A comparison of five methods for estimating general glaucomatous visual field depression

Abstract

The separation of local and diffuse visual field loss is important for evaluating the nature and extent of glaucomatous visual field damage. Here, five automated methods for estimating diffuse loss in glaucomatous visual fields (as measured with the Octopus G1 program) are compared. Four are taken from the published literature, and one is introduced in this investigation. It is shown that the new index (here called diffuse loss) provides the best agreement with a value determined using a more empirical approach.

An Update to Octopus Perimetry

“…However, the amount of local and diffuse loss was not calculated. Based on prior studies evaluating the cumulative defect curve, [15][16][17] Figure 2a), as using the average of a number of ranks rather than relying on a single rank is more resistant to accidental variability. The diffuse defect (DD) can be shown in the cumulative defect curve in two ways: first, as a difference in height of the individual curve compared with the 50th percentile of normality in ranks 12-16 (arrow in Figure 2a) and second, as the area between the original 50th percentile and the same curve shifted to match the individual defect curve in ranks 12-16.…”

A new diffuse loss index for estimating general glaucomatous visual field depression

“…A major obstacle in discriminating between local and diffuse damage and in analyzing mixed situations in which both seem to be present is due to the subjectivity and difficulty in deciding what one means by 'diffuse damage' and arriving at a satisfactory definition which can be coded in a computer algorithm [5]. This may be responsible in part for the contradictory results found in the literature, as mentioned above.…”

“…Although both categories of glaucoma may differ in the way they damage the visual field, considerable overlap exists [2]. This is shown by the fact that the mean defect (MD) and corrected loss variance (CLV) visual field indices are highly correlated in a population of glaucomatous eyes and glaucoma suspects [3], although some correlation is to be expected from the way in which they are defined [4,5].…”

“…In a previous paper [5], such a diffuse loss index was proposed and the results were compared with those produced by a number of other methods for estimating general depression in glaucomatous visual fields. The comparison was based on an approach for estimating diffuse toss which was empirical and consisted of two stages.…”

“…First, the diffuse loss index was calculated using the method presented in ref. [5]; then, for those visual fields in which diffuse loss seemed to be present, the cumulative loss curve was computed and the value at the 20th ranks location of the curve was taken as the estimated diffuse loss value. It was shown that the algorithm for computing the diffuse loss index (hereafter referred to as DLO) yielded results which were in better agreement with the 20th value method than those produced by the four other methods for estimating general visual field depression.…”