A Comparison of the Effects of Neutral Density Filters and Diffusing Filters on Motion Detection Perimetry, White-on-white Perimetry and Frequency Doubling Perimetry

Background: Motion detection perimetry and frequency doubling perimetry are methods that have been developed with the goal of detecting glaucomatous field defects earlier than conventional white-on-white perimetry. It is well recognized that the development of cataract and pupillary constriction can significantly influence perimetric thresholds when screening for, or following the progression of, glaucomatous field loss. Purpose: To simulate the effects of changes in pupil size and cataract with neutral density and diffusing filters and to compare these effects on motion detection, frequency doubling and conventional white-onwhite perimetry. Methods: The right eyes of seven normal subjects aged 22-34 years underwent: 1. standard white-onwhite automated perimetry on the Humphrey Field Analyzer (HFA) model 630 using the 30/2 Program and size III stimulus; 2. frequency doubling perimetry using the N30 Program on the Humphrey frequency doubling technology (FDT) visual field instrument; 3. motion detection perimetry (MDT) using a vertical line stimulus undergoing lateral displacements. For each procedure, no filter, a series of neutral density filters (0.6, 1.2 and 1.8 log units) or a diffusing filter, was mounted in random order in front of the eye to be tested. Results: The mean whole field sensitivities were calculated from the HFA results and the FDT results and compared with the thresholds of the MDT. The values from the tests done with the different filters were converted into standardized or Z scores using the means and standard deviations calculated from the corresponding results without any filter. Deviations greater than two standard deviations from the mean were seen for 67% of the FDT results with the filters and 61% of the HFA results with the filters. Thresholds for the motion detection were outside this range for only 7% of the results with the filters. Conclusion: These findings show that luminance reduction and light scattering have marked effects on frequency doubling and conventional white-on-white perimetry, but little effect on motion detection perimetry. Address for correspondence: F.W. Fitzke, Department of Visual Science, Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK 68.p65 12/1/99, 11:00 AM 75 76 L. Membrey et al.