RA/DA cumulative curve analysis of local and diffuse neuroretinal rim area damage in glaucoma patients

Abstract

Aim: To evaluate the validity of cumulative rim/disc area (RA/DA) curve analysis as a clinical tool for the identification of glaucoma induced optic disc pathology.

Methods: 71 normal and 83 glaucomatous eyes were evaluated from a series of 154 subjects recruited for this study. For each eye, the cumulative distribution of RA/DA was calculated from 36 equally spaced rim sectors of each optic disc obtained by the automatic evaluation of simultaneous videographics (Image-net X Rev.3/51b). To increase the sensitivity of this analysis in early glaucoma and in normal eyes, these cumulative curves were subsequently divided into two equal segments and the slopes of their respective regression lines compared.

Results: The median RA/DA value obtained from the 36 sectors was significantly different in glaucomatous eyes compared with normals (p < 0.001). Nevertheless, the curves (5th-95th percentile of the cumulative curves distribution) of early glaucomatous eyes fell within the normal range. When the cumulative curve of these marginal cases was then divided into two equal segments, the comparison of the slopes of the regression lines showed a significant difference (p < 0.05) in 100% of early glaucomatous eyes. Furthermore, normal eyes were shown to be true negatives in 93% of the cases in which no significant difference between the two slopes was observed.

Conclusion: Analysis of the RA/DA cumulative curve from 36 sectors of the optic disc was a valid method for the identification of glaucomatous disc pathology; however, a further calculation of the slopes of the two RA/DA regression lines was needed to identify early glaucomatous damage.

Figure 1

Cumulative RA/DA curves were generated in normal and glaucomatous patients by first dividing the rim of the optic disc into 36 equally spaced sectors, then sorting decrementally the rim/disc area of each sector to form a cumulative curve.

Figure 2

Distribution (percentage) of glaucomatous patients according to mean deviation (MD).

Figure 3

Distribution (percentage) of glaucomatous patients according to the corrected pattern standard deviation (CPSD).

Figure 4

Cumulative curve distribution of the rim/disc area in normal (continuous lines) and glaucomatous (broken lines) eyes. Evaluation of the median and the distribution of the 5th and 95th percentile allowed for a rapid visualisation of normal and glaucomatous discs (dotted lines: 5th and 95th percentile of glaucomatous eyes; broken line: median of glaucomatous eyes; thin continuous lines: 5th and 95th percentile of normal eyes; thick continuous line: median of normal eyes).

Figure 5

Cumulative curve of one of the six optic discs in which there was an overlapping of the 5th-95th percentile distribution of glaucomatous and normal eyes—that is, a glaucomatous curve within the normal range. The cumulative curve was then divided into two equal segments and the difference between the slope of the regression lines calculated.