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PubMed1990

[The physical and clinical eye refraction of preschoolers and young schoolchildren].

Physical and clinical eye refraction was studied in 608 children aged from 3 to 12 years. The formation of refraction of the eye at the time of its growth is based on correlative connexions between anatomo-optic parameters and between refractive media themselves. Spherical and astigmatic refraction are determined by refractive media having, in their most part, astigmatism. In the period of the growth of the eye, its physical and clinical refraction changes. To prevent a fall of visual functions and disturbances in the musculo-accommodative system of the eye, early optic correction of ametropia is recommended and, if indicated, pleoptic-orthoptic treatment.

Aging↗
PubMed1993

Explanation of isogyre formation by the eye lens.

The eye lens is considered to be birefringent and this property is thought to be responsible for the image of a cross which is formed within the lens when it is placed between crossed polarizers. This paper presents an alternative explanation for the pattern, as a phenomenon of refraction.

Birefringence↗
PubMed2006

Negative refractive index in artificial metamaterials.

We discuss optical constants in artificial metamaterials showing negative magnetic permeability and electric permittivity and suggest a simple formula for the refractive index of a general optical medium. Using the effective-field theory, we calculate the effective permeability and the refractive index of nanofabricated media composed of pairs of identical gold nanopillars with magnetic response in the visible spectrum.

Journal Article↗
PubMed1993

Dark focus of accommodation and uncorrected visual acuity.

We compared the dark focus of accommodation in 33 healthy children, 19 eyes with good uncorrected visual acuity (1.0 or more) vs. 14 with poor uncorrected visual acuity (below 1.0). The two groups were matched for age and cycloplegic refractive error. Cycloplegic refractive error ranged from +0.15 to +1.75 D in the good visual acuity group and from +0.25 to +1.87 D in the poor visual acuity group. The dark focus was defined as the difference between the refractive error in the dark and the refractive error under cycloplegia. Initially, visual acuity was measured subjectively. Next, refractive error in the dark was measured using the Nidek Autorefractometer AR1600 with its optical target light off. Refractive error under cycloplegia was measured 40 min after the instillation of cyclopentolate hydrochloride using the same autorefractometer. There was a significant correlation between the dark focus and the cycloplegic refractive error (r = -0.53, p < 0.01). Despite an equal refractive error under cycloplegia the dark focus was significantly larger in the eyes with good uncorrected visual acuity than in those with poor uncorrected visual acuity (p < 0.01). Tonic accommodation may influence uncorrected visual acuity.

Accommodation, Ocular↗
PubMed2005

Mid-infrared extinction spectra and optical constants of supercooled water droplets.

Complex refractive indices of supercooled liquid water have been retrieved at 269, 258, 252, and 238 K in the 4500-1100 cm(-1) wavenumber regime from series of infrared extinction spectra of micron-sized water droplets. The spectra collection was recorded during expansion experiments in the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. A Mie inversion technique was applied to derive the low-temperature refractive index data sets by iteratively adjusting the room-temperature optical constants of liquid water until obtaining the best agreement between measured and calculated infrared spectra of the supercooled water droplets. The new optical constants, revealing significant temperature-induced spectral variations in comparison with the room-temperature refractive indices, proved to be in good agreement with data sets obtained in a recent study. A detailed analysis was performed to elaborate potential inaccuracies in the retrieval results when deriving optical constants from particle extinction spectra using an iterative procedure.

Journal Article↗
PubMed2002

Quantitative performance of bifocal and multifocal intraocular lenses in a model eye: point spread function in multifocal intraocular lenses.

OBJECTIVE: To compare the optical properties of bifocal diffractive and multifocal refractive intraocular lenses. METHODS: A model eye with a pupil 4.5 mm in diameter was used to determine the point spread function (PSF) of the distance focus and near focus of a diffractive bifocal intraocular lens (IOL) (model 811E; Pharmacia Inc, Columbus, Ohio) and of a refractive multifocal IOL (model SA40N; Allergan Optical Inc, Irvine, Calif) to compare them with PSFs of foci of corresponding monofocal lenses. For interpreting the PSFs the through focus response, the modulation transfer function, and the Strehl ratio were evaluated. RESULTS: The intensity of the distance focus of the bifocal diffractive lens reached 58.5% and the near focus attained 42.7% of the intensity of a corresponding monofocal lens. The maximal halo intensity surrounding both foci was approximately 4.5%. The distance peak of the refractive multifocal IOL was 73.4% and the near peak 25.1% of a corresponding monofocal lens. The out-of-focus image overlaying the distance focus of the refractive multifocal IOL was approximately 3% of the light intensity of the distance focus, whereas the PSF of the near focus of the multifocal IOL is substantially affected by out-of-focus images. The computed modulation transfer functions show better results for the monofocal lenses, similar results for the tested distance foci, and clear advantages for the bifocal diffractive near focus. CONCLUSIONS: Modulation transfer functions reveal comparable properties for distance vision and a superiority of the bifocal diffractive lens over the refractive multifocal lens for near vision.

Eye↗
PubMed1990

Effect of hydrogen peroxide, DL-propranolol, and prednisone on bovine lens optical function in culture.

Lens refractive function was monitored during long-term bovine lens culture experiments in which low concentrations of potentially damaging agents were added to the culture media. The agents tested were the drugs DL-propranolol and prednisone, and hydrogen peroxide. A computer-driven scanning laser system was used to monitor lens focal length during culture. The system consists of a scanning helium-neon laser beam, a television video camera, and a video frame digitizer. The system first locates the optical center of the lens, defined as the position of little or no refractive deviation of the beam. The laser scans the lens in small steps (0.05 mm), while the digitizer measures focal length for each beam position. A graphic profile of lens focal variation is plotted. A concentration of 0.1 mM hydrogen peroxide produces no significant change in lens focus after 315 hr of incubation. When the concentration is increased 10-fold (1.0 mM), lens focal ability is radically disturbed after 60 hr of incubation. Lenses incubated with prednisone (0.03 mM) for up to 525 hr show no difference in focal characteristics in comparison to control lenses. Propranolol in a concentration of 0.1 mM disrupts lens focal ability after 250 hr of incubation, whereas a higher concentration (1.0 mM) produces a similar effect after only 150 hr. These results indicate that lens refractive function is a sensitive measure of lens function during culture.

Animals↗
PubMed1955

Investigation of the structure of the cornified epithelium of the human skin.

To explore the submicroscopic structure of the human callus by the polarization optical method, serial sections were prepared in three principal planes and the sign of double refraction as well as optic axes of various regions of the sections was determined. It was concluded that in areas under the grooves keratin is oriented parallel to the surface plane of the callus and to the direction of the grooves. In component structures of ridge areas such as in sweat duct areas a circumferential, in cross-band areas a linear, and in other parts a random structure was seen. The cross-bands of ridge areas in association with groove areas revealed a regular lattice-like submicroscopic pattern which was considered as an important mechanical system of the cornified epithelium.

Epithelium↗
PubMed2002

Dynamic optical coherence tomography in studies of optical clearing, sedimentation, and aggregation of immersed blood.

The concept of refractive-index matching to enhance the optical penetration depth of whole blood is discussed on the basis of in vitro studies that used the technique of near-infrared optical coherence tomography. It was found that optical clearing of blood is defined not only by refractive-index matching but also by changes in the size of red blood cells and in their aggregation ability when chemicals are added. For example, in whole blood diluted to twice its volume by saline with the addition of 6.5% glycerol, the total attenuation coefficient was reduced from 4.2 to 2.0 mm(-1), and the optical penetration at 820 nm was correspondingly increased to 117%. For the other agents tested (glucose, dextrans, propylene glycol, and trazograph) the enhancement of penetration was 20-150.5%. In the blood sedimentation study, regular or irregular oscillations or jumps of the red-blood cell-plasma boundary were observed. The 1-min time period of regular oscillations correlated well with the kinetics of the aggregation process as described by the two subsequent stages of formation of linear and three-dimensional aggregates. The results also showed that optical clearing of blood by osmotic agents is potentially useful not only in blood sedimentation and aggregation studies but also in intravascular optical coherence tomography imaging techniques.

Adult↗
PubMed2002

Transmission laser microscope using the phase-shifting technique and its application to measurement of optical waveguides.

A type of a transmission phase-shifting laser microscope, believed to be new, has been developed. In this microscope a biprism located between a magnifying lens and an observation plane was used as a beam splitter. The biprism is laterally translated to introduce phase shifts required for quantitative phase measurement with a phase-shifting technique. The disturbance caused by a Fresnel-diffracted wave from the splitting edge of the biprism is reduced by placement of a linear beam stopper at the center of an intermediate image plane. As the first application, the developed microscope is used to measure a refractive-index distribution in optical waveguides. A difference of refractive indices of less than 6 x 10(-5) is clearly measured in the submicrometer region.

Journal Article↗
PubMedDate not supplied

Wavefront aberrations following laser in situ keratomileusis and refractive lens exchange for hypermetropia.

PURPOSE: To compare the magnitude of aberrations in eyes after elective hypermetropic laser in situ keratomileusis (LASIK) and refractive lens exchange (clear lens replacement). METHODS: Forty-nine patients (92 eyes) had hypermetropic LASIK and 28 (48 eyes) had refractive lens exchange; 23 hypermetropic subjects (41 eyes) were the control group. LASIK was performed with the Nidek EC-5000 excimer laser; ablation zones 5.5 to 6.0-mm in diameter with transition zones 7.5 to 8-mm in diameter. For refractive lens exchange, all but four IOLs were made of foldable acrylic. Aberrations and corneal topography were measured with the Nidek OPD-Scan model ARK-10000 more than 12 months after surgery. The higher-order root-mean-square (HORMS) wave aberrations for combined third to sixth Zernike aberration orders and the Zernike spherical aberration coefficient C(0)(4) at both 4.2-mm and 6.0-mm pupil sizes were calculated. RESULTS: For the LASIK group, surgical refractive change correlated significantly with total, corneal, and internal HORMS and spherical aberrations (except with internal spherical aberration for a 4.2-mm diameter pupil). For the refractive lens exchange group, there were no significant correlations of surgical refractive change with any of these factors. Similarly, there were no significant correlations of refraction with any of these factors for the control group. For a 3-diopter change in refraction with 6-mm pupils, LASIK doubled the total HORMS aberrations. LASIK changed the sign of spherical aberration from positive to negative by increasing the negative asphericity of the anterior cornea. Taking age differences between groups into account, refractive lens exchange increased the total HORMS aberrations by 40% compared with that of the control group, but this was not statistically significant. However, refractive lens exchange significantly increased total spherical aberration. CONCLUSION: Refractive lens exchange was a better refractive procedure than LASIK for minimizing total higher order optical aberrations that accompany hypermetropic refractive surgery.

Adult↗
PubMed2005

Photorefractive keratectomy and laser in situ keratomileusis in refractive accommodative esotropia.

PURPOSE: To evaluate the efficacy of excimer laser refractive surgery as an alternative for optical correction in patients affected by fully refractive accommodative strabismus. SETTING: Eye Clinic, University of L'Aquila, L'Aquila, Italy. METHODS: After a simulation of the cycloplegic correction with contact lenses over a 30-day period, 18 patients (6 men, 12 women, mean age 32.4 years +/- 9.4 [SD]) affected by fully refractive accommodative esotropia had refractive surgery using an excimer laser; 8 patients had photorefractive keratectomy (PRK), and 10 patients had laser in situ keratomileusis (LASIK). RESULTS: The correction of the refractive error with excimer laser allowed a reduction of the angle of deviation in all but 1 patient, who presented with a regression of refractive error and of the angle of deviation 2 years posttreatment. The 2-year follow-up showed that the mean angle of deviation in PRK was 2(Delta) esophoria at near and 0.4(Delta) esophoria at distance (P<.06); in LASIK, it was 1.7(Delta) esophoria at near and 0.2(Delta) esophoria at distance (P<.06). The difference between the 2 groups was not statistically significant at near (P = .56), at distance (P = .74), or for spherical equivalent (P = .16). CONCLUSION: Excimer laser refractive surgery seems to be useful in the correction of fully refractive accommodative esotropia.

Accommodation, Ocular↗
PubMed2003

Photonic crystals: imaging by flat lens using negative refraction.

The positive refractive index of conventional optical lenses means that they need curved surfaces to form an image, whereas a negative index of refraction allows a flat slab of a material to behave as a lens and focus electromagnetic waves to produce a real image. Here we demonstrate this unique feature of imaging by a flat lens, using the phenomenon of negative refraction in a photonic crystalline material. The key advance that enabled us to make this observation lies in the design of a photonic crystal with suitable dispersion characteristics to achieve negative refraction over a wide range of angles.

Journal Article↗
PubMed2000

Spatially confined and temporally resolved refractive index and scattering evaluation in human skin performed with optical coherence tomography.

In the present applications of optical coherence tomography (OCT), parameters besides pure morphology are evaluated in skin tissue under in vivo conditions. Spatially mapped refractive indices and scattering coefficients may support tissue characterization for research and diagnostic purposes in cosmetics/pharmacy and medicine, respectively. The sample arm of our OCT setup has been arranged to permit refractive index evaluation with little mechanical adjustment of a lens within the objective. A simple algorithm has been derived. Known from atmospheric work, the Klett algorithm [J. D. Klett, "Stable analytical inversion solution for processing LIDAR returns," Appl. Opt. 20(2), 211-220 (1981)] has been applied to the same data set for retrieval of scattering coefficients. Both parameters have been measured in layered structures in skin like stratum corneum, epidermis and dermis. Significant water content in a localized sweat gland duct has been observed by refractive index evaluation. Time studies over 1.5 h permitted a first understanding about physiological changes in skin which are not obtainable by intrusive methods.

Algorithms↗