Liu Xiao Nicole, Yap Stephanie Ee Leen, Chen Xiao-Yu Eric, Philip Krupa, Naduvilath Thomas John, Sankaridurg Padmaja R
School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
Brien Holden Vision Institute, Sydney, Australia.
Curr Eye Res. 2025 Jan;50(1):101-109. doi: 10.1080/02713683.2024.2396383. Epub 2024 Sep 4.
Affecting one-third of the population worldwide and increasing, the sight-threatening condition myopia is causing a significant socio-economic burden. To better understand its etiology, recent studies investigated the role of ocular and systemic rhythms, yet results are conflicting. Here we profiled 24-h variations of axial length of the eye and salivary melatonin concentration in young adults with and without myopia and explored the potential impacts of bedtime on these rhythms.
A total of 25 healthy young adults (age 25.0 ± 4.8 years, 13 females) completed this study, including 13 myopes (mean spherical equivalent refractive error -2.93 ± 1.46 diopters) and 12 non-myopes (0.14 ± 0.42 diopters). Saliva sample collection and axial length measurements were repeated for seven times over 24 h starting from 8 am. Information on sleep and chronotype was collected at first visit with the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire.
Significant diurnal rhythms of axial length and salivary melatonin concentration were identified in both refractive groups (both < 0.001), with no myopia-related rhythm difference (interaction of measurement time-point × myopia, = 0.9). Late bedtime was associated with altered rhythms ( = 0.009) and smaller diurnal change ( = 0.01) in axial length. Elevated melatonin levels were observed in myopes ( = 0.006) and in late sleepers ( = 0.017).
These findings suggest that sleep/wake cycles may be involved in the regulation of axial length rhythms. Further research is needed to determine if there exists a causal relationship between the two.
