Flicker perimetry resists retinal image degradation.

The influence of refractive defocus and artificial media opacities on perimetric thresholds in automated light-sense and flicker perimetry was investigated in 20 eyes of 20 normal subjects. Thresholds were determined at 13 locations in the central visual field up to 25 degrees. Refractive defocus was induced by blurring with glasses of +1, +2, +3, +6 and +9 diopters spherical. Three diffusers were used as artificial media opacities, causing a mean reduction of visual acuity to 0.46, 0.08, and 0.02. Blurring of the retinal image by a small defocus or by slight artificial media opacities causes a measurable reduction of light-difference sensitivity. Mean sensitivity (MS) and defocus are related logarithmically (log(MS)/defocus, r = -0.9297; P < 0.0001). The correlation between MS and the luminance factor l15, characterizing the artificial media opacities, is linear (MS/l15, r = -0.9736; P < 0.0001). Flicker fusion frequency resists retinal image degradation much better. Mean flicker frequency (MF) and defocus are related logarithmically (log(MF)/defocus, r = -0.4960; P < 0.0001). The correlation between mean flicker frequency (MF) and the luminance factor l15 is nonlinear (MF/[l15]2, r = 0.8693; P < 0.0001). The results of the present study show that perimetric methods that use temporal threshold criteria, such as flicker fusion frequency, should be more suitable than methods that use static criteria for detecting neuronal damage in the presence of factors that disturb retinal image quality.