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chapter 8, Optical Metrics of Ocular Wavefronts
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Table of Contents
- 1. Introduction
Chapter Contents
- 8.1 Pupil Plane Metrics for Ocular Aberrations
- 8.1.1 Root Mean Square Wavefront Error
- 8.1.1.1 Zernike representation
- 8.1.1.2 Fourier representation
- 8.1.1.3 Taylor representation
- 8.1.2 Wavefront Refractions
- 8.1.2.1 Zernike representation
- 8.1.2.2 Fourier representation
- 8.1.2.3 Taylor representation
- 8.1.3 Other Metrics
- 8.2 Image Plane Metrics for Ocular Aberrations
- 8.2.1 Strehl Ratio
- 8.2.2 Full Width at Half Maximum
- 8.2.3 Encircled Energy
- 8.2.4 Modulation Transfer Function
- 8.2.5 Compound Modulation Transfer Function
- 8.2.6 Volume under Modulation Transfer Function
- 8.2.7 Visual Strehl Ratio
- 8.2.8 Other Metrics
- 8.3 Visual Performance Metrics
- 8.3.1 Manifest Refractions
- 8.3.2 Visual Acuity
- 8.3.3 Contrast Sensitivity
- 8.3.4 Neural Contrast Threshold
- 8.4 Simulation of Visual Outcomes
- 8.4.1 Analytic Point Spread Functions
- 8.4.2 Polychromatic Point Spread Functions
- 8.4.3 Calibration of the Point Spread Functions
- 8.4.4 Convolution of Point Spread Function and Vision Targets
- 8.4.5 Prediction of Visual Acuity from Ocular Aberrations
- Appendix 8.A Derivation of Eq. (8.9)
- Appendix 8.B Derivation of Eq. (8.28)
- Appendix 8.C Matlab Code for Calculation of Point Spread Functions
- Bibliography
Excerpt
For vision correction, our goal is to achieve perfect functional vision. In other words, we want to obtain the best visual outcome after vision correction. The questions are then, what kinds of ocular aberrations affect the visual performance the most, or which Zernike aberration may cause a particular visual symptom?
The technological advancement of aberrometry has given the vision correction industry the ability of precisely measuring the ocular aberrations in living human eyes. For the researchers and developers of vision correction techniques, it is very desirable to find some correlations between ocular aberrations and visual performance, at least optically.
Many authors[1, 2, 3, 4, 5, 6, 7, 8, 9, 10] have studied different optical metrics to best describe the relationship between the ocular aberrations and the visual performance. Among the various potential metrics, some are based on the optical path difference, or the RMS wavefront error on the pupil plane, and some are based on the calculation of the point spread functions on the retinal plane. Classically, the RMS wavefront error has been widely used as a very useful optical metric when it is very small, as given by the Maréchal approximation. [11] For normal human eyes,[12, 13] or even eyes corrected with adaptive optical systems, [14] the residual RMS wavefront error is still too large to apply the Maréchal approximation. In fact, it is generally accepted that the pupil plane metrics do not correlate as well with visual outcomes as the retinal plane metrics. Even so, both sets of optical metrics are useful in understanding the characteristics of the ocular aberrations.
8.1 Pupil Plane Metrics for Ocular Aberrations
As most commercial aberrometers measure ocular aberrations on the exit pupil plane, and the exit pupil plane serves as the aperture of the optics of the eye, it is very natural to evaluate the quality of such a system as seen from the aperture. On this plane, however, no images are formed.
©2008 Society of Photo-Optical Instrumentation Engineers
