The placido wavefront sensor and preliminary measurement on a mechanical eye

The placido wavefront sensor and preliminary measurement on a mechanical eye

Autor Carvalho, Luis Alberto Autor UNIFESP Google Scholar
Castro, Jarbas C. Autor UNIFESP Google Scholar
Instituição Univ Rochester
Universidade de São Paulo (USP)
Universidade Federal de São Paulo (UNIFESP)
Resumo Purpose. the hardware and software of a novel wavefront sensor was developed (The sensor presented here is patent pending.). It has the same principal of the Hartmann-Shack (HS) and other sensors that are based on slope information for recovery of wavefront surface, but a different symmetry, and does not use individual microlenses. This polar symmetry might offer differences during practical measurements that may add value to current and well-established gold standard techniques.Methods. the sensor consists of a set of concentric half-donut surfaces (longitudinally sectioned toroids) molded on an acrylic surface with a CCD located at the focal plane. When illuminated with a plane wavefront, it focuses a symmetric pattern of concentric discs on the CCD plane; for a distorted wavefront, a nonsymmetric disc pattern is formed (similar to images of a placido-based videokeratographer). From detection of shift in the radial direction, radial slopes are computed for a maximum of 2880 points, and the traditional least-squares procedure is used to fit these partial derivatives to a set of 15 conventional OSA-VSIA Zernike polynomials. Theoretical computations for several synthetic surfaces containing low-order aberration (LOA) and high-order aberration (HOA) were implemented for both the HS and the new sensor.Results. Root mean Square error (RMSE) in microns when theoretical data was taken as control, for HS sensor and new sensor, was 0.02 and 0.00003 for LOA (defocus, astigmatism) and 0.07 and 0.06 for HOA (coma, spherical, and higher terms), respectively. After this, practical preliminary measurements on a mechanical eye with a 5-mm pupil and 10 different defocus aberrations ranging from -5 D to 5 D, in steps of 1 D, were compared between sensors. RMSE for difference in measurements for HS and new sensor for sphere, cylinder, and axis, was 0.13 D, 0.07 D, and 110. Measurements were taken only on defocus aberrations. Qualitative images for astigmatism are shown.Discussion. Although practical in vivo tests were not conducted in this first study, we also discuss certain possible alignment differences that may arise as a result of the different symmetry of the new sensor. To take any conclusive assumption regarding the accuracy and/or precision of this new sensor, when compared with other well-established sensors, statistically significant in vivo measurements will need to be conducted.
Assunto wavefront sensing
Hartmann-Shack sensor
Zernike polynomials
Placido disc
Idioma Inglês
Data 2006-02-01
Publicado em Optometry and Vision Science. Philadelphia: Lippincott Williams & Wilkins, v. 83, n. 2, p. 108-118, 2006.
ISSN 1040-5488 (Sherpa/Romeo, fator de impacto)
Editor Lippincott Williams & Wilkins
Extensão 108-118
Direito de acesso Acesso aberto Open Access
Tipo Artigo
Web of Science WOS:000235875700009

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