Search results for "stigmat"
showing 10 items of 156 documents
Lateral magnification matrix from the dioptric power matrix formalism in the paraxial case.
2012
Background Previous studies have highlighted that power matrices fully characterize the concept of dioptric power of any astigmatic surface. Thus, the basic equations in physiological optics can be generalized using the matrix formalism of the dioptric power. Among others, lateral magnification has also been interpreted as a matrix but mainly concerning magnification modification induced by spectacle correction of refractive error. Purpose To provide a fresh look into a novel paraxial formulation for the assessment of the lateral magnification using power matrices and in presence of astigmatism for thin and thick imaging systems in general. Methods Linear optics provides the frame to genera…
The Dynamics of (De)Stigmatization : Boundary construction in the nascent category of organic farming
2020
This study finds that it is possible for organizations in emerging categories to resist stigmatization through discursive reconstruction of the central and distinctive characteristics of the category in question. We examined the emerging market of organic farming in Finland and discovered how resistance to stigmatization was both an internal and an external power struggle in the organic farming community. Over time, the label of organic farming was manipulated and the practice of farming was associated with more conventional and familiar contexts, while the stigma was diverted at the same time to biodynamic farming. We develop a process model for removal of stigma from a nascent category t…
Transconjunctival sutureless 25-Gauge versus 20-Gauge standard vitrectomy: correlation between corneal topography and ultrasound biomicroscopy measur…
2009
Purpose: To determine the correlation between corneal shape changes and ultrasound biomicroscopy (UBM) findings at the sclerotomy sites in conventional 20-gauge (G) pars plana vitrectomy (PPV) and 25-G transconjunctival sutureless vitrectomy (TSV) and to compare the effectiveness of the two surgical methods. Design: Prospective, comparative, observational case series. Methods: Sixty consecutive eyes (60 patients) undergoing primary 3-port PPV. Thirty eyes (30 patients, group 20-G) were treated with 20-G standard PPV and 30 eyes (30 patients, group 25-G) with 25-G TSV. We compared healing of the sclerotomy sites in the two groups. We determined the correlation between corneal shape changes (…
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…
Characterization of a compact low-cost Stokes lens for astigmatism compensation in optical instruments
2020
Variable power cross-cylinder lenses (or Stokes lenses) have been widely known in the literature for decades. In this paper, we describe how to build a low-cost Stokes lens and discuss its calibration and its application to two significant cases. The construction is in virtue of a phoropter’s Risley prism mount for assembling a couple of equal but opposite sign cylindrical lenses (we have selected ± 1.50 D). Thus, variable astigmatic power is achieved by relative rotation of the lenses in opposite directions, and the resulting astigmatic axis is defined by the global rotation of the device. Calibration measurements are performed using an automatic lensmeter (Topcon CL-300) and an aberromete…
Repeatability of whole-cornea measurements using a new swept-source optical coherence tomographer
2020
Purpose: The aim of this study was to evaluate the repeatability of several corneal parameters provided by a high-resolution swept-source optical coherence tomographer (SS-OCT). Methods: One eye from each of 74 patients was measured five times consequently using the ANTERION SS-OCT. The following corneal parameters were analyzed: average, steep and flat keratometry (K), astigmatism for anterior, posterior and total at 3-mm, average K and astigmatism at 6-mm, anterior and posterior eccentricity, higher-order aberrations (HOA) and spherical aberration ([Formula: see text]), and anterior and posterior best-fit sphere at 8-mm. The intrasubject standard deviation (Sw), coefficient of variation (…
Some predacious mites of Greece, with a description of one new species (Mesostigmata: Phytoseiidae)
1977
Typhlodromus hellenicus sp. nov. is described and illustrated. The following 11 additional species were recorded:T. pyri Scheuten, sensu Abbasova,T. exhilaratus Ragusa,T. recki Wainstein,T. kerkirae Swirski and Ragusa,Amblyseius cinctutus Livshitz and Kuznetsov,A. stipulates Athias-Henriot, A. aff.finlandicus (Oudemans), A. aff.aberrans (Oudemans),A. potentillae (Garman),Phytoseiulus persimilis Athias-Henriot, andPhytoseius (Phytoseius) finitimus Ribaga.
Three new species of phytoseiid mites from Kenya (Mesostigmata: Phytoseiidae)
1978
The following 13 species of predacious mites of the family Phytoseiidae are recorded from various plants in Kenya: Amblyseius albizziae sp. nov., A. kenyae sp. nov., A. natalensis Van der Merwe, A. lokele Pritchard & Baker, A. largoensis (Muma), A. rykei Pritchard & Baker, A. teke Pritchard & Baker, Typholdromus kikuyuensis sp. nov., T. magdalenae Pritchard & Baker, Phytoseius amba Pritchard & Baker, p. ferox Pritchard & Baker, Iphiseius degenerans (Berlese), I. gongylus Pritchard & Baker. The new species and the male of A. natalensis are described.
Myopic astigmatism correction: comparison of a Toric Implantable Collamer Lens and a bioptics technique by an adaptive optics visual simulator.
2013
Purpose To compare the optical and visual quality of a simulated Toric Implantable Collamer Lens (TICL) and a bioptics technique to treat high myopic astigmatism. Methods An adaptive optics visual simulator was used to simulate the vision after TICL implantation and a bioptics procedure from the wavefront aberration pattern for moderate and high-myopic astigmatism. Visual acuity (VA) at different contrasts and contrast sensitivity (CS) at 10, 20 and 25 cycles degree−1 were measured for 3 and 5-mm pupils. Modulation Transfer Function (MTF) and Point Spread Function (PSF) were calculated for a 5-mm pupil. Results At a 3-mm pupil we only found statistically significant differences in VA betwee…
Step-along power vector method for astigmatic wavefront propagation
2013
Purpose To propose both a new algebraic solution and a graphical monitoring method for astigmatic wavefront propagation in the framework provided by power vectors. Methods The generalised propagation equation describing the propagation of astigmatic wavefronts from one plane to another is adapted to the power vectors formalism using a novel algorithm based on a step-along method. The step-along procedure is directly applied to the tuple of power vectors [M, J0, J45] representing an arbitrary astigmatic wavefront and it permits the calculation of the tuple of power vectors [M′, J′0, J′45] after a given propagation distance. This is achieved mathematically first by temporarily rotating the as…