We used functional magnetic resonance imaging to assess abnormal cortical signals in humans with juvenile macular degeneration (JMD). These signals have been interpreted as indicating large-scale cortical reorganization. Subjects viewed a stimulus passively or performed a task; the task was either related or unrelated to the stimulus. During passive viewing, or while performing tasks unrelated to the stimulus, there were large unresponsive V1 regions. These regions included the foveal projection zone, and we refer to them as the lesion projection zone (LPZ). In 3 JMD subjects, we observed highly significant responses in the LPZ while they performed stimulus-related judgments. In control subjects, where we presented the stimulus only within the peripheral visual field, there was no V1 response in the foveal projection zone in any condition. The difference between JMD and control responses can be explained by hypotheses that have very different implications for V1 reorganization. In controls retinal afferents carry signals indicating the presence of a uniform (zero-contrast) region of the visual field. Deletion of retinal input may 1) spur the formation of new cortical pathways that carry task-dependent signals (reorganization), or 2) unmask preexisting task-dependent cortical signals that ordinarily are suppressed by the deleted signals (no reorganization).

Task-dependent LPZ responses are present in RP subjects, similar to responses measured in MD subjects. The results are consistent with the hypothesis that deleting the retinal input to the LPZ unmasks preexisting extrastriate feedback signals that are present across V1. The authors discuss the implications of this hypothesis for visual therapy designed to replace the missing V1 LPZ inputs and to restore vision.

Human visual sensitivity to a fairly broad class of dynamic stimuli can be modeled accurately using two temporal channels. Here, we analyze fMRI measurements of the temporal step response to spatially uniform stimuli to estimate these channels in human primary visual cortex (V1). In agreement with the psychophysical literature, the V1 fMRI temporal responses are modeled accurately as a mixture of two (transient and sustained) channels. We derive estimates of the relative contributions from these two channels at a range of eccentricities. We find that all portions of V1 contain a significant transient response. The central visual field representation includes a significant sustained response, but the amplitude of the sustained channel signal declines with eccentricity. The sustained signals may reflect the emphasis on pattern recognition and color in the central visual field; the dominant transient response in the visual periphery may reflect responses in the human visual attention system.

One-third of Japanese patients with nonsyndromic arRP carried probable pathogenic mutations in the EYS gene, including two founder mutations. Because the genotype was correlated with the phenotype, genotyping in the EYS gene could be a valuable tool for predicting long-term prognoses of Japanese patients with arRP and thus could be useful for genetic counseling and future gene therapy.

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These results suggest that the mRGC in humans may respond to 470-nm-wavelength light at 100 cd/m(2), and there is a possibility of affecting the sustained phase of the light reflex without changing visual performance.

We evaluated cyanopsia by means of achromatic-point settings at several time points started from the day before intraocular lens (IOL) implantation for cataract removal surgery. We intensively measured the initial drift in color appearance; we started the measurement less than 30 min after eyepatch removal, and the measurement continued for several weeks. The shifts were mainly observed in the direction of color space that selectively varies short-wavelength-sensitive cone (S-cone) responses. The time constant of shifts in color appearance was estimated at the initial stage of cyanopsia by fitting exponential curves. The result of fitting suggests that color appearance is recalibrated during cyanopsia by some neural mechanisms with a time constant of several hours. It also became clear that the migration of the achromatic point becomes slower within approximately 12 h after eyepatch removal.

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