Masahiro Shibutani

Calculation of ocular single-pass modulation transfer function and retinal image simulation from measurements of the polarized double-pass ocular point spread function.

The single-pass modulation transfer function (MTF(sgl)) is an important numerical parameter that can help elucidate the performance and some processes of the human visual system. In previous studies, the MTF(sgl) was calculated from double-pass point spread function (PSF) measurements. These measurements include a depolarized reflection component from the retina that introduces a measurement artifact, and they require long acquisition times to allow averaging to reduce speckle. To solve these problems, we developed a new ocular PSF analysis system (PSFAS) that uses polarization optics to eliminate the depolarized retinal reflection component, and a rotating prism to increase measurement speed. Validation experiments on one patient showed that the MTF(sgl) measured by PSFAS agrees closely with the MTF calculated from contrast sensitivity measurements. A simulated retinal image was calculated by convolution of Landolt rings with the calculated single-pass PSF provided by the PSFAS. The contrast characteristic then was calculated from the simulated retinal images. These results indicate that the MTF(sgl) obtained using the PSFAS may be a reliable measure of visual performance of the optics of the eye, including the optical effects of the retina. The simulated retinal images and contrast characteristics are useful for evaluating visual performance.

Simulated retinal images of Landolt rings in human eyes including asymmetric aberrations on the point spread function analysis system

To simulate the retinal images of the human eye including asymmetric aberrations is very important and interesting with using a new point spread function analysis system (PSFAS). The point light source (SLD 840 nm) was projected onto the subjects eye and the reflected image at the retina was captured by the charge coupled device which was in the conjugated point with the retina (double-pass formula). To obtain the modulation transfer function (MTF) of the optical system, equal sized apertures were used as entrance and exit pupils. To obtain the phase transfer function (PTF), unequal sized apertures were used. To obtain the simulated retinal images, the Fourier spectrum of the original chart was multiplied by the MTF and the PTF as the phase term of the original chart was added. The inverse Fourier transformation of the Fourier spectrum term and the phase term was the simulated retinal image. The simulated retinal images of the Landolt rings in human eyes might sufficiently involve asymmetric aberrations without losing the high-frequency range of spatial frequency. The PSFAS can simulate retinal images, which are based on not only the information from the symmetric aberrations and the scattering and absorption of haze but also on the information from the asymmetric aberrations. The PSFAS can objectively evaluate the characteristics of the human optical system and therefore is useful in an ophthalmology clinic setting.

Measurement of the single-pass modulation transfer function and simulation of the retinal image of the human eye with a newly developed point spread function analysis system

We developed a new point spread function (PSF) analysis system (PSFAS) to study the optical system of the human eye. An infrared point light source is projected on the retina, then the single-pass modulation transfer function (MTF) is derived from teh iamge of incoherent polarized reflection double-pass PSF measured by PSFAS. The retinal images and the contrast characteristics of various sized Landolts rings then are simulated with the single-pass PSF calculated by the single-pass MTF. The visual acuity (VA) is predicted from the retinal images. The single-pass MTF and the contrast characteristics of aged subjects were clearly lower than those of a young subject in mid-frequency, though the cut-off frequency was similar in the two subjects. The predicted VA from the simulated retinal images agreed with the actual VA in normal subjects and in those with myopic astigmatism. This becomes a useful system for elucidating the optical characteristics of the human eye. In addition, the visual simulation obtained using this system is clinically useful for objectively evaluating visual function.