Different fixation targets affect retinal sensitivity obtained by microperimetry in normal individuals

Purpose To determine the differences in the retinal sensitivities obtained by microperimetry with a single cross or a circular fixation target in normal individuals. Methods Thirty-two eyes of 16 healthy volunteers (mean age 28.9±1.4 years, range 24-44 years) were studied. The retinal sensitivity of the central 0 degrees and of the mean central 2 degrees consisting of 8 points were determined independently using the two different fixation targets with Microperimeter 3. The Goldmann III stimulus with a luminance of 1.0 cd/m2 was presented for 200 ms on a white background. Results The retinal sensitivity of the central 0 degrees was significantly better with the circular target than that with the cross target (P=0.003, right eyes; P=0.001, left eyes). The mean retinal sensitivity in the central 2 degrees was not significantly different between the cross and circular fixation targets. (P=0.07, right eyes; P=0.08, left eyes). Conclusion These results indicate that the circular fixation target is a better target to use to evaluate the central retinal sensitivity. The difference in the retinal sensitivity is most likely due to the cross fixation target overlapping the test stimulus target.