Regional Distribution of Choroidal Thickness and Diurnal Variation in Choroidal Thickness and Axial Length in Young Adults

Purpose: To examine the regional distribution of choroidal thickness (ChT) and the diurnal variation in ChT and axial length (AL) over a wide range of myopic refractive error. Methods: ChT was measured in thirty-four healthy young adults (age mean +/- SD: 25.2 +/- 2.8, range: 18-35 years) using spectral-domain optical coherence tomography and AL using an IOL-Master 500. Participants were divided into three refractive groups: emmetropes, myopes, and high myopes. We evaluated ChT in macular (foveal, parafovea, and perifovea) and peripheral regions (6-mm from the foveal pit) in four quadrants (superior, temporal, inferior, and nasal). To assess the diurnal variation, three measurement sessions of ChT and AL were taken at 8 AM, 12 PM, 4 PM. Results: ChT thins progressively towards the periphery. Superior and nasal quadrants exhibited the thickest (277 +/- 73 mu m) and thinnest (218 +/- 89 mu m) choroid, respectively. Higher myopic eyes showed an overall thinner choroid (237 +/- 48 mu m) compared to myopic eyes (264 +/- 78 mu m) (P < 0.05). Higher myopes exhibited a significant choroidal thinning in all quadrants except in the temporal quadrant (all p < 0.05). Both ChT and AL underwent a significant diurnal variation (p < 0.05). The ChT and AL diurnal variation amplitudes in higher myopes were significantly reduced (ChT: 14.6 +/- 11, AL: 14.5 +/- 13 mu m), compared to those in emmetropes (ChT: 21.4 +/- 15, AL: 21.3 +/- 8.5 mu m) and myopes (ChT: 19 +/- 17, AL: 19 +/- 9.7 mu m). Diurnal variation amplitude in ChT did not differ significantly across quadrants and choroidal eccentricity regions (p > 0.05). Conclusion: ChT distribution varies based on quadrant and eccentricity; superior choroid exhibited the thickest, and nasal showed the thinnest choroid. Higher myopes experience a reduced diurnal variation in ChT and AL.