All participants had a Snellen chart BCVA value greater than 20/25. The mean ± standard deviation values for age were 42.92 ± 12.36 years for the high-myopia group and 46.39 ± 18.74 years for the control group. The results for the demographic profiles of the study participants are presented in Table 1. The control group (AL < 26 mm) consisted of 105 eyes from 55 men and 50 women. The high-myopia group (AL ≥ 26 mm) comprised 59 eyes from 33 men and 26 women. The patients were classified into two groups based on AL (26 mm). This retrospective review of 378 participants revealed that 164 eyes from 164 individuals met the inclusion and exclusion criteria. We also evaluated the effects of age and sex on thickness of each retinal layer in these groups. The primary aim of our study was to investigate and compare the thicknesses of individual retinal layers of the macula between highly myopic eyes and control eyes. Considering that the worldwide trend of increasing incidence of myopic patients is relatively greater in Asian countries, our study could provide valuable insight into better understanding the distinguishing characteristics of high myopia compared with control eyes using SD-OCT segmentation analysis. Accordingly, we designed this study to focus on structural changes in the thickness of the individual layers of the retina, from the innermost layer (RNFL) to deepest layer (RPE) of the outer retina, between normal axial length and axially elongated highly myopic groups. Several studies have evaluated the effects of age and sex on retinal layer thickness in normal and myopic indivduals 19, 20, 21, 22. The latest development of software for segmentation analysis using SD-OCT can allow for easier and more accurate automated differentiation of each retinal layer and measurement of individual layer thickness 17, 18. It uses the interference patterns generated by low coherence light reflected by the retina and is a noninvasive tool for quantitative and qualitative measurement of the macula. The spectral domain optical coherence tomography (SD-OCT) device enables cross-sectional imaging of the retina. Thus, it is essential to examine macular layer thicknesses to further investigate myopia-related retinal tissue thinning and stretching and to identify differences in structural features in high myopic eyes compared with normal (control) eyes. These changes could be associated more significantly with individuals with a higher degree of myopia and might induce several retinal abnormalities that result in myopia-related visual loss. Myopic enlargement of the globe is mainly related to axial length prolongation and leads to retinal tissue stretching, thinning, and reduced retinal function 13, 14, 15, 16. Macular anatomic abnormalities were found in up to 22% of eyes with high myopia 12. Macular abnormalities and degenerative or atrophic change of the posterior segment, including macular holes, myopic macular schisis, choroidal neovascularization, chorioretinal atrophy, lacquer cracks, retinal detachment, posterior staphyloma, and epiretinal membrane are conditions associated with high myopia 7, 8, 9, 10, 11. It is associated with axial elongation of the globe and is one of the principal causes of visual impairment. High myopia is defined as a spherical equivalent (SE) <−6 diopters or an axial length (AL) ≥26 mm 4, 5, 6. The prevalence of myopia has been increasing worldwide and the incidence is relatively greater in East- and Southeast-Asian countries (i.e., up to 80%) 1, 2, 3. Axially elongated, non-pathologic highly myopic eyes had different structural features than control eyes, with significantly greater individual macular layer thicknesses independent of sex or age. There were no significant effects of sex on individual retinal thicknesses, and age had less negative effects on the thicknesses of retina layers in high-myopic eyes than normal eyes. In high-myopia group, the thicknesses of total retina and all individual retinal layers in central and entire perifoveal subfields were significantly thicker than the corresponding layers in control group after adjustment for ocular magnification (all P < 0.05). Individual retinal layer thicknesses of five subfields in the macula were measured using automated retinal segmentation software packaged with the spectral-domain optical coherence tomography and were compared. We assessed 164 subjects and divided them into two groups based on axial length (AL) (i.e., high-myopic group (AL ≥ 26 mm) and control group (AL < 26 mm)). This retrospective study aimed to compare the thicknesses of individual retinal layers between high-myopic and control eyes, and to evaluate the effects of age and sex on each retinal layer thickness. The incidence of myopia is increasing worldwide, and the investigation on pathophysiology of myopia is becoming more important.
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