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F.C. Ikeji, E.T. White, J.M. Shewry, P.G. Schlottmann, D.F. Garway–Heath; Comparison of the Test–Retest Variability of Neuroretinal Rim Area Measurements in Normal and Glaucoma Patients Using HRT II and OCT3 . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4820.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the reproducibility of neuroretinal rim area measurements in normal subjects and glaucoma patients by Optical Coherence Tomography (OCT3) and Heidelberg Retina Tomograph (HRT II). Methods: One eye was randomly selected from each of 25 normal subjects and 31 glaucoma patients and scanned using HRT II and OCT 3. Patients also underwent a full clinical examination. Diagnosis was based on SITA 24–2 visual field test repeatable defects. Eyes were imaged by two experienced observers on two visits. Time between visits ranged from 1 to 3 weeks. Repeatability was calculated for observer one and two, and visits one and two by means of Bland & Altman plots and Intraclass Correlation Coefficient (ICC) for the sequences interobserver–intravisit (1 – 2, 1’– 2’), interobserver–intervisit (1’– 2, 1 – 2’) and intraobserver–intervisit (2 – 2’, 1–1’). HRT scans were analyzed using the 50 microns reference plane. Disc margin contour lines were drawn by the first observer, on follow–up visits the baseline contour was automatically imported by the software. OCT scans were acquired using the Fast Optic Disc scan protocol and analysed with the Optic Nerve Head protocol. No corrections were made to the automatic recognition of the disc borders. The software defined a new disc margin on each scan. Results: The ICC values for Rim Area measurements for the sequence 1 – 2, 1’– 2 and 2 – 2’ with the OCT were 0.907, 0.894 and 0.912. The mean differences (95% limits of agreement) between measures for the same sequence were 0.06 (–0.01 to 0.13), –0.03 (–0.10 to 0.05) and 0.06 (–0.01 to 0.13). OCT Disc Area ICC ranged from 0.70 to 0.79. For the HRT the ICC values for the same sequence were 0.992, 0.987 and 0.972. Mean difference between measures were –0.01 (0.04 to 0.05), –0.01 (0.05 to 0.07) and –0.01 (0.07 to 0.10). Conclusions: HRT measurements, which transfer the same contour line from baseline scans to follow–up scans, show less variability between scans. In this case the repeatability of the Disc Area parameter will be perfect as it is the same contour–line for baseline and follow–up. OCT results are not affected by subjective contour line drawing as this is done automatically by the software, but the variability in Disc Area calculation may affect the reproducibility of Rim Area measurements. Image quality during acquisition may be the main source of variability on each scan as the automatic disc area detection will be impaired. The use of a transferable contour line from baseline to follow up scans reduces variability between scans.
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