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At least 127 records · Page 7Linked to original sources
PubMed2006

Microstructure of magnesium fluoride films deposited by boat evaporation at 193 nm.

Single layer magnesium fluoride (MgF2) was deposited on fused-silica substrates by a molybdenum boat evaporation process at 193 nm. The formation of various microstructures in relation to the different substrate temperatures and deposition rates were investigated. The relation between these microstructures (including cross-sectional morphology, surface roughness, and crystalline structures), the optical properties (including refractive index and optical loss) and stress, were all investigated. It was found that the laser-induced damage threshold (LIDT) would be affected by the microstructure, optical loss, and stress of the thin film. To obtain a larger LIDT value and better optical characteristics, MgF2 films should be deposited at a high substrate temperature (300 degrees C) and at a low deposition rate (0.05 nm s(-1)).

Journal Article↗
PubMed1992

[The most frequent causes of loss or impairment of vision in children and adolescents].

On the basis of examination of 100 persons aged 3-18 years registered in the Olsztyn Division of the Union of the Blind the authors determined the causes which led to the loss of vision or of its impairment. The most frequent cause of the invalidism of the visual system were: errors of refraction (32%), optic atrophy (24%), congenital cataract (16%), retinal and choroidal degeneration (9%), retrolental fibroplasia (6%), anophthalmia or malformation of the globe (4%), coloboma of the iris or choroid (3%), retinoblastoma (3%), injuries (2%) and congenital glaucoma (1%).

Adolescent↗
PubMedDate not supplied

[Interlamellar refraction keratoplasty with central keratectomy of superficial corneal laminae in the correction of aphakia].

Interlamellar refraction keratoplasty with central keratectomy of superficial laminae of the cornea was used to correct aphakia in 15 patients and the results followed up for 2.5-7 years. This method permits a simultaneous refraction and optic transplantation of the cornea. Corneal refraction was enhanced by 7.2-14.8 diopters (the mean value 11.03 diopters). The technique is an extraocular one and therefore may be widely used for aphakia correction, particularly in cases with superficial opacities of the cornea.

Adolescent↗
PubMed1981

Optical characterization of a low solubility organic compound.

The X, Y, and Z principal vibration directions along with the principal refractive indexes, optic angle, optical sign, birefringence, optical orientation, and crystal system for the low solubility compound 5-(tetradecyloxy)-2-furancarboxylic acid were determined with a polarizing microscope and spindle stage. The X and Z principal vibration directions are not coincident with the a and c crystallographic axes; however, the Y direction is considered to be coincident with the b axis. Therefore, the crystal is assigned to the monoclinic crystal system. The bladed/lath-shaped crystals rest on one of the two large orthopinacoid (100) faces and present the microscopist with a single plane of optical symmetry. A beta refractive index of 1.555 is observed with the crystal axis of elongation parallel to the polarizer, and a gamma of 1.600-1.660 is observed in the contiguous extinction position. Determination of the optic angle principal vibration directions, and principal refractive indexes was facilitated by mounting the crystals on a spindle stage for rotation about the b crystallographic axis (optic normal).

Crystallization↗
PubMed2006

Optical nonlinear absorption and refraction of CdS and CdS-Ag core-shell quantum dots.

The CdS and CdS-Ag core-shell quantum dots (QDs) have been prepared. The nanostructures of the QDs were revealed by transmisson electron microscopy and absorption spectra, respectively. The third-order nonlinear optical properties of the core-shell QDs have been studied by using Z-scan technique with femtosecond pulses at the wavelength of 790 nm. The value of the effective nonlinear absorption coefficient beta(eff) of CdS-Ag QDs is measured to be about 16.8 cm/GW, which is about 400 times larger than that of bare CdS QDs of 3.9 x 10(-2) cm/GW. The nonlinear refraction index gamma of CdS-Ag QDs is about -2.3 x 10(-4) cm(2)GW, which is about 200 times larger than that of bare CdS QDs of 1.0 x 10(-6) cm(2)GW.

Journal Article↗
PubMed2003

Effect of dextran-induced changes in refractive index and aggregation on optical properties of whole blood.

The purpose of the present study is to investigate systematically the mechanisms of alterations in the optical properties of whole blood immersed in the biocompatible agent dextran, and to define the optimal concentration of dextrans required for blood optical clearing in order to enhance the capability of light penetration depth for optical imaging applications. In the experiments, dextrans with different molecular weights and various concentrations were employed and investigated by the use of the optical coherence tomography technique. Changes in light attenuation, refractive index and aggregation properties of blood immersed in dextrans were studied. It was concluded from the results that the mechanisms for blood optical clearing are characteristic of the types of dextrans employed, their concentrations and the application stages. Among the substances applied, Dx500 at a concentration at 0.5 g dl(-1) gives the best result in improving light penetration depth through the blood. The increase of light transmission at the beginning of the addition of dextrans is mainly attributed to refractive index matching between the scattering centres and the ground matter. Thereafter, the transmission change is probably due to a dextran-induced aggregation-disaggregation effect. Overall, light scattering in the blood could be effectively reduced by the application of dextrans. It represents a promising approach to increasing the imaging depth for in vivo optical imaging of biological tissue, for example optical coherence tomography.

Adult↗
PubMed1980

Geometrical optics and the statistical analysis of refractive error.

Relationships among statistical quantities used in the analysis of refractive error are derived from geometrical optics principles. The accuracy of these results are verified using the data of Sorsby et al. As an application of these results, it is shown that there is difficulty in accounting for leptokurtosis of refractive error in terms of correlation among the optical parameters of the eye. Also, it is shown that the distribution of the optical parameters of the eye cannot be a joint-normal distribution.

Humans↗
PubMed1994

Refractive index of the human lens surface measured with an optic fibre sensor.

The refractive index of the human eye lens has been measured directly with a reflectometric, optic fibre sensor. Thirteen human lenses ranging in age from 27 to 84 years were examined. The results show that the refractive index is higher on the anterior than on the posterior surface with most of the values ranging from 1.364 to 1.381 and 1.338 to 1.357, respectively. There is no topographical variation along either surface and no evidence of age-related differences. Results using the sensor are compared with those from the Abbe refractometer on homogeneous materials. The refractive index of distilled water was found to be 1.332 with the fibre sensor and 1.3326 with the Abbe refractometer; of 0.5% agarose gel, it was 1.334 and 1.3355, respectively.

Adult↗
PubMed1999

Accuracy of Orbscan total optical power maps in detecting refractive change after myopic laser in situ keratomileusis.

PURPOSE: To determine whether the refractive change obtained using the Orbscan-derived total optical power (TOP) map is in concordance with the manifest refractive change produced by laser in situ keratomileusis (LASIK). SETTING: LASIK Vision Canada, Vancouver, BC, Canada (an ambulatory surgical center for refractive surgery). METHODS: Twenty eyes of 10 consecutive bilateral LASIK patients were included in the study. Orbscan topographical analysis and manifest refraction were performed preoperatively and at least 1 month postoperatively. The change in manifest refraction (corrected to the corneal plane) before and after LASIK was correlated with the corneal power change averaged within the 2.0, 3.0, 4.0, and 5.0 mm diameter zones of TOP and axial power maps. RESULTS: The central 4.0 mm zone TOP map gave the best correlation between manifest refractive change and Orbscan-measured corneal power change (r2 = 0.835, P < .004). The correlation was higher with TOP maps than with anterior axial power maps. CONCLUSION: The corneal power change measured by the Orbscan TOP maps correlated highly with the changes in manifest refraction after LASIK.

Cornea↗
PubMed2001

[The characteristics of the optically calculated axial length and the predicted refraction when using the intraoperative refraction].

PURPOSE: To understand the effect of the error in corneal refractive power on the optically calculated axial length (AXO) and the postoperative predicted refraction (Q'gl) calculated from the aphakic refraction (Qaph). METHOD: We used the Gullstrand's schematic eye, in which the intraocular lens (+20 D) was inserted at a depth of 5 mm, and calculated Qaph and postoperative refraction (Qgl) geometrically when the corneal radius of the anterior surface (Rfc) changed from 7 mm to 9 mm. AXO was calculated using the calculation formula from a previous report, and then Q'gl was calculated from the AXO and the true axial length (AXT) using the theoretical calculation formula (regarding the fictitious corneal refractive index as 1.3315). RESULTS: When the measured corneal radius of the anterior surface (K) was equal to Rfc, the error of the AXO was largest (AXO/AXT = 101.512) when K was 9 mm. The error in power prediction (Qgl-Q'gl) of the AXT was 7.7 times larger than that of AXO. CONCLUSION: If K is exact, AXO is useful to predict the intraocular lens depth because the error of AXO is small. The error in power prediction of AXO is smaller than that of AXT.

Cornea↗
PubMed1999

Refractive error consequences of reversed-optic AMO SI-40NB intraocular lens.

OBJECTIVE: To evaluate the refractive consequences of inadvertently implanting a reversed-optic AMO SI-40NB posterior chamber intraocular lens (IOL). DESIGN: Retrospective case series. METHODS: One surgeon (BLH) implanted 457 SI-40NB IOLs over a 2-year period beginning on January 1, 1996, and ending on December 31, 1997. Six of these IOLs (1.3%) were noted to have been implanted with a reversed optic. The authors retrospectively reviewed the target spherical equivalent refractive errors (SEREs) and actual postoperative SEREs for all 457 eyes. MAIN OUTCOME MEASURES: The SRK-II formula was used to predict target SEREs. Actual postoperative SEREs were determined at 1 month after surgery using either a manifest or an automated refraction. Target postoperative SEREs were subtracted from actual postoperative SEREs to calculate diopter surprises, or the degree to which the actual SEREs differed from the target SEREs. RESULTS: The mean (+/-standard deviation) diopter surprise for reversed-optic SI-40NB IOLs was 0.01 (+/-0.89) diopter (D) more myopic than predicted; diopter surprises ranged from -1.39 D to +1.42 D. The mean diopter surprise for nonreversed SI-40NB IOLs was 0.18 (+/-0.81) D more hyperopic than predicted; diopter surprises ranged from -1.88 D to +2.56 D. The difference between the mean diopter surprises (0.19 D) was not statistically significant (t = 0.56, P = 0.57). CONCLUSIONS: A reversed-optic SI-40NB IOL is as likely to produce a satisfactory refractive result as a nonreversed IOL. Therefore, the refractive consequences of a reversed-optic SI-40NB IOL do not warrant the risks associated with repositioning the lens.

Aged↗
PubMed1991

[Refractive surgery of the cornea. Corneal surgery--an alternative to optical aids?].

Errors of refraction of the eye can be corrected not only by means of spectacles, contact lenses or intra-ocular lenses, but also by operative procedures on the cornea. At present, correction of myopia is accomplished with radial keratotomy (RK), a procedure that achieves the best results in the range up to - 6.0 diopters. However, on account of its side effects, in particular poor predictability, the method is no true alternative to the use of optical aids. Epikeratoplasty done to correct hyperopia and aphakia, is even more imprecise, and should only be employed in exceptional cases. Laser surgery of the cornea is still undergoing clinical testing, but has already produced promising results.

Astigmatism↗
PubMed1975

[An eye-model to show fundamental optical properties as related to refraction and glasses-testing (author's transl)].

A new model of the eye is presented, that can demonstrate quantitatively the principal optical concepts such as focal distance, refractive power, principal point, nodal point etc. Ametropias and their correction can be shown. This model can be used to illustrate the dependence of the vertex distance on the effective refractive power of a spectacle lens and the influence of a spectacle lens on the image size on the retina. The phenomena of retinoscopy can also be demonstrated very clearly. An instruction manual for the model exists that contains theory, control tests and suggested experiments.

Eyeglasses↗
PubMed2004

Long-term observation of the refraction with a reversed-optic posterior chamber intraocular lens.

A 73-year-old man had phacoemulsification and implantation of a posterior chamber intraocular lens (PC IOL) in both eyes. In the right eye, the optic was unintentionally reversed in the bag. In the left eye, the posterior capsule was ruptured and the IOL haptics were fixated in the ciliary sulcus. The refraction in the sulcus-fixated left eye was stable from 1 month to 4 years. The right eye had a myopic shift at 1 month, with a regression of 1.50 diopters that continued for 2 years. The final IOL position in the right eye was 0.25 mm anterior to the position predicted by the SRK/T formula. It took 2 years for the refraction in the eye with the reversed-optic PC IOL to become stable. A large myopic shift and gradual regression in refraction may stem from a different wound-healing reaction than that of properly fixated IOLs.

Aged↗
PubMed2005

Counter-propagating optical trapping system for size and refractive index measurement of microparticles.

We propose and demonstrate a novel approach to measure the size and refractive index of microparticles based on two beam optical trapping, where forward scattered light is detected to give information about the particle. The counter-propagating optical trap measurement (COTM) system exploits the capability of optical traps to measure pico-Newton forces for microparticles' refractive index and size characterization. Different from the current best technique for microparticles' refractive index measurement, refractometry, a bulk technique requiring changing the fluid composition of the sample, our optical trap technique works with any transparent fluid and enables single particle analysis without the use of biological markers. A ray-optics model is used to explore the physical operation of the COTM system, predict system performance and aid system design. Experiments demonstrate the accuracy of refractive index measurement of Deltan=0.013 and size measurement of 3% of diameter with 2% standard deviation. Present performance is instrumentation limited, and a potential improvement by more than two orders of magnitude can be expected in the future. With further development in parallelism and miniaturization, the system offers advantages for cell manipulation and bioanalysis compatible with lab-on-a-chip systems.

Biopolymers↗