In new research published in the British Journal of Ophthalmology, investigators analyzed the short-term effect of different intensities of sunlight exposure on blood-flow perfusion (BFP) after reading.
Give me some background first.
Previous research has found that increased intensity and duration of sunlight exposure may reduce the risk of developing myopia.
- Additionally: Altered fundus blood flow is considered to play a role in the pathogenesis of myopia and serves as a predictive indicator for myopia development.
To back this up: Clinical studies have demonstrated that myopic patients often exhibit diminished choroidal and retinal BFP, contributing to scleral hypoxia and subsequent myopia progression.
Now, talk about the study.
Investigators conducted a parallel, randomized controlled trial (RCT) at the China-based Shanghai Eye Disease Prevention and Treatment Center from August to September 2022.
Participants selected were randomly assigned to either:
- Low-illuminance (4k lux) group
- N=40
- High-illuminance (10k lux) group
- N=41
Who was included in the study?
Out of 139 individuals assessed for eligibility, a total of 81 participants were included in the analysis with the following criteria:
- Aged 7 to 15
- A spherical equivalent refraction between -2.00 and +3.00 diopters
And how was it conducted?
Following 1 hour of indoor (with a luminance of 2k lux) reading (at a distance of 33 cm), participants received sunlight exposure at the intensity assigned to their respective group.
- Exposure duration: 15 minutes
Then: BFPs in the superficial retina, deep retina, and choroid were measured at:
- Pre-reading
- Post-reading
- Sunlight exposure timepoints
- 5 minutes
- 15 minutes
Findings?
The authors found that exposure to sunlight could mitigate the elevation of BFP caused by near work.
Case in point: Within the initial 5 minutes of sunlight exposure:
- 10k lux group showed a tendency for decreased BFP, particularly in the choroid:
- Superficial retina
- -0.2, 95% Confidence Interval (CI) -0.9 to 0.5
- Deep retina
- -0.1, 95% CI -0.6 to 0.4
- Choroid
- -0.4, 95% CI -0.8 to 0.0
- Superficial retina
- 4k lux group exhibited an increase in BFP
- Superficial retina
- 0.7, 95% CI 0.1 to 1.3
- Deep retina
- 0.3, 95% CI -0.2 to 0.8
- Choroid
- 0.1, 95% CI -0.2 to 0.5
- Superficial retina
Tell me more.
From 5 to 15 minutes, BFP decreased in both groups.
Further: At the 5-minute mark, the 10k lux group exhibited a greater decrease in choroid BFP.
- 10k -0.4 vs 4k 0.1, p=0.051
Notably, while 10k-lux sunlight was found to reverse the choroidal BFP within 5 minutes, this was not observed with 4k-lux sunlight.
Ultimately: No significant difference was observed after 15 minutes of exposure.
Any limitations?
The duration of sunlight exposure was short—and only two light intensities were compared.
The study authors also noted that participants may have become distracted during the 1-hour reading period, potentially affecting initial post-reading BFP.
- Why this matters: This could have decreased the significance level of the changes after sunlight exposure.
Lastly: Variations in systolic blood pressure may have impacted retinal and choroidal blood vessels.
Expert opinion?
The authors recommended, “To prevent myopia, continuous sunlight exposure for over 15 minutes is recommended to aid in reinstating the fundus BFP increased by near work.”
Take home.
Higher-intensity sun exposure may restore fundus BFP faster than lower-intensity sun exposure—however, duration is crucial.