Abstract: An improved cutter assembly is used to form an aperture in a lens capsule of an eye. The cutter assembly is resiliently deflectable between a contracted condition and an expanded condition. When the cutter assembly is in the contracted condition, it is moved through an opening in the eye into alignment with an anterior portion of lens capsule of the eye. The cutter assembly is then operated to the expanded condition and moved against the anterior portion of the lens capsule under the influence of fluid pressure. To move the cutter assembly against the anterior portion of the lens capsule, a seal engages an anterior portion of the lens capsule and a conduit connected with the cutter assembly is connected in fluid communication with a source of low pressure (vacuum).