by Dr. Alexander Wunsch, M.D., Ph.D.

Last week’s International Sunglasses Day serves as a timely reminder to consider the medical relevance of sunglasses. Used correctly, they provide important protection for the eyes—but if overused, they may impair chronobiological light perception and hormonal regulation.

Ophthalmological benefits of sunglasses:

• Protection of the lens and retina from high-energy ultraviolet radiation (particularly UV-B and UV-A)
• Prevention of light-induced eye diseases such as cataract, age-related macular degeneration, and photochemical retinal damage
• Reduction of glare in high-radiation environments (e.g. snow, water, mountains)
• Relief for people with light sensitivity or after eye surgery

Historical context:

Light-induced eye damage has been observed across cultures and centuries.
Already in antiquity, itinerant so-called “Starstechers” attempted to treat cataracts—often resulting from chronic UV exposure—by displacing the clouded lens into the vitreous body.

In Arctic cultures, the Inuit protected their eyes with bone goggles featuring narrow slits, effectively preventing snow blindness.
In medieval China, judges wore dark quartz lenses—not primarily for sun protection but to conceal their gaze—demonstrating early filter optics.

Possible disadvantages of overuse:

• Reduced stimulation of light-sensitive retinal photopigments (especially melanopsin, OPN4), which regulate sleep-wake cycles and hormonal rhythms
• Suppression of essential circadian signals (e.g. for melatonin, cortisol, dopamine regulation)
• Impaired adaptation to natural light conditions, especially in children or indoor workers
• Reduced activation of protective antioxidative mechanisms triggered by moderate light exposure

Medical recommendation:

Conventional sunglasses with strong tints (category 3–4) are appropriate in intense light conditions such as high altitudes, at sea, or on snow. However, for daily use in moderate daylight, excessive shielding may interfere with physiological light adaptation and chronobiological balance.

Alternative recommendation – selective filtering with BlueSync lenses:

Modern filter glasses like BlueSync by Ra Optics offer a well-balanced compromise. They are engineered to:

• filter harmful high-energy visible blue light (HEVL)
• allow beneficial circadian-effective blue light (470–490 nm) to pass through
• and maintain a low tint level (category 0–1) to avoid unnecessary darkening

This enables hormone-neutral, eye-friendly light exposure while reducing stress-inducing wavelengths. BlueSync is particularly suitable for individuals who spend time outdoors during the day and want to protect their eyes without disrupting their biological clock.

Conclusion:

Light is not just brightness—it is biological information. Sunglasses are a valuable tool when used appropriately. Today’s filter technologies allow for a more nuanced approach: protecting the eyes while preserving the positive effects of natural light.

Dr. Alexander Wunsch, MD, PhD, is a German physician, light therapist, scholar and non-fiction author who specializes in researching the effects of light on human health. He has given numerous lectures on topics such as light therapy, the impact of artificial light on chronobiology and the importance of natural light for the human organism. His work has helped to deepen the understanding of how light affects our biological clock and various physiological processes. As scientific consultant and inventor he is involved in the development of products and technologies for the improvement of human health and wellbeing.