Search results for "Refraction"
showing 10 items of 200 documents
Predictability of intraocular lens power calculation after small-incision lenticule extraction for myopia
2019
PURPOSE To evaluate and compare the predictability of intraocular lens (IOL) power calculation after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism. SETTING Department of Ophthalmology, Philipps University of Marburg, Marburg, Germany. DESIGN Retrospective comparative case series. METHODS Preoperative evaluation included optical biometry using IOLMaster 500 and corneal tomography using Pentacam HR. The corneal tomography measurements were repeated at 3 months postoperatively. The change of spherical equivalent due to SMILE was calculated by the manifest refraction at corneal plane (SMILE-Dif). A theoretical model, involving the virtual implantation of the same…
Residual astigmatism produced by toric intraocular lens rotation.
2010
Purpose To analyze changes in the eye’s refractive properties when a toric intraocular lens (IOL) rotates. Setting Fundacion Oftalmologica del Mediterraneo, Valencia, Spain. Design Experimental study. Methods The matrix definition of astigmatism was used in this theoretical study and compared with another vector representation. Two methods were compared: (1) The cylinder, C, resulting from the addition of 2 cylinders C1 and C2 whose axes form an angle a, is obtained by the addition of 2 vectors of values C1 and C2 forming an angle 2a; (2) the power matrix, F, of a thin astigmatic dioptric system that decomposes naturally into 3 orthogonal components: the purely spherical part Fnes, the orth…
Subjective Refraction Techniques in the Frame of the Three-Dimensional Dioptric Space
2001
A novel heuristic approach to the well-known representation of the dioptric power in a three-dimensional space is presented. It is shown how this theoretical framework is ideal for discussing the principles of several subjective refraction methods. In particular, this formalism is used to justify the stenopaic slit refraction, the Barnes subjective refraction technique, and the Jackson cross-cylinder procedure. In view of this analysis, some modifications to the traditional procedures are proposed.
Focusing in Depth: Post-Task Accommodation Shifts After Sustained Near Work with Volumetric Multi-Planar Display
2018
Post-task refraction shifts were evaluated with eccentric photorefraction technique to better understand response of visual system and eye accommodation to sustained near work with 3D image formed by volumetric display.
Ocular Refraction at Birth and Its Development During the First Year of Life in a Large Cohort of Babies in a Single Center in Northern Italy
2020
The purpose of this study was to investigate refraction at birth and during the first year of life in a large cohort of babies born in a single center in Northern Italy. We also aimed to analyze refractive errors in relation to the gestational age at birth. An observational ophthalmological assessment was performed within 24 h of birth on 12,427 newborns. Refraction was examined using streak retinoscopy after the administration of tropicamide (1%). Values in the range of between +0.50 ≤ D ≤ +4.00 were defined as physiological refraction at birth. Newborns with refraction values outside of the physiological range were followed up during the first year of life. Comparative analyses were condu…
Zero permeability and zero permittivity band gaps in 1D metamaterial photonic crystals
2007
We consider layered heterostructures combining ordinary positive index materials and dispersive metamaterials. We show that these structures can exhibit a new type of photonic gap around frequencies where either the magnetic permeability \mu or the electric permittivity \epsilon of the metamaterial is zero. Although the interface of a semi-infinite medium with zero refractive index (a condition attained either when \mu= 0 or when \epsilon= 0) is known to give full reflectivity for all incident polarizations, here we show that a gap corresponding to \mu = 0 occurs only for TE polarized waves, whereas a gap corresponding to \epsilon = 0 occurs only for TM polarized waves. These band gaps are …
The posterior chamber phakic refractive lens (PRL): a review
2012
Implantation of phakic intraocular lenses (pIOLs) is a reversible refractive procedure, preserving the patient’s accommodative function with minimal induction of higher order aberrations compared with corneal photoablative procedures. Despite this, as an intraocular procedure, it has potential risks such as cataracts, chronic uveitis, pupil ovalization, corneal endothelial cell loss, pigmentary dispersion syndrome, pupillary block glaucoma, astigmatism, or endophthalmitis. Currently, only two models of posterior chamber pIOLs are commercially available, the implantable collammer lens (STAAR Surgical Co.) and the phakic refractive lens (PRL; Zeiss Meditec). The number of published reports on…
Untersuchungen �ber eine akute Wirkung von Trijodthyronin auf Refrakt�rzeit und Leitungsgeschwindigkeit des Meerschweinchenvorhofs
1962
Es wird uber die Untersuchung einer akuten Wirkung von T3 in vitro auf die Refraktarperiode und die Leitungsgeschwindigkeit des Meerschweinchenvorhofs berichtet. T3 verkurzte die Refraktarzeit geringfugig (5,2%). Bei vermindertem K-Gehalt der Badlosung oder nach Vorgabe von ACh oder DNP trat die Verkurzung der Refraktarzeit unter T3 wesentlich deutlicher in Erscheinung, und es konnte Flimmern ausgelost werden, obwohl die Substanzen vor der Gabe von T3 vollstandig ausgespult waren. Adrenalin hatte keinen Einflus auf den T3-Effekt. Die Leitungsgeschwindigkeit wurde durch T3 nicht verandert.
Comprehensive formulation of the temperature dependent dispersion of optical materials; illustration with the case of temperature tuning of a mid-IR …
2009
International audience; The temperature dependence of refractive indices of optical materials is characterized in this work by what we call their normalized thermo-optic coefficients. These ones are determined experimentally through interferometric measurements of thermal expansion, and changes in optical thickness at a few laser wavelengths as function of temperature. A suitable vectorial formalism applied to these data allows predicting the thermal evolution of the refractive index all over the useful range of transparency. The validity and reliability of our methodology is demonstrated through temperature tuning of a mid-IR HgGa2S4 OPO, pumped at 1.0642 μm by a Nd:YAG laser. Measured the…
A computational method for the Helmholtz equation in unbounded domains based on the minimization of an integral functional
2012
Abstract We study a new approach to the problem of transparent boundary conditions for the Helmholtz equation in unbounded domains. Our approach is based on the minimization of an integral functional arising from a volume integral formulation of the radiation condition. The index of refraction does not need to be constant at infinity and may have some angular dependency as well as perturbations. We prove analytical results on the convergence of the approximate solution. Numerical examples for different shapes of the artificial boundary and for non-constant indexes of refraction will be presented.