Evidence-based recommendations on trabeculectomy with a biodegradable collagen matrix implant for glaucoma. This involves cutting a small flap in the white of the eye and putting a patch over the flap to help healing and prevent scarring. Fluid slowly drains out of the flap and the patch dissolves over time. The aim is to reduce pressure in the eye and slow or stop damage to sight. Is this guidance up to date? Next review: this guidance will be reviewed if there is new evidence or safety concerns.