Exposure to bright light is, according to convention, an important risk factor for age-related macular degeneration (AMD), and those at risk are advised to reduce their exposure to light wherever possible. Yet, for the cells of the macula to remain healthy, they need to divide periodically - but they can't do this without exposure to full-spectrum light.
The concept of light damage is based, in part, on faulty (and cruel) research in which scientists produced retinal damage by shining an intense ultraviolet light into an animal's eyes while mechanically holding their eyelids apart. But such studies do not reflect real-world response to light. Natural reflexes, such as blinking, prevent us from looking at light sources for prolonged periods of time.
Light can sometimes cause damage to our eyes, but the problem is most acute in people consuming a nutrient-depleted Western diet of processed foods and unsaturated fats (Cancer Res, 1985; 45: 6254-9). Those who eat more sensibly and supplement with antioxidants, such as vitamins C and E, rarely develop eye problems such as cataracts and AMD, even after extended sun exposure (Ophthalmology, 1998; 105: 831-6).
Research suggests that the blue spectrum of visible light is the most damaging to eyes. This is found in regular sunlight, but also in indoor fluorescent lighting and computer screens, and from industrial applications such as welding. It can also be used therapeutically to treat acne and depression. Excessive and unprotected exposure can trigger a photochemical reaction that produces free radicals that cause damage to the rod and cone cells of the retina. Older people have some natural protection against blue light - as the eye lens ages, it begins to yellow, which helps to filter out blue light and ultraviolet A. Children, however, have no such protection, suggesting that glaring light in childhood may set the scene for later deterioration of sight (J Occup Med, 1983; 25: 101-3).
Reducing exposure to blue light - for instance, with sunglasses (usually tinted red, yellow or brown) that filter out blue, or special goggle-type sunglasses that fully enclose your eyes - can be protective. But there's a catch. Researchers at Brigham and Women's Hospital in Boston and Jefferson Medical College have found that exposure to blue light, more than any other colour, is what sets our biological clocks and the release of melatonin (J Clin Endocrinol Metab, 2003; 88: 4502-5), which protects both the heart and eyes by keeping blood pressure low. So, as with so many other things in life, the best course is probably moderation - or sensible exposure.