Variation of choroidal thickness during the waking period over three consecutive days in different degrees of myopia and emmetropia using optical coherence tomography

Purpose: To investigate the diurnal variation in subfoveal choroidal thickness (SFCT) during the waking period over three consecutive days in different degrees of myopia and emmetropia.Methods: A total of 60 adult volunteers were grouped into low, moderate, high myopia, and emmetropia subgroups. SFCT, axial length (AL), anterior chamber depth (ACD), and intraocular pressure (IOP) were measured every 2 h from 8 AM to 8 PM for three successive days.Results: The mean values of daily change amplitude were 3.18 mmHg (IOP), 0.05 mm (AL), 0.17 mm (ACD), and 13.51 mm (SFCT). The values of AL and ACD increased simultaneously with spherical equivalent refraction (SER), but SFCT was the opposite. IOP had a diurnal variation, and there was no difference among the four groups. AL of the high myopia group, ACD of the emmetropia group, and SFCT of each myopia group had diurnal variation over three consecutive days. AL had a high mean value at noon every day, and SFCT had a low mean value at noon every day.Conclusion: The choroid thickness of subjects with different degrees of myopia had a significant diurnal variation. The change of diurnal variation between emmetropic and myopic subjects may be one of the causes of myopia.