The piggyback method of implanting two intraocular lenses in one eye has been successfully expanded to address pseudophakic refractive error in normal eyes and eyes that have undergone postpenetrating keratoplasty. Piggyback implantation has been combined with the use of newly available minus-power lenses to provide appropriate power for a cataract patient with keratoconus, as well as to correct pseudophakic myopia. The phenomenon of increased depth of focus in piggybacks may be explained by a contact zone between the lenses. The late complication of interlenticular cellular growth with resultant hyperopic shift, opacification, and loss of vision has recently become a concern.
Abbreviations:DOF depth of focus, IOL intraocular lens, PK penetrating keratoplasty
In 1993, Gayton  first described a unique solution to the problem of providing adequate intraocular lens (IOL) power to a patient with microphthalmos and extreme hyperopia—two IOLs implanted back to back. Since then, many surgeons have taken up the technique to less extreme cases of hyperopia in which a single high-power IOL would not have provided sufficient power and even to cases in which the required power was at or near the upper limit of power inventories  (Fig. 1). Implanting two IOLs in these cases is preferable, because when the optical centers of the lenses are aligned, they provide better optical quality than a single high-powered IOL. The procedure has been used not only to treat high hyperopia but also as a secondary technique to treat pseudophakic refractive errors to avoid the risks associated with lens exchange [3•]. With the advent of minus-power IOLs, the technique can benefit even myopic pseudophakes [3•,4]. Secondary piggyback implantation is helpful for patients who have had a corneal refractive procedure and are thus more likely to have postcataract surgery refractive error. Secondary piggybacks also can be used to correct the often high refractive errors of pseudophakic penetrating keratoplasty (PK) patients, for whom lens exchange presents even more risk [3•,5].