Efficacy of Second Forward-view Examination of Left Colon for Adenoma Detection During Colonoscopy

Inclusion Criteria: * Patients whose age are between 40-75, or aged 76-85 depending on his condition * Patients who have indications for screening * Patients who have signed inform consent form. Exclusion Criteria: * Patients who have undergone colonic resection * Patients with alarming signs and symptoms of colorectal cancer: hematochezia, melena, anemia, weight loss, abdominal mass, positive digital rectal examination * Patients with abnormal blood coagulation or taking antiplatelets or anticoagulants within 7 days before colonoscopy * Patients with inflammatory bowel diseases * Patients with a history of abdominal surgery, or highly suspected or confirmed colorectal cancers by radiographic and laboratory tests Patients with hereditary colorectal cancer syndrome (including familial adenomatous polyposis). * Patients with pregnancy, severe chronic cardiopulmonary and renal disease. * Patients with failed cecal intubation * Patients with poor BPQ that necessitated a second bowel preparation * Patients with therapeutic colonoscopy for existing lesions * Patients refusing to participate or to provide informed consent