Biomedical subjects

Kazuhiko Ukai

Publications and source records attributed to Kazuhiko Ukai.

5 recordsLinked to original sources

PubMed2006

Dynamic measurement of accommodation and pupil size using the portable Grand Seiko FR-5000 autorefractor.

PURPOSE: The purpose of this study was to evaluate the potential of the portable Grand Seiko FR-5000 autorefractor to allow objective, continuous, open-field measurement of accommodation and pupil size for the investigation of the visual response to real-world environments and changes in the optical components of the eye. METHODS: The FR-5000 projects a pair of infrared horizontal and vertical lines on either side of fixation, analyzing the separation of the bars in the reflected image. The measurement bars were turned on permanently and the video output of the FR-5000 fed into a PC for real-time analysis. The calibration between infrared bar separation and the refractive error was assessed over a range of 10.0 D with a model eye. Tolerance to longitudinal instrument head shift was investigated over a +/-15 mm range and to eye alignment away from the visual axis over eccentricities up to 25.0 degrees . The minimum pupil size for measurement was determined with a model eye. RESULTS: The separation of the measurement bars changed linearly (r2 = 0.99), allowing continuous online analysis of the refractive state at 60 Hz temporal and approximately 0.01 D system resolution with pupils >2 mm. The pupil edge could be analyzed on the diagonal axes at the same rate with a system resolution of approximately 0.05 mm. The measurement of accommodation and pupil size were affected by eccentricity of viewing and instrument focusing inaccuracies. CONCLUSIONS: The small size of the instrument together with its resolution and temporal properties and ability to measure through a 2 mm pupil make it useful for the measurement of dynamic accommodation and pupil responses in confined environments, although good eye alignment is important.

Accommodation, Ocular↗

PubMed2005

Target spatial frequency determines the response to conflicting defocus- and convergence-driven accommodative stimuli.

Asthenopia, or visual fatigue, is a frequent complaint from observers of stereoscopic three-dimensional displays. It has been proposed that asthenopia is a consequence of anomalous oculomotor responses generated by conflict between accommodative and convergence stimuli. The hypothesis was examined by measuring accommodation and convergence continuously with a Shin-Nippon SRW5000 infrared autorefractor and a limbus tracking device. Subjects viewed a high contrast Maltese Cross target at three levels of Gaussian filter target blur under conditions of relatively low- and high-conflict between accommodation and convergence stimuli, the latter inducing the sensation of stereopsis. Under the low-conflict conditions accommodation was stable, but convergence-driven accommodation was dominant when the target was extremely blurred. Under the high-conflict conditions the role of convergence-driven accommodation increased systematically with the degree of target blur. It is proposed that defocus-driven accommodation becomes weak when the target comprises low spatial frequency components. Large accommodative overshoots to step stimuli that are not blurred or only mildly blurred were consistently observed and are attributed to the initial accommodative response being convergence-driven. Whereas the possibility that high-conflict conditions are a cause of asthenopia has been previously reported, this is the first evidence that they specifically affect accommodative responses while viewing stereoscopic displays.

Accommodation, Ocular↗

PubMed2003

Binocular rivalry alternation rate declines with age.

The effect of aging on the time of spontaneous perceptual alternation in binocular rivalry was examined in 59 subjects. An earlier study reported the change of alternation time by comparing middle-age and elderly subjects. We also observed age-related prolongation in alternation time by comparing subjects in a lower age group (20-34 years) with those in both a middle-age group (35-49 years) and a higher age group (50-64 years). Aging of visual optical functions such as presbyopia or the reduction of contrast sensitivity has an accelerating effect over age and may not be related to the age-associated monotonic prolongation of alternation time in binocular rivalry. The origin of aging in binocular rivalry is still unclear but a neural interval generator for perceptual switching is suggested.

Adult↗

PubMed2002

Pupillary and cardiovascular responses to a video movie in senior human subjects.

The effects of watching video movies on autonomic functions were estimated by measuring changes in pupillary and cardiovascular parameters in 10 senior subjects. The subjects looked at a series of video images (with accompanied sounds) taken during the execution of motor vehicles. The images were rear-projected on a large screen for 15 min. Pupil diameter and parameters of the light reflex were measured by an infrared pupillometer before and after the video presentation. Their electrocardiograms (ECG) and blood pressure were measured continuously. Subjects were divided into two groups depending on their values of blood pressure and fasting plasma glucose level. Subjects in Group A had blood pressures of less than 140 mm Hg and a fasting plasma glucose level of less than 7 mmol/dl (normal group). Other subjects were included in Group B (mild hypertension or diabetes mellitus group). While changes in pupillary light reflex after video viewing were minimal in the members of Group A, amplitudes of the pupillary reflex in the members of Group B varied over a significantly wide range. By the spectral analysis of cardiovascular rhythm, %LF and %HF components of blood pressure rhythm were significantly different between the two groups before video viewing. However, the ratios of frequency components before and after video viewing were not significantly different between the two groups. Our findings suggest that pupillary light reflex was less precisely controlled in subjects with mild autonomic dysfunction after prolonged audiovisual stimulation.

Aged↗

PubMed2002

The use of video refraction to measure the dynamic properties of the near triad in observers of a 3-D display.

OBJECTIVE: Recording of the dynamic behaviour of the near triad during viewing of a three-dimensional (3-D) display is attempted. This may then be used to identify the possible origin of asthenopia and other ocular problems which occur whilst viewing such displays. METHODS: Subjects viewed a 3-D display through an image splitter. Video recordings of ocular responses (pupil diameter, vergence and accommodation) were made with a commercially available video refraction unit at a distance of 1.2 m from the subject. Continuous recordings were made whilst a step-wise disparity of up to 2.6 degrees was introduced between the targets presented to the two eyes, but the accommodative stimulus remained unchanged. Image analysis from the recordings was carried out on a personal computer. RESULTS: Results showed various complex patterns of response, with the accommodation and vergence recorded reflecting the effect of stimulus conflict. Difficulty in fusional convergence was recorded when disparity was large, and the recordings reflected the subjects' comments. CONCLUSION: The video refraction method is a useful tool for studying the dynamic behaviour of the near triad.

Accommodation, Ocular↗