If you don't get perfect vision after lasik surgery, it is possible to have lasik surgery a second time half a year later. However, you should go to see your surgeon and let him check your eyes to see whether you are suitable for a second surgery. In fact, your cornea must be thick enough to have the surgery a second time. Otherwise, you can't have lasik surgery twice.
As long as you have adequate corneal thickness after your first surgery, it is possible to have another surgery. However, you should consult your surgeon who will check how thick your current cornea is and how much cornea to be thinned. After the test, your surgeon will know whether you are suitable to have another surgery. In most cases, most people can have lasik surgery for a second time.
If your distance vision is not so good, you may have a second procedure. But that depends on whether there is enough tissue left. Your surgeon may choose a different type of refractive procedure for your second procedure according to the status of your cornea and technology available.
Whether you can have a second surgery should depend on the thickness of your cornea and other conditions. Generally the doctor would check your eyes condition to see if you are a good candidate before surgery.
Generally lasik surgery has a good rate success and most people can get a good result after first lasik surgery if you follow the doctor's instruction and have a good habit of using eyes. If the result is not satisfactory, you can have a reshape after half a year. But your cornea need to be thick enough and there is no other eye disease.