AVEH African Vision and Eye Health 2413-3183 2410-1516 AOSIS AVEH-85-1166 10.4102/aveh.v85i1.1166 Original Research Short-term impact of natural daylight exposure on choroidal thickness in emmetropic young adults https://orcid.org/0000-0002-4409-6441 Aldakhil Sulaiman 1 Department of Optometry, College of Applied Medical Sciences, Qassim University, Buraydah, Saudi Arabia Corresponding author: Sulaiman Aldakhil, s.dakhil@qu.edu.sa

How to cite this article: Aldakhil S. Short-term impact of natural daylight exposure on choroidal thickness in emmetropic young adults. Afr Vision Eye Health. 2026;85(1), a1166. https://doi.org/10.4102/aveh.v85i1.1166

 23072026 2026 85 1 1166 21012026 15062026 © 2026. The Author 2026 Licensee: AOSIS. This work is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. Background

Exposure to light has been identified as an important factor in the control of eye growth and the development of refractive error.

 Aim

The aim of this article is to examine the short-term impact of natural daylight exposure on choroidal thickness (ChT).

 Setting

The study was conducted at Qassim University, Saudi Arabia.

 Methods

In this prospective study, 60 healthy emmetropic adults aged 19 years – 26 years completed comprehensive eye examinations. Choroidal thickness was measured using Swept-Source Optical Coherence Tomography with radial scans across macular regions. Two experimental sessions were conducted under indoor illumination (200 lux) and another involving 1 h of outdoor daylight exposure (~20 060 lux). Baseline indoor Optical Coherence Tomography scans were collected, followed by post-exposure scans obtained after 1 h of either indoor or outdoor light conditions. General linear model-repeated measure was used to examine ChT changes across light conditions and macular regions.

 Results

Across all macular regions, no statistically significant differences were found between baseline and post-exposure measurements (all p > 0.05), except in the inner temporal macular region (p = 0.046). Baseline subfoveal ChT was similar between sessions (297 μm ± 69 μm indoors; 298 μm ± 67 μm outdoors), with no changes after 1 h in both light conditions.

 Conclusion

The results showed that natural daylight exposure for 1 h produced no measurable changes in ChT under the conditions of this study, with all variations considered within normal diurnal fluctuations. Future research should consider factors that influence ocular responses, including diurnal variations in ChT and the characterisation of choroidal responses to light exposure.

 Contribution

This study provides evidence that the human choroid shows limited short-term responsiveness to light exposure, with all variations considered within normal diurnal fluctuations.

 choroid light exposure diurnal variations environment development of refractive error risk factors Funding information The author received no financial support for the research, authorship and/or publication of this article. Introduction

The choroid is a highly vascularised tissue located between the retina and the sclera. It plays a critical role in retinal metabolism by delivering oxygen and essential nutrients to the outer retina, specifically the photoreceptors and retinal pigment epithelium (RPE) layer.1 The choroid is also suggested to contribute for thermoregulation of the retina, secretion of growth factors and altering retinal positioning through changes in choroidal thickness (ChT).2 Numerous studies on emmetropisation and development of refractive error, in both animal models and human subjects3,4,5 provide substantial evidence that myopia development is related to changes in ChT.

Previous studies on the human choroid have reported an association between refractive error and/or axial length and ChT.4,5,6,7,8 They found that myopic eyes with longer axial length have a thinner choroid, while hyperopic eyes with shorter axial length have a thicker choroid. This choroidal thinning generally occurs at an early stage in the development of refractive error.

The choroid, like other ocular and systemic tissues, follows a circadian rhythm that regulates its anatomical and physiological processes. The study of Kinoshita et al.9 reported that diurnal variations in the choroid were primarily driven by variation in the luminal (vascular) choroidal area and not the stromal choroidal area. Choroidal blood flow has been shown to be autoregulated10 although evidence also indicates an association with systemic circulation. Circadian fluctuations in subfoveal choroidal thickness (SFChT) have been shown to correlate positively with circadian variations in systolic blood pressure11,12 and to be associated with circadian variations of sympathetic nervous system activity.13

Evidence from animal14 and human studies15,16,17,18 indicates that the choroid shows significant diurnal variations in thickness throughout the day. The synchronisation of choroidal circadian rhythms is critically dependent on the daily cycles of light exposure.9 Numerous research studies, conducted on both animal models and human eyes, have shown anti-phase fluctuations where the choroid is typically thinnest in the morning and thickest at night with an average amplitude of ~25 μm.14,15,17,18 Chakraborty et al.15 found that the mean changes in ChT over the course of the day (from 09:00 to 21:00) were 29 μm ± 16 μm (range, 11 μm – 79 μm). In human eyes, several studies have demonstrated that the normal diurnal rhythm of the choroid can be disrupted, and rapid ChT changes were found when imposed optical defocus.19,20 These studies have reported a rapid reduction in ChT in response to hyperopic defocus, and an increase in ChT in response to myopic defocus.

Evidence suggests that ChT may exhibit significant responsiveness to light exposure. Experimental studies in tree shrews and rhesus monkeys reared under red-light conditions exhibited hyperopia and slower eye growth, accompanied by a significant thickening of the choroid compared to control animals exposed to standard lighting conditions.21,22 It has been proposed that ChT changes generally occurred rapidly and were detected prior to the long-term effects in eye growth.23

Exposure to light has been identified as an important factor in controlling eye growth and the progression of myopia.24,25 Studies have shown that spending more time outdoors and high levels of light exposure can lower myopia onset and slow axial length elongation in children.26,27 Evidence from an interventional study in Chinese school children showed that increasing classroom illumination by about 400 lux significantly lowered the myopia incidence and elongation of axial length.28 One study showed that exposing young myopic adults to bright evening illumination of 1000 lux during the pre-sleep period for 1 week disrupted circadian rhythms and induced an in-phase shift in ChT amplitude.29 Another study conducted by Read et al.30 also indicated that 30 min of daily morning light exposure over 1 week led to a small but statistically significant increase in SFChT (mean increase +5.4 μm ± 10.3 μm). Previous findings demonstrated the potential role of light exposure in regulating ocular growth and suggested that even minor changes in ambient illumination may influence the development of myopia. The exposure to high levels of ambient light on ChT in the human eye has received comparatively limited investigation. However, the mechanism underlying the protective effects of exposure to sunlight remains insufficiently understood.31

A comparative analysis of ambient daylight illuminance across different geographical regions revealed substantial variations. In Singapore, daylight recordings in open fields ranged from 11 080 lux to 18 176 lux, while indoor levels were much lower, averaging 112 lux – 156 lux.32 Similarly, in the southern part of India, the highest outdoor illuminance was recorded in open playgrounds, with values of 9300 lux (range, 4100 lux – 16 825 lux).33 In contrast, European countries typically reported lower ambient daylight under overcast conditions; for example, measurements in Watford, England, showed outdoor illuminance levels of around 1000 lux.34 Notably, climatic conditions in Saudi Arabia, characterised by abundant sunshine and limited cloud cover, result in consistently high levels of natural daylight illuminance throughout the year. These variations in the ambient daylight levels between countries highlight the influence of geography and climate on natural daylight exposure and their potential role in eye growth and myopia development. Therefore, the aim of the present study is to examine the short-term impact of natural daylight exposure on ChT in young emmetropic subjects.

 Research methods and design Study design and participants

Sixty healthy emmetropic subjects aged between 19 years and 26 years (mean age of 22.4 years ± 1.9 years) participated in this prospective study. Prior to recruitment, each subject underwent a comprehensive eye examination to determine their refractive status. All participants had visual acuity of 6/6 or better with no ocular or systemic disease. Emmetropic subjects were defined as having a mean spherical equivalent refractive error between –0.25 D and +0.75 D (inclusive), with astigmatic refractive error limited to < 1.00 D.35 The refractive errors were measured objectively using a non-cycloplegic autorefractometer (NIDEK autorefractor [RK-310]). All participants were students at Qassim University and met the inclusion criteria. Those with amblyopia, ocular pathology, any ocular anomalies or systemic disease were excluded.

 Swept-Source Optical Coherence Tomography

A Swept-Source Optical Coherence Tomography (SS-OCT) (Triton DRI; Topcon, Inc., Tokyo, Japan) was used to measure ChT, and it has been described in previous studies as demonstrating high accuracy and repeatability.36,37,38,39 This device has an acquisition rate of 100 000 A-scans per second and utilises a centre wavelength of 1050 nm, providing an axial resolution of 8 μm in tissue. These features enable deeper tissue penetration beyond the RPE, allowing high-quality imaging of the choroid. Choroidal thickness was defined as the distance between the anterior boundary (outer border of the RPE and Bruch’s membrane complex) and the posterior boundary (choroid–sclera interface) (see Figure 1). The software of the SS-OCT Triton features an algorithm that allows automated segmentation of the retina and choroidal layers, enabling precise measurement of various thicknesses. In this experiment, a radial scan protocol was used to acquire the average thickness values across the nine subfields of a 6 mm × 6 mm macular area centred on the fovea, following the ETDRS (early treatment diabetic retinopathy study) grid. The ETDRS grid divides the macula into three concentric zones: (1) a single 1 mm central area, (2) an inner 3-mm ring and (3) an outer 6-mm ring. These are divided into four quadrants: (1) superior, (2) nasal, (3) inferior and (4) temporal. The central area of 1-mm diameter represents the baseline SFChT, whereas the 3-mm inner ring and 6-mm outer ring define the inner and outer macular regions (see Figure 1).40 Additionally, the device is equipped with a fundus-guided acquisition (FGA) mode, allowing precise alignment of scan locations for repeat imaging and enabling accurate comparisons.

Posterior pole area scanned with the Swept-Source Optical Coherence Tomography Triton using the radial scan protocol.

 Data collection procedures

In this study, a radial scan protocol was employed to obtain average ChT measurements across nine subfields of the macular region. All scan images with an image quality score of 45 or higher were included in the analysis. Each scan was manually reviewed, and any images with artefacts or misalignment were excluded from further evaluation. Data were collected from both eyes; however, only right-eye data were presented for analysis to avoid interocular correlation effects.41 All data were collected at the same time each day, between 10:00 and 11:00, to minimise potential confounding effects related to diurnal variation.12 Prior to the measurements, participants were instructed to refrain from consuming caffeinated or alcoholic beverages to reduce potential confounding influences of these substances on the thickness of the choroid.42,43 On each measurement day, participants were asked to sit in the Optical Coherence Tomography (OCT) room and perform a binocular distance viewing task for 20 min (watching video movie displayed at a 6-m distance) to avoid the potential confounding effects of any prior visual tasks or physical activity on the ChT.44,45

The OCT measurements were conducted during two separate experimental sessions, spaced 1 week apart, with each session lasting approximately 1 h. This experimental protocol was designed to evaluate the changes in ChT under different ambient illumination conditions while maintaining consistent imaging procedures with the use of FGA mode for enabling a serial comparison of images at the same area in the choroidal region.

Indoor light exposure

During the first experimental session, ChT measurements were obtained under controlled indoor conditions (OCT room), where ambient illumination was controlled and standardised at 200 lux and measured using a photometer (Testo 540; Testo SE & Co. KGaA, Lenzkirch, Germany). The device is equipped with a sensor aligned to the photopic spectral response, providing measurements consistent with human visual perception, with a reported accuracy of ±3%.46,47,48 Baseline measurements of ChT were acquired initially, followed by a subsequent measurement performed under the same illumination conditions after a 1 h interval.

 Outdoor light exposure

In the second experimental session, baseline ChT measurements were obtained under the same standardised indoor conditions (200 lux, OCT room). Participants were then seated outdoors in a shaded area, avoiding direct sunlight and exposed to natural daylight for 1 h before returning indoors for the post-exposure ChT measurements.

Outdoor illumination was measured using a photometer (Testo 540), and at the beginning of each session, three consecutive readings were obtained and averaged, resulting in a mean illuminance of ~20 060 lux (ranging from 19 350 lux to 21 290 lux). Environmental conditions, including weather and daylight fluctuations, were monitored, and measurements were conducted under clear, sunny conditions to minimise variability in light intensity.

 Statistical analysis

Data were first entered into Microsoft Excel, where the measurements of ChT were reviewed and checked for missing values. All statistical analyses were performed using SPSS statistical software, Version 24 (IBM Corp., Armonk, NY, US). Data are presented as mean ± standard deviation unless otherwise specified. General linear model-repeated measures were used to examine the changes in macular regions at indoor and outdoor light exposure. All measurements of the nine subfields of the macular region were analysed using a repeated measures general linear model-repeated measures where the within-subject factors were light exposure (indoor light exposure and outdoor light exposure vs. baseline measurements). This analytical approach has also been employed in previous studies to assess the changes in ChT.17,18,20

 Ethical considerations

Ethical clearance to conduct this study was obtained from the Qassim University Committee of Research Ethics (No. 25-11-16).

 Results Demographic features of the participants

The study included 60 subjects aged between 18 years and 25 years, with a mean age of 22.4 years ± 1.9 years. Among the participants, 34 (56.70%) were female. The one-sample Kolmogorov–Smirnov test demonstrated that ChT measurements in the nine subfields of the macular region did not significantly deviate from a normal distribution (p > 0.05). The mean spherical equivalent refractive error was –0.08 D ± 0.38 D.

 Baseline choroidal thickness and the mean changes in the nine subfields of the macular region following 1 h of indoor and outdoor light exposure

Baseline ChT and its changes after 1 h of indoor and outdoor light exposure were assessed across the nine subfields of the macular region, as shown in Table 1. At the SFChT region, the mean baseline ChT was 297 μm ± 69 μm indoors and 298 μm ± 67 μm outdoors. After 1 h, minimal changes were observed, with values of 298 μm ± 69 μm indoors and 299 μm ± 67 μm outdoors (p = 0.673), indicating no statistically significant difference as shown in Figure 2.

Baseline choroidal thickness and the mean changes in the nine subfields of the macular region following 1 h of indoor and outdoor light exposure.

Macular region Indoor baseline (μm) 95% CI Indoor 1 h (μm) 95% CI Outdoor baseline (μm) 95% CI Outdoor 1 h (μm) 95% CI p-value
SFChT 297 ± 69 279–315 298 ± 69 281–316 298 ± 67 280–315 299 ± 67 281–316 0.673
Inner superior 296 ± 73 277–314 296 ± 76 276–315 299 ± 72 280–317 298 ± 73 279–317 0.401
Outer superior 298 ± 67 281–316 300 ± 64 284–317 300 ± 67 283–317 299 ± 66 282–316 0.749
Inner nasal 280 ± 63 264–296 280 ± 63 264–296 281 ± 62 266–297 283 ± 65 266–300 0.665
Outer nasal 245 ± 62 229–261 247 ± 63 231–263 245 ± 62 229–260 247 ± 62 231–262 0.361
Inner inferior 300 ± 72 283–319 300 ± 71 282–319 301 ± 70 283–319 303 ± 70 285–322 0.689
Outer inferior 301 ± 67 284–318 302 ± 71 284–320 304 ± 68 287–321 304 ± 68 286–321 0.321
Inner temporal 295 ± 64 278–312 291 ± 64 274–307 291 ± 61 275–308 291 ± 63 275–308 0.046
Outer temporal 279 ± 56 264–294 278 ± 56 264–292 281 ± 55 267–295 280 ± 56 265–294 0.645

SFChT, subfoveal choroidal thickness; CI, confidence interval; h, hour.

Mean change in choroidal thickness following one hour of indoor and outdoor light exposure: (a) Choroidal thickness at central foveal (b) Inner nasal choroidal thickness (c) Outer nasal choroidal thickness (d) Inner temporal choroidal thickness.

For the inner superior region, thickness remained stable (296 μm ± 73 μm at baseline compared to 296 μm ± 76 μm after indoor; 299 μm ± 72 μm compared to 298 μm ± 73 μm outdoors), with p = 0.401. Similarly, the outer superior region showed insignificant variation (298 μm ± 67 μm compared to 300 μm ± 64 μm indoors; 300 μm ± 67 μm vs. 299 μm ± 66 μm outdoors; p = 0.749).

The inner nasal and outer nasal areas exhibited slight increases after outdoor light exposure (inner nasal: 281 μm ± 62 μm to 283 μm ± 65 μm; outer nasal: 245 μm ± 62 μm to 247 μm ± 62 μm), but these changes were not statistically significant (p = 0.665 and 0.361, respectively), as presented in Figure 2.

For the inner inferior and outer inferior regions, thickness values remained consistent across conditions (inner inferior: 300 μm ± 72 μm compared to 300 μm ± 71 μm indoors; 301 μm ± 70 μm compared to 303 μm ± 70 μm outdoors; p = 0.689; outer inferior: 301 μm ± 67 μm compared to 302 μm ± 71 μm indoors; 304 μm ± 68 μm compared to 304 μm ± 68 μm outdoors; p = 0.321).

Interestingly, the inner temporal region showed a slight decrease indoors (295 μm ± 64 μm to 291 μm ± 64 μm) and remained unchanged outdoors (291 μm ± 61 μm to 291 μm ± 63 μm), though this was not statistically significant (p = 0.046) as presented in Figure 2. The outer temporal meridian exhibited minimal variation (279 μm ± 56 μm to 278 μm ± 56 μm indoors; 281 μm ± 55 μm to 280 μm ± 56 μm outdoors; p = 0.645).

Overall, no statistically significant differences in ChT were observed between indoor and outdoor light exposure or across time points (all p > 0.05), except in the inner temporal macular region (p = 0.046). This finding suggests that short-term exposure to natural daylight does not produce clinically significant changes in ChT.

Post-hoc analysis of inner temporal ChT (Table 2) showed a small but significant decrease from baseline to 1 h under indoor light exposure (mean difference = 4.33 μm, p = 0.015) and from indoor baseline to outdoor baseline (mean difference = 4.20 μm, p = 0.027). However, no significant differences were observed between indoor and outdoor conditions at the 1 h time point or between outdoor baseline and outdoor after 1 h (all p > 0.05). Overall, these findings indicate that short-term light exposure was associated with modest, condition-specific changes in inner temporal ChT, without consistent differences between indoor and outdoor environments.

Post-hoc pairwise multiple comparisons of choroidal thickness changes in the inner temporal region after 1 h of indoor and outdoor light exposure.

(I) ChT (μm) (J) ChT (μm) Mean difference (I–J) s.e. p-value 95% CI for difference
Lower bound Upper bound
Indoor baseline Indoor 1 h 4.333 1.727 0.015 0.878 7.789
Outdoor baseline 4.200 1.847 0.027 0.503 7.897
Outdoor 1 h 3.700 2.415 0.131 −1.132 8.532
Indoor 1 h Indoor baseline −4.333 1.727 0.015 −7.789 −0.878
Outdoor baseline −0.133 2.114 0.950 −4.364 4.097
Outdoor 1 h −0.633 2.589 0.808 −5.815 4.548
Outdoor baseline Indoor baseline −4.200 1.847 0.027 −7.897 −0.503
Indoor 1 h 0.133 2.114 0.950 −4.097 4.364
Outdoor 1 h −0.500 1.973 0.801 −4.448 3.448
Outdoor 1 h Indoor baseline −3.700 2.415 0.131 −8.532 1.132
Indoor 1 h 0.633 2.589 0.808 −4.548 5.815
Outdoor baseline 0.500 1.973 0.801 −3.448 4.448

ChT, choroidal thickness; CI, confidence interval; h, hour; s.e., standard error; I, the reference group; J, the comparison group.

 Discussion

The results of this study showed no significant changes in ChT after 1 h of short-term daylight exposure in emmetropic subjects. Our data showed no significant differences across all macular regions under both indoor and outdoor light exposure. A small increase (~2 μm) was observed in the inner and outer nasal macular regions following outdoor light exposure; however, these changes were not statistically significant (p = 0.665 and 0.361, respectively), as shown in Figure 2. These findings differ slightly from those reported by Read et al.,30 who reported that after 30 min of daily morning light exposure over 1 week produced a small but statistically significant increase in SFChT in young participants aged 20 years – 29 years (mean increase +5.4 μm ± 10.3 μm; 95% CI, +0.8 μm to +9.9 μm; p = 0.02). They also found that the changes in ChT across all macular regions were also very small ranged from +3.2 μm ± 7.9 μm to +5.4 μm ± 10.3 μm.

The repeatability of automated ChT measurements using SS-OCT has been reported previously,36,37,38,39 with this technique achieving an axial resolution of 8 μm. In this study, the observed changes in ChT fall within the expected range of measurement variability.

Consideration of the diurnal fluctuations in ChT is essential when evaluating the impact of daylight exposure on ChT. Chakraborty et al.15 demonstrated that the choroid was typically thinnest in the morning and thickest at night, and they found that the mean changes in ChT over 1 day (from 09:00 to 21:00) were 29 μm ± 16 μm (range, 11 μm – 79 μm). This substantial diurnal variability in ChT introduces significant challenges as it can obscure or confound the detection of ChT alterations during the daylight exposure, particularly when the exposure period exceeds 1 h.49 Lou and Ostrin50 examined the effects of 1 h of narrowband light exposure on ChT in humans, similarly the study of Read et al.30 investigated the effect of 30 min of daily morning light exposure on ChT in healthy young adults. These studies adopted a short exposure duration to reduce the influence of diurnal variation in ChT.

In human eyes, few studies have shown that the normal diurnal rhythm of the ChT can be disrupted, and changes in ChT were observed during daylight exposure.29,30 However, the magnitude of changes in the ChT after the short-term exposure to bright light was relatively small compared with the animal studies, particularly in chicks that have shown a relatively larger amount of ChT changes after a similar short period of bright light exposure. Evidence from a chick model study further demonstrated that a 2 h light exposure administered during the middle of the night disrupted the normal sinusoidal diurnal rhythm of ChT. The results showed that ChT in experimental eyes changed by a mean of 9 μm compared to control animals exposed to a normal light–dark cycle.51 Another animal study also suggests that the chicks’ ocular response when imposed optical defocus and form deprivation varies according to the time of day of exposure, at which the stimulus regulating eye growth exhibits diurnal variation in its sensitivity and is strongly influenced by the timing of exposure.52,53 The differing magnitudes of ChT changes reported in humans and animal models indicate fundamental species-specific differences in choroidal responsiveness to bright-light exposure, reflecting structural and anatomical differences between the chick and human choroid.

Although daylight exposure may show an association with increases in ChT, the underlying mechanism remains incompletely understood. One study proposed a plausible pathway in which light-induced elevations in retinal dopamine trigger nitric oxide release, subsequently leading to choroidal thickening in the chick eye.54 This mechanism may also be relevant in humans, given established evidence that increased light exposure modulates retinal dopamine levels55 and that nitric oxide plays a key role in regulating choroidal blood flow under varying illumination conditions.56 The association between ambient light exposure and circadian rhythms makes it challenging to distinguish the relative influence of choroidal thickening arising directly from increased light exposure compared with changes occurring indirectly through circadian rhythms. Accordingly, further investigation is needed to clarify the relative contributions of these mechanisms and their potential interactions to the choroidal changes observed following light therapy.

An important methodological limitation of the current study is that participants continued their habitual daily routines across the two measurement days, introducing the potential for day-to-day variability in environmental exposures that may have influenced the observed outcomes. In addition, the order of indoor and outdoor sessions was not randomised, which may have introduced potential order effects. Blood pressure and intraocular pressure were not assessed in this study, representing an additional limitation. Another potential limitation was the absence of axial length measurements in the current experimental protocol although some studies have shown that the relationship between changes in axial length and ChT is non-linear.30,57 Future studies should consider randomising the order of light-exposure sessions and include measurements of axial length, intraocular pressure and blood pressure, which may provide a more comprehensive assessment of the changes in ChT.

 Conclusion

This study found that 1 h of natural daylight exposure does not produce measurable changes in ChT in emmetropic adults under the conditions of this study. The observed variations remained within the range of physiological diurnal fluctuation, and regional differences were minimal and not statistically significant. These results suggest that the human choroid may exhibit limited short-term responsiveness to light exposure compared with findings reported in animal models. Future research should consider factors that influence ocular responses, including diurnal variations in ChT and the characterisation of choroidal responses to light exposure.

 Acknowledgements Competing interests

The author, Sulaiman Aldakhil, declares that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.

 CRediT authorship contribution

Sulaiman Aldakhil: Conceptualisation, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualisation, Writing – original draft, Writing – review & editing. The author confirms that this work is entirely their own, has reviewed the article, approved the final version for submission and publication and takes full responsibility for the integrity of its findings.

 Data availability

The data that support the findings of this study are not openly available and are available from the corresponding author, Sulaiman Aldakhil, upon reasonable request.

 Disclaimer

The views and opinions expressed in this article are those of the author and are the product of professional research. They do not necessarily reflect the official policy or position of any affiliated institution, funder, agency or that of the publisher. The author is responsible for this article’s results, findings and content.

 References Remington LA. Clinical anatomy and physiology of the visual system. 3rd ed. St Louis, MO: Elsevier; 2012. Nickla DL, Wallman J. The multifunctional choroid. Prog Retin Eye Res. 2010;29(2):144–168. https://doi.org/10.1016/j.preteyeres.2009.12.002 Nickla DL, Jordan K, Yang J. Brief hyperopic defocus or form deprivation have varying effects on eye growth and ocular rhythms depending on the time of day of exposure. Exp Eye Res. 2013;116:71–81. Alrasheed SH, Gammoh Y. Characteristics of the retinal and choroidal thicknesses in myopic young adult males using swept-source optical coherence tomography. PeerJ. 2025;13:e19030. https://doi.org/10.7717/peerj.19030 Ikuno Y, Kawaguchi K, Nouchi T, Yasuno Y. Choroidal thickness in healthy Japanese subjects. Invest Ophthalmol Vis Sci. 2010;51(4):2173–2176. https://doi.org/10.1167/iovs.09-4383 Wang S, Wang Y, Gao X, Qian N, Zhuo Y. Choroidal thickness and high myopia: A cross-sectional study and meta-analysis. BMC Ophthalmol. 2015;15(1):70. https://doi.org/10.1186/s12886-015-0059-2 Li XQ, Jeppesen P, Larsen M, Munch IC. Subfoveal choroidal thickness in 1323 children aged 11 to 12 years and association with puberty: The Copenhagen Child Cohort 2000 Eye Study. Invest Ophthalmol Vis Sci. 2014;55(1):550–555. https://doi.org/10.1167/iovs.13-13476 Jin P, Zou H, Zhu J, et al. Choroidal and retinal thickness in children with different refractive status measured by swept-source optical coherence tomography. Am J Ophthalmol. 2016;168:164–176. https://doi.org/10.1016/j.ajo.2016.05.008 Kinoshita T, Mitamura Y, Shinomiya K, et al. Diurnal variations in luminal and stromal areas of choroid in normal eyes. Br J Ophthalmol. 2017;101(3):360–364. Polska E, Simader C, Weigert G, et al. Regulation of choroidal blood flow during combined changes in intraocular pressure and arterial blood pressure. Invest Ophthalmol Vis Sci. 2007;48(8):3768–3774. https://doi.org/10.1167/iovs.07-0307 Usui S, Ikuno Y, Akiba M, et al. Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects. Invest Ophthalmol Vis Sci. 2012;53(4):2300–2307. https://doi.org/10.1167/iovs.11-8383 Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral-domain optical coherence tomography. Invest Ophthalmol Vis Sci. 2012;53(1):261–266. https://doi.org/10.1167/iovs.11-8782 Tan CS, Lim LW, Chow VS, et al. Diurnal variation of choroidal thickness in normal, healthy subjects measured by enhanced depth imaging optical coherence tomography. Invest Ophthalmol Vis Sci. 2016;57(2):478–486. Nickla DL. Ocular diurnal rhythms and eye growth regulation: Where we are 50 years after Lauber. Exp Eye Res. 2013;114:25–34. https://doi.org/10.1016/j.exer.2012.12.013 Chakraborty R, Read SA, Collins MJ. Diurnal variations in axial length, choroidal thickness, intraocular pressure, and ocular biometrics. Invest Ophthalmol Vis Sci. 2011;52(8):5121–5129. https://doi.org/10.1167/iovs.11-7364 Seidel G, Aschinger GC, Singer G, et al. Circadian macular volume changes in the healthy human choroid. Am J Ophthalmol. 2015;159(2):365–371.e2. https://doi.org/10.1016/j.ajo.2014.11.002 Read SA, Collins MJ, Iskander DR. Diurnal variation of axial length, intraocular pressure, and choroidal thickness in human eyes. Invest Ophthalmol Vis Sci. 2010;51(11):5479–5485. Chakraborty R, Read SA, Collins MJ. Monocular myopic defocus and daily changes in axial length and choroidal thickness of human eyes. Exp Eye Res. 2012;103:47–54. https://doi.org/10.1016/j.exer.2012.08.002 Chakraborty R, Read SA, Collins MJ. The temporal relationship between axial length and choroidal thickness changes during imposed defocus. Invest Ophthalmol Vis Sci. 2013;54(13):8134–8143. Chiang ST, Phillips JR, Backhouse S. Effect of retinal image defocus on the thickness of the human choroid. Ophthalmic Physiol Opt. 2015;35(4):405–413. https://doi.org/10.1111/opo.12218 Gawne TJ, Ward AH, Norton TT. Long-wavelength (red) light produces hyperopia in juvenile and adolescent tree shrews. Vision Res. 2017;140:55–65. https://doi.org/10.1016/j.visres.2017.07.011 Gawne TJ, Siegwart JT, Jr, Ward AH, Norton TT. The wavelength composition and temporal modulation of ambient lighting strongly affect refractive development in young tree shrews. Exp Eye Res. 2017;155:75–84. https://doi.org/10.1016/j.exer.2016.12.004 Hung LF, Arumugam B, She Z, Ostrin L, Smith EL, III. Narrow-band, long-wavelength lighting promotes hyperopia and retards vision-induced myopia in infant rhesus monkeys. Exp Eye Res. 2018;176:147–160. https://doi.org/10.1016/j.exer.2018.07.004 Norton TT, Siegwart JT. Light levels, refractive development, and myopia: A speculative review. Exp Eye Res. 2013;114:48–57. https://doi.org/10.1016/j.exer.2013.05.004 Ramamurthy D, Lin Chua SY, Saw SM. A review of environmental risk factors for myopia during early life, childhood, and adolescence. Clin Exp Optom. 2015;98(6):497–506. https://doi.org/10.1111/cxo.12346 Rose KA, Morgan IG, Ip J, et al. Outdoor activity reduces the prevalence of myopia in children. Ophthalmology. 2008;115(8):1279–1285. https://doi.org/10.1016/j.ophtha.2007.12.019 Read SA, Collins MJ, Vincent SJ. Light exposure and eye growth in childhood. Invest Ophthalmol Vis Sci. 2015;56(11):6779–6787. https://doi.org/10.1167/iovs.14-15978 Hua WJ, Jin JX, Wu XY, et al. Elevated light levels in schools have a protective effect on myopia. Ophthalmic Physiol Opt. 2015;35(3):252–262. https://doi.org/10.1111/opo.12207 Ahn J, Ahn SE, Yang KS, Kim SW, Oh J. Effects of a high level of illumination before sleep at night on chorioretinal thickness and ocular biometry. Exp Eye Res. 2017;164:157–167. https://doi.org/10.1016/j.exer.2017.09.001 Read SA, Pieterse EC, Alonso-Caneiro D, et al. Daily morning light therapy is associated with an increase in choroidal thickness in healthy young adults. Sci Rep. 2018;8(1):8200. https://doi.org/10.1038/s41598-018-26635-7 Chakraborty R, Ostrin LA, Nickla DL, Iuvone PM, Pardue MT, Stone RA. Circadian rhythms, refractive development, and myopia. Ophthalmic Physiol Opt. 2018;38(3):217–245. https://doi.org/10.1111/opo.12453 Lanca C, Teo A, Vivagandan A, et al. The effects of different outdoor environments, sunglasses, and hats on light levels: Implications for myopia prevention. Transl Vis Sci Technol. 2019;8(4):7. https://doi.org/10.1167/tvst.8.4.7 Bhandary SK, Dhakal R, Sanghavi V, Verkicharla PK. Ambient light level varies with different locations and environmental conditions: Potential to impact myopia. PLoS One. 2021;16(7):e0254027. https://doi.org/10.1371/journal.pone.0254027 Ticleanu TC, Littlefair PJ. Melanopic equivalent daylight illuminance in Watford, Southern England: Comparisons to daylight exposure recommendations. J Environ Light Res. 2025;18(3):210–222. McBrien NA, Millodot M. Clinical evaluation of the refractive status of the eye. Am J Optom Physiol Opt. 1986;63(1):46–51. Mansouri K, Medeiros FA, Tatham AJ, Marchasea N, Weinreb RN. Assessment of choroidal thickness and volume using swept-source optical coherence tomography and their relationship with visual field sensitivity in glaucoma. Am J Ophthalmol. 2014;157(5):936–944.e2. https://doi.org/10.1016/j.ajo.2014.02.008 Mansouri K, Medeiros FA, Marchase N, Tatham AJ, Weinreb RN. Comparison of anterior and posterior segment optical coherence tomography for measurement of anterior chamber depth. Invest Ophthalmol Vis Sci. 2013;54(3):1321–1327. Copete S, Flores-Moreno I, Montero JA, Duker JS, Ruiz-Moreno JM. Direct comparison of spectral-domain and swept-source OCT in the measurement of choroidal thickness in normal eyes. Br J Ophthalmol. 2014;98(3):334–338. https://doi.org/10.1136/bjophthalmol-2013-303904 Alkhaldi SA, Aldakhil S, Gray LS. Choroidal thickness measurements in different ethnicities using swept-source optical coherence tomography: Repeatability and assessment. Clin Exp Optom. 2022;105(5):527–533. https://doi.org/10.1080/08164622.2021.1943319 Tan CS, Cheong KX. Macular choroidal thicknesses in healthy adults: Relationship with ocular and demographic factors. Invest Ophthalmol Vis Sci. 2015;56(9):4944–4953. Newcombe RG, Duff GR. Eyes or patients? Traps for the unwary in the statistical analysis of ophthalmological studies. Br J Ophthalmol. 1987;71(9):645–646. https://doi.org/10.1136/bjo.71.9.645 Altinkaynak H, Ceylan E, Kartal B, Keleş S, Ekinci M, Olcaysu OO. Measurement of choroidal thickness following caffeine intake in healthy subjects. Curr Eye Res. 2016;41(5):708–714. Kang HM, Woo YJ, Koh HJ, Lee CS, Lee SC. The effect of ethanol consumption on subfoveal choroidal thickness in the acute phase. Br J Ophthalmol. 2016;100(3):383–388. https://doi.org/10.1136/bjophthalmol-2015-306969 Mallen EA, Kashyap P, Hampson KM. Transient axial length change during the accommodation response. Ophthalmic Physiol Opt. 2006;26(4):497–501. Read SA, Collins MJ. The short-term influence of exercise on axial length and choroidal thickness in human eyes. Invest Ophthalmol Vis Sci. 2011;52(6):3769–3775. Zhang M, Zhang R, He M, et al. Self correction of refractive error among young people in rural China: Results of cross sectional investigation. BMJ. 2011;343:d4767. https://doi.org/10.1136/bmj.d4767 Eppig T, Speck A, Gillner M, Nagengast D, Langenbucher A. Photochromic dynamics of ophthalmic lenses. App Opt. 2012;51(2):133–138. https://doi.org/10.1364/AO.51.000133 Nyman TJ, Lampinen JM, Antfolk J, Korkman J, Santtila P. The distance threshold of reliable eyewitness identification. Law Hum Behav. 2019;43(6):527. https://doi.org/10.1037/lhb0000342 Woodman EC, Read SA, Collins MJ. Axial length and choroidal thickness changes accompanying prolonged accommodation in myopes and emmetropes. Vision Res. 2012;72:34–41. https://doi.org/10.1016/j.visres.2012.09.009 Lou L, Ostrin LA. Effects of narrowband light on choroidal thickness and the pupil. Invest Ophthalmol Vis Sci. 2020;61(10):40. https://doi.org/10.1167/iovs.61.10.40 Nickla DL, Totonelly K. Brief light exposure at night disrupts circadian rhythms in eye growth and choroidal thickness in chicks. Exp Eye Res. 2016;146:185–195. https://doi.org/10.1016/j.exer.2016.03.003 Nickla DL, Jordan K, Yang J, Totonelly K. Brief hyperopic defocus or form deprivation have varying effects on eye growth and ocular rhythms depending on time of day of exposure. Exp Eye Res. 2017;161:132–142. https://doi.org/10.1016/j.exer.2017.06.003 Nickla DL, Thai P, Zanzerkia Trahan R, Totonelly K. Myopic defocus in the evening is more effective at inhibiting eye growth than defocus in the morning: Effects on rhythms in axial length and choroid thickness in chicks. Exp Eye Res. 2017;154:104–115. https://doi.org/10.1016/j.exer.2016.11.012 Lan W, Feldkaemper M, Schaeffel F. Bright light induces choroidal thickening in chickens. Optom Vis Sci. 2013;90(10):1199–1206. https://doi.org/10.1097/OPX.0000000000000074 Brainard GC, Morgan WW. Light-induced stimulation of retinal dopamine: A dose–response relationship. Brain Res. 1987;424:199–203. https://doi.org/10.1016/0006-8993(87)91211-X Huemer KH, Garhofer G, Aggermann T, Kolodjaschna J, Schmetterer L, Fuchsjäger-Mayrl G. Role of nitric oxide in choroidal blood flow regulation during light/dark transitions. Invest Ophthalmol Vis Sci. 2007;48:4215–4219. https://doi.org/10.1167/iovs.07-0176 Read SA, Collins MJ, Sander BP. Human optical axial length and defocus. Invest Ophthalmol Vis Sci. 2010;51(12):6262–6269. https://doi.org/10.1167/iovs.10-5457