Patients are given a topical anesthetic (eye drops) to numb the eye, so they experience no pain during the procedure. When the surgeon applies the vacuum ring, the patient experiences a sensation of slight pressure just before his or her vision fades away for a few seconds. Neither the precision flap-making instrument--nor the laser cause any pain or discomfort. For several hours after the procedure, many patients describe a mild "foreign body" sensation, such as after opening the eyes while swimming in chlorinated water. Some people feel as though there is a dirty contact lens in their eye. After the first few hours, this uncomfortable feeling usually subsides.