According to World Health Organization criteria, a patient should be either monocular or functionally blind in both eyes in order to be considered eligible for a Boston keratoprosthesis (KPro). As success rates for keratoprostheses continue to increase, many surgeons have turned to support keratoprosthesis surgery despite intact vision in the contralateral eye. This spreading sentiment is largely due to the potential for improved visual function, restoration of binocularity, and enhanced cosmesis in patients postoperatively, even if initial pathology resides in only one eye [1, 2]. It has also been established that an ideal surgical candidate should have vision no better than light perception with projection in all four quadrants, yet this concept has recently been challenged by surgeons achieving excellent visual outcomes in patients with better preoperative vision [1]. To optimize outcomes, patients must possess certain essential characteristics, including adequate lid anatomy, good blink function, and sufficient tear production. Fornices should be evaluated as well keeping in mind the need to fit a large bandage contact lens after surgery. Some patients may benefit from fornix reconstruction before implantation of the Boston keratoprosthesis. A thorough history and examination can help the surgeon determine the possibility of significant optic nerve dysfunction, retinal pathology, or dense amblyopia in the eye being considered for keratoprosthesis surgery. Furthermore, the surgeon should perform an assessment of visual potential. Because in most of these patients there is no view to the posterior segment of the eye, B-scan ultrasonography can aid the evaluation of retinal anatomy.

Autoimmune diseases (such as Stevens-Johnson syndrome [SJS] or ocular cicatricial pemphigoid [OCP]) had once been deemed a relative contraindication due to their propensity for corneal melts [3]. More recently, improvements in postoperative management have expanded the realm of keratoprosthesis surgery to include these complicated patient populations, although selection of such patients should still be done with a heightened level of precaution [3, 4].

Prior to surgery, it is crucial that the patient understands the commitment to frequent postoperative visits, as well as the necessity for indefinite postoperative topical medications. The procedure should be performed by a surgeon well experienced in penetrating keratoplasty and who has direct access to a multidisciplinary ophthalmology team (glaucoma, retina, and oculoplastics specialists) due to the frequent need for implantation of glaucoma drainage, pars plana vitrectomy, and lid reconstruction at or around the time of keratoprosthesis placement [1, 5].

The Boston type I keratoprosthesis is available for order from the Massachusetts Eye and Ear Infirmary (Boston, MA). Currently, there are three components to the threadless Boston type I keratoprosthesis. These include a front plate and its connected stem that includes the optical element manufactured from medical-grade polymethylmethacrylate (PMMA), a larger back plate, and a titanium locking ring. These are assembled around a corneal allograft with a central 3 mm trephination. The front plate, which is either 5 or 6 mm in diameter, has an attached posterior stem that is segmented into three parts. The first segment of the stem, which accommodates the corneal graft, is 3.35 mm in diameter and 0.62 mm in height. The second segment is 3 mm in diameter and 0.84 mm in height, and this portion accommodates the back plate. There is a single groove anterior to the innermost section of the stem into which the locking ring snaps tightly. The dimensions of this groove are 2.74 mm in diameter and 0.33 mm in height.