After trials with radically different KPro designs, we settled on a collar button-shaped polymethylmethacrylate (PMMA) device, to be implanted into a carrier corneal graft—this combination then transplanted and sutured into the patient’s cornea like a standard graft [
31] (Fig.
1). It was felt that retention was improved by placing the haptic (the back plate) totally behind the cornea, rather than having it placed in the stroma. Later, large holes in the back plate were made to facilitate diffusion of nutrients from the aqueous to the graft keratocytes [
42]. Also a new threadless design was introduced to better protect the graft Descemet’s membrane and endothelium of the graft from damage during assembly [
34]. The metal titanium, which has been widely used elsewhere in the body, and had previously been incorporated as intrastromal haptics in KPro devices [
45,
51,
55], was adopted by us as back plate in 2005 (Fig.
2). We have found this material (actually an alloy, medical grade 23, consisting of titanium 90 %, aluminium 6 %, and vanadium 4 %) to be better tolerated by corneal tissues than PMMA, in vitro as well as in vivo [
4,
79]. The somewhat shiny appearance of the metal can be cosmetically troublesome (Fig.
2) but it can be dampened by electrolysis, creating a blue or brown surface [
61] (Tinted soft contact lenses can also be cosmetically helpful). The diameter of the titanium back plate is normally chosen as 8.5, or 7.0 mm, but in selected cases, a larger diameter (9.5 mm) has been found to clamp the graft wound better and may reduce the incidence of retroprosthesis membranes (RPMs), anterior synechia formation, and possibly even glaucoma [
25], although the subject is still controversial. Recent experiments have shown that coating also the stem of the B-KPro with titanium strongly improves tissue adhesion, most likely making passage of bacteria or fungi into the eye less likely [
72]. Coating the stem with a thin, inert antimicrobial substance may have similar effect [
11].
Another design, labeled B-KPro II (Fig.
1) has an added anterior nub to protrude between closed lids or through the upper lid—similar to lid arrangement used by Strampelli (1963) and DeVoe [
19]. This device is reserved for the most desperate of corneal diseases such as totally dry eyes from autoimmune diseases or chemical burns [
16,
59,
75].