Preliminary results of a high-resolution refractometer using the Hartmann-Shack wave-front sensor: part I

Carvalho, Luciane Bizari Coin de; Romão, António; Stefani, Marcos; Carvalho, Lucila; Castro, Jarbas C.; Yasuoka, Fátima M. M.; Júnior, Francisco Scannavino; Santos, Juselino dos; Schor, Paulo; Chamon, Wallace

doi:10.1590/s0004-27492003000300002

Cited by 1 publication

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“…From this time up to modern days an incredible amount of techniques and instrumentation for visual quality measurements were implemented. Among them are the highly successful application of the Hartmann-Shack wavefront sensor [16][17][18][19] and other sensor with different symmetries [20], to measure higher order aberrations of the human eye, which are described by a set of Zernike Polynomials [21][22]. There is also the double-pass technique [23] which can be used to measure even higher frequency aberrations associated with scatter.…”

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confidence: 99%

Different schematic eyes and their accuracy to the in vivo eye: a quantitative comparison study

Almeida¹,

Carvalho²

2007

Braz. J. Phys.

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Current ophthalmic technology allows the manipulation of eye components, such as anterior cornea and lens, of the human eye with a considerable precision and customization. This technology opens up the possibility of exploiting some characteristics of the eye in order to improve the methods of correcting optical aberrations. Moreover, product development and research for the eye-care professional has reached very high standards, since there is nowadays software available to design and simulate practically any mechanical or optical characteristic of the product, even before it is thrown into production line. Although quite similar in the general form, different human eye models simulate the image formation by considering different property combinations in the constitutive elements of the eye structure (such as refraction index and surface curvatures), producing retinal images that resemble very closely those of the biological eye. Using optical design software, we have implemented a simulation of 5 well-known schematic eyes available in the literature. These models were the Helmholtz-Laurance, Gullstrand, Emsley, Greivenkamp and Liou & Brennan. The optical performance of these different models was compared using different quantitative optical quality parameters. The model of Liou and Brennan, contains features of the biological eye that were not considered in previous models, as the distribution of a gradient refraction index and a decentered pupil. Furthermore, it has great reliability since it takes into account the mean value of empirical measurements of the in vivo eye in order to define size and parameters such as anterior and posterior curvature of cornea, lens, axial length, etc. Comparisons between the MTF (Modulation Transfer Function), spot diagrams and ray fan showed the difference in image quality between eye models, and the Strehl Ratio was also used as a parameter of comparison. A careful comparison between the different models showed that the first four schematic eyes have better optical quality than what is expected for the general and healthy emmetropic in vivo eye. Liou and Brennan schematic eye is the one that most closely resembles the in vivo biological eye. Therefore, in applications, such as research or product development for customized vision correction, which must consider optical properties intrinsic to the biological eye, we recommend this latter model; for applications that do not require refraction-limited performance, most of the other models should be a good approximation.

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