Bidimensional Spatial Distortion in Quadrantanopia Depends on the Cortical Damage and not on the Deprived Region in the Visual Field

Abstract

Aims: To assess whether the spatial distortion underlying the so-called “thin man phenomenon” experienced by cortically impaired patients with homonymous defects depends on the cortical damage or on the scotoma itself. Study Design: Analysis of a representative case. Place and Duration of the Study: Service of Neuro-Ophthalmology, University of Turin, Italy, from January 2017 to July 2017. Methodology: Spatial relationship perception, that is the function able to discriminate the extent of a shape along the cardinal coordinates, has been estimated in the visual field of a patient with left inferior quadrantanopia due to cerebral stroke at different eccentricities. The threshold as a function of the distance from the border of the scotoma was compared with two normal subjects after the same defect has been simulated. Results: Spatial relationship perception was not affected by the simulated scotoma in the normal subjects, as shown by the lack of correlation between this variable and the distance from the upper border vs the nasal border of the deprived region. On the contrary, in the patient spatial relationship perception was anisotropic close to the boundary of the scotoma, and the effect decreased as a function of the distance from the blind region (R2=0.77, P: .04). Conclusion: This finding suggests that the cortical impairment and not the scotoma itself is responsible for the spatial distortion in the presence of homonymous visual field defects.