It's a risk mostly to small children as far as I understand. There's been a few case of semi-permanent eye issue I think in pretty young kids (6 or so ?), and temporary issues in older kids (10-13?), but I can't find the papers back.
Since these studies, it has become harder to experiment on small kids as it would be unethical, but on the other hand there's no specific report on kids older than 13 if I remember well.
Then a decent number of adults have been using the headsets for prolonged periods without anything critical reported at this point. It should still be used with awareness of potential risks, but I don't think there's any strong evidence of long term effects.
Since these studies, it has become harder to experiment on small kids as it would be unethical, but on the other hand there's no specific report on kids older than 13 if I remember well.
Then a decent number of adults have been using the headsets for prolonged periods without anything critical reported at this point. It should still be used with awareness of potential risks, but I don't think there's any strong evidence of long term effects.