Chapter 3 - Wavefront Sensing and Diagnostic Uses

Wavefront Sensing and Diagnostic Uses

GEUNYOUNG YOON
University of Rochester, Rochester, New York

3.1   WAVEFRONT SENSORS FOR THE EYE

Various wavefront sensing techniques have been developed for the human eye
[1–12]. Wavefront sensing is a key technique required to better understand
the optical quality of the eye and to develop advanced vision correction
methods, such as adaptive optics, customized contact lenses, and customized
laser refractive surgery. It is also a necessary technique for high-resolution
imaging of the retina. The most commonly used wavefront sensors are the
spatially resolved refractometer, the laser ray tracing technique, and the
Shack–Hartmann wavefront sensor. Wavefront sensors measure the aberrations
of the entire eye generated by both corneal surfaces and the crystalline
lens, whereas corneal topography can only measure the aberrations induced
by the anterior or both anterior and posterior corneal surfaces. Since wavefront
sensing light needs to pass through the cornea and crystalline lens, the
eye’s pupil is the absolute limiting aperture of wavefront sensing, which may
require pupil dilation. Wavefront sensing may be very difficult if parts of the
eye have opacities, such as cataracts and corneal scars.

Wavefront sensors can be categorized by whether the measurement is
based on a subjective or objective method and whether the wavefront sensor
measures the light going into the eye or coming out of the eye, as shown in
Figure 3.1. However, all wavefront sensors developed for vision science and
ophthalmology are based on the same principle, which is an indirect measurement
of local wavefront slopes and the reconstruction of the complete wavefront
by integrating these slopes, as illustrated in Figure 3.2. The relationship
between wavefront slope (the first derivative of the wavefront) and the spot
displacement, Δx_S and Δy_S with respect to the x and y directions, can be
expressed as:

where F is the focal length of the focusing optics. With the measured
spot displacements in the x and y directions at each sampling point, the
original wavefront can be calculated using different reconstruction
algorithms.

In this section, the principle of operation and advantages and disadvantages
for each wavefront sensor will be summarized.

Wavefront Sensing and Diagnostic Uses

GEUNYOUNG YOON
University of Rochester, Rochester, New York

3.1   WAVEFRONT SENSORS FOR THE EYE

Various wavefront sensing techniques have been developed for the human eye
[1–12]. Wavefront sensing is a key technique required to better understand
the optical quality of the eye and to develop advanced vision correction
methods, such as adaptive optics, customized contact lenses, and customized
laser refractive surgery. It is also a necessary technique for high-resolution
imaging of the retina. The most commonly used wavefront sensors are the
spatially resolved refractometer, the laser ray tracing technique, and the
Shack–Hartmann wavefront sensor. Wavefront sensors measure the aberrations
of the entire eye generated by both corneal surfaces and the crystalline
lens, whereas corneal topography can only measure the aberrations induced
by the anterior or both anterior and posterior corneal surfaces. Since wavefront
sensing light needs to pass through the cornea and crystalline lens, the
eye’s pupil is the absolute limiting aperture of wavefront sensing, which may
require pupil dilation. Wavefront sensing may be very difficult if parts of the
eye have opacities, such as cataracts and corneal scars.

Wavefront sensors can be categorized by whether the measurement is
based on a subjective or...