Relationship between the morphology of the posterior pole of the eyeball and changes in choroidal structure and blood flow in myopia

Background: The eyeball axial length (AL) is an important biological indicator of myopia, which has been widely studied. However, little research has been conducted on the relationship between eye shape and fundus structural changes in myopia. This study aimed to analyze the relationship between the shape of the posterior pole of the eye, and choroidal characteristics by comparing with the relationship between AL and choroidal characteristics. And to investigate the clinical significance of the shape of the posterior pole in the pathophysiological changes related to myopia. Methods: In this study, the data of 147 eyes (22 emmetropic and 125 myopic) of participants aged 20-30 years, examined in 2021, were collected. Optical coherence tomography (OCT) was used to analyze the posterior-pole images, choroidal thickness (ChT), choroidal vascular volume (CVV), and three-dimensional choroidal vascular index (3DCVI). The least squares method was used to fit the ellipse that was most consistent with the actual shape of the posterior pole. Multiple stepwise regression analysis was used to investigate the relationships between the fitting posterior-pole vertex curvature (fPVC), and ChT, CVV, and 3DCVI. Results: The mean AL of the participants was 25.15 +/- 1.35 mm (22.30-27.92 mm), the mean spherical equivalent was -3.59 +/- 2.62 D (+0.5 to -11.75 D), and the mean fPVC was 0.158 +/- 0.036 mm-1. The fPVC was positively correlated with the AL (r=0.639, P<0.001)and negatively correlated with the spherical equivalent (r=-0.666, P<0.001). The AL and fPVC were independently negatively correlated with the ChT and CVV in the macular region (0-6 mm). In the peripheral area (6-9 mm), the fPVC (ChT: beta=-0.529, P<0.001; CVV: beta=-0.441, P<0.001) was more closely associated with the ChT and CVV than the AL (ChT: beta=-0.140, P=0.127; CVV: beta=-0.127, P=0.190). The 3DCVI may be nonlinearly correlated with the AL and fPVC, and the relationship curve between the fPVC and 3DCVI was clearer than that between the AL and 3DCVI. Conclusions: In addition to the AL, the shape of the posterior pole is related to the ChT and choroidal vascular changes, and more closely related to the peripheral choroid than AL. Our findings provide another perspective for the prevention and monitoring of myopic-related pathological changes in clinical practice.