Light exposure and daily axial length variations in emmetropes and progressing myopes

Purpose Evidence from animal studies suggests that the eye’s natural diurnal rhythms are disrupted by altering the light/dark cycle and during refractive error development. Although diurnal variations in axial length (AxL) are well documented in human eyes, the relationship between ambient light exposure, refractive error progression and diurnal AxL variations is not well understood. Therefore, we aimed to quantify the ambient light exposure and daily variations in AxL in young adult emmetropes and progressing myopes. Method Sixteen emmetropes and 18 progressing myopes (mean age: 22 ± 4 years) had a series of AxL measurements collected ~every 3 hours from 9 am to 9 pm (i.e. 5 measurement sessions per day) using the Lenstar optical biometer. These daily AxL variations were assessed on a weekday and a weekend in winter and then six months later in summer. Personal ambient light exposure was also collected in winter and summer using wrist-worn light sensors (Actiwatch-2) worn for 14 days over the same period of time when the AxL measures were collected