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P.T. Quaid, J.G. Flanagan; The Effect of Dioptric Blur on Flicker Defined Form Phase Contrast Thresholds . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5660.
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Purpose: To determine the effect of dioptric blur on Flicker Defined Form (FDF) phase contrast thresholds, and the effect of blur with increasing eccentricity. Methods: The effect of dioptric blur ranging from 0 to +20 dioptres sphere (DS) in 2 dioptre steps was examined in 10 subjects at 0, 3, 9, 15 and 21o eccentricity using a circular target of 5o diameter. Repeated measures ANOVA was used to determine the resistance to blur (p<0.05; Tukey’s post–hoc). The phase contrast threshold associated with each level of blur was assessed on two separate visits to determine the co–efficient of repeatability at each eccentricity. Results: The average increase in phase contrast threshold per dioptre of blur was 0.079, 0.045, 0.032, 0.027 and 0.021 log units for 0, 3, 9, 15 and 21o eccentricity respectively (relative to a dioptric range of 0 to +10DS). The FDF illusion was found to be resistant to +4DS of blur at eccentricities of 0o and 3o whilst at eccentricities of 9o, 15o and 21o it was resistant to +6DS, +10DS and +10DS of blur respectively. No significant difference in phase contrast thresholds were found between visits for any level of dioptric blur. The co–efficient of repeatability (CoR) with zero blur at 0o eccentricity was 0.166 log units and at 21o eccentricity was 0.137 log units. The CoR decreased slightly for +4DS of blur with values at 0o eccentricity of 0.095 log units and at 21o eccentricity of 0.131 log units. Conclusions:Flicker Defined Form phase contrast thresholds were found to be relatively resistant to dioptric blur at all eccentricities. This resistance to dioptric blur increased with increasing eccentricity.
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