Biomedical subjects

Kazuhiko Ohnuma

Publications and source records attributed to Kazuhiko Ohnuma.

3 recordsLinked to original sources

PubMedDate not supplied

Visual simulation of retinal images through a decentered monofocal and a refractive multifocal intraocular lens.

PURPOSE: To evaluate the effect of decentration of a monofocal intraocular lens (IOL) and a refractive multifocal IOL on retinal image quality using a new visual simulation system. METHODS: Using a new visual simulation system, we performed visual simulation of a monofocal and a multifocal IOL at 5, 4, 3, 2, 1, and 0.4 m with several decentered IOL positions from 0 to 1.0 mm through a 3- or 4-mm aperture using Landolt visual acuity (VA) charts. The VA was estimated under each condition from the simulated retinal image. RESULTS: With a monofocal IOL, the image was affected minimally by decentration at 4 and 5 m; at 2 and 3 m, the image contrast decreased slightly with increased decentration. With the multifocal IOL, some loss of image contrast developed at all distances compared with the monofocal IOL; however, the images of the Landolt's rings were still recognizable under all conditions. CONCLUSIONS: Our results suggest that up to 1.0 mm of decentration of a monofocal and multifocal IOL would not greatly affect the retinal image quality.

Foreign-Body Migration↗

PubMedDate not supplied

Evaluation of optical function using a new point spread function analysis system in cataractous and pseudophakic eyes: preliminary results.

PURPOSE: To evaluate optical function in cataractous and pseudophakic eyes using the new point spread function (PSF) analysis system in a clinical setting. METHODS: We applied this new analysis system in the study of two cataractous eyes and one pseudophakic eye of two patients. Using a PSF analyzer, double-pass PSF was measured directly for each subject, and the single-pass modulation transfer function (MTF) and single-pass PSF were calculated. The simulated retinal images of various sizes of Landolt's rings and their contrast characteristics were also calculated by the PSF analyzer. RESULTS: The MTF and the contrast of the simulated retinal images degraded in cataractous eyes were compared with data for normal eyes; the degradation pattern depended on the opacification pattern. The MTF and the contrast of the simulated retinal images in the pseudophakic eye improved significantly compared with the cataractous eyes, although both values were lower in the pseudophakic eye than in young normal eyes. CONCLUSIONS: Our data showed degradation of optical function in cataractous and pseudophakic eyes in comparison with optical function in young normal eyes. If further accumulations of PSF data are made, it may be possible to establish an objective standard by which to measure the progression of cataract, as well as an objective indication for treatment in the future.

Aged↗

PubMedDate not supplied

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.

Adult↗