Figure 7.

Relative frequency distributions of normal subjects (number of subjects, normalised within each test size) as a function of threshold (dB) for test sizes within a representative eccentric location (peripheral: yellow; and paracentral: red, in the inset graph). The ranges of threshold values along the x‐axis for (a)–(b) and (c)–(e) have been equated to allow for better visual comparison of the width of the normative distributions. Frequency distributions have been fitted with Gaussian functions (all passed D'Agostino & Pearson normality test p > 0.05). The black dotted line in the middle of the function denotes the mean threshold, and the dotted line to the left indicates a threshold level 1.645 S.D. less than the mean (numerical value shown in brackets; for example: in (a), 4.48 dB indicates 1.645 times the S.D. (2.723 dB) away from the mean). For each stimulus location (a)–(b) for peripheral, and (c)–(e) for paracentral), coloured dashed lines and the above subject (S) number show the threshold values of representative glaucoma patients. Thus, coloured lines that are situated to the left of the 1.645 S.D. black dotted line indicate thresholds that are outside the approximate 95% normative distribution, i.e. detected as an ‘event’.