Tonography assessment using quantitative and qualitative analysis of the aqueous humor outflow mechanism

To perform qualitative evaluation of the aqueous humor (AH) outflow mechanism in glaucoma and nonglaucoma patients by means of tonography assessment and mathematical analysis.

Sixty-two primary open angle and 58 pseudoexfoliation glaucoma patients were recruited in a non-interventional, observational study between 2004 and 2007. Qualitative and quantitative outflow assessment was acquired by means of a digital tonographer and mathematical analysis. Qualitative results were represented using slope analysis of the change of the AH outflow rate over the tonography study. The results were compared to the control group (CG; n=100) as well as to a pseudoexfoliation group (PEX; n=46).

Regarding quantitative analysis, glaucoma groups exhibited significantly lower outflow facility compared to nonglaucoma ones (p<0.001). Outflow facility value was significantly correlated to cup to disc ratio (Pearson correlation r=-0.3, p<0.001). Regarding qualitative analysis, the primary open-angle glaucoma (POAG) group presented a significant profile variation at the beginning of the tonography, expressed as an increased resistance of the AH outflow. Both glaucoma groups exhibited profile stabilization at the end of the measurement, suggesting that the outflow rate remained constant, while nonglaucoma groups followed a continuous reduction of the AH outflow rate throughout the study.

The POAG, PXG, PEX, and CG groups demonstrated both qualitative and quantitative tonographic profile differences. The observed differences in the glaucoma groups suggest a distinct pathomechanism between POAG and PXG. It is suggested that POAG patients have a temporary disruption of the AH flow pathway, while PXG patients have a generalized increased flow resistance.