Biomedical subjects

Katsuhiko Kobayashi

Publications and source records attributed to Katsuhiko Kobayashi.

4 recordsLinked to original sources

PubMed2005

Genetic features, clinical phenotypes, and prevalence of sensorineural hearing loss associated with the 961delT mitochondrial mutation.

To examine the frequency of the 961delT mitochondrial point mutation, considered to be associated with aminoglycoside-induced hearing loss, restriction fragment length polymorphism (RFLP) analysis was performed in (1) 334 unrelated sensorineural hearing loss (SNHL) patients and (2) 56 patients with aminoglycoside antibiotic injection history. Approximately 2% of the SNHL patients had the 961delT mutation, raising the possibility of a relatively high prevalence of this mutation among hearing impaired populations. However, the following findings cast doubt on whether this mutation is truly associated with hearing loss: (1) a similar frequency found in the control subjects, (2) hearing loss that was not segregated within the families, (3) rates of heteroplasmy and aging that were not correlated with the severity of hearing loss, and (4) a low prevalence among the aminoglycoside-induced hearing loss patients (1/56=1.8%). The present analysis did not agree with the concept that the 961delT mutation causes aminoglycoside-induced hearing loss.

Adolescent↗

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↗

PubMedDate not supplied

Internal sclerostomy with the Er:YAG laser using a gradient-index (GRIN) endoscope.

BACKGROUND AND OBJECTIVE: To show that sclerostomy, a glaucoma filtering surgery, can be performed using an Er:YAG laser. Scarring at the filtering site, a recurrent problem, may be reduced through proper positioning of the sclerostomy by using an intraocular endoscope. MATERIALS AND METHODS: Ab interno full-thickness sclerostomies were performed on eye bank eyes with an Er:YAG laser through a custom made optical delivery system. The intraocular laser probe consisted of a low OH silica fiber inserted in a metallic tapered sheathing. A rigid intraocular endoscope based on gradient-index lenses allowed visualization of the filtration site. RESULTS: A clear view of the anterior chamber angle was obtained through the endoscope, allowing for precise location of the sclerostomy. Full-thickness sclerostomies could then be performed at the desired location. Histologic sections showed thermal necrosis less than 50 microm thick in tissue adjacent to the sclerostomy. CONCLUSIONS: A sclerostomy performed with a combined procedure using an Er:YAG laser and intraocular endoscopy increases the speed of the procedure. The use of a high-resolution intraocular endoscope may increase the success rate of ab interno laser glaucoma surgeries.

Endoscopy↗