Why does a patient's pupil size matters to his or her suitability for LASIK?

If the patients' pupils are very large, especially the night time diameter, then the patient can get glares and haloes if the treatment zone is not big enough to cover the entire pupil diameter. The clinic has to ensure that the ablation zone is big enough to cover the pupil diameter. If the ablation zone is smaller than the actual night time diameter, the patient could suffer from glare and haloes.