Use of the GDx to detect differences in retinal nerve fibre layer thickness between normal, ocular hypertensive and early glaucomatous eyes

Purpose The GDx is a scanning laser polarimeter that has been developed to allow the quantitative analysis of retinal nerve fibre layer (RNFL) thickne ss. The purpose of this study was to determine whether differences in the R NFL thickness between normal, ocular hypertensive and glaucomatous eyes cou ld be detected using the GDx. Methods RNFL analysis was carried out using the GDx on 33 normal, 145 ocula r hypertensive (OHT) and 44 glaucomatous (POAG) eyes. The inclusion criteri a for entry into the study did not include the clinical appearance of the R NFL or optic disc, thus eliminating an important source of selection bias. The Kruskal-Wallis one-way analysis of variance was used to determine wheth er any significant differences existed among the groups in mean total and q uadrantic RNFL thickness. When significant differences were found, specific inter-group analysis was carried out using the Mann-Whitney U-test. Results Significant differences in RNFL thickness were found for the mean t otal, superior and inferior quadrant values between normals and OHT eyes as compared with POAG eyes. No significant differences were found for these v alues between the normal and OHT eyes. Conclusion Analysis of RNFL thickness using the GDx was able to detect diff erences between POAG eyes compared with normal and OHT eyes, although there was considerable overlap between groups. Further assessment of the techniq ue is required to determine whether it may be useful in screening for the p resence of early glaucomatous damage.