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At least 955 records · Page 53Linked to original sources
PubMed2005

The autofluorescence of plastic materials and chips measured under laser irradiation.

Plastic materials have the potential to substitute for glass substrates used in microfluidic and microTAS systems adding flexibility in materials' choices. Optical quality plastic materials with a low autofluorescence are crucial for optimal detection by fluorescence and laser induced fluorescence techniques. This paper summarizes a series of optical investigations on commercially available plastic chip materials (PMMA, COC, PC, PDMS) and chips made from those materials. Intrinsic optical constants of plastic materials-refractive index for bulk materials-determined by spectroscopic ellipsometry and transmission spectroscopy in the visible range are presented. The laser-induced autofluorescence of materials and chips was assessed at four laser wavelengths, namely, 403, 488, 532 and 633 nm. Considerable bleaching of the autofluorescence was observed under continuous laser illumination. Overall, the longer wavelength laser excitation sources yielded less autofluorescence. PDMS exhibited the least autofluorescence and was comparable to BoroFloat glass. In all cases, chips exhibited slightly higher autofluorescence than the raw plastic materials from which they had been made.

Equipment Failure Analysis↗
PubMed2002

Effects of optical defocus and spatial contrast on anterior chamber depth in chicks.

The goal of this study was to investigate the effect of optical defocus and spatial contrast on refractive development and, in particular,on anterior chamber growth. Ninety chicks were raised from day 4-10 post-hatching wearing monocular lenses (+/-10 Dor 0 D), in an environment with either high, low or no spatial contrast patterns: 30%, 6% or 0% contrast, respectively. At day 10, the chicks' refractive state and ocular components were assessed using retinoscopy and A-scan ultrasonography. Ocular defocus resulted in sign-dependent significant differences in refractive error, axial length and vitreous chamber depth. Lens wear also led to significant spatial contrast dependent changes in anterior chamber depth. Varying ambient spatial contrast in the chick's environment did not inhibit emmetropization processes; however, anterior chamber growth was particularly susceptible to changes in spatial contrast.

Animals↗
PubMed2001

The effect of conventional CR39 and Fresnel prisms on high and low contrast acuity.

The effect of conventional CR39 and Fresnel prisms on high and low contrast letter acuity was studied. Visual acuity of the fully corrected better eyes of 15 subjects was measured with the high (90%) and low (10%) contrast logMAR letter charts, while they wore prisms of varying power. The results showed that when the power of the conventional CR39 prism and the Fresnel prism reached 10 prism dioptres and 5 prism dioptres, respectively, significant reduction (1 tail t-test, p < 0.05) of the high and low contrast acuity occurred. The Fresnel prism caused a significantly greater acuity reduction than the conventional CR39 prism for powers ranging from 5 to 30 prism dioptres for both contrasts. The rate of acuity reduction with increasing prism power was greater with the low contrast targets than with the high contrast targets for both prisms. In addition, the rate of acuity reduction with increasing prism power was greater with the Fresnel prism than with the conventional CR39 prism for both contrasts. The conventional CR39 prism reduced acuity by a ratio of about 0.8-0.9 of that of the Fresnel prism for powers ranging from 5 to 20 prism dioptres and by about 0.7 for 30 prism dioptres. These ratios applied for both high and low contrast acuity, and therefore were independent of the level of contrast used.

Adult↗
PubMed2001

The gradient index and spherical aberration of the lens of the human eye.

We present equations for analysing the primary spherical aberration of the crystalline lens, both as a whole and of its contributing parts. We apply these equations to two examples of gradient index lenses. The spherical aberration of one lens is well outside that expected for real lenses, but that of the other is within this range. We assess the sensitivity of the aberration to changes in surface shape and gradient index distribution. The process is applicable to other models of the gradient index of the lens.

Adolescent↗
PubMed2003

Effect of soft contact lenses on the measurements of intraocular pressure with non-contact pneumotonometry.

PURPOSE: To evaluate the effect of soft contact lenses with different lens power on the measured value of the intraocular pressure with non-contact pneumotonometry. METHODS: 120 eyes (80 healthy volunteers: 50 women, 30 men, aged 22 to 61 years) were included in this study. Intraocular pressure was measured with a pneumotonometer Canon X-10 before and after insertion of the Ciba Vision Focus Night&Day soft contact lens. We used contact lenses with different lens power of + 0.25 D, + 1.00 D, + 4.00 D, - 1.00 D, and - 4.00 D. The averages of three measurements were taken as representative IOP values that were statistically evaluated. RESULTS: IOP measured over myopic lenses of - 1.00 and - 4.00 D showed lower values within the mean range of 1 mm Hg. The difference between the measurements over the myopic lenses was mostly smaller than +/- 2 mm Hg (78% when using - 1.00 D and 90% when using - 4.00 D contact lens). All the differences using + 0.25 D contact lens were smaller than +/- 2 mm Hg. The difference was considerably higher in measurements over + 1.00 and + 4.00 hyperopic contact lenses and showed strong increase with the lens power. CONCLUSIONS: In our study we showed that intraocular pressure can be reliably measured with non-contact pneumotonometry over myopic lenses or hypermetropic lenses with small lens power. This suggests that non-contact pneumotonometry is a useful method in patients wearing therapeutic contact lenses and contact lens wearers who, when measuring the eye pressure, would not need to remove the contact lenses before the examination.

Adult↗
PubMed2005

[Supernormal sight and high-resolution retinal imaging: a review].

BACKGROUND: An analysis of the wavefront in human eyes has yielded new findings with respect to the cones and other elements of the retina. But the correction of higher-order wavefront aberrations in photorefractive processes is still associated with basic difficulties. MATERIALS AND METHODS: The world literature relating to wavefront corrections in experimental research and the correction of photorefractive aberrations in the human eye is surveyed. RESULTS AND CONCLUSIONS: The correction of higher-order aberrations has permitted a vast improvement in the resolution of the cone-pattern picture existing in vivo. As a consequence, new findings with regard to colour physiology have been forthcoming. On the other hand, the application of wavefront corrections in photorefractive procedures has been only partially successful.

Color Perception↗
PubMed1994

[Limitation of lens power in automobile drivers].

High plus lenses may cause defects in the peripheral visual field. Simple full vision lenses or lenticular lenses without a masked transition zone caused an absolute ring scotoma in the mid-periphery. Patients who were glasses of this type cannot see well enough to drive safely. Although modern edge finishes with masking of the transition zone reduce this problem, visual disturbances in the periphery of the lenses cannot be completely eliminated. A recommendation recently issued by the German Ophthalmological Society concerning maximum lens powers for motorists is aimed at preventing visual field defects of this type.

Automobile Driver Examination↗
PubMed1994

[Theoretical and clinical image properties of refractive 3-zone multifocal lenses with different distribution of far and near focus].

BACKGROUND: The optic of common multifocal IOLs (MIOLs) is effecting an even light distribution to far and near focus. New MIOL designs were developed by Jacobi to improve distance or near contrast, by favouring the far or near focus with 60-70% of the light energy. For binocular implantation, an "asymmetrical" MIOL-combination is possible with accentuation of distance focus in one eye and near focus in the other eye. METHODS: By means of an optical system described by Jacobi and Reiner "artificial eyes" with the new MIOLs were implanted in 7 young healthy subjects and contrast sensitivity was measured for distance and near. Clinical implantation was performed in 46 patients and visual acuity, contrast sensitivity, depth of focus and binocular functions were determined after 6 months. RESULTS: MIOL designs with accentuation of distance vision did not show a significant reduction of distance contrast compared with a monofocal IOL. Asymmetrical binocular implantation of the new lenses resulted in a better distance and near contrast sensitivity than implantation of MIOLs with an even light distribution. Binocular functions were not impaired. CONCLUSION: Asymmetrical implantation of the new MIOLs with uneven light distribution to far and near focus enables distance vision comparable to monofocal IOLs, but with the advantage of an increased depth of focus.

Adult↗
PubMed1993

["Physical eyes" for evaluating various intraocular lenses for monocular and binocular use].

We developed a "physical eye system" to evaluate visual impression after physical implantation of monofocal and multifocal intraocular lenses (IOLs). The system is constructed as two identical astronomical telescopes. The objectives imitate the cornea and behind this cornea the IOL is inserted. The image quality represents exactly the quality of the intraocular lens.

Equipment Design↗
PubMed1992

[An instrument for projecting visual perception by monofocal and bifocal intraocular lenses].

With the aid of a simple optical system similar to an astronomical telescope, images of spectacle lenses, contact lenses and intraocular lenses can be projected in front of, onto or into the eye. These optical images function like real lenses and enable their performance to be evaluated. In the case of intraocular lenses, visual perception through monofocal or bifocal lenses and teledioptric systems can be reproduced.

Equipment Design↗
PubMed1991

[Theoretical and practical vision quality with diffractive-multifocal lenses].

I investigated the discrimination of objects with diffractive bifocal contactlenses, when objects in different distances are presented simultaneously. Computer assisted considerations suggested an impairment of discrimination as compared to monofocal correction for far as well as for near. The theoretical loss of image information has been shown to occur also in a visual test with steric arrangement of object points. However, the experiments suggested, that this kinds of visual quality impairment does not play a dominant role in the qualification of diffractive bifocals, since a rather sophisticated procedure was needed to demonstrate the expected effect.

Computer Simulation↗
PubMed1990

[Diffractive multifocal intraocular lenses. A prospective clinical study].

Forty-three patients were examined three months after implantation of a multifocal or bifocal intraocular lens following cataract extraction. With far vision correction, simultaneous bifocal function with far acuity better than 0.5 and near acuity better than Nieden 3 was achieved in 95.4% of these cases. Glare sensitivity was tested with the BAT and mesopic visual acuity was examined with the Ocutrast. No statistical differences were found between these patients and a control group with monofocal IOLs.

Aged↗
PubMed1988

[A rare trial eyeglass case with binocular trial lenses].

In this article the author describes a rare trial frame case in the medical history collection of the Ruhr University at Bochum. It has 24 binocular trial lenses which are similar to be early "Nuremberg wire spectacles." The lens power is expressed as the focal length, measured in Rhenish inches. Converted into diopters, the refractive power of the lenses ranges from +/- 1.0 to +/- 8.0 D.spherical. The case also contains six pairs of plane lenses tinted in various intensities of azure blue and four pairs of plane lenses tinted smoke-gray. It contains no astigmatic lenses. Since the metric system, with the diopter as a unit of refractive power, was introduced in the optical industry in 1875, it may be assumed that this case was in use before then. However, the design of the binocular trial frames suggests that they may be considerably older.

Eyeglasses↗
PubMed1988

[Optical consequences of implantation of a negative intraocular lens in myopic patients].

The implantation of a concave intraocular lens (IOL) (Worst-Fechner Biconcave Lens) is a new method of correcting myopia. This paper describes how to compute the effective power of an IOL on the basis of corneal curvature and anterior chamber depth, i.e., which lens will neutralize a specific myopia. The authors also discuss the size of the retinal image of an eye corrected by an intraocular lens as compared to an eye corrected by a spectacle glass.

Humans↗
PubMed1988

[Technical aspects of measurement for optically sophisticated eyeglasses].

This paper deals with the question of how aspherical ophthalmic lenses can be measured outside the reference point given by the manufacturer in order to make a lens comparison or to test the shape faithfulness of the lens surface. Three procedures are presented with measuring examples - vertex power measurement with swiveled lens mount, probe scan in a three-coordinate measurement, and interferometer measurement using a non-ideal reference lens. The basic problem inherent in an application-related interpretation of the measuring data sets gained by these methods is shown.

Eyeglasses↗
PubMed1987

[Use of aspherical and atoric surfaces in the optics of eyeglasses].

As early as the beginning of this century, eyeglass lenses with aspherical surfaces were calculated at the behest of Gullstrand and M. von Rohr. There are considerable advantages in their use for the correction of hyperopic, aphakic, and myopic patients. The advantages lie not only in the better optical image produced by the lenses, but also in their lower weight and more pleasant appearance. The image quality of astigmatic lenses can be enhanced by means of atoric surfaces.

Astigmatism↗
PubMed1987

[Centering of eyeglasses with special reference to aspheric single-power lenses].

In the positive power range, aspheric single-power lenses have clear advantages for the spectacle wearer over highly curved spherical lenses in terms of cosmetic appearance and comfort in wear. Correspondingly flat spherical lenses would not be acceptable, due to their dramatically poorer image reproduction properties. Only with an aspheric surface design is it possible to combine a flat lens with optimum image reproduction properties. In order to realize these advantages of aspheric surfaces, the lenses have to be centered in accordance with the ocular pivot point. Several examples are given to illustrate the effects of incorrect centering on the image reproduction properties of both spherical and aspheric single-power lenses. The negative effect of incorrect centering in accordance with the ocular pivot point is clearly far greater with the mathematically much more complex aspheric surfaces than with highly curved spherical lenses. Although the image reproduction quality of the aspheric lens is superior--at least on paper--when it is correctly centered, it is equally true that in practice these lenses quickly prove inferior if incorrectly fitted.

Eyeglasses↗