Fixation examination with the MP-1 microperimeter (Nidek Technologies Srl., Vigonza, PD, Italy) determines the preferred retinal loci and fixation stability in patients with central vision loss. It is typically done for periods of 15 to 30 s as per the manual’s recommendations, which are arbitrary. In this study, we examined (1) whether fixation stability depends on the duration of recording and (2) whether fixation stability changes over time.
Raw eye-position data from 76 patients with bilateral central vision loss (mean age = 80 ± 9.6 yrs) who had fixation examination recordings with the MP-1of at least 15 s were used. Bivariate contour ellipse areas (BCEAs) were calculated and compared for intervals of 0 to 5 s, 0 to 10 s, and 0 to 15 s and for three consecutive 5-s intervals (0–5 s, 5–10 s, and 10–15 s). Ellipse’s centroid location, axes extent, and tilt angle were also evaluated for each of these intervals.
BCEA worsened significantly with increasing the time of fixation recording (P < .001). Compared to the BCEA during the first 5 s of examination recording, median BCEA increased by a factor of 1.4 for the first 10 s and of 1.6 for the first 15 s of recording. However, the bivariate ellipses for the three consecutive 5-s intervals were the same in terms of area, centroid location, and axes extent, but differed significantly in tilt angle (P = .005). Fixation stability (BCEAs) results were also confirmed with an additional analysis performed on shorter sampling intervals.
Fixation stability deteriorates with increasing duration of the fixation recording, but when fixation is evaluated in shorter consecutive 5-s intervals, only a difference in ellipse’s tilt angle is found. These results suggest that the current recommendations for fixation stability recording with the MP-1 can be shortened to a less demanding duration.