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At least 685 records · Page 38Linked to original sources
PubMed2001

Glass particles in footwear of members of the public in south-eastern Australia--a survey.

A total of 776 pairs of shoes collected from random members of the public in south-eastern Australia were examined for the presence of glass fragments. From the samples collected a total of 110 fragments were recovered from 57 pairs of shoes (7.3% of the pairs examined). This study shows that the prevalence of glass fragments in footwear is dependent upon the area of the shoe from which the fragments were recovered. A much higher percentage of shoes were found to have fragments embedded in the sole (5.9%) than in the upper area of the shoe (1.9%). These shoes were also more likely to have multiple fragments from multiple sources of glass. Only a very small percentage of shoes contained fragments in both the upper and the sole (0.3%). These findings and their significance for the interpretation of glass evidence involving footwear are discussed in this study.

Adolescent↗
PubMed2002

The interpretation of multi-exponential water proton transverse relaxation in the human and porcine eye lens.

We report results of 1H NMR transverse relaxation experiments on human and porcine eye lenses. Several authors have reported that transverse relaxation is not mono-exponential when observed by the Carr-Purcell-Meiboom-Gill (CPMG) sequence and have interpreted the results by postulating the presence of "pools" of water molecules in different binding environments that do not exchange rapidly on the NMR timescale. We have compared CPMG data for intact lenses with results for lens homogenates and have combined a CPMG spectroscopic pulse train with NMR micro-imaging to study the nature of the transverse relaxation process in human and porcine lenses. Fast exchange of water protons with the lens proteins (crystallins) leads to an enhanced transverse relaxation rate that varies linearly with protein concentration. At the resolution of NMR micro-imaging the transverse relaxation process is mono-exponential. The results show that the multi-exponential CPMG data observed spectroscopically for whole lenses reflect spatial variations in crystallin content through the lens rather than the presence of distinct "bound" and "free" water pools.

Adolescent↗
PubMed2003

Quantification of 5-HMF and dextrose in commercial aqueous dextrose solutions.

5-Hydroxymethylfurfural (5-HMF) is the major thermal decomposition product formed in aqueous dextrose solutions during sterilization and upon storage. Current compendial tests employ a spectrophotometric assay for 5-HMF and a separate assay based on optical rotation for dextrose. Efforts herein focused on identification of approaches to simultaneously quantify both 5-HMF and dextrose in aqueous solutions. Initial studies employed anion exchange chromatography with pulsed amperometric detection (PAD). These studies showed that the low anion exchange column loading capacity and concentration mismatch of dextrose and 5-HMF in typical commercial solutions makes simultaneous quantitation impractical at a single sample concentration. However, mixed modes of detection for each analyte using refractive index (RI) detection for dextrose and UV detection for 5-HMF proved viable for simultaneous quantitation. The performance of both approaches was evaluated and extremely high sensitivity for 5-HMF demonstrated (30-50 ppb). The formation of 5-HMF upon the forced thermal decomposition of dextrose was monitored and compared with results from the USP spectrophotometric assay.

Chromatography, High Pressure Liquid↗
PubMed1998

Comparison of LC detection methods in the investigation of non-UV detectable organic impurities in a drug substance.

HPLC Analysis with different detection methods was shown to be essential in the separation and identification of unknown organic impurities in a drug substance. The impurities were found to exhibit very weak or no response to standard ultraviolet (UV) absorption detection. LC-MS, LC-NMR, indirect, refractive index and evaporative light-scattering detection were used to quantify and identify the impurities in this specific case. The drug substance studied was found to be an ideal analyte for demonstrating the advantages and limitations of several chromatographic detection systems for impurity profile analysis.

Chromatography, High Pressure Liquid↗
PubMed2001

Analysis of postoperative glare and intraocular lens design.

PURPOSE: To assess the potential for reflected glare images from commonly used intraocular lens (IOL) materials and designs. SETTING: Mayo Clinic, Rochester, Minnesota, USA. METHODS: The interaction of reflected light rays from 3 commonly used IOLs (Bausch & Lomb LI61U and P359UV; Alcon AcrySof(R) MA60BM) with different optic designs (equi-biconvex: 10.0 and 15.0 mm anterior radius of curvature; unequal biconvex: 32.0 mm anterior radius of curvature) and optic materials (silicone, poly[methyl methacrylate], and acrylic) were examined in an eye model using the Zemax optical design program. The potential of each IOL model to produce subjective glare was determined from the size of the defocused reflected glare image at the retina. RESULTS: The unequal biconvex design concentrated reflected light on a retinal area that was 60-fold smaller than that of the equi-biconvex design. Increasing the refractive index of the IOL material from 1.43 (silicone) to 1.55 (acrylic) increased the amount of reflected light 5-fold. Compared to an equi-biconvex design composed of a lower refractive index material, the unequal biconvex design with a higher refractive index material increased the relative intensity of reflected light at the retina 300-fold, and for eyes with low corneal power the intensity increased 3500-fold. Similarly, for external glare apparent to an outside observer, the intensity of reflected light increased 400-fold and for low corneal power it increased 6000-fold. CONCLUSION: An unequal biconvex IOL design (32.0 mm anterior radius of curvature) composed of a higher refractive index material increased the potential for postoperative glare and external reflections.

Computer Simulation↗
PubMed2001

Poly(methyl methacrylate) model study of optical surface quality after excimer laser photorefractive keratectomy.

PURPOSE: To evaluate lenses produced by excimer laser ablation of poly(methyl methacrylate) (PMMA) plates. SETTING: University research laboratory. METHODS: Two Nidek EC-5000 scanning-slit excimer laser systems were used to ablate plane-parallel plates of PMMA. The ablated lenses were examined by focimetry, interferometry, and mechanical surface profiling. RESULTS: The spherical optical powers of the lenses matched the expected values, but the cylindrical powers were generally lower than intended. Interferometry revealed marked irregularity in the surface of negative corrections, which often had a positive "island" at their center. Positive corrections were generally smoother. These findings were supported by the results of mechanical profiling. Contrast sensitivity measurements carried out when observing through ablated lenses whose power had been neutralized with a suitable spectacle lens of opposite sign confirmed that the surface irregularities of the ablated lenses markedly reduced contrast sensitivity over a range of spatial frequencies. CONCLUSION: Improvements in beam delivery systems seem desirable.

Contrast Sensitivity↗
PubMed1995

Evaluation of 35 consecutive SI-30 PhacoFlex lenses with high-refractive silicone optic implanted in the capsulorhexis bag.

Thirty-five PhacoFlex foldable open-loop lenses with high-refractive silicone optics were evaluated. All lenses were implanted using a folding forceps and were fixated in the bag. Mean follow-up was 14 months. With adequate forceps, the lens may be inserted through a 3.2 mm incision, using a 3 mm long self-sealing sclerocorneal tunnel. With a well-centered 4 mm to 5 mm capsulorhexis opening, centration was very satisfactory. Moderate decentration occurred in two cases, one from a small, heavily shrinking capsulorhexis and the other from a poorly shaped capsulorhexis that captured the optic along its edge. Except in one case of combined cataract and filtering surgery, all optics were at a pronounced distance from the iris. Consequently, signs of iris chafing or iridocapsular synechias and cellular invasion were not seen. The optic typically exhibited a slight bluish tint and minute granular inclusions without clinical significance. Neither discoloration nor haze was present. Best visual acuity was 20/25 or better in all cases. The small wound required for insertion makes the PhacoFlex especially appropriate for clear corneal incision surgery. Attempts are being made to minimize the grainy appearance of the optic. Increasing the rigidity of the loops may be advantageous.

Aged↗
PubMed1991

Ray tracing error correction in ophthalmic optics.

Ray tracing error correction (RTEC), a new method for various refractive calculations, is introduced. It consists of two procedures: (1) ray tracing that determines whether the ray originating from an infinite point focuses on the fovea and (2) error correction that varies the curvature of the different refractive surfaces according to an error correction formula when the ray is not focused at the fovea. These calculations are continued until the ray is focused at the fovea. The refraction of Gullstrand's schematic eye at relaxation and at accommodation, the desired postoperative corneal curvature for postoperative emmetropia after corneal ablation surgery, and the intraocular power of convex-plano, biconvex, and plano-convex intraocular lenses are presented.

Accommodation, Ocular↗
PubMed1992

Optical quality of intraocular lenses.

The ANSI Z80.7 standard for intraocular lens quality is being updated. This paper identifies areas that require revision and suggests that a clear distinction between the lens design and the quality control test methods be made. The standard monofocal lens design consists of two spherical surfaces, and lens power can be specified by the thick lens equation, using body temperature refractive index values at a wavelength of 550 nm. Interferometry might be used as a primary manufacturing test method for poly(methyl methacrylate) lenses; tolerance values for lens surface errors are suggested. Other test methods can also be used. Measuring the modulation transfer function in fluid may be the most useful.

Humans↗
PubMed1990

Development of the SRK/T intraocular lens implant power calculation formula.

A new implant power calculation formula (SRK/T) was developed using the nonlinear terms of the theoretical formulas as its foundation but empirical regression methodology for optimization. Postoperative anterior chamber depth prediction, retinal thickness axial length correction, and corneal refractive index were systematically and interactively optimized using an iterative process on five data sets consisting of 1,677 posterior chamber lens cases. The new SRK/T formula performed slightly better than the Holladay, SRK II, Binkhorst, and Hoffer formulas, which was the expected result as any formula performs superiorly with the data from which it was derived. Comparative accuracy of this formula upon independent data sets is addressed in a follow-up report. The formula derived provides a primarily theoretical approach under the SRK umbrella of formulas and has the added advantage of being calculable using either SRK A-constants that have been empirically derived over the last nine years or using anterior chamber depth estimates.

Anterior Chamber↗
PubMed1990

Comparison of the SRK/T formula and other theoretical and regression formulas.

We compared the predictive accuracy of the SRK/T formula to the SRK II, Binkhorst II, Hoffer, and Holladay formulas in seven series of cases totaling 1,050 eyes. In the combined group, the SRK/T and Holladay formulas performed only slightly better than the other formulas. In short eyes (less than 22 mm), all formulas performed well, with the SRK/T, SRK II, and Holladay formulas performing marginally better. In moderately long eyes (greater than 24.5 mm, less than or equal to 27 mm), the Hoffer and Binkhorst II formulas had a greater proportion of cases with greater than 2 diopters (D) of error and the SRK/T and Holladay were again marginally better. In the very long eyes (greater than 27 mm and less than or equal to 28.4 mm), there were only 11 cases and all formulas performed well since none had greater than 2 D of prediction error. In an extremely long eye data set (greater than 28.4 mm), the SRK II formula clearly gave the poorest result. Eyes of this length occurred in only 0.1% of cases in our unselected series. Results support the contention that the present second and third generation IOL power formulas give fairly equivalent accuracy. Other factors, such as availability, ease of use, and ability to tailor or individualize, become major considerations.

Eye↗
PubMed1990

Multifocal intraocular lenses.

Current multifocal intraocular lens designs incorporate refractive or diffractive optical principles to achieve increased depth of focus. Information about four basic design concepts is presented. Early clinical results with two of these, the IOLAB Nuvue two-zone refractive multifocal and the 3M diffractive multifocal, are summarized.

Clinical Trials as Topic↗
PubMed1991

Optical design of low index intraocular lenses.

The effect of shape of low index (1.43) intraocular lenses on optical performance of pseudophakic eyes was investigated. A range of image quality criteria was used. The optimum lens for on-axis vision was biconvex, with the more curved surface facing the cornea. For small off-axis angles, optimum lens shape varied with the ocular parameters. A recommended range of intraocular lenses is plano-convex (with the curved shape facing the cornea) to equi-convex. Compared with conventional poly(methyl methacrylate) lenses (1.492 index), optimum lens shapes of low index lenses were less sensitive to changes in eye parameters and lens fitting position. The magnitudes of aberration of pseudophakic eyes varied more with changes in lens shape and lens position in low index lenses than in conventional lenses.

Humans↗
PubMed1987

Comparison of the keratometer and the lens bench in measuring intraocular lens power.

Intraocular lenses (IOLs) from six manufacturers were measured on a Terry keratometer and on a calibrated lens bench for lens power. Differences between the two methods appeared when the IOLs were a different refractive index than polymethylmethacrylate (PMMA) and a shape other than planoconvex. These differences were consistent for ultraviolet absorbing PMMA and for meniscus lenses.

Lenses, Intraocular↗
PubMed1988

Silicone intraocular lens resolution in air and in water.

The resolution efficiencies of 31 biconvex silicone intraocular lenses, ranging in power from 16.0 to 23.5 diopters, were tested in air and in water to see if a predictable relationship existed as previously reported with polymethylmethacrylate lenses. Resolution efficiency is defined as the percentage ratio of the actual resolving power of a lens to that of a perfect lens of the same focal length which is only limited in resolution by diffraction. The lenses ranged from 29% to 58% resolution efficiency in air. No lenses exhibiting multiple images were included. All 31 lenses achieved at least 73% resolution efficiency in water, and one lens achieved 82%. Based on these findings, a biconvex silicone lens that exceeds 30% resolution efficiency in air and does not produce multiple images can perform near its diffraction limit when implanted in the eye.

Air↗