The data says a lot of people have mild/moderate visual visual artifacts (halos, starbursts, etc.) and dry eye prior to getting lasik. Lasik appears to make some of those symptoms disappear in many people, but also causes symptoms to appear in a smaller number of people.

E.g. for dry eye, from PROWL-1 [2], table 2: before: 45% any severity, 6% severe; after 6 months: 27% any severity, 3% severe; and those changes included 19.5% of those without symptoms developing new symptoms and 65% of those with prior symptoms seeing those resolve.

But it's really hard to interpret the data because a surprisingly large fraction of people report changes (both no symptoms to symptoms and vice versa) over some period of time without having lasik at all! ("14% (95% CI, 3%-35%) to 29% (95% CI, 13%-49%) of participants answered that they either did or did not have a symptom on the test and vice versa on the retest")

See my comment [1] for more.

[1] https://news.ycombinator.com/item?id=21547710

[2] https://jamanetwork.com/journals/jamaophthalmology/fullartic...