Why do your eyes burn when you open the oven while baking bread?

When the oven door is first opened during baking, hot air wafts out. This air is hot enough to quickly evaporate some of the moisture off the surface of the eyes, making them feel dry (and uncomfortable). The nerves for the surface of the eyes are very sensitive, because the eye is fragile, so they are also detecting the heat from the air as well as the dryness of the eye.