Purpose: To identify threshold values above which the intersession reduction of the retinal nerve fibers layer (RNFL) can be considered significant.
Method: In 79 eyes (41 patients) we have performed RNFL measurements with the Stratus OCT twice in the same session. The differences between these measurements were used to calculate the test-retest variability (on clock hours, quadrants and the average RNFL thickness) using the formula: Test-retest variability = 1.96 x standard deviation (95% confidence) The resulted "threshold values" were used to identify the possible progression in a study group of 119 eyes (61 patients), followed for an average of 2 years.
Results: RNFL reduction exceeding the "threshold values" in 2 consecutive sessions was noticed in 18 eyes (15.12%). 12 eyes (10.08%) have fulfilled this criterion on 2 or more clock hours. 3 patients have had the criterion present on both eyes.
Conclusions: This appears to be a plausible method for identifying the progression of structural damage in glaucoma, deserving further researches for validation.