Purpose. To evaluate the change in the functional activity of retinal ganglion cells (RGCs) in response to intraocular pressure (IOP) drop in patients with newly diagnosed early stage primary open-angle glaucoma (POAG) using a pattern electroretinogram (PERG). Material and methods. A prospective non-randomized cohort study included 12 patients (24 eyes) including 5 men, 7 women, aged 63.42 ± 2.96 years with newly diagnosed early stage POAG in at least one eye, who underwent PERG (Diopsys Nova, Diopsys, Inc.) in addition to an ophthalmologic examination. After being diagnosed with POAG, all patients were prescribed prostaglandin analogues as monotherapy. One and four months into the treatment, repeated examinations took place. Results. At these time points, a significant decrease in IOP was noted, accompanied by an increase in PERG parameters , which indicates an improvement in the functional activity of RGCs, yet no linear relationship between the IOP decrease and the improvement in PERG parameters could be found. Conclusion. Early stage naïve-treatment POAG patients with minimally impaired visual fields as determined by threshold computer perimetry may have their RGCs functional activity partially restored and IOP lessened thanks to continuous IOP-lowering therapy with prostaglandin analogues. PERG can be used as a method for evaluating the effectiveness of glaucoma hypotensive therapy in terms of maintaining and improving the functional activity of RGCs.