Novel Heidelberg retina tomograph-based morphological parameters derived from optic disc cupping surface processing.

PURPOSE: To explore new features of the optic nerve head morphology using the Heidelberg retina tomograph (HRT) and to assess their discriminating power between glaucomatous patients and normal subjects.

METHODS

HRT reports, exported as TIFF images, from 97 normal subjects and 97 primary open-angle glaucoma (POAG) patients were used. For each image the contour of the dominant region of the optic disc cupping surface (dROCS) was transformed into a data series by calculating the distance of each contour pixel from the centroid. The length of contour (LC) and SD of contour (SDC) along with the dROCS area divided by the disc area (DA) HRT parameter were examined as novel parameters.

RESULTS

The means of LC and SDC, after adjustment for cup area (CA) and DA HRT parameters, and dROCS/DA, after adjustment for CA, presented statistically significant differences (ANCOVA, P < 0.001) between the two groups. Using LC and SDC together in discriminant analysis with leave-one-out cross-validation, 75.3% of cases were correctly classified. Using dROCS/DA together with SDC, the correct classification percentage was 80.6%. The area under the ROC curve was 0.782 for LC, 0.725 for SDC, 0.861 for dROCS/DA, and 0.879 for the linear discrimination function that combines dROCS/DA and SDC.

CONCLUSIONS

These findings suggest that LC, SDC, and dROCS/DA can be exploited to the discrimination between glaucomatous and normal subjects. LC and SDC seem to arise from the difference in the shape of the contour of dROCS between the groups, suggesting bigger deviations and irregularities in the POAG group.