Electron gun using carbon-nanofiber field emitter.

An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10

Application of visual evoked potentials for preoperative estimation of visual function in eyes with dense cataract.

PURPOSE: To determine whether the temporal frequency characteristics of the visual system as determined by visually evoked potentials (VEP) can be used for a preoperative estimation of the visual function in eyes with cataracts. METHODS: Light stimuli driven by a pseudorandom binary sequence (PRBS) of 40950 ms duration were presented and EEG recordings were made from 13 control and 20 patients with cataracts preoperatively and 1 week after cataract operation. The first kernel of the PRBS-VEP was obtained as the first-order cross-correlation function between PRBS and PRBS-VEP. The Fourier transform of this function was used as the temporal frequency characteristic (TFC). RESULTS: The mean +/- standard deviation of the latency and amplitude of the VEP in normal controls were 110.8+/-4.3 ms and 2.01+/-0.67 microV, respectively. A high correlation (r>0.7) between the pre-and postoperative VEP waveform was obtained in 13 eyes (65%), and 14 eyes (70%) in the VEP-TFC curves. The sensitivity of the examination was 73%, 27%, and 91% for the latency, amplitude and TFC of the VEP, respectively. The specificity of the examination was 67%, 100%, and 89% for the same measures. Eleven of 12 eyes with abnormal TFC preoperatively showed retinal or optic nerve lesions postoperatively. False-negative results were seen in cases with delayed corneal edema. CONCLUSION: Postoperative visual function of patients with cataracts can be predicted by preoperative measurement of the TFC obtained by PRBS-VEP.

Modeling the electron field emission from carbon nanotube films.

A theoretical framework for the electron field emission from carbon nanotubes (CNTs) is discussed. Using the tunneling theory, the influence of the detailed electron energy dispersion is proven to be of little importance for the electron field emission. By means of numerical computations in a simplified model, the influence of the environment on the local field on a CNT is discussed for an aligned CNT film. In a simple triangular model for the potential energy barrier at the tube end, a tunneling probability was obtained. A statistical model was developed for the structural and functional parameters of aligned CNT films. Practical CNT films of excellent alignment, obtained directly on a tungsten wire by plasma-enhanced chemical vapor deposition, were analyzed by this statistical model. Their distribution in the enhancement factors was thus deduced. An indirect method to get the average electrical parameters of the film using only a limited amount of experimental data was thus established.

Visual temporal frequency characteristics determined by pseudorandom stimuli.

PURPOSE: To investigate whether a rapid and practical determination of the temporal frequency characteristic (TFC) of the visual system can be obtained by using the visually evoked potentials (VEPs) elicited by pseudorandom binary sequence (PRBS) stimulation. METHODS: VEPs were recorded from eight volunteers. For the conventional steady state VEPs (S-VEP), the eye was stimulated with five stimulus frequencies. To acquire the PRBS-VEPs, the eye was stimulated with a PRBS stimulus for 40 seconds. The TFC for the S-VEP was calculated from the root mean squared amplitude for each frequency using Fourier transform. For the PRBS stimulus, a cross-correlation function between PRBS (x[t]) and PRBS-VEP (y[t]) was calculated to obtain the TFC. RESULTS: The TFCs obtained by the PRBS and S-VEP methods were highly correlated (P < 0.05), and the TFC curves resembled those in the literature. Most important, the data necessary to determine the TFCs using the PRBS stimulus could be obtained in 4 minutes, whereas that for the S-VEP required 60 minutes for the two eyes. CONCLUSIONS: The high correlation between the TFCs obtained by the two methods indicated that the PRBS technique gives a good measure of the TFC of the human visual system. The significantly shorter time required for this method demonstrated that it is a practical method for determining the linear (and nonlinear) property of the visual system and that it may be useful in clinical applications.

Influences of the accommodative stimulus and aging on the accommodative microfluctuations.

The effects of the accommodative stimulus and age on the accommodative microfluctuations were investigated in human subjects. Accommodative responses were measured by using an infrared (IR) optometer, and accommodative microfluctuations were quantified by power spectrum analysis. Two frequency bands were determined: low frequency components (< 0.5 Hz, LFC) and high frequency components (1.3 to 2.2 Hz, HFC). Among younger subjects, the changes in the HFC in response to the accommodative stimuli differed between subjects. The activity of the HFC reached a peak in the center of the accommodation range, whereas the activity of the LFC was its maximum in the presence of darkness or blur in the over-accommodation range. Smaller changes in the magnitude of the HFC were observed in older subjects. Although the LFC may be controlled neurologically, the HFC seems to arise from mechanical and elastic properties of the lens, and may be modulated by other physiological rhythmic variations.

Decision support for psychiatric diagnosis based on a simple questionnaire.

This paper compares two classifiers: Pseudo Bayesian and Neural Network for assisting in making diagnoses of psychiatric patients based on a simple yes/no questionnaire which is provided at the outpatient's first visit to the hospital. The classifiers categorize patients into three most commonly seen ICD classes, i.e. schizophrenic, emotional and neurotic disorders. One hundred completed questionnaires were utilized for constructing and evaluating the classifiers. Average correct decision rates were 73.3% for the Pseudo Bayesian Classifier and 77.3% for the Neural Network classifier. These rates were higher than the rate which an experienced psychiatrist achieved based on the same restricted data as the classifiers utilized. These classifiers may be effectively utilized for assisting psychiatrists in making their final diagnoses.

Effects of tinted intraocular lens on contrast sensitivity.

We evaluated contrast sensitivity and glare in 64 pseudophakic eyes. An ultraviolet-absorbing intraocular lens (IOL) was implanted in 32 eyes and a noncyanopsia yellow-tinted IOL was implanted in 32 eyes. The latter lens was designed to effectively absorb light below a wave-length of 500 nm. Contrast sensitivity was measured at a pupil diameter of 3 mm using an artificial pupil. The implanted yellow-tinted IOL showed improved contrast sensitivity in the middle spatial frequencies of 6 and 12 c/deg in photopic and mesopic vision. In addition, the yellow-tinted IOL decreased the effect of central glare on the contrast sensitivity.

[Relationship between kinetic visual acuity and visual acuity with limited exposure].

Using a kinetic vision tester which we developed, kinetic visual acuity (KVA) at target velocity of 0-100 km/h was measured at background luminance of 0.1-200 cd/m2 in 19 eyes of 10 normal volunteers ranging in age from 20 to 31 years. The decrease in KVA was slow at a target velocity of 30 km/h or more as reported before. KVA was best at background luminance of 100 cd/m2. In 3 eyes of 2 normal subjects, 3 eyes of 2 patients with tonic accommodation and 1 eye of 1 patient with central serous chorioretinopathy, visual acuity at limited exposure times was also measured. In patients with tonic accommodation, visual acuity at limited exposure times was good, but KVA was poor as compared to normal eyes. In the eyes of patients with central serous chorioretinopathy, results were poor for both. The quantity of light required to obtain the same visual acuity was similar for both normal eyes and eyes with central serous chorioretinopathy in terms of both KVA and visual acuity at limited exposure times. In eyes with tonic accommodation, difference was seen in the required quantity of light. We conclude that functions of accommodation are involved in kinetic vision and that higher visual functions are required than those for visual acuity at limited exposure times.

[Measurement of temporal summation of visual acuity with the use of a trial tachistoscope].

Visual acuity was measured in eighteen normal eyes of 10 subjects ranging from 20 to 30 years of age, using a modified tachistoscope. We changed the exposure time of the target (1-1,000 msec) or background luminance (0.1-200 cd/m2). The visual acuity rose with increasing exposure time. At background luminance over 10 cd/m2, the critical duration time was about 500 msec. However, at low luminance below 10 cd/m2, the critical duration was prolonged. This tendency was also seen when the pupil diameter was fixed at 3 mm with an artificial pupil. Similar by luminance detection, visual acuity was also determined by the product of background luminance and exposure time. From theses findings, we concluded that Bloch-Bunsen-Roscoe law was statisfied.

Accommodation in astigmatic eyes.

PURPOSE: To investigate the effect of target chart contours and the severity of astigmatism on accommodation in astigmatic eyes. METHODS: The accommodative responses of 30 subjects were measured with an automated refractometer (Canon RK-1) using star pattern and bar pattern targets. RESULTS: The mean accommodative response was greatest when the bar pattern was parallel to the stronger principal meridian of the eye, followed by the star pattern and the bar pattern parallel to the weaker meridian on both meridians. Similar results were obtained in subjects with astigmatism greater or less than 1.25 D. The mean slopes of AR/AS plots decreased in the same order as the accommodative response and the change was significant in subjects with astigmatism exceeding 1.25 D. In addition, about one-third of the subjects showed a consistent decrease in astigmatism with accommodation. CONCLUSIONS: These results indicate that the type of target chart and the severity of astigmatism influence the accommodative response.

Time-varying properties of respiratory fluctuations in pupil diameter of human eyes.

The time varying properties have been investigated of respiratory components in fluctuations of the pupil diameter (PDF) of the human eye. PDF and instantaneous lung volume were simultaneously measured for 45 minutes under natural binocular viewing conditions. The short-term Fourier transform and the autoregressive signal modeling together with the recursive least squares algorithm have been applied for the estimation of nonstationary power spectra. Data analysis showed a bursting type non-stationarity in the appearance of the respiratory component in PDF.

[Aging changes in accommodation--comparison of subjective method with objective method].

We investigated age-related changes in accommodation of the human eye by measuring the subjective amplitude of accommodation with a Visual Display Terminals Accommodometer (Tokyo-Medical NP-200) and the objective amplitude with an Auto Refkeratometer (Canon, RK-1). The accommodative responses of 5 normal eyes of 5 subjects ranging from 29 to 32 years of age were measured with 6 different sizes of targets. A distinct tendency for the subjective amplitude of accommodation to increase was observed with the targets of larger sizes, but no definite tendency was found in the objective amplitude. The accommodative responses of 92 normal eyes of 92 subjects ranging from 15 to 58 years of age were measured. Both the subjective and objective amplitude of accommodation decreased with aging. In subjects under 44 years of age, the objective amplitude was 2.2-2.5D less than the subjective amplitude, but over 45 the difference between the subjective and objective amplitude was 1.2-1.4D.

Binocular infrared optometer for measuring accommodation in both eyes simultaneously in natural-viewing conditions.

A binocular IR optometer has been developed to measure accommodation continuously and simultaneously in both human eyes in conditions close to natural viewing where a subject gazes at an actual target with binocular vision. Measurement accuracy is ~ 0.24 D with a precision of 0.05 D within a refractive-power range of + 10 to -10 D in model eyes. The dynamic response is over 100 D/s. In addition we measured simultaneously and continuously accommodation, pupil diameter, and eye position of both human eyes in near-reflex conditons using this binocular optometer. Development of the tracking IR binocular optometer is discussed in detail.

Eye-tracking infra-red optometer.

An eye-tracking infra-red optometer has been developed to measure dynamic refractive power during slow horizontal eye movement. It consists of two instruments: an optometer to measure the refractive power of the human eye, and an eye tracker. When measuring refractive power, the eye tracker is used to maintain automatically the optical axis of the optometer coincident with the visual axis of the human eye. The measurement range of the optometer is approximately -10 to +10 D; refractive power is measured with an accuracy of about 0.4 D and with a precision of 0.05 D over an eye movement range of 60 degrees. The maximum trackable eye movement velocity is over 100 deg s-1, with a time delay of about 0.13 s. Furthermore it was confirmed that eye refraction measurement during vergence is possible using this eye-tracking infra-red optometer.

[Accommodation in ametropia and the effect of targets on astigmatism].

Measurements of accommodative responses in 28 astigmatic eyes (22 patients, 19-32 years of age) were made with an objective Auto Refkeratometer (Canon, RK-1). We constructed an actual target representative instrument with a star burst chart and a fine line chart, and attached this instrument to the Auto Refkeratometer. The fine line chart was turned around the sight line of the eye at a fixed distance. The amount of mean accommodative responses decreased in the following order; the fine line chart parallel to the first principal meridian of subjects, the star burst chart, the fine line chart parallel to the second principal one. This tendency was also shown in cases of subjects with astigmatism less than 1.25 diopters. The slopes of mean accommodative response curves reduced in the similar order as above, significantly in the cases of astigmatism over 1.25 diopters. These results suggest that target charts for accommodation and the degree of astigmatism have influence on the amount of accommodative response and the slope of its curve.