Purpose To evaluate the optical characteristics of the Boston Keratoprosthesis (KPro), identify glare sources, evaluate possible glare control, and examine the benefit of implanting when the fellow eye has normal vision. Methods Computed and optical-bench-measured point spread function (PSF) and glare sources were compared. A translucent plastic cornea was used to determine the impact of glare due to scatter in the cornea, and its control with a dark-iris tinted contact lens. The effect of glare in implanted eyes was measured with a Mentor Brightness Acuity Test (BAT), with and without the dark-iris contact lens. The computed and measured visual fields were compared. Stereopsis was measured in patients with an intact fellow eye. Results The computed and measured MTFs for the KPro were found to be very close to the diffraction limit. Both the model-eye measurements and patients' BAT glare responses identified that the hazy corneal graft surrounding the KPro is the main source of glare, and can be controlled with a dark-iris contact lens. The lid effectively blocks the light that would be scattered in the hazy cornea of patients implanted with the Type II KPro. An intact fellow eye remains the dominant eye, with better acuity, and the KPro eye supports only minimal stereo ability and does not expand the binocular visual field. Conclusion Glare can be reduced significantly with the use of a contact lens with a dark iris. Implanting the KPro in a patient whose fellow eye has normal or near normal vision does not seem to improve visual function.

Purpose To evaluate the optical characteristics of the Boston Keratoprosthesis (KPro) in relation to visual function. To determine glare sources and evaluate possible glare control. To explore the feasibility of fundus imaging. To examine the binocular consequences of implanting the device when the fellow eye has normal vision. Methods The computed and optical bench measured point spread function and corresponding modulation transfer function (MTF), as well as glare sources, were compared. A model eye construct was used to determine the relative impact of different sources of glare and its control. The effect of glare in eyes implanted with a KPro was measured with a Brightness Acuity Test (BAT) with and without a dark iris contact lens (dCL) for 8 eyes with Type I and 2 eyes with Type II KPro. Computed and measured visual fields were compared. The power of a lens that provides a wide field view of the fundus was calculated. Images with a fundus camera and lenses were obtained. Stereopsis was measured in 5 Type I KPro patients with an intact fellow eye. Results The computed and measured MTF for the KPro were found to be very close to the diffraction limit. Both the model eye and patients testing identified the hazy corneal graft as the main source of glare, which was controlled with a dCL. In 3 patients with an intact fellow eye, modest stereo acuity was gained with KPro implantation. Binocular visual field is not expanded when implanting a patient with normal fellow eye. Good image quality of the fundus is achieved in eyes with clear media. Conclusion Disability glare can be reduced with the use of a dCL. Implanting the KPro in a patient with an intact fellow eye only marginally improves visual function. Adequate fundus imaging can be obtained.