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A New Wavefront Sensor With Polar Symmetry: Quantitative Comparisons With a Shack-Hartmann Wavefront Sensor
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PURPOSE
A novel wavefront sensor has been developed. It follows the same principle of the Shack-Hartmann wavefront sensor in that it is based on slope information. However, it has a different symmetry, which may offer benefits in terms of application.
METHODS
The new wavefront sensor consists of a set of donut-shaped acrylic lenses with a charge coupled device located at the focal plane. From detection of shift in the radial direction, radial slopes are computed for 2880 points. Theoretical computations for higher order aberrations and lower order aberrations were implemented for the Shack-Hartmann wavefront sensor and the new wavefront sensor, and practical measurements were conducted on several sphere-cylinder trial lenses.
RESULTS
The overall mean value of root mean square error (RMSE) (in microns) for theoretical computations was 0.03 for the Shack-Hartmann wavefront sensor and 0.02 for the new wavefront sensor. The mean value of RMSE for lower order aberrations (1-5) was 0.01 and 0.00003, and for higher order aberrations was 0.02 and 0.02, for the Shack-Hartmann and new wavefront sensors, respectively. For practical measurements (sphere, cylinder, axis), the standard deviation was 0.04 diopters (D), 0.04 D, and 4° for the new wavefront sensor and 0.02 D, 0.02 D, and 5° for the Shack-Hartmann wavefront sensor.
CONCLUSIONS
Precision of the new wavefront sensor when measuring astigmatic and spherical surfaces is compatible with the Shack-Hartmann wavefront sensor. Centration with this new sensor is an absolute process using the center of the entrance pupil, which is where the line of site passes. This wavefront sensor, similar to the Shack-Hartmann sensor, does not eliminate the possibility of tilt. For more conclusive and statistically valid data, in vivo measurements are needed. [J Refract Surg. 2006;22:954-958.]
AUTHORS
From Grupo de Óptica, Instituto de Física de São Carlos, Universidade de São Paulo (Carvalho, Castro), and the Departamento de Oftalmologia, Escola Paulista de Medicina, Universidade Federal de São Paulo (Chamon, Schor), São Paulo, Brazil.
This study was partially funded by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, process #00/06810-4).
All authors have proprietary interests in the instrumentation presented herein.
The sensor presented herein is patent pending.
The authors thank technicians Antonio Carlos Romao, Marcos Steffani, Thiago Orlando, and Paulo Carozelli for their help in the manufacturing process of the different sensors and taking the pictures shown in this article.
Correspondence: Luis A. Carvalho, PhD, Grupo de Óptica, Instituto de Física de São Carlos, Universidade de São Paulo, Av Trabalhador Sãocarlense, 400 Cx. Postal 369 - CEP: 13560-970, São Carlos - SP, Brazil. E-mail: lavcf@if.sc.usp.br