Structure-function relationship is stronger with enhanced corneal compensation than with variable corneal compensation in scanning laser polarimetry

PURPOSE: To compare the structure-function relationship between peripapillary retinal nerve fiber layer (RNFL) retardation, measured with scanning laser polarimetry (SLP) with both enhanced and variable corneal compensation (ECC [enhanced corneal compensation] and VCC [variable corneal compensation], respectively; features of the GDx Nerve Fiber Analyzer; Carl Zeiss Meditec, Inc., Dublin, CA), and visual field (VF) sensitivity, measured with standard automated perimetry (SAP) in normal and glaucomatous eyes and the effect of marked atypical birefringence patterns (ABPs) on this relationship.

METHODS: Thirty-three healthy subjects, and 68 patients with primary open-angle glaucoma (POAG) took part in the study. ECC and VCC images were taken in one randomly selected eye of each subject. VF tests were also obtained in the same eyes. The structure-function relationship was assessed in six peripapillary sectors and their matching VF areas and was reassessed after eliminating eyes with marked ABPs.

RESULTS: Correlations (Spearman's correlation coefficients, r(s)) in the structure-function relationship were generally stronger in images taken with ECC than in those taken with VCC. With ECC, the relationship was significantly more curvilinear when VF sensitivity was expressed in the standard decibel scale and more linear when VF sensitivity was expressed in an antilog scale than with VCC. When eyes with marked ABP images were removed from the analysis, the structure-function relationship with VCC improved, and no statistically significantly differences were found in the relationships between VCC and ECC.

CONCLUSIONS: The structure-function relationship between RNFL retardation and SAP VF sensitivity was stronger in images obtained with the GDx ECC than with the GDx VCC (Carl Zeiss Meditec, Inc., Dublin, CA). ABPs, which appeared more markedly with VCC than with ECC, weakened the structure-function relationship.