The main potential risk of participating in the study is the possibility of corneal abrasion. Previous studies at the Mayo Clinic using the same techniques did not result in any corneal abrasions in over 300 eyes of more than 150 patients. Based on this result, we estimate the risk of a corneal abrasion to be minimal. If a corneal abrasion occurs, the patient will be removed from the study. The patient will be treated with antibiotic drops or ointment and followed until the abrasion has completely healed.