Survey of Ophthalmology
Volume 45, Supplement 3 , Pages S297-S303, May 2001

Clinical Detection of Optic Nerve Damage:☆☆☆

Measuring Changes in Cup Steepness with Use of a New Image Alignment Algorithm

  • Reinhard O.W Burk, MD, PhD

      Affiliations

    • Corresponding Author InformationReprint address: Prof. Dr. Reinhard Burk, Eye Clinic, Staedt. Kliniken, Teutoburger Str. 50, D-33604 Bielefeld, Germany. Email: burk,
    • ,
  • R Rendon, MD

Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany

Abstract 

The purpose of this study was to study the effect of a subpixel image alignment algorithm on the standard deviation (SD) of mean topography images obtained by laser scanning tomography and to evaluate changes of the cup shape measure parameter (CSM) over time based upon the individual parameter variability using the new algorithm. Triple measurements from optic nerve heads of 132 eyes of 132 subjects were obtained using the Heidelberg Retina Tomograph HRT. To calculate a mean topography image from three single topography images, alignment of the raw optical section image data was performed with the standard software and again with a new subpixel-based image alignment algorithm. The effect on the averaged (SD) of the mean topography images was evaluated. CSM was evaluated in 15 eyes of 15 normal subjects (N) and 28 eyes of 14 glaucoma patients (G) over a period of 28.6 ± 4.6 months (N) and 28.56 ± 5.2 months (G) respectively. A change in the CSM value over time was considered significant if CSM measurements exceeded two standard deviations of this variable determined for the individual eye. Mean-topography image SD was 22.86 ± 8.2 microns (min. 9.5 μm; max. 47.8 μm) with the standard alignment procedure and 15.46 ± 6.8 μm (min. 6.8 μm; max. 42.8 μm) with the new algorithm. The average SD improvement was 7.46 ± 3.9 microns (min. −8.1μm; max. 28.7μm). The coefficient of correlation of both methods was R2 = 0.77 (p < 0.0001). No control group eye demonstrated significant changes of CSM in the follow-up period. The CSM indicated an increase in cup steepness in 4 eyes of 4 glaucoma patients. In one of these four eyes, a deterioration of the visual field was identified by white on white perimetry. The new image alignment algorithm significantly reduces the SD of mean topography images calculated from identical raw data. If topometric variables are evaluated over time, the individual variability of data should be taken into account.

Keywords:  confocal laser scanning, cup shape measure, follow-up, glaucoma, laser scanning tomography, optic nerve head, primary open angle glaucoma

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☆ The software algorithm was provided by Dr. Gerhard Zinser, Heidelberg Engineering, Heidelberg, Germany

☆☆ The authors do not have a financial interest in the methods and apparatus used for the study.

PII: S0039-6257(01)00203-X

Survey of Ophthalmology
Volume 45, Supplement 3 , Pages S297-S303, May 2001

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