We found out a couple weeks ago that my 21 year old cousin has melanoma in her eye. When she was born, she had a half blue/half brown eye. I always thought it was cool and cute, but apparently can be an indicator of cancer. So, she's had her eye checked about every 6 months or so to make sure it's all OK. As you can imagine, her last visit to the doctor didn't go so well. There was a shadow in her eye, indicating melanoma, and the tumor had been vascularized (meaning, it had directed blood vessels toward it to feed it). The doctor recommended removing the entire eye. Could you imagine? Having a glass eye at 21? Don't get me wrong, melanoma is really f-ing BAD. Melanoma originates from pigmented cells. These pigmented cells originated from a region of tissue in the embryo called the neural crest. Neural crest migrates throughout your body during development and is important in forming parts of the skin, the heart, the inner ears and the eyes (as well as many other things). The problem with these cells is that they already know how to move. And cancer is really bad when things start to move around (i.e. spread). Thankfully, her tests have come back negative for malignancy. She has been accepted into a clinic at UCSF that specializes in this particular type of cancer. And they have said they can perhaps save her eye. She will likely lose some of her vision, but not all of it. And she won't need a glass eye.
What's the moral here? Take care of what you've got. Because you have no idea how long you've got here. And it's worth it.
PS: also, quit tanning. seriously. it's stupid to expose yourself to UV rays. Yeah, the same UV rays us scientists use to mess up organisms. Duh!