Many people, especially those of us who are pigmenatally-challenged (not to be mistaken with people who are pigmentally-confused... urbandictionary.com), have suffered from the occasional sunburn. You get it on your shoulders, your back, even your face. But what about on or inside your eye? Yes, it can happen.
Photokeratitis, aka Solar keratitis, is basically sunburn of the cornea (the clear dome at the front of the eye). It happens when the eye is exposed to high amounts of UV light even if only for a short period of time. This can occur from natural sources (ie. the sun) or, more commonly, from artificial light (welder's arc).
The consequences are similar to those of corneal abrasions. Pain, redness, blurred vision, and potential scarring of the cornea which can lead to permanently decreased vision. Just like regular sunburns, you don't notice the pain until a few hours after the excessive exposure.
Solar maculopathy is the same problem but in the back of the eye, on the retina. The macula is the small central point on the retina where all of the light that enters the eye is focused. Maculopathy usually occurs when a person looks directly at a very bright light or UV source for an extended period of time.
The problem most commonly occurs when people stare at the sun. There are quite a few people (more than you might expect) who believe that sungazing provides spiritual and wellness benefits. There is no scientific evidence to support this.
The consequences of solar maculopathy can be severe. In the worst cases, there can be permanent loss of central vision. In other cases, the loss of vision is temporary and is recovered over time.
All of the enery and heat from the sun is focused by the eye to one tiny point on the retina. Its the same idea as using a magnifying glass to kill ants.
A few years ago, there was a story in the news about people in India who were looking for an image of the Virgin Mary during a solar eclipse. Not surprisingly, a lot of them developed serious problems with their vision! Read this story here.
Take home message: Wear your sunglasses, wear your welding mask, and DON'T STARE AT THE SUN!! (please)