Reproducibility of pixel-by-pixel analysis of Heidelberg retinal flowmetry images: The Thessaloniki eye study

Leonidas Mavroudis, Alon Harris, Fotis Topouzis, M. Roy Wilson, Fei Yu, Eleftherios Anastasopoulos, Archimidis Koskosas, Brent Siesky, Theofanis Pappas, Panayiota Founti, Anne L. Coleman

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Abstract

Purpose: To identify the investigator effect in the analysis results of Heidelberg retinal flowmetry (HRF) images when pixel-by-pixel analysis is performed. Mehods: Thirty-two of 732 HRF images were randomly selected from a population-based study. Pixel-by-pixel analysis was performed by two trained masked graders in the following way: A square window of 40 × 40 pixels or two windows of 30 × 30 pixels or four windows of 20 × 20 pixels free from blood vessels at the peripapillary retina were identified. Using a 1 × 1-pixel window, the grader performed pointwise analysis according to a specific protocol. The analysis process was performed by each observer three times (A, B, C) at 1-week intervals. The percentage of pixels with < 1 arbitrary unit of flow (zero flow), the 10th, 25th, 50th, 75th and 90th percentiles and mean flow values were calculated. The difference between the results of analyses B-A and C-A for all HRF parameters was estimated using the Wilcoxon signed rank test. Mixed-effect regression models were also used after controlling for grader effect and correlation within subjects. Results: There was no statistically significant difference between the results of analyses B-A and C-A or for any parameter in the mixed-effect regression models. Intraclass correlation was 0.9665 for the percentage of zero flow pixels. Conclusions: Pixel-by-pixel analysis of HRF images by trained graders remains a highly reproducible method. No grader effect was found. If a precise protocol is followed, the results are independent of the exact placement of the analysis windows and the pointwise analysis of the identified and mapped retinal tissue.

Original languageEnglish (US)
Pages (from-to)81-86
Number of pages6
JournalActa Ophthalmologica
Volume86
Issue number1
DOIs
StatePublished - Feb 1 2008

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Keywords

  • Blood flow
  • Glaucoma
  • Heidelberg retina flowmeter
  • Laser Doppler flowmetry
  • Neuroretinal rim

ASJC Scopus subject areas

  • Ophthalmology

Cite this

Mavroudis, L., Harris, A., Topouzis, F., Wilson, M. R., Yu, F., Anastasopoulos, E., Koskosas, A., Siesky, B., Pappas, T., Founti, P., & Coleman, A. L. (2008). Reproducibility of pixel-by-pixel analysis of Heidelberg retinal flowmetry images: The Thessaloniki eye study. Acta Ophthalmologica, 86(1), 81-86. https://doi.org/10.1111/j.1600-0420.2007.01003.x