Learn Croatian: Oftalmolog tvrdi da je moj vid slabiji nego prije. - The ophthalmologist claims that my vision is weaker than before.

Yes! The adjective tvrd means hard or solid. The verb tvrditi essentially means to make a statement solid or firm, which translates perfectly to asserting a fact or claiming.

Why is the enclitic verb je placed right after da instead of after moj vid?

In Croatian, enclitics like je must take the second position in their clause. The conjunction da counts as the first position in the subordinate clause, so the enclitic anchors right to it, resulting in da je moj vid instead of da moj vid je.

Could I say od prije instead of nego prije to mean "than before"?

No, you must use nego here. When making comparisons, you can use od followed by a noun or pronoun in the genitive case, like slabiji od tebe (weaker than you). But because prije is an adverb rather than a noun, you must use nego.

Why use vid for vision instead of pogled?

vid refers specifically to the medical or biological sense of sight, which is what an ophthalmologist tests. pogled translates to a look, a glance, or a view, such as a nice view from a window.