The fovea centralis was determined by identifying the point of maximum depression in the central 500-micron-diameter area. The internal and external choroidal margins were determined manually in the section passing through the fovea centralis. These margins were drawn based on criteria defined by Boonarpha et al.[15]. The posterior edge of the hyperreflective band corresponding to the retinal pigment epithelium-Bruch's membrane complex was determined as the anterior border of the choriocapillaris. The posterior border of the choriocapillaris was demarcated as the hyperreflective band corresponding to the sclerochoroidal interface or the hyporeflective line corresponding to suprachoroidal space. In cases where these two anatomic structures could not be visualized, measurement was done using the prominent straight line corresponding to the posterior margin of the large choroidal vessels. Patients in whom choroidal margins could not be clearly distinguished were not included in the study.