A complication of refractive surgery. In perfect centration, the centre of the corneal ablation exactly coincides with the centre of the visual axis and/or pupil. This is like looking through the very centre of your spectacle lens. If you look through the periphery of your lens, you might end up seeing partly through the lens and partly through the edge of the lens-this is decentration. Decentration can cause various symptoms including edge glare or even monocular double vision. Other factors such as the normal size of the pupil, whether it is dark out (your pupil will enlarge), or the size of the ablation zone will affect the severity or presence of symptoms.