An optical coupler is disclosed for mounting at a distal end of an optical imaging device for visualizing a surface area covered with an opaque fluid and/or particulate matter. The coupler includes a visualization section at one end of the coupler and an attachment section connected to and extending away from the visualization section. The attachment section is dimensioned to be mounted at the distal end of the optical imaging device. The visualization section includes a proximal surface for engaging the distal end of the optical imaging device. The visualization section includes an outer surface spaced apart from the proximal surface. The outer surface extends continuously from a first outer side boundary across to a second opposite outer side boundary of the visualization section. The visualization section may include a hollow instrument channel extending from the proximal surface toward the outer surface.