Intrinsic Optical Properties of Boston Keratoprosthesis

Abstract

To benchmark the optical performance of Boston Keratoprosthesis (B-KPro). Methods: Back focal lengths (BFL) of B-KPros for various eye axial lengths were measured using an optical bench, International Organization for Standardizationcertified for intraocular lens characterization, and compared against manufacturer's specification. The modulation transfer function (MTF) and the resolution efficiencies were measured. The theoretical geometry-dependent higher-order aberrations (HOA) were calculated. The devices were characterized with optical profilometry for estimating the surface scattering. Aberration correction and subsequent image quality improvement were simulated in CODE-V. Natural scene-imaging was performed in a mock ocular environment. Retrospective analysis of 15 B-KPro recipient eyes were presented to evaluate the possibility of achieving 20/20 best-corrected visual acuity (BCVA). Results: BFL measurements were in excellent agreement with the manufacturerreported values (r = 0.999). The MTF specification exceeded what is required for achieving 20/20 visual acuity. Astigmatism and field curvature, correctable in simulations, were the primary aberrations limiting imaging performance. Profilometry of the anterior surface revealed nanoscale roughness (root-mean-square amplitude, 30-50 nm), contributing negligibly to optical scattering. Images of natural scenes obtained with a simulated B-KPro eye demonstrated good central vision, with 10/10 visual acuity (equivalent to 20/20). Full restoration of 20/20 BCVA was obtainable for over 9 years in some patients. Conclusions: Theoretical and experimental considerations demonstrate that B-KPro has the optical capacity to restore 20/20 BCVA in patients. Further image quality improvement can be anticipated through correction of HOAs. Translational Relevance: We establish an objective benchmark to characterize the optics of the B-KPro and other keratoprosthesis and propose design changes to allow improved vision in B-KPro patients.

Corneal power values for use with keratoprostheses and intraocular lenses

“…The Boston Keratoprosthesis (KPro) is the most widely used artificial cornea, and its optical properties have been described previously. [2][3][4][5][6][7]10 It is sketched in profile in Figure 1b, and details of the design are provided by Sayegh et al, 2 Helms et al 4 and Hui et al 7 (although the parameters may not always be listed correctly). The material is rigid polymethyl-methacrylate (PMMA), which has a much higher refractive index than the natural cornea (1.492 compared to 1.376).…”

“…The Boston Keratoprosthesis (KPro) is the most widely used artificial cornea, and its optical properties have been described previously 2–7,10 . It is sketched in profile in Figure , and details of the design are provided by Sayegh et al ., 2 Helms et al 4 .…”

“…included refractive results for the Boston KPro, and indicated that the refractive error was much lower for the aphakic patients (−0.70 ± 1.6 D), than for the pseudophakic patients (−3.25 ± 3.2 D). This is presumably because the KPro power was personalised when the eye was aphakic, as described by Hui et al 7 …”

“…1 Various designs have previously been evaluated, and the most widely used artificial cornea is the Boston KPro (masseyeandear.org/medicalprofessionals/keratoprosthesis), whose design and optical properties have been described. [2][3][4][5][6][7] Minimising the postoperative refractive error is much less important than achieving a stable eye that is free of infection and other complications, although the overall goal is to improve vision without the need for additional correction. However, visual acuity results that are reported for a KPro are often only 'best corrected' values, and the actual refractive errors are rarely included in published reports.…”

“…Utine et al 10 included refractive results for the Boston KPro, and indicated that the refractive error was much lower for the aphakic patients (−0.70 ± 1.6 D), than for the pseudophakic patients (−3.25 ± 3.2 D). This is presumably because the KPro power was personalised when the eye was aphakic, as described by Hui et al 7 These papers indicate that the anterior KPro radius of curvature is adjusted to focus at the retina for the aphakic Type 1 device, although there is no specific evaluation as to how accurate the method is clinically. Further, no method is described to combine a KPro and an IOL to control the refractive error of a pseudophakic eye.…”