Electrophysiological markers of advanced stages of glaucomatous optic neuropathy

Purpose: to determine the changes in electrophysiological parameters reflecting specific dysfunctions of retinal ganglion cells (RGCs) at advanced stages of glaucomatous optic neuropathy (GON).

Material and methods. The study involved 35 patients (55 eyes) aged 51–76 (63.1 ± 7.7 years) with primary open-angle glaucoma (POAG), divided into two subgroups depending on POAG stages: developed (24 patients, 27 eyes) and advanced stages (24 patients, 28 eyes). The age-matched control group (aged 51–72, 59.8 ± 5.9) included 28 relatively healthy individuals (32 eyes). Transient and steady-state pattern ERG (PERG) and photopic negative response (PhNR) were recorded according to ISCEV standards.

Results. A decrease in the amplitude of the transient PERG's N95 and P50-waves and steady-state PERG was found, the degree of which showed an inverse dependence on the angular size of the stimulus, which clearly distinguished the developed and advanced POAG stages from the initial GON. The developed stages are characterized by a decrease in the PhNR amplitude, calculated from the baseline, and the PhNR/b index, the reduction of which was the more significant the greater the intensity of the flash. A significant delay of the N95 peak for patterns of all angular sizes and a less pronounced lengthening of the latency of the P50 wave (significant only for small stimuli 0.8° and 0.3°) in comparison with the age norm were found. The latencies of the steady-state PERG and PhNR practically did not differ from the age norm values.

Conclusion. The revealed reduction in the amplitudes of N95 and P50 waves of transient and steady-state PERG, PhNR, and the PhNR/b index, as well as an increase in the peak latency of N95 and P50 waves of transient PERG, may be markers of functional changes in the retina associated with non-adaptive plasticity or reflecting a combination of the processes of adaptive plasticity and degeneration of RGCs. Further research in this area will help give a more accurate characterization of the found regularities and apply the obtained results in clinical practice.

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