Comparison of Images Obtained by Different Heidelberg Retina Tomograph I Instruments

Abstract

Abstract: : Purpose: Confocal scanning laser tomography is increasingly used to detect topographic change in the optic disc and peripapillary retina. In practice images may be taken on different instruments at each visit. This study aims to compare the accuracy of images taken using different Heidelberg Retina Tomograph (HRT) machines. Methods: A laboratory designed model eye was used to produce a circular optic disc image on three HRT I machines. The axial length of the model eye could be adjusted by means of a vernier scale (accuracy of 0.01mm). The refraction dial on each HRT instrument was set at one of ten different settings (range –5D to +5D), where each refraction setting corresponded to a specific axial length on the model eye. Images were acquired at each of the refractive settings. A circular contour line was drawn and the resulting disc area computed was recorded. This was repeated at each of the ten refractive settings and independently by three observers. Agreement between the observers and between the three machines was tested using intraclass correlation coefficients (ICCs). Results: Interobserver agreement was substantial for one HRT machine (ICC=0.84) and almost perfect for the other two (ICCs=0.93, 0.94). The mean disc areas obtained for each HRT machine were 2.995±0.11, 3.009±0.12 and 3.049±0.11; the mean paired differences were 0.054±0.035, 0.040±0.036 and 0.014±0.036 (mm²). Comparing the results between each of the three machines, agreement was almost perfect in each case (ICCs= 0.97, 0.98, 0.98). Conclusions: For a model eye the interobserver agreement for the HRT parameter disc area was substantial to almost perfect. Agreement between three HRT machines was found to be almost perfect indicating that the results obtained by the three HRT instruments for this parameter were interchangeable. It would therefore seem possible to accurately analyse a longitudinal series of HRT images taken by different HRT instruments.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, S • image processing • imaging/image analysis: non-clinical