[Stereometric parameters of the optic disc. Comparison between a simultaneous non-mydriatic stereoscopic fundus camera (KOWA WX 3D) and the Heidelberg scanning laser ophthalmoscope (HRT IIII)].

BACKGROUND: The Heidelberg retina tomograph (HRTIII, Heidelberg Engineering, Germany) in conjunction with the Moorfields regression analysis (MRA) allows monitoring for the progression of early damage to the optic nerve suspicious of early stage glaucoma. The confocal scanning laser ophthalmoscope provides clinicians with an objective and reproducible analysis of morphological parameters of the optic disc. Margins of the optic disc are approximated with a contour line to calculate the stereometric parameters leading to interobserver and intraobserver variability of the MRA. New devices enabling 3D fundus photography might be an alternative to the established HRT. It was the goal of this study to compare the methods by assessing the differences in the topographic parameters obtained by the HRT and the Kowa nonmyd WX 3D (2D/3D non-mydriatic retinal camera, Kowa, Japan) in a representative sample.

METHODS: This retrospective study included 45 eyes of normal patients, 40 eyes of patients with macropapillae and 45 eyes of glaucoma patients. Each patient underwent an HRT examination and fundus photography with the Kowa nonmyd WX 3D on the same day. Excluded from the study were eyes with hazy media (cornea, lens, vitreous) or refractive anomalies higher than >4 dpt or astigmatisms >2 dpt. Eyes with previous refractive surgery history or other retinal diseases affecting the optic nerve were also excluded from the study. Bland-Altman plots were used for statistical evaluation. Distribution of parameters was described by 95% confidence intervals (CI).

RESULTS: In normal eyes (n=45) a mean difference in the disc area of 0.33 mm(2) was found (95 % confidence interval CI: 0.22-0.43), in the cup-disc ratio (CDR) of 0.02 (95% CI: -0.06-0.14), in the cup volume of 0.03 mm(3) (95% CI: -0.04-0.01), in the rim volume of 0.04 mm(3) (95%-CI: -0.04-0.13) and in the maximum cup depth of 0.28 mm (95 %-CI: 0.34-0.23). All differences, except for the rim volume, were statistically significant (p<0.05). Patients exhibiting a macropapilla (n=40) displayed a mean difference of 0.03 mm(2) (95 % CI: -0.18-0.11) for the disc area, a difference in CDR of 0.09 (95% CI: -0.05-0.13), a difference in maximum cup depth of 0.28 mm (95% CI: 0.23-0.34) and a cup volume of 0.14 mm(3) (95%-CI: 0.10-0.18). In addition, there were no significant differences in rim volume (difference: -0.02 mm(3), 95% CI: -0.07-0.12) or in disc area. In glaucomatous eyes (n=45), the mean difference for cup area was 0.33 mm(2) (95% CI: 0.22-0.43), an area of 0.09 mm(2) (95% CI: 0.06-0.13) for the CDR, -0.03 mm(3) (95 % CI: -0.09-0.02) for the cup volume and 0.08 mm(3) (95% CI: 0.03-0.13) for the rim volume. Mean maximum cup depth difference was 0.25 mm (95% CI: 0.20-0.31). Mean differences in CDR, maximum cup depth and cup area were all statistically significant. The mean differences did not exceed the interobserver and intraobserver variability found in HRT measurements of other studies.

CONCLUSIONS: To the best of our knowledge this study is the first comparing optic disc parameters of HRT and 3D photography. Mean differences in stereometric parameters did not exceed the known interobserver and intraobserver variability. The combination of non-mydriatic fundus photography and optic disc analysis is a very attractive and time-saving method. However, before progression of early glaucoma can be monitored or suspected glaucoma can be appraised over longer time periods, further studies are needed to clarify test and retest variability.