Future directions in lamellar corneal transplantation

The concept of lamellar keratoplasty (LK) is that of targeted lamellar replacement of corneal tissue while retaining normal cornea. It involves replacing either anterior stroma [anterior lamellar keratoplasty (ALK)] or posterior replacement of deep stromal and endothelial layers [posterior lamellar keratoplasty (PLK) or endothelial keratoplasty]. Despite the distinct advantages of ALK surgery, penetrating keratoplasty (PK) remains the most common procedure-largely because lamellar surgery is more technically demanding and time consuming, and interface irregularity arising from manual lamellar dissection often results in suboptimal visual outcomes. Recent improvements of surgical technique and advances in instrumentation such as microkeratome-assisted lamellar transplantation have contributed to improved visual quality with LK surgery. Long-term graft survival rates and endothelial cell counts after PK continue to drop for many years after surgery, clearly showing the disadvantage of unnecessary replacement of healthy endothelium in anterior-stromal disorders. The aim of this review is to evaluate the shifting emphasis from penetrating to lamellar forms of corneal transplantation and to highlight some future directions in lamellar surgery including new techniques in both ALK and PLK and the use of microkeratomes and femtosecond lasers to enhance outcomes.