The dangers of the sun for the eyes.
Children's eyes are more sensitive than those of adults, because their crystalline lens (the part of the eye that focuses light on the retina) is clearer and therefore lets more UV rays through. The crystalline lens doesn't become protective until the age of 12, and doesn't become fully operational until adulthood. Before this age, the crystalline lens allows over 75% of UV rays to pass through, and from 0 to 1 year, 90% of UV rays reach the retina in children.
As children spend more time outdoors than the average adult, they are also more exposed to risks such as photokeratitis and photoconjunctivitis (inflammation of the cornea and conjunctiva respectively). These often painful effects require treatment, but can easily be avoided by wearing sunglasses.
It's therefore important to get a young child used to wearing the right sunglasses as soon as possible, in order to protect his or her solar capital. So, if you're wondering "at what age should a baby start wearing sunglasses?", our answer is "as early as possible". Sunglasses are essential for prolonged exposure to the sun, or in bright sunlight.