Variability in digital analysis of optic disc topography

Abstract

We determined the magnitude of variability in optic disc topographical parameters on digital analysis of the optic disc using the IS 2000. The variability introduced by the system, the observer, the observer and patient, and by clinically different types of discs was assessed in the measurement of the vertical cup-to-disc ratio, horizontal cup-to-disc ratio, cup area-to-disc area, cup volume, neuroretinal rim area, and neuroretinal rim area-to-disc area. The system itself accounted for no variability. The variability introduced by one observer for the parameters ranged from 1% to 7%, and by one observer and patient from 1% to 28%. The variation among five observers ranged from 1% to 55%. Direct image acquisition (using video cameras) gave results that were no different from those obtained by digitizing the slides. Contrast-enhancement techniques did not decrease observer variability. A change in the flash intensity level at which optic disc images were acquired from 94.5 to 15.0 Watt-seconds introduced a variability of 3% to 21%. These results are less variable than those obtained on clinical observation and comparable to those of the Rodenstock image analyzer in evaluating these aspects of optic disc topography.

A three-year prospective, randomized and open comparison between latanoprost and timolol in Japanese normal-tension glaucoma patients

“…The principles and outline of the instrument are described elsewhere. [17][18][19][20] The inner border of the whitish Latanoprost in normal-tension glaucoma G Tomita et al 985 scleral ring is referred to as the disc edge. The examiner defined four points at the disc edge, and the computer then calculated an ellipse fitting these points.…”

Technical Procedures and Software for Magnification-Corrected Morphometry of Optic Disk Photography

“…More recently, computerized image analysis [3,4] and manual measurements with digitizing pads [5,6] Their actual values can ultimately be obtained by correcting for the magnification or minification factors due to the optical system of the camera and patients' ametropia [7], In the pre sent paper, wc describe our procedure and the dedicated software.…”

Detection of changes of the optic disc in glaucomatous eyes: Clinical examination and image analysis with the Topcon Imagenet system

“…The quantitative computerized analysis of the optic disc with the ImageNet system has been described elsewhere (Varma et al 1988. During the analysis the observer marked four points over the optic disc boundary (superior, left, inferior, right) and an ellipse delimited by those points was drawn.…”

“…Qualitative or semiquantitative estimates of the optic nerve head by disc drawings or fundus photography (Lichter 1976;Klein et al 1985Klein et al , 1987Tielsch et al 1988;Varma et al , 1992Odberg & Rise 1985;Abrams et al 1994;Coleman et al 1996) and computerized quantitative techniques (Varma et al 1988;Dandona et al 1989;Dreher et al 1991;Burk et al 1993;Cioffi et al 1993;Weinreb et al 1993;Mikelberg et al 1993;Hoskins et al 1994;Varma et al 1994;Tezel et al 1996) can be used to record the appearance of the optic nerve head. Computerized disc analysis and laser scanning devices seem attractive but are expensive and their clinical utility has not been established yet in longitudinal studies.…”