Evaluation of Glaucoma Progression by Measuring the Rate of Change of Retinal Nerve Fiber Layer Thickness

Abstract

Purpose: : To evaluate progression with retinal nerve fiber layer thickness (RNFLT) measurements obtained with OCT and to measure the rate of change of RNFLT in glaucoma patients.

Methods: : This is a retrospective longitudinal study following 72 eyes of 41 glaucoma patients within a period of 5 years. All eyes had at least 4 serial RNFL measurements obtained with the Stratus OCT, and with the first and last measurements separated by at least 3 years. Visual field (VF) was performed with Humphrey VF analyzer at the same visits of RNFL imaging. Serial average and clock hour RNFLT were analyzed with a trend based algorithm - Guided Progression Analysis (GPA), which is a linear regression between RNFLT and age. Three strategies for progression were evaluated. Progression was defined when a significant trend was detected between average RNFLT and age - GPA (average RNFLT); or between RNFLT at any clock hour and age - GPA (any clock hour); or between 2 adjacent clock hour RNFLT and age -GPA (2 adjacent clock hours). VF progression was analyzed with linear regression between MD and age. Specificity was estimated by the proportion of eyes with significant improvement. Correlation analysis was performed to investigate the relationship between age, refraction, baseline RNFL thickness and the rate of change of average RNFLT.

Results: : A total of 586 OCT scan visits were included and the median number of OCT scans for each eye was 9.5. GPA (average RNFLT) detected more eyes (19 eyes) with progression compared with trend analysis with visual field MD (12 eyes) at specificity of 95%-99%. The rate of average RNFLT progression ranged between -1.1 and -15.4 µm/year. The agreement between progression by GPA (average RNFLT) and VF MD was poor (Figure 1a). A Venn diagram comparing the three GPA progression strategies is shown in Figure 1b. 7 o’clock, which corresponds to the inferotemporal sector, was the most frequent location that showed a significant trend of progression. Baseline RNFL thickness was positively correlated with the rate of RNFL reduction.

Conclusions: : GPA offers a new approach to analyze localized and diffuse loss of RNFLT. The rate of RNFLT reduction was variable among glaucoma patients with a higher rate of reduction in patients with a higher baseline RNFLT value.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: clinical • optic disc