Relationship of structural and functional rates of change as a function of glaucoma severity

Abstract

Purpose: To investigate the longitudinal relationship between structural and functional rates of change in patients at different stages of glaucoma severity.

Methods: This retrospective longitudinal study included 360 eyes of 278 patients who were divided into 4 groups according to the baseline severity of glaucoma. All patients had 3 or more good-quality confocal scanning laser ophthalmoscopic examinations and 4 or more reliable visual field (VF) examinations with follow-up time of 4 or more years. A pointwise exponential regression was used to perform trend analysis on thresholds at each visual field test location. The test locations were ranked according to their decay rates and were partitioned into slow and fast components for each eye’s visual field series. The mean rates of change of the slow and fast components were measured. Linear regression of the mean deviation (MD), Visual Field Index (VFI) and global rim area were performed against time. The longitudinal relationship between structure and function was assessed with two methods: 1) bivariate correlation analyses, and 2) a linear mixed model was built to explore the adjusted associations of structural change with the functional parameters (MD, VFI, mean sensitivities in slow and fast VF rate components).

Results: Seventy one eyes diagnosed as glaucoma suspect, 92 eyes with preperimetric glaucoma, 134 eyes with early glaucoma and 63 eyes with advanced glaucoma were included. Global rim area rate was positively correlated with MD rate, VFI rate, and fast rate in preperimetric and early glaucoma (all P<0.05); the highest correlations were observed between the RA rate and fast rate. However, rim area rate was not significantly correlated with slow rate in any of the severity groups. Change in global rim area was directly associated with longitudinal measurements of MD and VFI in preperimetric and early glaucoma (all P<0.05). Change in global rim area was directly associated with longitudinal measurements of mean sensitivities of fast component regardless of baseline severity of glaucoma (all P≤0.019). Mean sensitivities of the slow component were not significantly associated with change in global rim area in any groups.

Conclusions: We conclude that the identification of the fast component can help clinicians measure and predict rates of glaucoma progression, and is a more robust measure of change than are the global indices MD and VFI.