Increased Long-term measurement variability with scanning laser polarimetry employing enhanced corneal compensation: an early sign of glaucoma progression.

PURPOSE: To investigate whether the intervisit standard deviation (ISD) of various scanning laser polarimetry parameters is increased, in progressing glaucoma.
METHODS: GDx-variable corneal compensation (VCC) and GDx-enhanced corneal compensation (ECC) measurements, and Octopus G2 visual field tests, were performed at 6-month intervals on 27 healthy subjects and 52 consecutive glaucoma patients. One eye per participant was analyzed. Fifteen patients progressed (on the basis of visual field criteria) and 37 remained stable, during the 2.6+/-0.4 years follow-up.
RESULTS: Baseline visual field indices and the stage of glaucoma did not differ between the glaucoma groups. No regression with time was found for any GDx parameter in any group. The ISD of GDx-ECC nerve fiber indicator (NFI), but not GDx-VCC NFI, was significantly higher in progression than in the stable glaucoma group (Mann-Whitney U test with Bonferroni correction, P=0.028). Also, several other ISD values tended to increase in the progressing group. Logistic regression analysis revealed that ISD of NFI [odds ratio (OR)=1.22, P=0.013], inferior average (OR=1.80, P=0.035), and average thickness along the measuring ellipse (OR=2.00, P=0.042), as determined with GDx-ECC (but not with GDx-VCC), all associated with visual field progression, independently of patient age.
CONCLUSIONS: With GDx-ECC, increase of ISD is an early sign of glaucoma progression, precedes the development of detectable parameter changes, and is associated with visual field progression.