Abstract

Several transformations play a role if one wants to relate the metric of visual field defects to that of the underlying retinal abnormality: (1) Most perimeters currently used present stimuli inside a half-spherical bowl with the tested eye in the center and map the visual field in planar polar coordinates, leading to a planimetric distortion. (2) Ray tracing instead of paraxial geometric optics needs to be used to relate extraocular and intraocular light paths. (3) Although the retina is reasonably well represented by a sphere, the center of this sphere does not coincide with that of the perimeter bowl. If perimetry charts are used to estimate areas of diseased retina, or the position of a lesion, these transformations should be taken into account. This has been recognized: Drasdo and Fowler¹ mapped the optical and geometric properties of the schematic eye, and Kirkham and Meyer² described the transformation from perimeter to planar chart. Overall relationships of eccentricities and areas in field chart and retina are shown. Tables can be derived that limit the inaccuracy of most measurements in real eyes to less than a few percent.

© 1987 Optical Society of America