Contact lens solution does not contain a borate-type preservative. The active ingredient in contact lens solution is boric acid. There are some contact lens solutions that don't contain boric acid but they won't make slime. You need boric acid to make slime and you can either get it from Borax or contact lens solution.

Borax has been getting negative press recently and I see people recommending contact lens solution as an alternative. But why is contact lens solution safer than Borax, when the active ingredient in both is boric acid?