Search results for "Refraction"

Validity of automated refraction after segmented refractive multifocal intraocular lens implantation

2017

Aim To evaluate the clinical utility of automated refraction (AR) and keratometry (KR) compared with subjective or manifest refraction (MR) after cataract or refractive lens exchange surgery with implantation of Lentis Mplus X (Oculentis GmbH) refractive multifocal intraocular lens (IOL). Methods Eighty-six eyes implanted with the Lentis Mplus X multifocal IOL were included. MR was performed in all patients followed by three consecutive AR measurements using the Topcon KR-8000 autorefractor. Assessment of repeatability of consecutive AR before and after dilation with phenylephrine 10%, and comparison of the AR and KR with MR using vector analysis were performed at 3mo follow-up. Results Ana…

Ortokeratoloģijas ietekme uz acs garuma un refrakcijas izmaiņām bērniem ar miopiju

2017

Darbs uzrakstīts angļu valodā uz 68 lapaspusēm, satur 17 attēlus, 10 tabulas un 73 literatūras atsauces. Darba mērķis bija salīdzināt acu aksiālā garuma un refrakcijas izmaiņas divām grupām tuvredzīgo jauniešu. Vienai grupai tuvredzība tika koriģēta ar ortokeratoloģiskajām kontaktlēcām (OK), bet otrajai ar brillēm. Pēc 18 mēnešiem tuvredzīgo pacientu grupai koriģētai ar brillēm acs aksiālais garums vidēji palielinājās par 0,20 mm, turpretī pacientiem koriģētiem ar OK kontaktlēcām tas bija tikai 0,05 mm. Pacientu grupai koriģētai ar OK kontaktlēcām tuvredzības pieaugums vidēji bija tikai -0,04 D, bet pacientiem koriģētiem ar brillēm tas bija -0,40 D. Refrakcijas izmaiņu atšķirība 0,36 D bija…

Heritability of anterior chamber depth and axial length: a population-based twin study among 66 to 79-year old female twins.

2014

Akomodācijas un verģences sistēmas darbības traucējumu izplatība Azerbaidžānā

2020

Maģistra darb ir uzrakstīts angļu valodā uz 35 lpp. Tas satur 19 tabulas, 2 pielikumus un 16 atsauces uz literatūras avotiem. Maģistra darba mērķis ir izvērtēt akomodācijas un verģences traucējumu izplatību un veidus Azerbaidžānas galvaspilsētas baku studentu vidū. Pētījumā piedalījās 192 dalībnieki (15-36 g.v.). Visiem tika veikta bezmaksas redzes pārbaude, kur detalizēti tika izvērtēta refrakcija, akomodācija un verģence. Rezultāti parāda, ka 51 ± 4 % dalībniekiem novēro dažāda veida akomodācijas un verģences darbības traucējumus vai to kombinācijas. Visbiežāk novērotās problēmas ir akomodācijas ekscess un konverģences nepietiekamība. Netiek novērota dzimuma un vecuma ietekme uz akomodāci…

Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films

2021

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 …

Ray optics behavior of flux avalanche propagation in superconducting films

2015

Experimental evidence of wave properties of dendritic flux avalanches in superconducting films is reported. Using magneto-optical imaging the propagation of dendrites across boundaries between a bare NbN film and areas coated by a Cu layer was visualized, and it was found that the propagation is refracted in full quantitative agreement with Snell's law. For the studied film of 170 nm thickness and a $0.9\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ thick metal layer, the refractive index was close to $n=1.4$. The origin of the refraction is believed to be caused by the dendrites propagating as an electromagnetic shock wave, similar to damped modes considered previously for normal …

Engineered surface waves in hyperbolic metamaterials

2013

We analyzed surface-wave propagation that takes place at the boundary between a semi-infinite dielectric and a multilayered metamaterial, the latter with indefinite permittivity and cut normally to the layers. Known hyperbolization of the dispersion curve is discussed within distinct spectral regimes, including the role of the surrounding material. Hybridization of surface waves enable tighter confinement near the interface in comparison with pure-TM surface-plasmon polaritons. We demonstrate that the effective-medium approach deviates severely in practical implementations. By using the finite-element method, we predict the existence of long-range oblique surface waves. This research was fu…

Investigation of Nonlinear Optical Processes in Mercury Sulfide Quantum Dots

2022

European Regional Development Fund (1.1.1.5/19/A/003), State Assignment to Higher Educational Institutions of Russian Federation (FZGU-2020-0035), Russian Foundation for Basic Research (18-29-20062). Institute of Solid State Physics, University of Latvia as the Center of Excellence acknowledges funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.

IMI Prevention of Myopia and Its Progression

2021

The prevalence of myopia has markedly increased in East and Southeast Asia, and pathologic consequences of myopia, including myopic maculopathy and high myopia-associated optic neuropathy, are now some of the most common causes of irreversible blindness. Hence, strategies are warranted to reduce the prevalence of myopia and the progression to high myopia because this is the main modifiable risk factor for pathologic myopia. On the basis of published population-based and interventional studies, an important strategy to reduce the development of myopia is encouraging schoolchildren to spend more time outdoors. As compared with other measures, spending more time outdoors is the safest strategy…

Performance analysis of Latvian zenith camera

2018

Since finalizing of design in 2016, the digital zenith camera of the University of Latvia was involved in a number of test observations as well as field observations at about 70 different sites. The paper presents analysis of observation results, estimation of instrument’s performance and accuracy. Random and systematic error sources are outlined. Impact of anomalous refraction on vertical deflection determination is discussed. Results of adaptation of GAIA reference star catalog for astrometric data reduction are reported.