What are ortho-k lenses used for: myopia (nearsightedness) or astigmatism?

Both: Ortho-k is an expensive and non-sensible treatment. With this, you wear contact lenses while you sleep that mould the cornea. This allows better vision. During the day, the cornea reshapes itself to normal. What this means is that you see well for a few hours and your vision fades as the day progresses. A more sensible and cheaper solution is to wear contact lenses during the day.