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At least 145 records · Page 8Linked to original sources
PubMed2002

Refractive-index profiling of embedded microstructures in optical materials.

We describe use of a phase-sensitive low-coherence reflectometer to measure spatial variation of refractive index in optical materials. The described interferometric technique is demonstrated to be a valuable tool to profile the refractive index of optical elements such as integrated waveguides and photowritten optical microstructures. As an example, a refractive-index profile is mapped of a microstructure written in a microscope glass slide with an ultrashort-pulse laser.

Journal Article↗
PubMed2002

[Highly refractive silicone lens with sharp optic edge (CeeOn Edge, Model 911): one year results of a multicenter clinical trial on performance and efficacy].

PURPOSE: To investigate the performance and efficacy of a new high refractive index (1.46) silicone intraocular lens with sharp optic edges. MATERIALS AND METHODS: In this open prospective multicenter study 149 patients underwent cataract surgery and implantation of CeeOn Edge in one eye. Best corrected visual acuity was determined at day 1 - 2, week 1 - 2, month 6 and month 12 postoperatively. Posterior capsule was clinically evaluated according to existence or absence of posterior capsule opacification (PCO). PCO was defined as relevant if the visual acuity loss exceeded at least two lines. The intraoperative handling of the lens was assessed concerning foldability, haptic handling, positioning, unfolding and general assessment. RESULTS: Visual acuity increased from preoperatively 0.3 to 0.9 after one year. PCO with impact on visual acuity (loss of 2 lines or more) was recorded in only two patients, after 2 weeks (YAG) resp. 1 year (no YAG). The handling and implantation was considered to be good to very good. No lens-related complications were seen during the one year study period. CONCLUSIONS: CeeOn Edge, Model 911, restores visual acuity after cataract surgery and shows promising handling results. The low rate of PCO and YAG is most probably related to the sharp edge of the lens.

Aged↗
PubMed2004

Optical properties of porous helical thin films.

Porous dielectric thin films, composed of isolated helical columns, are fabricated by the glancing angle deposition technique. The selective reflection of circularly polarized light and the optical rotation of linearly polarized light are investigated as a function of film material and helical morphology. The strongest chiral optical response is observed for titanium-dioxide films because of its large refractive index. Optical rotatory powers as high as 4.5 degrees are observed in 830-nm-thick helical films. By tailoring the pitch of the helical columns, the wavelength dependence of the circular reflection band is tuned to preferentially reflect red, green, or blue light, a promising quality for display applications.

Journal Article↗
PubMed1990

[Predicting visual acuity in media opacities and uncorrectable refractive errors. Assessing so-called "retinal visual acuity"].

Three different components contribute to the modulation transfer function of the visual system: (1) formation of the optical image (refractive media, pupil); (2) scattering of light in the prereceptoral layers of the retina; (3) neuronal processing in the retina und superior visual centers. In the presence of media opacities or non-correctable refractive errors, the clinical question often arises as to which macular function can be expected under the assumption of normal optical image formation (e.g. prior to cataract extraction, corneal transplantation, or vitrectomy). Simple tests such as light projection, color discrimination, and two-point discrimination cannot provide adequate information about macular function. The same holds true for the global luminance ERG. The X-ray phosphene is obsolete. The Maddox rod (with limitations), transilluminated Amsler grid, and various entoptic phenomena (Purkinje vascular phenomenon, foveal chagrin, Haidinger's brushes, blue field phenomenon) are available as qualitative subjective tests. Maxwellian view systems with pinhole aperture (potential acuity meter PAM) and the interferometers (retinometer, visometer, SITE-IRAS interferometer) provide quantitative subjective methods. The flash VECP is primarily a qualitative objective test that allows semiquantitative acuity prediction under special conditions (unilateral opacities). Psychophysical criteria that are less affected by the quality of the retinal image show promising developments in future subjective tests, e.g. optotypes in positive contrast, optotypes or targets superimposed on a background of optical noise, or hyperacuity. Future objective test developments are pattern VECP or even pattern ERG elicited by interferometric stimulation, speckle VECP and focal ERG.

Cataract↗
PubMed1993

Micromanipulation by "multiple" optical traps created by a single fast scanning trap integrated with the bilateral confocal scanning laser microscope.

We have developed a novel micromanipulator consisting of multiple optical traps created by scanning one single beam trap along a variable number of positions. Among other things, this enables the orientation of irregularly shaped and relatively large structures which could not be oriented by just one trap as is demonstrated on long Escherichia coli bacteria filaments. We expect that the multiple trap manipulator will broaden the field of applications of optical trapping as a micromanipulation technique. For example, it facilitates the study of mechanical properties of extended structures as illustrated by a "bending"-experiment using E. coli bacterium filaments. A special application of the multiple trap manipulator is the "indirect trapping" of objects which we did by keeping them held between other optically trapped particles. Indirect trapping makes it possible to trap particles which either cannot be trapped directly due to their optical properties (refractive index) or for which exposure to the laser radiation is undesirable. The multiple optical trap manipulator is controlled interactively by a UNIX workstation coupled to a VME instrumentation bus. This provides great flexibility in the control of the position and the orientation of the optical traps. Micromanipulation makes it desirable to have real time 3D microscopy for imaging and guidance of the optical traps. Therefore we integrated optical micromanipulation and a specially developed real-time confocal microscope. This so called bilateral confocal scanning laser microscope (bilateral CSLM) [Brakenhoff and Visscher, J Microsc 165:139-146, 1992] produces images at video rate.

Lasers↗
PubMed1994

[Suitability of the open loop lens Phacoflex XI-30 for capsular sick implantation by self-sealing sclerocorneal tunnel incisions].

SCOPE OF THE STUDY: We studied a new intraocular lens implant with a high-refractive silicone optic and prolene C-loops. Suitability for folding and implantation with the recommended instruments as well as its performance as a capsular bag implant were evaluated. The impact of the self-sealing wound construction used on postoperative corneal stability was also studied. PATIENTS AND METHODS: We included 35 consecutively operated eyes. Capsulorhexis and phacoemulsification were performed. A well-centered and round 4-5 mm anterior capsular opening was aimed at. Using the Fine Universal or the Livernois-McDonald folder the optic was folded lengthwise and the leading loop tucked within the crease. The lens was implanted through a self-sealing sclerocorneal tunnel which measured 3.0 mm in length and 3.2 mm in width. RESULTS: With the instrumentation described, a 3.2 mm incision was adequate. - The lens centered well. In one case each decentration resulted from an optic-edge-by-rhexis-rim capture with an inappropriately shaped rhexis and from excessive capsular bag shrinkage with a too small rhexis. As a rule, the posterior capsule was distended and, with five exceptions, firmly attached to the optic. Fibrosis had resulted in only two cases where the rhexis had evaded the optic edge. Except for a single case where a filtering procedure had been simultaneously performed, optic-to-iris clearance was pronounced in all cases. Consequently, signs of iris chafing were never seen and iridocapsular synechiae had never formed in the latter. - Typically, fine granules scattered within the material and a bluish-violet tint were noted. However, neither intensive haze nor brownish discoloration as well as shell- or inner contour-phenomena were never present. - Vector analysis showed a negligible initial astigmatic shift against the wound that did not progress further on. CONCLUSION: This new implant performs very satisfactory. It may be even further improved by eliminating the granular inclusions and increasing the haptic rigidity. In order to prevent fibrotic opacification of the posterior capsule full circular overlap of the optic periphery by the anterior capsular leaf should be aimed at. The advantage of the reduced incision width required for insertion makes it very appropriate for clear corneal incision surgery.

Aged↗
PubMed1994

Race-, age-, gender-, and refractive error-related differences in the normal optic disc.

OBJECTIVE: To determine race-, age-, gender-, and refractive error-related differences in the size and topography of the optic disc in healthy Americans. DESIGN: Population-based study. SETTING: Eastern and southeastern health districts of Baltimore, Md. PARTICIPANTS: A population-based sample of 4877 non-institutionalized black and white individuals aged 40 years or older without evidence of optic nerve disease. MAIN OUTCOME MEASURE: Race-, age-, gender-, and refractive error-related differences in optic disc measurements: disc area, neural rim area, cup area, cup-to-disc ratio, and neural rim area-to-disc area ratio. RESULTS: We analyzed simultaneous stereoscopic optic disc photographs from 3387 (1534 black and 1853 white) of the 4877 healthy individuals using an image analyzer (Topcon Image Analyzer, Topcon Instrument Corporation, Paramus, NJ). A total of 1490 individuals were excluded owing to the absence of good-quality images from either eye. The image analyzer defined the cup margin 150 microns below the surface of the disc margin. On average, blacks had significantly larger disc areas (blacks, 2.94 mm2; whites, 2.63 mm2), larger cup areas (blacks, 1.04 mm2; whites, 0.71 mm2), larger cup-to-disc ratios (blacks, 0.56; whites, 0.49), similar neural rim areas (blacks, 1.90 mm2; whites, 1.92 mm2), and smaller neural rim area-to-disc area ratios (blacks, 0.66; whites, 0.74) compared with whites. There were no age-related differences in any of the disc measurements. Male subjects had 2% to 3% larger optic discs compared with female subjects. No association between refractive error and any of the optic disc measurements studied was detected. CONCLUSIONS: Racial differences in the normal optic disc are present among urban Americans, and these differences must be considered in evaluation of the optic disc for glaucoma and other optic neuropathies. Among the individuals in our study, all of whom were 40 years of age or older, no progressive age-related decline in neural rim area was detectable. Neither gender nor refractive error were associated with any significant differences in the size and topography of the normal optic disc.

Adult↗
PubMedDate not supplied

Effect of an elliptical optical zone on outcome of photoastigmatic refractive keratectomy.

BACKGROUND: This study presents the effect of an elliptical optical zone on the accuracy of correction of astigmatism in patients undergoing photorefractive astigmatic keratectomy (PARK) for myopic astigmatism. METHODS: We reviewed a consecutive case series of 102 eyes that underwent PARK with a Nidek EC-5000 excimer laser by a single surgeon. Group A consisted of 50 eyes treated using a circular optical zone of 6.5 mm x 6.5 mm with a 7.5-mm x 7.5-mm transition zone. Group B consisted of 52 eyes treated using an elliptical optical zone of 5.5 mm x 6.5 mm with a 6.5-mm x 7.5-mm transition zone. Refraction was measured preoperatively and postoperatively, and vector analysis was used to study the change in astigmatism induced by surgery. RESULTS: Mean correction index improved from 75% in Group A to 100% in Group B. Mean angle of error was reduced from 15.8 degrees in Group A to 7.5 degrees in Group B. Hyperopic shift was reduced from +0.70 D in Group A to +0.20 D in Group B. CONCLUSIONS: Excimer laser photorefractive astigmatic keratectomy using an elliptical optical zone improved the correction index for astigmatic change and reduced the mean angle of error. An elliptical optical zone is more effective than the circular optical zone for the treatment of astigmatism in patients with compound myopic astigmatism.

Astigmatism↗
PubMed1989

Optic disc photogrammetry: magnification factors for eye position, centration, and ametropias, refractive and axial; and their application in the diagnosis of optic nerve hypoplasia.

To determine if image magnification from ametropia or other factors required correction in the photogrammetric diagnosis of optic nerve hypoplasia, the following variables were studied using two standard 30 degrees field fundus cameras (Zeiss FF-3 and Kowa RC-2): (1) distance between the camera and the subject--variations in this distance do not change the image size; (2) decentration of the camera (i.e., decentration of the optic disc image within the field)--no effect was found using the Kowa camera, but in the Zeiss, a 2% (0.07 mm) increase in disc image size was found for each mm of optic disc decentration in the field; (3) ametropia, refractive experimental (induced in one subject with soft contact lenses, from +8.00 diopters (D) to -8.00D)--no significant change in image size was found (In addition, in 50 healthy adult eyes with various refractive errors, including ten with uncorrected aphakia, there was no significant difference found for the size of the optic nerve in different refractive ametropias. No correction factor was necessary for aphakia or for other refractive ametropias); and (4) ametropia, axial--axial myopia showed minor but significant magnification: a linear increase in the horizontal diameter of the optic disc image of 2% (0.07 mm) was found for each diopter of axial ametropia exceeding 3D. There was insufficient data for axial hyperopia. These magnification factors should be applied when measuring the optic disc on 35-mm transparencies to make a diagnosis of optic nerve hypoplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Aphakia↗
PubMed2002

Anomalous refraction and diffraction in discrete optical systems.

We experimentally prove that light propagation in a discrete system, i.e., an array of coupled waveguides, exhibits striking anomalies. We show that refraction is restricted to a cone, irrespective of the initial tilt of the beam. Diffraction can be controlled in size and sign by the input conditions. Diffractive beam spreading can even be arrested and diverging light can be focused. The results can be thoroughly theoretically explained.

Journal Article↗
PubMed2004

Correction of refractive error in the adult population of Bangladesh: meeting the unmet need.

PURPOSE: To assess the extent of uncorrected refractive error and associated factors in Bangladesh and to suggest ways in which this need can be met. METHODS: A nationally representative sample of 12,782 adults (>/= 30 years of age) was selected. Of them, 11,624 subjects underwent a demographic interview, visual acuity (logarithm of the minimum angle of resolution [logMAR]) measurement, automated refraction, and optic disc examination. Subjects with visual acuity less than 6/12 in either eye also had a corrected refraction measurement, cataract grading, and dilated retinal examination. RESULTS: Of the 11,624 subjects examined, 2,469 (22.1%) were myopes (less than -0.5 D) and 2,308 (20.6%) hyperopes (more than +0.5 D). The spectacle coverage percentage, calculated as [met need/(met need + unmet need) x 100%] was 25.2% and 40.5%, using 6/12 and 6/18 visual acuity cutoffs, respectively, and was higher in men and urban inhabitants. Older subjects and the literate and more highly educated were more likely to wear spectacles; however, most spectacle wearers (81%) had inadequate correction. Of the 1142 subjects who would benefit from spectacles, 827 (72.4%) would be suitable for off-the-shelf spectacles. Subjects without spectacles with less than 6/12 in the better eye (n = 835), would achieve 6/12 or better with correction (unmet need). Extrapolation to the national population yields an estimate that 1.5 million (6.7%) adult men and 1.8 million (9.2%) women have an unmet need for refractive correction. CONCLUSIONS: In Bangladesh, there is low spectacle coverage with a large unmet need. This survey identified risk groups, in particular women and those living in rural areas. This description of the availability of refractive services suggests areas for improvement (e.g., off-the-shelf spectacles) that may enable Bangladesh to achieve the goals of the World Health Organization's Vision 2020 initiative.

Adult↗
PubMed1994

Effects of optically induced blur on the refractive status of young monkeys.

In each of eight rhesus monkeys, one eye was defocused with a -9 D contact lens beginning before 1 month of age for periods of 2-3 months. At the end of the rearing period, interocular comparisons showed that one subject had developed a relative axial myopia (3.0 D), however, five monkeys had developed a relative axial hyperopia (2.0-3.5 D). After discontinuing the contact-lens rearing procedure, the induced refractive errors diminished over time in all subjects. These results indicate that the defocus threshold for form-deprivation myopia is relatively high and that substantial levels of optical defocus which do not exceed this threshold typically produce axial hyperopia. The recovery data suggests that monkeys have an emmetropization mechanism which is sensitive to optical defocus, but the failure of this mechanism to compensate for the refractive errors simulated during the lens-rearing procedures suggests that this mechanism has a limited operating range.

Animals↗
PubMed2006

Optical parameters and upconversion fluorescence in Tm3+/Yb3+-doped alkali-barium-bismuth-tellurite glasses.

Tm(3+)/Yb(3+)-doped alkali-barium-bismuth-tellurite (LKBBT) glasses have been fabricated and characterized. Density, refractive index, optical absorption, absorption and emission cross-sections of Yb(3+), Judd-Ofelt parameters and spontaneous transition probabilities of Tm(3+) have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of a 980 nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm(3+) indicate that Tm(3+)/Yb(3+) co-doped LKBBT glasses are promising upconversion optical and laser materials.

Fluorescence↗
PubMed2002

Mismatch between flap and stromal areas after laser in situ keratomileusis as source of flap striae.

PURPOSE: To calculate theoretically the magnitude of the excess area between the lower surface of the flap and the underlying ablated stroma. METHODS: On the initial assumptions of a nonextensible flap and a spherical cornea, flap and ablated stromal areas were determined as a function of myopic correction in the range of 0 to -12 diopters (D) for typical values of corneal radius (7.8 mm) and flap thickness (160 microm), together with a range of ablation zone diameters (4.0 mm, 6.0 mm, 8.0 mm, and 10.0 mm). RESULTS: Excess flap area increases with the magnitude of the refractive correction and the diameter of the ablated zone. For a -6.0 D correction and an 8.0 mm ablation zone, the excess area is nominally about 1.0 mm(2), giving a potential overlap of the flap at the edge opposite the hinge of about 100 microm. CONCLUSIONS; Excess flap area may cause striae because of wrinkling. Although a nonextensible flap is assumed in the model, any stretching or contraction due to cutting the flap will be independent of the refractive correction. Hence, a mismatch in areas must still occur. This geometric effect may have clinical consequences in optical aberration, refractive regression, or impaired wound healing.

Astigmatism↗
PubMedDate not supplied

Principles of Tscherning aberrometry.

Higher-order optical errors of the human eye are often responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction. These optical aberrations are of natural origin or can result from operations on the eye involving optical structures. The presented wavefront analyzer is based on Tscherning's aberroscope. A collimated laser beam illuminates a mask with regular matrix pin holes which forms a bundle of thin parallel rays. These rays form a retinal spot pattern on the retina that is more or less distorted according to the optical errors of the eye. This retinal spot pattern is imaged onto the sensor of a low-light CCD camera by indirect ophthalmoscopy. The deviations of all spots from their ideal regular positions are measured by means of a personal computer, and from these values the optical aberrations are computed in the form of Zernike polynomials up to the 8th order.

Diagnostic Techniques, Ophthalmological↗