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Samuel Steven, Vyas Akondi, Alfredo Dubra; Chromatic Shack-Hartmann wavefront sensor with adaptive optics correction of monochromatic aberrations. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4613.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate a custom Shack-Hartmann wavefront sensor (SHWS) designed to measure the chromatic variation of the ocular aberrations.
A chromatic SHWS was designed with all reflective optical elements in the light collection path, other than for the lenslet array (see Figure 1). Back reflections from the cornea are mitigated through polarization control, while those from beam splitting optical elements are mitigated using Brewster’s angle or deviated through wedged elements. An 850 nm superluminescent diode and a supercontinuum light source connected to an acousto-optic tunable filter are alternated to drive a deformable mirror for correction of monochromatic aberrations and to record chromatic aberrations, respectively. Accuracy and repeatability were tested using three different lenses: an achromatic doublet, a plano-convex singlet and an plano-asphere singlet. These lenses were selected because they have lower, comparable and higher longitudinal chromatic aberration than that of the average human eye, respectively. The SHWS camera was focused at the geometrical focus of the lenslet array to minimize measurement bias at partially illuminated lenslets.
After correction of monochromatic aberrations at 850 nm, measurements of longitudinal chromatic aberration in the 500-900 nm range (50 nm steps), are consistent with lens specifications and with an average repeatability (standard deviation, N=30) of 0.04 diopters (D) or better (see Figure 2). Cylindro-chromatism would be theoretically zero for all three lenses and we found that this is the case to within measurement noise (~0.015D).
A novel chromatic SHWS for human use was designed, built, and demonstrated using model eyes with varying longitudinal chromatic aberration. This design incorporates features that address prior limitations including all-reflective light collection path, back-reflection minimization, monochromatic aberration correction, large pupil (7.5 mm), motorized source focusing for maximal SNR and broad bandwidth.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Custom chromatic Shack-Hartmann Wavefront sensor layout.
Longitudinal chromatic aberration of three lenses measured with a custom Shack-Hartmann wavefront sensor.
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