Recurrence of myopia after 6 years of LASIK Laser - what could have caused this?

I have done lasik laser in 2015..my numbers were -8 before surgery ... after surgery I had a perfect vision but now I am having difficulty in seeing distant objects so I consult doctor and again I got number of -3.25..why is that so ? Lasik laser is the permanent solution so why there is a recurrence in my case .kindly guide