Gwen Stefani was "kind of heartbroken" when she found out her son had to wear glasses

She said: "When you find out your kid needs to wear glasses, it’s like, 'Ah, no' because it means that’s going to be their look their whole life - it’s kind of heartbreaking. But then it becomes your thing, and you choose [the glasses] together. He’s in elementary school, and the other kids are jealous and want to wear glasses because of Zuma."

And the 48-year-old singer has teamed up with L.A.M.B. and gX by Gwen Stefani for Tura Inc. for new glasses and sunglasses collections, which were inspired by her son's glasses.

She added: "Zuma has so many colorful, fun glasses, so doing this collection has been super exciting because he knows he’s part of the inspiration. He’s super proud. None of his [two] other brothers wear glasses, he’s the only one. And so having that kid’s perspective is a good thing."

And Gwen - who also has Kingston, 11, and Apollo, three, with her ex-husband Gavin Rossdale - admits she is quite a "self-centered" designer.

She told People magazine: "I’m very self-centered when it comes to designing. I do it for myself. I just want to make some that are super cute and I get excited to wear. You want to make sure it’s something that you love, that represents your style, that you can look back on and love ... There are a lot of choices and you should really wear something that makes you feel confident. But it is fun that nowadays that we have the choice to do whatever makes you happy."