occluder

An object that partially or completely impedes the amount of light reaching the eye.

(medicine) An implement designed to temporarily block light to one eye.

(medicine, cardiology) A catheter-delivered device that blocks a hole in the wall of a heart, often having an umbrella-type design and folded up until the catheter arrives at the area of the defect in the heart. Once in place the occluder is unfolded on both sides of the defect so that pressure from both sides keeps it in place.