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PubMed2006

Elliptical concentrators.

Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used to produce optical devices, including the use of reflective and refractive components or inverse engineering techniques. However, many of these optical components are based on translational symmetries, rotational symmetries, or free-form surfaces. We study a new family of nonimaging concentrators called elliptical concentrators. This new family of concentrators provides new capabilities and can have different configurations, either homofocal or nonhomofocal. Translational and rotational concentrators can be considered as particular cases of elliptical concentrators.

Journal Article↗
PubMed1994

[Analysis on refraction status of eyes with normal vision].

Refractive status of 1,324 eyes with normal vision of the juvenile students in four grades was analysed. It was raised that the meaning of refractive status was different between the medical physiological optics and the physical or geometrical optics. "Emmetropia" did not really mean "the normal eye" in refraction as viewed from normal physiology, and the problem about the physiological refractive status of eyes in the juvenile was discussed preliminarily.

Adolescent↗
PubMed1994

The effect of cycloplegia on measurement of the ocular components.

PURPOSE: The purpose of this study was to examine the effect of cycloplegic agent on the measurement of refractive error and the ocular components. METHODS: We compared two commonly used topical cycloplegic agents, 1% tropicamide and 1% cyclopentolate, for their effect on the measurement of refractive error (by Canon R-1 autorefraction), accommodative response (by Canon R-1 autorefraction and by the conventional, subjective "pushup" method), crystalline lens power (by video phakometry and by calculation), and axial ocular dimensions (by A-scan ultrasonography) in 20 emmetropic to moderately hyperopic children. RESULTS: Comparison of refractive error at each drug's reported time of maximum cycloplegia (30 minutes for tropicamide and 60 minutes for cyclopentolate) showed that distance autorefraction in the vertical meridian differed by +0.20 +/- 0.30 diopters (D) (P = 0.008). The average difference was +0.07 +/- 0.10 mm for anterior chamber depth (P = 0.004), -0.03 +/- 0.05 mm for crystalline lens thickness (P = 0.025), -0.65 +/- 0.69 D for phakometrically measured crystalline lens power (P < 0.001), +0.03 +/- 1.55 D for calculated crystalline lens power (P = 0.94), and -0.09 +/- 0.19 mm for vitreous chamber depth (P = 0.062, all paired t tests; positive signs denote greater values with cyclopentolate). Residual accommodation was 0.47 and 0.67 D greater with tropicamide when measured by autorefraction and the pushup method (P = 0.013 and 0.08 respectively, paired t test). All significant differences were consistently in the direction of poorer cycloplegia with tropicamide. CONCLUSIONS: Although tropicamide, as expected, showed poorer cycloplegia compared to cyclopentolate, the degree of difference appeared to be small, with minimal effect on the measurement of distance refractive error and the ocular optical components.

Accommodation, Ocular↗
PubMed2006

Reflection contrast microscopy: The bridge between light and electron microscopy.

Reflection contrast microscopy (RCM) is a light microscopic method to image cells at high definition and enhanced sensitivity compared to conventional bright-field microscopy. RCM images have very high contrast, which makes them easily applicable for digital image analysis. Because ultrathin sections are mostly used in this method, RCM also functions by bridging light with electron microscopy: the combination of ultrastructural with histochemical studies. RCM can also replace electron microscopy for rapid and simple screening of large quantities of samples for immunocytochemical staining. Special attention is paid to small biological objects, which have to be processed for RCM. If you encounter the limits of brightfield microscopy, in resolution, sensitivity or handling of the specimen, RCM will be a feasible option. Reflection contrast microscopy methods use only slightly adjusted electron microscopy methods for specimen preparation. Therefore, many familiar techniques for ultrathin specimen preparation can be applied. It is essential that only refractive index differences exist in those areas that are of interest and that the further specimen is as optically homogenic as possible, with a refractive index as close to that of glass as possible. Therefore, plastic embedding is recommended.

Animals↗
PubMed2002

Action from tunable periodic structures. II. Experimental observation of electric field-induced diffraction peaks.

As previously predicted [Appl. Opt. 40, 5583 (2001)], we have now observed electric field-induced diffraction peaks in transmission and reflection experiments by use of a LiNbO3 sample with interdigital planar electrodes that serve as a diffraction grating. The magnitudes of the new peaks in the reflection experiments are ten times larger than those in the transmission experiments. We interpret these effects in terms of a field-induced refractive-index change produced by the linear electro-optic effect. The positive and negative changes in the refractive index produce two diffraction gratings that are period doubled with respect to the original grating and that have a phase difference between them. The superposition of the diffracted light from these gratings is shown to account for the new peaks. From the relative magnitude of the new peak to that of the central peak, we estimate the refractive-index change to be 0.004.

Journal Article↗
PubMed2004

Ocular axial length in homocystinuria patients with and without ocular changes: effects of early treatment and biochemical control.

PURPOSE: To establish whether myopia in homocystinuria could be due to increased ocular axial length. METHODS: Measurement of ocular axial length by A-scan ultrasound in eyes of homocystinuria patients. RESULTS: Patients were divided into three groups. Group I, with no ocular pathology (28 eyes), had mean refractive error of -0.25 D (spherical equivalent) and mean axial length of 23.4 mm +/- 0.9 (+/-1 standard deviation) mm. Group II, with phacodonesis or lens subluxation (12 eyes), had mean refractive error of -10.7 D and mean axial length of 23.8 mm +/-1.9 mm. Patients with phacodonesis had simple myopia whereas those with lens subluxation had marked myopic astigmatism. Group III included patients with complete lens dislocation in at least one eye (12 eyes) and were optically aphakic with a mean refractive error of +12.9 D and mean axial length of 24.9 mm +/- 0.9 mm. All Group I patients had good long-term metabolic control while those in Groups II and III did not. Group III eyes had significantly longer mean axial length than Group I (P =.0018) or normal eyes (P =.0163). There was no statistical difference in mean axial length between Group I and normal eyes. CONCLUSIONS: Ocular axial length is significantly increased in individuals with homocystinuria and lens dislocation. Increased axial length is a complication that has not been previously described in homocystinuria and may be preventable with early treatment and good biochemical control.

Adolescent↗
PubMed2002

Topographic changes in corneal asphericity and effective optical zone after laser in situ keratomileusis.

PURPOSE: To determine the relationship between the spherical refractive change after myopic excimer laser surgery and the effective optical zone (EOZ) and corneal asphericity determined by corneal topography. SETTING: Baylor College of Medicine, Houston, Texas, USA. METHODS: Preoperative and postoperative topographies along with refractions were evaluated in all patients who had had laser in situ keratomileusis since January 1999 and had at least 6 months of follow-up. The VISX Smoothscan S2 excimer laser and the Hansatome microkeratome (Bausch & Lomb) were used in all cases. Because optical zones are oval with astigmatic treatments with the VISX laser, only patients with spherical refractions and treatments were included. Thirty-nine cases met the criteria; their treatments ranged from -1.50 to -18.00 diopters (D). The preoperative and postoperative corneal asphericities (Q-values) were taken directly from the Holladay Diagnostic Summary Report on the EyeSys 2000, version 4.0. The mean diameter of the optical zone was measured on the local radius of curvature map using the outer edge of the yellow zone, which corresponds to 2 color changes or approximately 0.50 D steepening from the mean central radius (green). RESULTS: The EOZ decreased as the amount of treatment increased. The decrease was slightly nonlinear, decreasing slightly more rapidly at higher treatments. For an "intended" 6.0 mm optical zone, the nominal EOZs from the least-squares second-order polynomial regression were 6.0 mm for -1.5 D, 5.4 mm for -5.0 D, 4.6 mm for -10.0 D, 3.8 mm for -15.0 D, and 3.2 mm for -18.0 D. The least-squares second-order polynomial regression yielded a standard error of the estimate (SEE) of +/- 0.22 mm (R(2) = 0.90). The asphericity increased nonlinearly in a positive direction (oblate) with the amount of treatment, indicating greater amounts of correction produced progressively more oblate corneal surfaces. The least-squares second-order polynomial regression yielded an SEE of +/- 0.42 (R(2) = 0.55). CONCLUSIONS: The EOZ decreased and the Q-value increased with the amount of myopic excimer laser treatment. The optical zone was approximately 4.3 mm with a spherical treatment of -12.0 D. These findings may explain the clinical studies that indicate high myopic treatments (above -12.0 D) are associated with poor visual outcomes.

Cornea↗
PubMed2005

Spectral characteristics and nonlinear studies of crystal violet dye.

Solid-state dye-doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the spectral characteristics and the nonlinear optical properties of the dye crystal violet are studied. The spectral characteristics of crystal violet dye doped poly(methylmethacrylate) modified with additive n-butyl acetate (nBA) are studied by recording its absorption and fluorescence spectra and the results are compared with the corresponding liquid mixture. The nonlinear refractive index of the dye in nBA and dye doped polymer film were measured using z-scan technique, by exciting with He-Ne laser. The results obtained are intercompared. Both the samples of dye crystal violet show a negative nonlinear refractive index. The origin of optical nonlinearity in the dye may be attributed due to laser-heating induced nonlinear effect.

Absorption↗
PubMed2005

Ultrafast deflection of spatial solitons in AlxGa(1-x)As slab waveguides.

We demonstrate ultrafast all-optical deflection of spatial solitons in an AlxGa(1-x)As slab waveguide, using 190 fs, 1550 nm pulses to generate and deflect the spatial soliton. The steering beam is focused onto the top of the waveguide near the soliton pathway, and the soliton is steered by refractive-index changes induced by optical Kerr, or free-carrier (Drude), effects. Angular deflections up to 8 mrad are observed.

Journal Article↗
PubMedDate not supplied

Radiative transport in the delta-P1 approximation: accuracy of fluence rate and optical penetration depth predictions in turbid semi-infinite media.

Using the delta-P(1) approximation to the Boltzmann transport equation we develop analytic solutions for the fluence rate produced by planar (1-D) and Gaussian beam (2-D) irradiation of a homogeneous, turbid, semi-infinite medium. To assess the performance of these solutions we compare the predictions for the fluence rate and two metrics of the optical penetration depth with Monte Carlo simulations. We provide results under both refractive-index matched and mismatched conditions for optical properties where the ratio of reduced scattering to absorption lies in the range 0< or =(micro(s')/micro(a))< or =10(4). For planar irradiation, the delta-P(1) approximation provides fluence rate profiles accurate to +/-16% for depths up to six transport mean free paths (l*) over the full range of optical properties. Metrics for optical penetration depth are predicted with an accuracy of +/-4%. For Gaussian irradiation using beam radii r(0) > or =3 l*, the accuracy of the fluence rate predictions is no worse than in the planar irradiation case. For smaller beam radii, the predictions degrade significantly. Specifically for media with (micro(s')/micro(a))=1 irradiated with a beam radius of r(0)=l*, the error in the fluence rate approaches 100%. Nevertheless, the accuracy of the optical penetration depth predictions remains excellent for Gaussian beam irradiation, and degrades to only +/-20% for r(0)=l*. These results show that for a given set of optical properties (micro(s')/micro(a)), the optical penetration depth decreases with a reduction in the beam diameter. Graphs are provided to indicate the optical and geometrical conditions under which one must replace the delta-P(1) results for planar irradiation with those for Gaussian beam irradiation to maintain accurate dosimetry predictions.

Computer Simulation↗
PubMed2000

Quantitative analysis of the effect of near lens addition on accommodation and myopigenesis.

PURPOSE: To develop a quantitative, objective, and scientific basis for understanding the effects of applying near bifocal additions (ADDs) on oculomotor control and myopia development. This is important because myopia is a major public health problem that affects 25% of the U.S. population and 75% or more in Asian countries. It is also associated with an increased risk for vision-threatening conditions, such as retinal breaks and detachments, as well as glaucoma. METHODS: A comprehensive model of refractive error development was constructed based on a dual-interactive feedback model of accommodation and vergence, which represented the short-term dynamics pathway, with the addition of both genetic and environmental (defocus-induced axial growth) components in a long-term pathway. An alternating near- and far-viewing paradigm was simulated, with varying amounts of ADDs, to obtain a parametric relationship between the root mean square of accommodative error (AE) and the induced refractive error (IRE). The parametric relationship provided the crucial linkage between the long-term growth pathway and the conventional short-term dynamics pathway. ADD is the simulated lens placed before the eyes only during near viewing, whereas IRE is the simulated lens fixed before the eyes that represents the optical effect of slowly progressive refractive development caused by near work. RESULTS: A V-shaped functional relationship was found between AE and IRE. The left half of the curve is associated with hyperopic defocus and myopigenesis, whereas the right half is associated with myopic defocus and hyperogenesis. Introduction of an ADD shifts the V-shaped curve horizontally. Thus, an "optimal" ADD can be used to shift the minimum of the accommodative error curve to the zero IRE point, and thereby reduce or eliminate retinal defocus and its potential towards myopigenesis. On the other hand, sensitivity analysis of model parameters shows that increasing the accommodative convergence crosslink gain (AC) shifts the curve to the right and results in a tendency towards myopigenesis, which is consistent with clinical findings in progressive myopia. CONCLUSIONS: The model can be used to specify the precise ADD needed for an individual to retard or eliminate retinal defocus-induced myopic progression. If future experiments show that using the "optimal" ADD results in the greatest benefit (i.e., least myopia progression), there will be considerable worldwide public health benefit.

Accommodation, Ocular↗
PubMed1987

A method for raytracing through schematic eyes with off-axis components.

A linear algebraic method for tracing skew rays through aspheric surfaces is described. The advantage of this method is that the refracting surfaces can be translated and rotated with respect to each other. The method is used to investigate the optical factors affecting the location of Purkinje images.

Cornea↗
PubMed2002

Selective optical detection of aromatic vapors.

A sensitive layer system of amorphous Teflon AF on silver has been coated on a glass substrate. With a monochromatic light source the reflectivity of the layer system as a function of the angle of incidence exhibits the surface-plasmon resonance as well as a set of leaky-mode resonances. These optical resonance phenomena are sensitive to small refractive-index changes that may be induced by diffusion of particles into the Teflon AF layer. On the basis of this effect, the aromatic vapors benzene; toluene; and o-, p-, and m-xylene have been investigated with different vapor concentrations. By selection of a distinct angle at a particular resonance, dynamic measurements can be performed. Assuming a diffusion process in accordance with Fick's law, the diffusion profile can be calculated as a function of time. As described by the Lorentz-Lorenz relation a refractive-index profile is induced that consequently interacts with the electromagnetic fields of the optical modes. With the function of the diffusion-induced refractive-index profile the shift of the resonance lines can be calculated from the measured reflectivity change as a function of time. The characteristic diffusion coefficients of the particular vapor allow for a distinction between the different types of aromate, even between the different xylenes.

Journal Article↗
PubMed2004

Tunable photonic band gap crystals based on a liquid crystal-infiltrated inverse opal structure.

Composite materials comprised of nematic liquid crystals (LCs) and SiO(2) inverse opal films were fabricated. Their optical properties were quite different from those of inverse opal films without the LCs. The optical properties could be controlled by changing the refractive indices of the LCs, which vary with orientation, phase, and temperature. In particular, the optical properties were drastically changed by thermal or photoinduced isothermal phase transitions of the LCs. This means that the photonic band structure could be controlled, and tunable photonic crystals have been achieved, based on the inverse opal structure. The mechanism of this change was investigated by the evaluation of the effective refractive indices. As a result, it was found that the change in optical properties was derived from the orientation of the LC molecules in the voids in the inverse opal film. Furthermore, once the mechanism was understood, it was also possible to control the position of the reflection peak by changing the alignment of the LCs. Such materials have the possibility for practical use in optical devices and fundamental research systems.

Journal Article↗