This thesis pertains to the relationship between myopia and choroidal thickness (ChT). The first section presents a wider perspective on nearsightedness, emphasizing a number of anatomical changes in myopic eyes, which has led to a need for new classification and definitions. The next section is dedicated to the dynamic choroid and its measuring methods. ChT is more and more often considered a biomarker of myopia progression, as thinning of this structure has been found in myopic individuals compared to emmetropic patients. The research section aimed to verify these observations using optical coherence tomography (OCT) to measure choroidal thickness. In patients with high myopia, a correlation between choroidal thickness and axial length of the eye (AXL) was additionally investigated.