[ska]

It's probably higher than appears at first blush, at least to do at scale. But not a huge barrier.

But there isn't an open market for manufactured lenses, you have to get them into consumers hands, and you have to get prescriptions, and people want fitting and ability to try frames.

Superficially it seems that glasses are highly vertical in practice, which is why budget outfits like zenni and warby parker seem mostly to be focused on the margins of direct-to-consumer.