An endoscope accessory, such as a coupler device, is provided that includes a main body with a visualization section for allowing viewing of tissue by the endoscope and a proximal end configured for attachment to a distal end portion of the endoscope. The device includes a passage within the main body having an open distal end and a proximal end aligned with the working channel of the endoscope. A locking element on the coupler device secures an angle of exit of an instrument passing through the passage.