Comparisons of retinal sensitivity obtained by microperimetry with two different fixation targets in normal individuals
Abstract
Purpose
To determine the retinal sensitivities obtained by microperimetry with an one degree single cross (Cr) or an one degree circular (Ci) fixation target in normal individuals.
Methods
The retinal sensitivity within the central 2 degrees was measured in 32 eyes of 16 healthy volunteers (mean age 28.9 ± 1.4, range 24–44) with Microperimeter 3 (MP-3, Nidek, Italy) using two fixation targets. The retinal sensitivity of the central 0 degree and mean central 2 degrees consisting of 8 points were measured with the two fixation targets. The Goldmann III stimuli were presented for 200 msec on a white background with a luminance of 31.5 asb.
Results
The mean central retinal sensitivity (0 degrees) was 24.4 ± 0.8 dB with the Cr and 29.8 ± 0.6dB with the Ci targets. The central retinal sensitivity with the Ci target was significantly higher than that with the Cr. (P = 1.2 × E-5). The mean retinal sensitivity of the central 2 degrees was 32.0 ± 0.3 dB with the Cr target and 31.4 ± 0.3 dB with the Ci target. The mean central 2 degrees retinal sensitivity with the Cr was significantly higher than that with the Cr target (P = 0.006).
Conclusions
The differences in the retinal sensitivity is probably because the fixation targets overlap the stimuli. These results indicate that the size and shape of the fixation target must be considered when evaluating the central retinal sensitivity.
