Very cool that you saw a snowy owl! There's been a lot of sightings even here (Wisconsin) this year, which is atypical. I've been driving the back farm roads looking for one, but haven't been lucky enough to see one this year, yet. They're tame, not being used to humans (normally they're north into Canada where there aren't as many people), but easily stressed, so it was good that you backed off for the bird's sake. Wish you'd had a camera, though!
The loss of eyesight from pigeons poop is not that far-fetched. Pigeon quano can transmit a fungal disease (I believe it's histoplasmosis) that can be deadly to humans. It's a particular danger if the material is dry and powdery and it gets inhaled I've been told.
Good luck on finding that net! If you're in the US and you find it, make sure you report it to the state dept of natural resources (they may have some regulations) and for sure to the US Fish & Wildlife Service. The US F&W service regulates banding and will probably be interested in someone using a mist net illegally.