An adjustable intraocular lens system is provided by detachably attaching a secondary intraocular lens having a thin, contact lens-type optic onto a primary intraocular lens that has previously been implanted into an individual's eye. The preliminary intraocular lenses have two or more shallow, narrow slits formed adjacent the optical peripheries thereof. These slits may be formed in or through the preliminary intraocular lens optic itself or outside the optic in tabs, in haptic attachment regions or in plate-type haptics. The associated secondary intraocular lens optics are formed having two or more insertion tabs extending radially from the optical peripheries thereof. The secondary intraocular insertion tabs are shaped and located to penetrate corresponding ones of the primary intraocular lens slits and have wedge-shaped free end regions to facilitate slit insertion. The secondary intraocular lens provides a required power correction to the primary intraocular lens to which it is attached.