Interobserver variability of optic disk variables measured by confocal scanning laser tomography☆

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Abstract

PURPOSE: To assess the interobserver variation of confocal laser scanning tomographic measurements of the optic nerve head and to address the question of whether the addition of clinical optic disk photographs is helpful in outlining the optic disk margin and in reducing the observer-related variation of the measurements.

PATIENTS AND METHODS: Optic disk variables for 16 eyes of 16 patients with glaucoma, generated by confocal laser scanning laser tomography (Heidelberg Retina Tomograph), were independently evaluated by four experienced glaucoma specialists, and the interobserver variability was calculated. A second separate review by the same observers included the use of clinical stereoscopic color optic nerve head photographs to aid definition of the optic disk margin.

RESULTS: Optic disk parameters with the smallest interobserver variation were cup shape measure, maximum cup depth, height variation contour, and mean height contour. The intraobserver variation of these parameters did not increase when clinical optic disk slides were additionally available. Parameters with the highest interobserver variation were volume below surface, volume below reference, volume above surface, and volume above reference. The observer variation of these optic disk parameters increased significantly for two of the four examiners when clinical optic disk slides were additionally available for outlining the optic disk margin.

CONCLUSION: Confocal laser scanning tomography of the optic nerve head can be improved significantly if clinical optic disk photographs are additionally available to help in outlining the optic disk margin. Because interobserver variation in the tomographic optic disk measurements can be significant, even if experienced observer are involved, tomographic optic disk measurements may be centralized in reading centers in the case of multicenter studies.

Section snippets

Methods

Sixteen subjects were randomly selected from the existing Heidelberg Retina Tomograph records of one clinician’s (Dr Mikelberg’s) practice by one Heidelberg Retina Tomograph user (Dr Iester). For all subjects, the Heidelberg Retina Tomograph image of one eye was randomly selected for inclusion in this study. Mean vertical cup/disk ratio was 0.63 ± 0.14. All of the selected subjects had to have a Heidelberg Retina Tomograph image and stereoscopic slides of the optic disk done within 3 months of

Results

Optic disk parameters that showed the smallest interobserver variation and the highest Kendall’s coefficients of concordance were cup shape measure, maximum cup depth, height variation contour, and mean height contour TABLE 1, TABLE 2, TABLE 3. Correspondingly, the intraobserver variation of the latter parameters did not vary significantly when the Heidelberg Retina Tomograph evaluation without additional clinical optic disk slides available was compared with the Heidelberg Retina Tomograph

Discussion

The results of the study suggest a relatively high agreement between the four experienced examiners in the assessment of optic nerve parameters as measured by confocal laser scanning tomography. The findings, however, do also show that, at least for some of the trained examiners, the intraobserver variation in the Heidelberg Retina Tomograph measurements can be significantly improved if clinical optic disk photographs are available to help in outlining the margin of the optic nerve head. Taking

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This work was supported in part by a G Gaslini Institute grant (Dr Iester) and by National Eye Institute grant EY 11008 (Dr Zangwill) and EY 11158 (Dr Weinreb).

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