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X. Wei, L. N. Thibos; Measuring Ocular Aberrations in Peripheral Vision With Scanning Shack-Hartmann Aberrometer. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4300.
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Peripheral vision and off-axis aberrations not only play an important role in daily visual tasks but may also influence eye growth and refractive development. Given the methodological difficulty of subjective refraction of the peripheral field, it is important to develop instrumentation for measuring off-axis wavefront aberrations of human eyes objectively and efficiently.
We incorporated a Shack Hartmann wavefront sensor (SHWS) into a double-pass scanning-system. We refer to this instrument as a scanning Shack-Hartmann aberrometer (SSHA). With this system, the eye fixates a single target while the entering probe beam rotates about the center of the entrance pupil via the scanning system to place the laser beacon in a sequence of locations in the peripheral retina. Correspondingly in the reverse direction, Light (wavefront) reflected from the eye is de-scanned through the same scanning system for measurement by the fixed SHWS.
The prototype SSHA successfully measured the off-axis wavefront aberrations at 36 locations (3 eccentricities, 12 meridia) over +/- 15 degree visual field within 7 seconds. In a validation experiment with a wide angle model eye (4mm pupil), the instrument measured the Zernike defocus aberration accurately (<0.02µm error) and precisely (<0.03µm error). In an evaluation experiment with a human eye, the full sequence off-axis aberration measurements over the +/-15 degree visual field was repeated five times with realignment of eye to instrument between each measurement. The root-mean-square error of the wavefront deviation among the five measurements was 0.14µm or less for all locations in the visual field.
The developed SSHA is a feasible and reliable instrument for characterizing the eye’s optical quality over a large portion of the visual field in basic and applied clinical research and diagnosis.
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