Will I be able to get 20/20 vision after Advanced Surface Lasik?

Hi. I got my assessment for LASIK done today and they said my cornea is thin for LASIK ( didn't tell me the measurement) . They referred me ASL because of thin corneas but they said still I won't be able to get perfect vision ( some of the number will be left) as I have a high prescription i.e. -6 diopter. Can someone please guide me about it ? Also please guide me about the recovery time after ASL as he said it takes longer. Thanks

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