OBJECTIVE: This study aimed to assess the natural history of eyes after deep sclerectomy with collagen implant (DSCI), a nonperforating glaucoma-filtering surgery. DESIGN: The design was a prospective, longitudinal, observational, and nonrandomized study. PARTICIPANTS: Forty-five eyes of 41 patients with medically uncontrolled open-angle glaucoma were studied. INTERVENTION: Deep sclerectomy with collagen implant was performed. MAIN OUTCOME MEASURES: Ultrasound biomicroscopy (UBM) of the sclerectomy site was performed 1, 2, 3, 6, 9, 12, and 18 months after surgery. The following parameters were assessed: length and height of the collagen implant, thickness of the residual trabeculodescemetic membrane, and bleb appearance. RESULTS: Mean intraocular pressure decreased from a preoperative value of 26.3 +/- 3.5 mmHg (mean +/- standard deviation) to a postoperative value of 16.6 +/- 3.1 mmHg (mean +/- standard deviation) at 18 months (P < 0.001). The UBM findings showed a subconjunctival filtration with a nonperforated thin trabeculodescemetic membrane. In 23 eyes (51%), a hypoechoic area in the suprachoroidal space was observed. The thickness of the trabeculodescemetic membrane was stable throughout the study with a mean value of 0.13 mm +/- 0.02 (mean +/- standard deviation) at 18 months. The collagen implant dissolved slowly within 6 to 9 months, leaving a tunnel in the sclera. CONCLUSIONS: The UBM findings are consistent with intraocular pressure lowering by aqueous filtration through the thin remaining trabeculodescemetic membrane to an area under the scleral flap, which was maintained open by the collagen implant. The authors speculate that aqueous humor then reached the subconjunctival space and, eventually, was filtered through the thin scleral wall into the suprachoroidal space. Complete resorption of the collagen implant occurred between 6 and 9 months after surgery.