It's not just the drug, it's the delivery agent as well. A petroleum-based delivery agent may be just fine for your skin, but not so good for your eyes. While it may not harm your eyes (I don't know this), it may be uncomfortable or not disolve well in tears and you then end up looking through a smeared haze for a while. I would recommend using medicines as they are intended to be used by the manufacturers in cases like this.