Search results for "contact lens"
showing 10 items of 119 documents
Optical quality of rotationally symmetrical contact lenses derived from their power profiles.
2017
To present a methodology for evaluating the optical quality of rotationally symmetrical contact lenses (CLs) from a single power profile.Simulated rotationally symmetrical power profiles corresponding to different CLs designs (monofocal, two-zone center-near bifocal, and four-zone center-distance bifocal) were used to calculate the wavefront error profile by means of numerical integration. Then, each lens wavefront error profile was spun around the center to obtain the lens wavefront error surface. From the surface, monochromatic optical transfer functions (OTF), simulated images and the visual Strehl ratio based on the OTF (VSOTF) were obtained for different distances and pupil sizes (3 an…
In vitro power profiles of multifocal simultaneous vision contact lenses.
2013
Abstract Purpose To evaluate the power profile of multifocal contact lenses (CLs) using a new technology based on quantitative deflectometry. Methods The Nimo TR1504 was used to analyze the power distribution of multifocal CLs. The CLs under study were: Air Optix Aqua Multifocal Low, Medium and High Addition and Focus Progressives. Three lenses of each model were considered. Results All multifocal CLs showed a power profile characterized by a change toward more positive power values when aperture sizes become smaller. The near refractive addition of the lenses under study was +2.61 D, +1.44 D, +1.30 D and +0.30 D for the Focus Progressives, the Air Optix Aqua Multifocal High, Medium Add and…
Determination of the oxygen transmissibility and permeability of hydrogel contact lenses
1999
To test the validity of the method of stacked hydrogel contact lenses to obtain the oxygen permeability and transmissibility coefficients of the lenses, the coefficients of one low hydration (38% water) and two high hydration (55 and 58% water) hydrogel contact lenses stacked one to five on an oxygen electrode were deter- mined. From the oxygen diffusion through the lenses, the current intensity in the stationary state was determined, and from this the "instrument" the oxygen transmis- sibility was obtained. The permeability coefficients of the lenses, corrected for edge effects, were obtained from the slope of the plot of the reciprocal of the transmissibility coefficients versus the lens …
Tears as a source of biomarkers for ocular and systemic diseases
2013
The main focus in clinical proteomics is the discovery of new protein or peptide biomarkers which are correlated with a certain disease. Tear proteins have been investigated extensively in the past and distinct relations between the levels of certain tear proteins to different disorders have been demonstrated. In this review we attempt to summarize proteomic technologies for biomarker identification in tears and some disease related biomarkers in tear fluids that were discovered through different proteomic techniques in different conditions like dry eye, Sjogren's syndrome, contact lens wearers, glaucoma, diabetic retinopathy or cancer. Proteomic analysis of tear fluid has proven to be a pr…
The effect of fractal contact lenses on peripheral refraction in myopic model eyes.
2014
Purpose: To test multizone contact lenses in model eyes: Fractal Contact Lenses (FCLs), designed to induce myopic peripheral refractive error (PRE). Methods: Zemax ray-tracing software was employed to simulate myopic and accommodation-dependent model eyes fitted with FCLs. PRE, defined in terms of mean sphere M and 90–180 astigmatism J180, was computed at different peripheral positions, ranging from 0 to 35 in steps of 5, and for different pupil diameters (PDs). Simulated visual performance and changes in the PRE were also analyzed for contact lens decentration and model eye accommodation. For comparison purposes, the same simulations were performed with another commercially available conta…
Surgical management of acute angle-closure glaucoma after toric implantable contact lens implantation
2006
A case of pupillary block after implantation of an implantable contact lens (ICL) is reported, and surgical management and prevention are discussed. In a myopic patient, the best corrected visual acuity in the right eye was 20/50 with -15.50 -3.00 x 175. After uneventful implantation of an ICL, painful acute glaucoma developed with an intraocular pressure beyond measurable values. Apparent anterior vaulting of the ICL suggested a sizing problem. In a situation of a mid-wide dilated pupil, immediate explantation of the ICL was performed. Then, using a preoperative iris photography as guidance, an anterior chamber iris-claw toric phakic intraocular lens was implanted. On postoperative examina…
Qualitative and quantitative characterization of the in vitro dehydration process of hydrogel contact lenses
2007
Purpose: To investigate the in vitro dehydration process of conventional hydrogel and silicone-hydrogel contact lens materials. Methods: Eight conventional hydrogel and five silicone-hydrogel contact lenses were dehydrated under controlled environmental conditions on an analytical balance. Data were taken at 1-min intervals and dehydration curves of cumulative dehydration (CD), valid dehydration (VD), and dehydration rate (DR) were obtained. Several quantitative descriptors of the dehydration process were obtained by further processing of the information. Results: Duration of phase I (r 2 5 0.921), CD at end of phase I (r 2 5 0.971), time to achieve a DR of � 1%/min (r 2 5 0.946) were stron…
Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses
2008
Abstract: Purpose. To evaluate the qualitative and quantitative topographic changes in the surface of worn contact lenses (CLs) of different materials using atomic force microscopy (AFM). Methods. The topography of five different CL materials was evaluated withAFM over a surface of 25 lm2 according to previously published experimental setup. Average roughness (Ra) and root mean square (Rms) values were obtained for unworn and worn samples. Results. The Ra value increased for balafilcon A (11.62–13.68 nm for unworn and worn samples, respectively), lotrafilcon A (3.67–15.01 nm for unworn and worn samples, respectively), lotrafilcon B (4.08–8.42 nm for unworn and worn samples, respectively), g…
Refractive index and equilibrium water content of conventional and silicone hydrogel contact lenses
2006
Prova tipográfica (In Press)
Presbyopia and the aging eye: Existing refractive approaches and their potential impact on dry eye signs and symptoms.
2020
Every part of the human body is subject to aging, including the eye. Increased prevalence of dry eye disease with age is widely acknowledged: aging threatens ocular surface homeostasis, altering the normal functioning of the lacrimal functional unit and potentially leading to signs and symptoms of dry eye. Parallelly, two additional degenerative processes take place within the crystalline lens, leading to presbyopia and cataractogenesis. With continuously increasing life expectancies both conditions are expected to impact society further. Correction strategies for presbyopia and cataracts either directly or indirectly challenge ocular surface additionally. On one hand, contact lens presbyop…