Advancing a Model to Account for Abnormal Spatial Relationship Perception in Bulbar Cyclotorsion

In a previous study dated back to 2001, a small sample of cyclotropic patients were found to be affected by abnormal spatial relationship perception (aspect ratio judgment) with increased discrimination threshold of elliptical targets oriented along the horizontal axis. The angular amount of incyclodeviation correlated significantly with the discrimination threshold along the horizontal axis. Our group made a similar finding some years later in subjects suffering from Menière’s syndrome. In both cases, we advanced bulbar torsion to be responsible for the reduced sensibility to spatial relationship along the x-coordinate. Still, a possible explanation and a tentative model accounting for the results at that time had not been provided. This paper aims at making up for the gap, advancing a paradigm that explains the increased discrimination threshold in cyclotropic eyes as a function of the angular discrepancy between the horizontal coordinate on the retinal plane, corresponding to the maculopapillary axis (the “retinal horizon”), and the horizontal coordinate in the visual space (the “spatial horizon”). This angular discrepancy is posited to produce abnormal encoding of the spatial relationship of the target, leading to an unbalanced activation of the two antagonistic cellular pools responsible for the analysis of the aspect ratio at the cortical level. Such a model of the "dual horizon" seems to be able to account for the experimental finding described in the previous paper, providing a theoretical explanation for the defective sense of space in patients suffering from cyclotropia.

[1]  C. Aleci,et al.  Evaluation of Spatial Anisotropy by Curvature Analysis of Elliptical Targets , 2010, The open ophthalmology journal.

[2]  Z. Pizlo.  Perception viewed as an inverse problem , 2001, Vision Research.

[3]  H E Bedell,et al.  Identifying Amblyopia Using Associated Conditions, Acuity, and Nonacuity Features , 1985, American journal of optometry and physiological optics.

[4]  F. Campbell,et al.  On the nature of the neural abnormality in human amblyopia; neural aberrations and neural sensitivity loss , 1978, Pflügers Archiv.

[5]  T. Brandt,et al.  Cyclorotation of the eyes and the subjective visual vertical. , 1992, Bailliere's clinical neurology.

[6]  Marousa Pavlou,et al.  Effect of semicircular canal stimulation on the perception of the visual vertical. , 2003, Journal of neurophysiology.

[7]  M. Pugh.  VISUAL DISTORTION IN AMBLYOPIA* , 1958, The British journal of ophthalmology.

[8]  Ian S. Curthoys,et al.  On the relation between ocular torsion and visual perception of line orientation , 2008, Vision Research.

[9]  I. Curthoys,et al.  The Effect of Ocular Torsional Position on Perception of the Roll-tilt of Visual Stimuli , 1997, Vision Research.

[10]  Ruxandra Sireteanu,et al.  Two-dimensional spatial distortions in human strabismic amblyopia , 1991, Vision Research.

[11]  D. Regan,et al.  Shape discrimination and the judgement of perfect symmetry: Dissociation of shape from size , 1992, Vision Research.

[12]  H E Bedell,et al.  Normal and abnormal space perception. , 1983, American journal of optometry and physiological optics.

[13]  M. C. Flom,et al.  Monocular spatial distortion in strabismic amblyopia. , 1981, Investigative ophthalmology & visual science.

[14]  R. Sireteanu,et al.  Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes. , 1989, Investigative ophthalmology & visual science.

[15]  R. Sireteanu,et al.  Distortions in two-dimensional visual space perception in strabismic observers , 1993, Vision Research.

[16]  M. Bertolini,et al.  Developmental dyslexia and spatial relationship perception , 2012, Cortex.

[17]  T. Brandt,et al.  Ocular torsion and tilt of subjective visual vertical are sensitive brainstem signs , 1993, Annals of neurology.