Aims: To investigate the influence of age, disc size and axial length on the retinal nerve fibre layer (RNFL) thickness measurements of Heidelberg Retina Tomograph (HRT) and optical coherence tomography (OCT).
Methods: A total of 162 eyes of 162 Japanese normal subjects aged between 20 and 83 were enrolled in this study. The disc area and mean RNFL thickness were measured with HRT. The disc area was also measured using the fast optic nerve scan protocol, and the average RNFL thickness was measured using the fast RNFL thickness scan mode with Stratus OCT. The correlations of age, disc area and axial length with RNFL thickness measured with HRT and OCT were analysed. The associations between axial length and disc area measured with HRT and OCT were also calculated.
Results: RNFL thickness measured with the two instruments decreased with age. There was a significantly negative correlation between the mean RNFL thickness and disc area measured with HRT. The RNFL thickness measured with OCT correlated positively with the disc area measured with OCT, but not with the disc area measured with HRT. Both RNFL thickness and disc area measured with OCT were inversely correlated with axial length, whereas the two parameters measured with HRT had no association with axial length.
Conclusion: In addition to the effect of ageing, the disc size affected the RNFL thickness measured with HRT, whereas the axial length influenced the RNFL thickness and disc area measured with OCT. These variables must be taken into consideration when measuring eyes with the lower or upper boundary of the normal range.
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