normative data for future clinical investigations.

Keywords: Curvatures perception, ellipses recognition, spatial relationship perception, anisotropy.