Data from 270 eyes with series of at least eight visits were available. The number of eyes included in analyses, however, varied greatly depending on the cutoff used, because eyes were required to have a significant worsening of both MD and CMD when using that cutoff. At cutoff 19 dB, a total of 133 eyes with progressive glaucoma (defined as a significant rate of worsening of MD and CMD) were available.
Table 1 presents the characteristics of the study population when the cutoff was set at 19 dB, restricted to the eligible series. The mean age was 69.1 (±10.97) years. The mean follow-up duration was 11.31 years (±2.15).
Figure 1 shows histograms of signal (rate of change) for MD (left) and CMD (right) respectively. The mean MD rate of change was −0.28 dB/year (
Display Formula\( \pm 0.15\)). Likewise, the mean CMD rate of change was −0.26 dB/year (
Display Formula\( \pm 0.09\)). This indicates that the mean rate of progression appeared to be faster for uncensored data (MD) than censored data (CMD).
Figure 2 shows histograms of noise for MD (left) and CMD (right) data, respectively. The mean noise for MD rate of change was 0.73 dB (
Display Formula\( \pm 1.17\)). Likewise, the mean noise for CMD rate of change was 0.55 dB (
Display Formula\( \pm 0.42\)). The mean noise for CMD was smaller than the mean noise for MD.
To identify the ideal cutoff for reducing variability, and hence improving LSNR, we compared LSNR
CMD with LSNR
MD at various cutoffs.
Table 2 presents the means of LSNR
MD and LSNR
CMD and the ratios of LSNR
CMD to LSNR
MD at various cutoffs, 12 to 19 dB. Censoring appeared to be effective for any cutoff between 15 and 19 dB. For example, at cutoff 19 dB, the LSNR
CMD was −0.68 (
Display Formula\( \pm 0.62),\), which was significantly (
Display Formula\(P\) <0.001) lower (better) than the corresponding LSNR
MD, −0.57 (
Display Formula\( \pm 0.52\)). Furthermore, the ratios LSNR
CMD/LSNR
MD was significantly greater than 1 at the 19 dB (
Display Formula\(P\)<0.001). At all cutoffs below 15 dB, LSNR
CMDs and LSNR
MDs were statistically equivalent (
Display Formula\(P \gt 0.05)\). At the 12 dB cutoff, the ratio LSNR
CMD/LSNR
MD was not significantly greater than 1 (
Display Formula\(P = 0.062\)).