Search results for " topography"
showing 10 items of 102 documents
Anterior Segment Biometry and Their Correlation with Corneal Biomechanics in Caucasian Children.
2018
Purpose: To assess the relationship between the corneal biomechanical parameters and the anterior segment parameters in Caucasian children. Methods: This study included 293 eyes from 293 healthy children aged between 6 and 17 years. Corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer, axial length (AL) with IOLMaster and the anterior segment with Pentacam. Anterior segment parameters obtained were the following: central corneal thickness (CCT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and mean anterior and posterior keratometry. Two multiple linear regression models were constructed to assess th…
Optical quality after instillation of eyedrops in dry-eye syndrome
2010
Purpose To study the effect of eyedrop instillation on the optical quality of the air–tear film interface at the anterior cornea in cases of dry eye. Setting University of Valencia, Valencia, Spain. Methods Corneal aberrations (total, spherical-like, and coma-like) were determined from corneal elevation maps and purpose-designed software in cases of dry eye before, immediately after, and 10 minutes after lubricating eyedrop instillation (Blink Intensive Tears). All data were decomposed using Zernike polynomials to yield the root-mean-square wavefront deviations for pupil diameters of 3.0 mm and 5.5 mm. Outcome measures included comparison with clinical tear breakup time (TBUT). Results Wave…
Corneo-scleral contact lenses in an uncommon case of keratoconus with high hyperopia and astigmatism
2017
Purpose: To analyse the visual quality achieved by fitting corneo-scleral contact lenses (CScL) in an uncommon case of bilateral keratoconus, high hyperopia and astigmatism. Methods: A 45-year-old man presented for eye examination due to the unsatisfactory quality of his vision wearing soft toric contact lenses. He presented high hyperopia and astigmatism with bilateral keratoconus. He was fitted with CScL to correct his irregular astigmatism and ocular aberrations. A diagnostic trial set was used in the fitting process and he was assessed according to standardised fitting methodology. Visual acuity, corneal topography, biometry and ocular aberrations were evaluated. The follow-up period wa…
Toric intraocular lens versus opposite clear corneal incisions to correct astigmatism in eyes having cataract surgery.
2009
To compare toric intraocular lens (IOL) implantation with paired opposite clear corneal incisions (OCCIs) for astigmatism correction in patients having cataract surgery.Ophthalmology Service, Donostia Hospital, San Sebastián, Spain.This randomized prospective clinical study comprised eyes with more than 1.00 diopter (D) of preexisting corneal astigmatism. One group had AcrySof toric IOL implantation and the other, paired 2.75 mm/3.20 mm OCCIs in the steep axis with spherical IOL implantation. Uncorrected (UCVA) and best corrected (BCVA) visual acuity, refraction, corneal and total higher-order aberrations (HOAs), photopic and mesopic contrast sensitivity, and toric IOL axis were measured 3 …
Implantation of a toric poly(methyl methacrylate) intraocular lens to correct high astigmatism
1999
Abstract A 57-year-old man experienced a decrease in visual function because of cataract formation. Corneal astigmatism was 13.4 diopters (D) because he had had a penetrating keratoplasty 27 years before. Cataract surgery was planned, and biometric data for toric intraocular lens (IOL) implantation were collected for the manufacture of a custom IOL. After phacoemulsification, a toric poly(methyl methacrylate) (PMMA) IOL of +19.0 D spherical and +12.0 D cylindrical power was implanted via a sclerocorneal tunnel incision. Three months postoperatively, corneal astigmatism was 14.3 D and best corrected visual acuity (BCVA), 20/25. Postoperative refraction (+1.5 −3.0 × 90) and BCVA remained stab…
Prevention of hyperopic surprise after LASIK in patients with refractive multifocal intraocular lenses.
2011
Purpose. Three cases of patients who developed a similar hyperopic defect in refraction following laser in situ keratomileusis (LASIK) after multifocal intraocular lens (IOL) implantation are described. Methods. Ophthalmologic evaluation including refractive status, corrected and uncorrected visual acuity (both at far and near), and corneal topography in patients presenting similar hyperopic refractive surprise in one eye as a result of LASIK refinement of residual ametropia after refractive multifocal IOL implantation. Results. Laser in situ keratomileusis enhancement for residual ametropia of −1.00 to −1.50 D in patients with a prior implantation of refractive multifocal IOL resulted in a…
Astigmatism among myopics and its changes from childhood to adult age: a 23‐year follow‐up study
2014
Purpose To study the prevalence of and changes in astigmatism from the onset of myopia at school age. Methods Two hundred and forty myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983–1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Three annual examinations with subjective cycloplegic refraction were performed for 237–238 subjects. Subsequent examinations were performed at the mean ages of 23.2 and 33.9 years for 178 and 163 subjects, and the last examination, including data from prescriptions of different ophthalmologists, for 32 subjects. Corneal topography was studied at baseline, at the 3-year follow-up and at t…
Structural defects in Hg1−xCdxI2 layers grown on CdTe substrates by vapor phase epitaxy
1997
Hg1−xCdxI2 20–25-μm-thick layers with a uniform composition in the range of x = 0.1–0.2 were grown on CdTe substrates by vapor phase epitaxy (VPE). The growth was carried out using an α-HgI2 polycrystalline source at 200 °C and in the time range of 30–100 h. The layers were studied by scanning electron microscopy (SEM) and high resolution synchrotron x-ray topography (SXRT). The SEM and SXRT images of Hg1−xCdxI2 VPE layers allow one to identify the defects affecting the layer structure. The two main types of structural defects in the layers are subgrain boundaries and densely spaced striations similar to those referred generally to as vapor grown HgI2 bulk crystals. The effect of the growth…
Nanofabrication on 2D and 3D Topography via Positive‐Tone Direct‐Write Laser Lithography
2019
Direct laser writing (DLW) lithography using two‐photon absorption is a powerful technique mostly used for fabrication of complex structures in micro‐ and nanoscale, by photopolymerizing a negative‐tone resist. In contrast, in this study it is demonstrated that DLW is also well suited for fabricating nano‐ to microscale metallic structures using lift‐off and a positive‐tone photoresist. It is shown first that versatile, fast and large area fabrication is possible on flat two‐dimensional insulating substrates, and an expression for how the line width varies with the scanning speed is derived, with excellent agreement with the experiments. Even more interestingly, a unique application for the…
The effects of precipitates on CdZnTe device performance
2005
A high-intensity X-ray beam collimated down to a 10-micrometer spot size, available at Brookhaven's National Synchrotron Light Source (NSLS), was employed to perform X-ray mapping to measure the correlation between microscopic defects (precipitates) and variations in the collected charges in long-drift CdZnTe (CZT) detectors. First, we use X-ray diffraction topography (XDT) measurements at the high-energy beamline and IR microscopy to identify the defects distribution and strains in the bulk of CZT crystals. Then, we perform X-ray raster scans of the CZT detectors to measure their responses with 10-micrometer spatial resolution. The brightness of the source allows for good statistics in ver…