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R. R. Sayegh, L. Avena Diaz, F. Vargas-Martín, R. H. Webb, C. H. Dohlman, E. Peli; Optical Qualities of the Boston Keratoprosthesis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1037. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the optical characteristics (in particular glare effects) of the Boston keratoprosthesis (KPro) computationally, experimentally and clinically.
A model of the PMMA KPro was created in Zemax (Focus Software Inc, San Diego, Calif), and the theoretical modulation transfer function (MTF), point spread function (PSF), and visual fields were computed. An artificial schematic eye construct including a translucent plastic cornea with a KPro was used to measure and identify the source of glare in eyes implanted with a KPro. Visual acuity (VA), glare sensitivity, contrast sensitivity, and visual fields were obtained prospectively from 10 patients (mean age 53 ± 20 years old, range 19 to 84 years), implanted with the device 2.6 ± 2.4 years prior. The effect of a soft bandage contact lens with a painted black iris on glare was measured. All eyes had a VA of 20/60 or better over at least 10 months. Three of the 10 eyes had glaucoma.
The MTF for the KPro was found to be close to the diffraction limit. The artificial eye experiment identified the hazy corneal graft surrounding the KPro as the main source of glare.Mean LogMAR near VA in 5 patients (3 of which with a type I KPro) was 0.15 ± 0.16 (range 0.00 to 0.40). Mean LogMar distance visual acuity (VA) in the 8 patients with a type I KPro using the Mentor BAT was 0.30 ± 0.15 under no glare, 0.38 ± 0.16 under low glare, 0.83 ± 0.54 under medium glare, and 1.36 ± 0.42 under high glare setting. With the iris-painted contact lens in placed, the VAs were 0.23 ± 0.13, 0.33 ± 0.13, 0.47 ± 0.15, and 0.84 ± 0.27 respectively, and the difference under high glare (about 3 lines) was significant (p = 0.01). Visual fields (horizontal) were about 95° wide in eyes with a type I KPro, and 90° in type II. No color deficiencies were detected on the Ishihara Color Test. The stereo acuity at 16 inches ranged from 400 to 800 seconds.
The optics of the Boston KPro were found to be adequate for normal vision. The hazy cornea surrounding the device was identified as a significant source of glare. Such glare can be significantly reduced with the use of a soft bandage contact lens painted with a black iris.
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