## 4 Discussion
The ROC curve highlights that the area of the optical disk is a good predictor in determining severe SAS. Although not statistically significant, the mean level of central macular thickness in the study eye was lower in severe SAS between the groups with and without glaucoma. More suggestive changes are achieved when evaluating the average level of C/D ratio in the study eye, which was higher in moderate obstructive SAS and lower in mild obstructive SAS. The regression line validates the indirect correlation of the C/D ratio with age and the direct correlation with the severity of SAS. Thus, we can say that there is a significant change in the retinal nerve fibers at the level of the optic nerve for the patients with moderate or severe SAS. The evaluation of biomechanical properties in glaucoma patients is introduced by various studies [17, 18, 19, 20, 21]. By comparing 1200 patients with glaucoma vs. 1000 healthy subjects a recent meta-analysis by [PERSON] et al. show that corneal properties seem to differ among the patients with glaucoma and healthy subjects. The results also underline the relevance of the biomechanical properties of the cornea in interpreting the intraocular pressure and it should support further studies on the influence of CH and CCT in glaucoma screening and diagnosis [22, 23, 24, 25, 26]. Changes in the properties of corneal biomechanics by associating sleep apnea syndrome with glaucoma are a starting point for further studies, as there are few studies in the literature that refer to these changes that may occur in patients with SAS. Hypoxia is associated with significant changes in central corneal thickness (CCT) and endothelial cell density (ECD) [27, 28, 29, 30, 31]. The severity of hypoxemia and the increase in AHI values reduce the CCT and endothelial cell density in patients [25, 30, 31, 32]. In our study, the IOP level was significantly lower in Glaucoma + SAS group in the study eye. Among the biomechanical and corneal parameters, the PIOcc level, the PIOg level was significantly lower in Glaucoma + SAS in the study eye. The level of CH, the average levels of CRF and those of GCC were not significantly different according to the presence or lack of SAS in the study eye. The multivariate analysis reveals that age and BMI are good predictors of CRF in the study eye. Thus, it can be said that SAS worsens glaucoma through an independent pressure mechanism (hypoxia could be a plausible factor). However, our results are preliminary, a longer follow-up period and a more complex database could produce statistically significant results. The only study of [PERSON] et al. [27] which directly refer to the change in the corneal biomechanics in patients with SAS compares a total of 54 patients with mild or moderate SAS vs. 20 healthy subjects. They concluded that the patients with severe SAS had lower CH and CRF scores compared to mild and moderate as well as controls. Lower scores of the CH and CRF within the severe group were possibly related to changes in the structural properties of the cornea. Further studies on large groups of patients with SAS during various stages may show significantly structural changes and can prevent glaucoma even in the early stages of the disease. _Limitations._ They are mainly represented by the short follow-up period, the small number of enrolled cases and the lack of data on the BMI and AHI in the control group. The use of data from chronic patients with SAS, with a longer prevalence of the disease compared to another group would bring valuable information about the structural and corneal biomechanical changes of patients with SAS.