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S. Chiesa, C. Dainty; Investigation of Pyramid Wavefront Sensor Sensitivity for Ophthalmic Applications. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2308.
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© ARVO (1962-2015); The Authors (2016-present)
One interest of using a wavefront sensor for the detection of ocular aberrations is to retrieve a more accurate measurement of ocular aberration than with the use of ophthalmic lenses.In this view, most ophthalmic research instruments use shack-hartmann wavefront sensors. Generally, an appropriate design of the wavefront sampling and aberration sensitivity of this sensor suffice to study ocular aberrations, but in cases of sensor saturation or if a very accurate wavefront measurement is needed, in-situ adjustment is almost impossible.
We designed a pyramid-wavefront sensor based adaptive optics system for use with the eye, aimed ultimately at retinal imaging. The wavefront sensor response to constant amounts of tip, tilt, defocus and typical distribution of ocular aberrations encoded as Zernike coefficients in a phase plate was carefully calibrated for three sensitivity settings. These settings are determined by the rotation of the point image over the pyramid tip, and values of 9, 21, and 33 /D, were used, where is the wavelength and D is the pupil diameter.We measured the ocular aberration for a 6mm pupil diameter for 5 subjects over typical time scales of 5 seconds. The pupil sampling was approximately 100 microns.
The sensor response to the tip and tilt at all three sensitivity settings was consistent with that predicted from the geometrical optics approximation for our sensor. The response to the Zernike phase plates (representing typical aberrations) agreed with measurements taken on a commercial Twyman-Green interferometer. In dynamic operation, low-order ocular aberrations of high amplitude (0.25 dioptres of Z5) were best observed for the 33 /D modulation, and higher orders of decomposition (less than 0.125micrometers of amplitude) best observed for the 9 and 21/D modulation.
We have verified that the variable sensitivity of the pyramid wavefront sensor retrieves an accurate value of wavefront aberration with respect to the amplitude of the Zernike term considered.This confirms the important advantage over the uniquitous Shack-Hartmann wavefront sensor, as predicted by the geometrical optics prediction
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