If you create a hide all items rule, it will hide lenses. You have no way to unhide lenses that I’m aware of, other than a show all items rule. It shouldn’t be possible to hide items with loot filter rules that have no actual loot filter rules.
Lenses should either be added, at the very least, to the item types so that you can choose not to hide them. More realistically, as I don’t think lenses actually drop and they’re not particularly rare or valuable at 500 gold, they shouldn’t be filterable at all. That way, if you drop one on the ground by accident, it will be obvious.