Cartographic deformations in a parabolic visual field map.
Visual fields are traditionally represented in the polar azimuthal equidistant projection. In this map, field areas are increasingly exaggerated with increasing visual angle. To facilitate description of central field defects, enlargement of the central visual field by a parabolic, non-linear projection has been proposed. The cartographic deformations associated with this projection were studied by using mathematical isopter models. A change from equidistant to parabolic projection not only altered relative isopter sizes but also their shapes. Also, the normal nasal-temporal asymmetry was obscured. Thus, the parabolic projection may conceal some types of visual field defects, e.g. loss of the temporal cresent. Neither projection represented surface areas correctly. It is argued that the area-true Lambert's projection would be ideal for visual field representation.
Lindblom
B
B
Department of Ophthalmology, University of Göteborg, Sweden.
D006801:Humans; D008722:Methods; D058609:Visual Field Tests; D014794:Visual Fields