Introduction: Caffeine and its metabolites have antioxidant activity, scavenging reactive oxygen species. The aim of our study was to measure caffeine concentrations in vitreous samples after peroral caffeine intake. Methods: This prospective study included patients scheduled for 23-G pars plana vitrectomy with membrane peeling due to epiretinal membranes. The study was performed in two parts: in the first part, patients were recruited into three different groups: group A consisted of habitual coffee drinkers who agreed to drink coffee containing 180 mg caffeine 1 h before surgery (n = 10), group B consisted of habitual coffee drinkers who were not offered coffee before surgery (n = 5), and group C consisted of non-habitual coffee drinkers, forming the control group (n = 5). In the second part (group D) patients (habitual coffee drinkers) agreed to give additional blood serum samples for measurement of caffeine concentration. Harvested samples of vitreous (groups A–D), epiretinal membranes (groups A–C), and blood serum samples (group D) were examined for concentrations of caffeine with gas chromatography-mass spectrometry. Results: Samples of 40 eyes of 40 patients were harvested. The concentrations of caffeine in the vitreous samples were 1,998 ± 967 ng/mL in group A and 1,108 ± 874 ng/mL in group B. In group C, caffeine concentrations were below 176 ng/mL in all vitreous samples. Both groups A and B had significantly higher concentrations of caffeine in the vitreous samples than group C (p < 0.002, p < 0.01, Mann-Whitney U test). Caffeine concentrations in epiretinal membranes were below the limits of detection. Correlation of caffeine concentrations between blood serum samples and vitreous samples in group D was high, with significantly higher caffeine concentrations in the blood serum. Conclusion: Coffee consumption leads to significant caffeine levels in the vitreous compared to patients in the control group, and caffeine concentrations in the vitreous showed a high correlation to blood serum concentrations of caffeine after peroral coffee consumption.

<b><i>Introduction:</i></b> Fourier-transform infrared imaging (FTIRI) enables examination of protein secondary structure in the analyzed tissues. The aim of our study was to examine the distribution of secondary structures in epiretinal membranes (ERMs) and internal limiting membranes (ILMs), and to explore possible associations to other diagnostic variables. <b><i>Methods:</i></b> This prospective pilot study included patients scheduled for pars plana vitrectomy with membrane peeling. ERMs and ILMs were harvested during surgery and placed on a BaF₂ window for postsurgical FTIRI analysis. Infrared hyperspectral images were subjected to second and fourth derivative analysis to obtain information of the protein secondary structures present in the tissues. <b><i>Results:</i></b> Samples of 43 patients were analyzed, with the triple helical domain showing the highest prevalence in the examined tissues. The other secondary structures (beta-sheet, random coil, and beta-turn) showed a heterogenous distribution in the examined samples, without specific associations to indication of surgery, comorbidities, outcomes from optical coherence tomography, and intrasurgical findings. <b><i>Conclusions:</i></b> FTIRI enables analysis of the spatial distribution of protein secondary structures in the examined tissues; thus, it is a useful analytical technique for the analysis of ERMs and ILMs.

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