A clinical study of perimetric probability maps
A. Heijl and P. Asman
Department of Ophthalmology, University of Lund, Malmo General Hospital, Sweden.
Perimetric probability maps depict visual field results in terms of the
frequency with which the measured findings are seen in a normal population.
We tested clinically the importance of the model of the normal visual field
used to calculate such maps. Forty-one eyes of 41 normal subjects and 58
eyes of 46 glaucomatous patients were studied. Probability maps were
calculated by means of two different models of the normal visual field. The
first model assumed gaussian threshold distributions with constant
variability across the field. The second used empirically determined
nongaussian location-dependent threshold distributions. Probability maps
using the empiric model allowed better separation between glaucomatous and
normal eyes, and the number of significant points in normal subjects was in
better agreement with the theoretically expected number. The gaussian model
yielded an unacceptably high frequency of significant points in normal
fields, particularly in the midperiphery. The clinical usefulness of
perimetric probability maps depends critically on the choice of normal
visual field model.
