Estimating the rate of retinal ganglion cell loss to detect glaucoma progression

Abstract

 

Purpose

 

To evaluate the relationship between glaucoma progression and the estimate of the retinal ganglion cells (RGCs) obtained by combining structure and functional measurements in patients with glaucoma.

 

Methods

 

This study examined 60 eyes of 39 glaucoma patients that were followed for an average of 5.3 years by standard automated perimetry (SAP) and optical coherence tomography (OCT). All eyes underwent at least five serial retinal nerve fiber layer (RNFL) measurements performed by Cirrus OCT, with the first and last measurements separated by at least three years. Visual field (VF) testing was performed by using the Swedish Interactive Threshold Algorithm (SITA) Standard 30-2 program of the Humphrey Field Analyzer (HFA) on the same day as the RNFL imaging. After obtaining estimates of the RGC counts from SAP and OCT, a weighted average was used to obtain a final estimate of the number of RGCs for each eye. The rate of RGC loss was calculated using linear regression. Both serial RNFL thicknesses and VF progression were evaluated by trend analysis.

 

Results

 

The OCT parameter, average RNFL thickness, was able to detect progression in 12 of the 80 eyes examined, whereas the MD slope detected progression in 30 eyes. A statistically significant rate of RGC loss was found in 27 of the 80 eyes, with progression detected by either RNFL thickness or MD slope in 25 of these 27 eyes.

 

Conclusions

 

Estimation of the rate of RGC loss by combining structure and function measurements provided better detection of glaucoma progression than either OCT or SAP.