Measuring higher order optical aberrations of the human eye: techniques and applications

Abstract

In the present paper we discuss the development of wave-front, an instrument for determining the lower and higher optical aberrations of the human eye. We also discuss the advantages that such instrumentation and techniques might bring to the ophthalmology professional of the 21st century. By shining a small light spot on the retina of subjects and observing the light that is reflected back from within the eye, we are able to quantitatively determine the amount of lower order aberrations (astigmatism, myopia, hyperopia) and higher order aberrations (coma, spherical aberration, etc.). We have measured artificial eyes with calibrated ametropia ranging from +5 to -5 D, with and without 2 D astigmatism with axis at 45º and 90º. We used a device known as the Hartmann-Shack (HS) sensor, originally developed for measuring the optical aberrations of optical instruments and general refracting surfaces in astronomical telescopes. The HS sensor sends information to a computer software for decomposition of wave-front aberrations into a set of Zernike polynomials. These polynomials have special mathematical properties and are more suitable in this case than the traditional Seidel polynomials. We have demonstrated that this technique is more precise than conventional autorefraction, with a root mean square error (RMSE) of less than 0.1 µm for a 4-mm diameter pupil. In terms of dioptric power this represents an RMSE error of less than 0.04 D and 5º for the axis. This precision is sufficient for customized corneal ablations, among other applications. CorrespondenceL.

Keratoconus prediction using a finite element model of the cornea with local biomechanical properties

“…We think this has happen mainly due to the refractive surgery field. The development of better and more efficient excimer lasers (such as the flying spot lasers (1)(2)(3) ) and more precise techniques for measuring cornea and whole eye aberrations (such as the Hartman-Shack wavefront sensor (4)(5)(6)(7)(8)(9)(10) or the cylindrical sensor introduced by our research group (11)(12)(13) ) allowed for the development of better ablation algorithms and, ultimately, customized methods. Nevertheless, there has been a considerable amount of frustration regarding results obtained with recent algorithms for certain keratoconus suspicious cases.…”

The Placido Wavefront Sensor and Preliminary Measurement on a Mechanical Eye

“…19,21 In this preliminary practical analysis, only defocus aberration was measured and pupil diameter was fixed at 5 mm. 19,21 In this preliminary practical analysis, only defocus aberration was measured and pupil diameter was fixed at 5 mm.…”

“…This procedure will not be reproduced here given the existence of an abundant amount of literature on the subject (see, for example, references 5,6,19 ). Therefore, the term to the right in equation 3 should be negligible to avoid the skew-ray error problem, and of course it depends on how distorted the surface is.…”

Opto-mechanical artificial eye with accommodative ability

“…Opto-mechanical artificial eyes (OMAEs) imitate the basic image formation of a human eye, and are mainly used for the in-vitro test of the optical performances of refractive correction devices such as intraocular [1][2][3][4], contact [5,6], or ophthalmic [7][8][9] lenses. OMAEs are also used in the calibration of optical systems, for instance as test beds for measuring and characterizing the optical wavefront [10][11][12], and to practice clinical refraction [13,14].…”