A decentered ablation is an infrequent complication of LASIK eye surgery that occurs when the laser treatment is not properly centered over the pupil. Laser ablations that are off-center by as little as 0.5mm can cause visual symptoms, including glare and halos, ghost images, and blurred vision.
This problem can arise if the suction ring that attaches the microkeratome or femtosecond laser to the eye for creating the flap is not aligned properly over the center of the pupil. Another cause is something called pupil centroid shift, which refers to a change in the lateral or vertical position of the pupil as it dilates or constricts. It's important for the surgeon to compensate for centroid shifts to avoid decentered ablations.
Technology called iris registration used with wavefront-guided LASIK greatly reduces the risk for decentered ablations. Instead of using the pupil as a guide, iris registration uses the corneal limbus (the edge of the cornea where it meets the white sclera) as a reference point during preoperative measurements that guide the laser ablation during surgery.
Vision problems caused by decentered ablations can often be corrected with a wavefront-guided LASIK or PRK enhancement procedure.