Restoration of retinal ganglion cell function in early glaucoma after intraocular pressure reduction: a pilot study

Abstract

Purpose: To investigate the changes of pattern electroretinogram (PERG) after intraocular pressure lowering in glaucoma patients and normal controls.

Design: Interventional retrospective cross-sectional study.

Participants: Twenty-five patients (49 eyes) with ocular hypertension or glaucoma undergoing topical treatment to lower IOP served as a study group; 22 patients (44 eyes) with ocular hypertension or glaucoma observed without treatment served as a control group for treated glaucoma patients; 9 normal subjects (18 eyes) receiving a 250-mg acetazolamide tablet served as a second study group; and 17 normal subjects (34 eyes) from a previous study served as a second control group for treated normal subjects.

Method: Pattern electroretinograms were recorded simultaneously from both eyes using skin electrodes and automated analysis. Visual field (VF) analyses were performed with white-on-white standard automated perimetry (SAP). Intraocular pressure was measured with Goldmann applanation tonometry; central corneal thickness was measured with pachymetry.

Main outcome measures: Pattern electroretinogram amplitude (microvolts), phase (pi rads), and test-retest variability (test 2-to-test 1 ratio, in decibels), SAP mean deviation (decibels), and IOP (millimeters of mercury).

Results: In 56% of right eyes and 21% of left eyes of the treated glaucoma subgroup, the PERG amplitude and/or phase improved beyond the 95% confidence intervals of the test-retest variability of the untreated glaucoma control group. Pattern electroretinogram improvement with IOP lowering occurred in both high- and low-tension glaucoma eyes. Eyes with severely impaired VFs showed little improvement in PERG; however, eyes of normal subjects treated with acetazolamide did not show significant PERG changes relative to the test-retest variability of normal controls.

Conclusions: Retinal ganglion cell function can be at least partially restored after IOP reduction in glaucomatous eyes with early VF impairment.

Figures

Figure 1

Example of pattern electroretinogram (PERG) waveforms and response analysis. A, B, Pattern electroretinogram waveforms (black tracings) recorded for the right eye of a normal subject in 2 different sessions. Gray sinusoidal tracings superimposed on the PERG waveforms represent the response component at the contrast-reversal frequency isolated by means of digital Fourier transform analysis. ms = milliseconds; div = division.

Figure 2

Scatterplots of test versus retest PERG amplitude (microvolts; left panels) and phase (π rads; right panels). Circles represent right eyes, and squares, left eyes.

Figure 3

Scatterplots of amplitude ratio versus phase ratio. Amplitude and phase ratios were evaluated as 10*log (test 2/test 1). Circles represent right eyes, and squares, left eyes. Dotted and dashed boxes represent the 95% tolerance intervals for right and left eyes, respectively, derived from data displayed in C. dB = decibels.

Figure 4

Pattern electroretinogram (PERG) amplitude (microvolts) before and after intraocular pressure (IOP)–lowering treatment in normal controls and glaucoma patients with 2 different levels of severity of visual field (VF) defects. Note that PERG amplitude improvements are larger in eyes with little or no VF defects than in eyes with severe defects.

Figure 5

Pattern electroretinogram (PERG) amplitude (microvolts) before and after intraocular pressure (IOP)–lowering treatment in glaucoma patients with 2 different levels of baseline IOP. Note that significant PERG improvement may occur for baseline IOP either lower than or higher than 21 mmHg.