An instrument for inserting a flexible intraocular lens or other flexible membrane into an eye which includes a compressor for laterally compressing the lens into a small cross-sectional configuration to pass the lens through a narrow incision. The compressor includes retainers along the interior of the inserter to maintain the side edges of the lens in a substantially planar orientation during compression. The retainers preferably extend through the inserter to hold the lens during advancement toward the eye to prevent an uncontrolled rotation of the lens. A haptic guide may be placed through the distal end of the inserter to properly position the leading loop haptic of the lens.