This study will be conducted at the Kansas City VA Medical Center, Kansas City, MO. The investigators have the pCLE system that the investigators are currently using in a multicenter study evaluating patients with Barrett's esophagus. Patients referred for screening and/or surveillance colonoscopy will be prospectively enrolled in this study. Inclusion criteria - referral for screening and/or surveillance colonoscopy and the ability to provide informed consent. Exclusion criteria: prior surgical resection of any portion of colon, prior history of colon cancer, history of inflammatory bowel disease, use of anti-platelet agents or anticoagulants that precludes removal of polyps during the procedure, poor general condition or any other reason to avoid prolonged procedure time, history of polyposis syndrome or HNPCC, inability to give informed consent, inadequate bowel preparation, allergy to fluorescein, pregnancy, and renal insufficiency. Moderate sedation for the procedure will be administered in a standard fashion with intravenous midazolam, meperidine or fentanyl. This will be a single arm study with all procedures being performed with a standard white light colonoscope (CF - H180AL, Olympus America). After cecal intubation, the colonic mucosa will be carefully visualized during withdrawal under high-definition white light and if a polyp is detected, its characteristics will be documented: size, location, and morphology \[Polypoid (sessile, pedunculated) or Non-polypoid: (superficial elevated, completely flat, depressed)\]. Then 5ml of 10% fluorescein sodium will be injected intravenously. Following this the pCLE probe will be passed through the biopsy channel of the colonoscope and placed on the polyp to obtain confocal images and video sequences. During the initial phase unblinded comparisons of the confocal images and videos with the polyp histology (20 adenomas, 20 hyperplastic) will be performed in order to evaluate the criteria described by the Mayo Jacksonville group (22) that differentiate between neoplastic and non neoplastic polyps. Following this initial phase, these criteria will be applied in a prospective manner to predict polyp histology (100 polyps) real time during the procedure prior to their removal. Multiple confocal images and videos of each polyp will be saved with appropriate labeling. Pathologists will be blinded to the endoscopic and pCLE findings of the polyps. Polyp size will be assessed by comparing with sheath of a polypectomy snare or open span of a biopsy forceps. Photo documentation of the polyps will be performed. Polyps will then be removed in the standard fashion with a biopsy forceps or snare and sent for histopathological evaluation. Each polyp will be sent in a separate jar and labeled accordingly. The bowel preparation will be evaluated and graded according to previously reported criteria (24): excellent, good, fair, and inadequate. Patients with inadequate bowel preparation will be excluded. Complications including gastrointestinal bleeding (requiring intervention) and perforation will be recorded.

Outcomes:

The predicted histology of polyps based on the confocal images and videos and the correlation with actual histology for accuracy of prediction will be the primary outcome. Secondary outcome will be the inter-observer variability in polyp histology prediction based on the confocal images and videos of polyps (by kappa statistics).