[Physiology and pathology of visual information processing]

Abstract

(1) Human crystalline lens and vision In order to investigate the hue changes in eyes with UV-absorbing intraocular lenses (IOLs) and tinted IOLs, we simulated the changes in the chromaticity coordinates of the 16 colors of the Farnsworth dichotomous test-panel D-15 (panel D-15), considering the ratio of the spectral transmittance of the IOL and the human crystalline lens, and the results were plotted on a CIE chromaticity diagram. The chromaticity coordinates of each color for UV-absorbing IOLs shifted to close to the origin of coordinates while retaining their hue circle. However, the chromaticity coordinates for the eyes with tinted IOLs did not change much compared to the coordinates for phakic eyes. As a result, it was suggested that cyanopsia after UV-absorbing IOL implantation could be explained by this simulation. As far as the color perception is concerned, it was also felt that tinted IOLs were superior to UV-absorbing intraocular lenses. Next, in order to evaluate the hue changes after IOL implantation, the achromatic point settings were measured once before surgery and several times at intervals after surgery after taking off the eyepatch. Four subjects participated in the experiments. There was a large shift into the "yellowish" region of color space immediately after taking off the eyepatch after cataract surgery. Then, the achromatic point returned to the chromaticity near the achromaticpoint measured prior to the surgery, with the time course of a long time, compared to color constancy in our daily life, which takes as long as several hundreds of seconds to reach an asymptote. Therefore, the mechanism of achromatic point shifts after cataract surgery may be different from the color-constancy mechanism in everyday life. (2) Molecular genetics and vision We demonstrated new clinical and genetic aspects of congenital red-green color vision defects, congenital achromatopsia, enhanced s-cone syndrome (ESCS), and Oguchi disease in Japanese patients. We clinically diagnosed 88 male dichromats(31 protanopes, 56 deuteranopes, and one unclassified subject). This subject had a new form of X-linked pigment gene with a unique arrangement of exon 5(Y277 from the long-wavelength-sensitive gene and A 285 from the middle-wavelength-sensitive gene). Mutational analysis of patients with achromatopsia disclosed CNGA3 mutations (p.R 436 W, p.L633 P) in one of 14 patients, suggesting low frequency (7%, 1/14) of CNGA3 mutations in the Japanese population. Three novel NR2E3 mutations (p.R 104 Q, p.R 334 G, p.Q 350 X) were identified in both mild and severe forms of ESCS. A novel homozygous GRK1 mutation (p.P 391 H) was found in the Oguchi disease patient with reduced cone responses. This is the first reported Japanese patient with GRK1 -associated Oguchi disease. 3. Information processing of the visual cortex and vision Regarding information processing in the visual cortex, we developed the stimulus to improve identifying retinotopy of the human visual cortex. We performed two types of fMRI experiments. One provided a quick method of mapping retinotopy using a composite stimulus with both ring- and wedge-shaped stimuli. The other provided a method which can show the horizontal meridian clearer. We explored the activation of the visual cortex associated with color perception. In our studies of the color center, we first researched the symptoms and lesions of cerebral achromatopsia, and we next performed the fMRI experiments with a pseudoisochromatic plate test and with a color arrangement test. After this we also performed the fMRI experiments with a complex color painting. We realized objective perimetry with functional brain images. We first developed the software to depict a visual field from the signals of MR imaging. Next we performed the experiment with hemifield stimulation and showed the possibility of its clinical application. Then we showed its reproducibility, performing the experiment with more complicated letter-shaped masked visual stimulation. Finally, we applied the technique to patients with cerebral dysfunction. We performed diffusion tensor imaging (DTI) with a clinical 1.5 T MR machine to visualize optic radiation. With patients who were clinically expected to show disorder of optic radiation, these visualizations were consistent with their pathologies. It was suggested that this new DTI technique is useful for estimating functional disorder of optic radiation.