Nonpenetrating Foldable Intrastromal Keratoprosthesis: A Review of the Literature

Purpose: To review the literature focusing on the clinical outcomes of KeraKlear (KK) (KeraMed), a foldable intrastromal keratoprosthesis. Methods: We searched 6 databases using 4 keywords: KeraKlear, Foldable Keratoprosthesis, Intrastromal Keratoprosthesis, and Non-penetrating Keratoprosthesis. Included studies had to be conducted in vivo on humans, published until January 3, 2023, and had to investigate the implantation of the KK. Eyes were considered at high risk of keratoprosthesis retention failure whenever there was an active inflammatory ocular surface disorder or in case of previous KK failure. We aimed at recording the postoperative complications, rate of prosthesis retention, and mean improvements in visual acuity. Results: We identified 144 publications, 6 of which (38 eyes) met the inclusion criteria. No randomized controlled trials were found, and some studies had significant limitations regarding sample size and follow-up duration. With a mean follow-up of 28 ± 18.8 months, postoperative complications of any kind occurred between 0% and 50% and 24% had an implant extrusion/needed a reoperation. The mean postoperative visual acuity improvement on the last follow-up was −0.83 ± 0.27 LogMAR, that is, −0.57 ± 0.3 for high-risk and −1.03 ± 0.25 for low-risk eyes, whereas 1 year after implantation, 50% of the prostheses were retained in the former and 81% in the latter group. None of the eyes developed glaucoma, endophthalmitis, or expulsive hemorrhages; none had to be eviscerated/enucleated. Conclusions: Despite the limited quality and quantity of evidence, the available literature seems to suggest the KK to be a valuable tool in the treatment of complicated corneal disorders. Because in many parts of the world, the access to corneal transplantation is limited, this prosthesis could represent a valid alternative.