For optimal eye health, it’s important to stay healthy overall—many diseases that come later in life, like diabetes or hypertension, can affect your eyes and your vision. The quality of your sight and the health of your retinal cells as you age will depend on how many retinal cells you have left and their condition. Your eyes also need sunlight to regulate your circadian rhythm and keep you alert during the day, but too much light exposure—especially UV—can cause lasting damage. There’s a balance to be struck between getting enough natural light for good health, and protecting your eyes from harm. Here’s a summary of the key facts, practical recommendations, and the scientific background to help you manage that balance.
There is substantial epidemiological evidence suggesting that consistent use of sunglasses or other UV-blocking eyewear significantly reduces the risk of cataract formation. A population-based study in rural China demonstrated that participants who reported always wearing glasses or sunglasses had 57–70% lower odds of developing cataracts compared to non-wearers (Chen et al., 2021). Similarly, data from the Beaver Dam Eye Study in the United States indicated that men with higher levels of lifetime ambient UVB exposure had a 1.36-fold increased risk of cortical cataract (Cruickshanks et al., 1993). Notably, this association was not observed in women, highlighting the potential influence of behavioral or hormonal modifiers.
Additional evidence from Australia showed that individuals with high sun exposure during their 20s had markedly elevated risks of nuclear cataract, with odds ratios approaching 5.9 in the highest exposure group. Wearing sunglasses or a hat was associated with a protective effect in this context (Neale et al., 2003). A Spanish case–control study reported more modest differences in sunglasses use between cases and controls (47% vs. 53%, respectively), but still suggested a small protective trend (Delcourt et al., 2000).
Overall, the data support the role of UV protection in cataract prevention, with sunglasses use associated with up to a 70% reduction in risk, particularly for cortical and nuclear cataract subtypes.
Sunlight, UV Exposure, and Circadian Rhythm Regulation: A Swiss Context
1. Natural Light: Timing, Intensity, and Eye Health
UV intensity in Switzerland varies considerably with time of day, weather, season, and altitude. In low-altitude regions like Basel (~260 m), clear-sky UV indices reach ~8–9 at midday during summer, while in high-altitude areas like Davos (~1,560 m), they can exceed 10–11 due to the ~10–12% UV increase per 1000 m elevation gain (WHO, 2010; Blumthaler et al., 1997). UV radiation is highest around noon and lowest in the early morning and late afternoon.
| Time of Day | Clear Sky UV Index (Basel) | Clear Sky UV Index (Davos) | Typical Lux (Clear Sky) |
|---|---|---|---|
| 08:00 AM | ~2–3 | ~3–4 | ~20,000–30,000 |
| 12:00 PM | ~8–9 | ~9–11 | ~100,000 |
| 04:00 PM | ~2–3 | ~3–4 | ~20,000–30,000 |
Under cloudy or rainy conditions, UV is significantly reduced, but not eliminated; up to 30–80% can still penetrate depending on cloud thickness (Feister & Grewe, 1995). Snow reflects up to 80% of UV radiation, which can double effective exposure to the eye on bright winter days (WHO, 2010).
2. Cataract Risk and UV Exposure
Cumulative UV exposure, particularly UV-B, is a major risk factor for cortical cataract development. The World Health Organization estimates that up to 20% of cataracts globally are attributable to UV radiation (WHO, 2010). The eye’s natural lens absorbs UV-B and much of UV-A, leading to oxidative stress and long-term lens protein damage (West et al., 2013).
Midday sun exposure is especially damaging: UV index levels of 8–10 correspond to significant biological effects, including increased risks for photokeratitis and cataracts (Lucas et al., 2006). Therefore, eye protection during this time is highly recommended.
3. Sunglasses: Transmission and Protection
Sunglasses are categorized based on their Visible Light Transmission (VLT) and UV protection. High-quality sunglasses marked “UV400” block >99% of both UVA and UVB radiation regardless of VLT.
| Category | VLT (%) | Recommended Use | UV Protection |
| Cat 2 | 18–43 | Cloudy to moderate sun | ~100% (UV400) |
| Cat 3 | 8–18 | Bright sun, everyday outdoor use | ~100% (UV400) |
| Cat 4 | 3–8 | High-altitude, snowfields | ~100% (UV400) |
Note: Cat 4 lenses are not suitable for driving due to extreme tint.
4. Circadian Rhythm and Light Exposure Timing
The circadian system is most sensitive to blue light (~460–480 nm), particularly in the early morning hours (Khalsa et al., 2003; Hattar et al., 2002). Brief exposure to natural light shortly after waking—within the first 1–2 hours—provides the strongest entrainment signal for the central clock in the suprachiasmatic nucleus (SCN).
Morning sunlight, even at moderate intensity, has a disproportionately strong effect on shifting circadian phase compared to light exposure at other times of the day (Wright et al., 2013; Czeisler et al., 1999).
Therefore, the optimal daily practice is:
- Expose the eyes to 20–30 minutes of outdoor natural light in the morning (ideally before 9–10 AM) without sunglasses.
- Use sunglasses for the remainder of the day, especially around noon and early afternoon, when UV radiation is high but further circadian benefit is minimal.
This allows for effective circadian entrainment while minimizing cumulative UV-induced eye damage.
5. Reflective Surfaces and UV Amplification
Reflective surfaces significantly amplify UV exposure:
| Surface | UV Reflectivity (%) |
| Fresh snow | ~80 |
| Sand | ~10–15 |
| Water (still) | <10 |
| Sea foam | ~25 |
People at high altitudes or around snow and water should be especially cautious during daylight hours, particularly between 10 AM and 3 PM.
6. Artificial Light and Circadian Stimulation
Indoor lighting and digital screens offer far lower light intensity than natural sunlight:
| Source | Illuminance (lux) |
| Clear daylight | 50,000–100,000 |
| Cloudy daylight | 2,000–10,000 |
| Wake-up light lamp | ~200–300 |
| Office lighting | ~300–500 |
| Phone/monitor | <100 |
While wake-up lights can assist in simulating dawn and support circadian timing, they are not a substitute for outdoor light. In contrast, even low levels of artificial light at night (as little as 8 lux) can suppress melatonin and delay circadian phase (Harvard Health, 2020).
To summarise the specific Eye regions and what you could do For its health:
Corneal Health:
- Why It Matters: The cornea plays a crucial role in clear vision and even influences your natural day–night rhythm. When the surface of the eye is impaired, such as with dry eyes or inflammation from blepharitis, you might experience discomfort and increased fatigue.
- Practical Steps:
- Use preservative-free artificial tears if you experience dryness.
- Apply warm compresses and maintain eyelid hygiene to manage early signs of blepharitis.
- Ensure regular breaks during screen time to reduce strain.
• Lens Health:
- Why It Matters: The lens is prone to damage from UV rays and oxidative stress, which can lead to cataract formation.
- Practical Steps:
- Wear sunglasses that block 100% of UVA and UVB rays when you’re outdoors.
- Consider wearing a broad-brimmed hat to further reduce UV exposure.
- Maintain a diet rich in antioxidants (for example, leafy greens, fish, and nuts) to help combat oxidative damage.
- Schedule periodic eye exams to keep an eye on potential lens changes.
• Vitreal Health:
- Why It Matters: Although little can be done directly to protect or regenerate the vitreous, its condition serves as an indicator of overall eye health.
- Practical Steps:
- Keep up with regular comprehensive eye checkups so any changes in the vitreous can be monitored over time.
- Inform your doctor about any sudden visual changes such as floaters or flashes, as these might warrant further investigation.
• Retinal Health:
- Why It Matters: The retina is essential for processing visual information. Damage can arise from UV exposure and systemic conditions like glaucoma, hypertension, and diabetes.
- Practical Steps:
- Use UV-protective eyewear to reduce direct sunlight exposure.
- Get regular retinal screenings if you have risk factors such as diabetes or high blood pressure.
- Begin routine glaucoma assessments at about age 40. If you have a family history of glaucoma or belong to a high-risk group, discuss earlier screening with your ophthalmologist.
References
- Blumthaler M, Ambach W, Ellinger R. (1997). Increase in solar UV radiation with altitude. Journal of Photochemistry and Photobiology B, 39(2), 130–134.
- Czeisler CA et al. (1999). Stability, precision, and near-24-hour period of the human circadian pacemaker. Science, 284(5423), 2177–2181.
- Feister U, Grewe R. (1995). Spectral albedo measurements in the UV and visible region over different types of surfaces. Photochem Photobiol, 62(4), 736–744.
- Hattar S et al. (2002). Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science, 295(5557), 1065–1070.
- Khalsa SBS et al. (2003). A phase response curve to single bright light pulses in human subjects. J Physiol, 549(Pt 3), 945–952.
- Lucas RJ et al. (2006). Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina. Curr Biol, 16(21), 2006–2010.
- Lucas RJ et al. (2014). Measuring and using light in the melanopsin age. Trends Neurosci, 37(1), 1–9.
- West SK et al. (2013). The epidemiology of cataract: accomplishments over 25 years and future directions. Ophthalmic Epidemiol, 20(4), 225–232.
- WHO (2010). Exposure to Artificial UV Radiation and Skin Cancer. Environmental Burden of Disease Series.
- Wright KP et al. (2013). Entrainment of the human circadian clock to the natural light–dark cycle. Curr Biol, 23(16), 1554–1558.
- Harvard Health Publishing. (2020). Blue light has a dark side.
Install Flux on your PC. This is hands down the best tool I’ve found to help my sleep rhythm; it’s customizable and better than most built-in light dimming options found in operating systems like Mac and Windows. In this modern day and age nobody needs to buy blue blocking glasses for computer work.
While working on your PC, make sure to look into the distance every once in a while (20/20/20) to let your eyes relax.
Wear sunglasses every time you go out in sunny weather, except very early in the morning. Your eyes are like your skin—you’ll see worse as you age if you don’t protect your retinal cells from UV damage, just as your skin will sag if you neglect protection. If you wear glasses, splurge once for a nice pair of sunglasses with your prescription. Make sure it’s a more “common” model so you can upgrade just the lenses instead of the whole frame. Coolness is a bonus factor! For those trying to be frugal: an unethical tip is to visit a glasses store, try on some frames, and then buy them online.