Do Your Eyes Sting?

Recently I've come to notice that in the penultimate posture of the standing series (where your legs are apart and your forehead must touch your knee) that my eyes have begun to sting. Quite badly. I can't concentrate and it's quite painful. I assume it's the sweat getting into my eyes and I'm not sure whether it's because I'm actually trying to get my forehead onto my knee as opposed to the bridge of my nose?