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MW Dul, WH Swanson; Estimating Effects of Prereceptoral Factors on Frequency Doubling Technology Perimetry . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2133.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To estimate the effects of pupillary miosis and lenticular density on the Frequency Doubling Technology (FDT) perimeter and to determine if the magnitude of these effects can be predicted. FDT perimetry measures contrast sensitivity for high-frequency flicker. Since decreased retinal illuminance can have a greater effect on sensitivity at higher versus lower temporal frequencies, these prereceptoral factors could influence the results of FDT perimetry. Methods: Subjects were experienced visual field testers who were free of ocular disease. A Zeiss-Humphrey/Welch Allyn FDT Visual Field Instrument was used with a Threshold N-30 test strategy. We manipulated retinal illuminance with two separate experiments. Study 1: We tested 11 eyes of 11 subjects ranging in age from 24-46 (mean ± 1 SD = 33.0 ±8.3 yrs). Testing was performed first with natural pupil, then pupils were dilated (0.5% Tropicamide). Following stable dilation, subjects were retested with neutral density filters of 0.0, 0.6, 1.2, and 1.6 log units, counter-balanced to minimize the effect of practice and fatigue. Data were fit with contrast-versus-retinal-illuminance (CVR) functions. Study 2: Seventeen eyes of 17 subjects (43 ±11 yrs) were tested first with natural pupil then, following stable miosis, the FDT N-30 was repeated and pupillary area was measured with an ISCAN system. Results: Study 1: Mean defect (MD) varied by 10 to 14 dB across a 1.6 log unit range of retinal illuminances. CVR analysis yielded mean ± SD = 2.3 ± 0.1 log Troland for the semi-saturation constant (value at which MD falls to 6 dB below maximum). The mean semisaturation value allows estimation of effects of pupil size: e.g, a reduction in pupil size from 3 mm to 2 mm would cause a drop in MD by -2.2 dB. Study 2: Miotic pupil diameter was 2.4 ± 1.0 mm, and the decrease in MD (Δ;MD) under miosis was 2.8 ± 2.5 dB. The eight subjects with the greatest miosis had mean pupil diameter of 1.5 ± 0.2 mm, and mean Δ;MD of -4.6 ± 2.2 dB. Measured Δ;MD was highly correlated with Δ;MD predicted from the semi-saturation constant from Study 1 (r2=0.71, p <0.0001). Conclusion: These studies indicate that FDT perimetry results are affected by mean retinal illuminance, and that pupillary miosis and increased lenticular density may reduce FDT perimetry sensitivity in healthy eyes. Clinically, effects of prereceptoral factors should be considered when analyzing abnormal FDT perimetry results.
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