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At least 253 records · Page 14Linked to original sources
PubMed1978

Corneal edema in divers wearing hard contact lenses.

Polymethylmethacrylate (hard) contact lens-wearing Navy divers involved in hyperbaric research complained of ocular discomfort, halos, specular highlights, and decreased visual acuity during and immediately after the decompression phase of dry chamber dives. These symptoms were related to bubbles in the tear film between the cornea and hard contact lens. The bubbles developed during the decompression phase of the dive and represented the trapping (by the hard contact lens) of nitrogen outgassing from the cornea and precorneal tear film. The bubbles effected nummular patches of corneal epithelial edema persisting up to two hours after diving. Gas trapping and corneal edema were not observed in uncovered corneas or corneas covered with membrane lenses.

Adult↗
PubMed1994

[Use of highly hydrated contact lenses for therapeutic purposes].

The paper deals with the therapeutic use of contact lenses made from a new highly hydrated material developed in the Institute of Macromolecular Chemistry in Prague. Contact lenses made from a meshed copolymer of n-vinyl pyrrolidone with acetoxyethyl meta-acrylate were applied to a group of 83 patients--a total of 87 eyes. A favourable therapeutic effect was achieved in all groups of patients--in simple traumatic erosions, superficial keratopathies, relapsing erosions, bullous keratopathies, corrosion of cornea, for mechanical protection of epithelization and in persisting ulcerations. In 71 eyes (82%) the contact lens was removed after the therapeutic effect was achieved, in 4 (5%) treatment still proceeds. In the remaining patients treatment was discontinued on account of complications, persistence of the pathological finding and frequent losses of contact lenses. In the group there was no case of complicating keratoconjunctivitis. Progressing vascularization was detected in three cases in the group with persisting ulcerations. The authors did not observe development of corneal vascularization in conjunction with application of the lens. Transient corneal oedema was revealed in the group of relapsing erosions in 6 (40%) patients and in the group of persisting superficial keratopathies in 4 (31%). The rare occurrence of inflammatory complications can be explained by the sterile application of contact lenses for the necessary length of time, the local administration of antibiotics while the defect persisted and frequent check-up examinations. Contact lenses made from the described material proved useful for therapeutic application.

Contact Lenses, Hydrophilic↗
PubMedDate not supplied

Absorption of topical disodium cromoglycate and its preservatives by soft contact lenses.

Disodium cromoglycate (2%) (DSCG) was administered four times daily for one month to 10 patients using extended wear contact lenses. The same regimen was also followed for five days by 25 patients using daily wear soft contact lenses. The contact lenses and their soaking solutions were collected at the end of the wearing period and analyzed for DSCG, benzalkonium chloride (BAK), 2-phenylethanol, and EDTA. The lens soaking solutions and eluates prepared from the lenses were tested. In the extended wear group, small amounts of DSCG were detected in both the eluates and the soaking solutions. In the daily wear group DSCG was detected in small amounts in the soaking solutions but not in the eluates. BAK, EDTA, and 2-phenylethanol were not detected in any of the eluates or soaking solutions. During the study, no side effects of DSCG were observed in any of the patients. In animal experiments, radioactive DSCG was applied once to a series of rabbit eyes. Four hours after administration of the labelled DSCG, the animals' tears, cornea, and aqueous humor were examined for DSCG. Of the instilled dose, approximately 0.2% was found in the cornea, and less than 0.04% was found in the aqueous humor. We conclude that commercial DSCG applied topically to contact lenses does not result in the accumulation of either the drug or its preservatives in lenses and that DSCG can be safely applied directly onto a worn contact lens.

Animals↗
PubMedDate not supplied

Videokeratography for quantitative surface analysis of used soft contact lenses.

The greater utilization of soft contact lenses calls for the development of new and objective methods of evaluating the optical performance of the different lens types, in situ. We used videokeratography to examine the surface topography of soft contact lenses that had been worn for more than 1 year on 27 eyes of 23 patients, and compared the resulting color-coded maps and topographic indices as well as contact lens-corrected visual acuities, with those obtained with new replacement lenses on the same eyes. Visual inspection of the color-coded maps revealed differences in the surface characteristics of the used and new lenses. Comparison of quantitative indices including the SAI (Surface Asymmetry Index), IAI (Irregular Astigmatism Index), SRI (Surface Regularity Index), and SDP (Standard Deviation of Powers) showed that asymmetry, surface irregularity, potential visual acuity (derived from the SRI), and corneal power distribution were significantly poorer with the used lenses than with the new (P = 0.0001). The videokeratoscope is useful for evaluating the soft contact lens surface in situ, as an indicator of optical quality; it also permits the objective evaluation of lens cleaning techniques.

Adolescent↗
PubMed1986

The effects of hard and soft contact lenses on the corneal endothelium.

We examined the morphologic characteristics of the corneal endothelium in three groups of contact lens wearers: those who had used daily-wear soft contact lenses for an average of 6.3 years, long-term (greater than 20 years) users of hard contact lenses, and former users of hard contact lenses who had worn them for an average of 9.6 years but who had discontinued them for an average of 4.3 years. When compared to age-matched controls, all groups had similar endothelial cell densities but demonstrated significant increases in variation of cellular size (polymegethism) and shape (pleomorphism). We found that daily-wear soft contact lenses can cause endothelial polymegethism and pleomorphism similar to those caused by hard contact lenses and that the endothelial changes induced by hard contact lenses are more profound with greater duration of wear and are apparently not completely reversible.

Adult↗
PubMed1996

Polymers, Dk, and contact lenses: now and in the future.

PURPOSE: The polymers used in conventional contact lenses are briefly reviewed as are the factors that contribute to their gas permeability. The chemistry and gas permeability of future hydrogel contact lenses are discussed. RESULTS: Interchain packed zones in polymers are less permeable than the amorphous zones. Polymers with thick bulky groups in rigid gas permeable lenses hinder interchain packing, allowing oxygen and carbon dioxide to diffuse through the polymer voids. Also, the flexibility of the siloxane groups facilitates the diffusion of gases. In hydrogel contact lenses, the polymer segments are separated by the aqueous phase. The gas diffusivity increases with hydration, but is limited by the rigid polymer network. Research on new hydrogel contact lenses aims to develop hydrogels with gas permeability enhancing polymers. In these hydrogels, the gas permeability depends not only on their hydration but also on the permeation of the gas through the polymer phase. CONCLUSIONS: The new hydrogel contact lenses will contain highly permeable polysiloxane domains. A potential problem with the new hydrogels is decreased wettability due to the migration of hydrophobic moieties to the lens surface.

Compliance↗
PubMed1996

The use of computerized videokeratography as an aid in fitting rigid gas permeable contact lenses.

PURPOSE: To assess the efficacy of computerized corneal topography in (1) fitting cosmetic rigid gas permeable contact lenses on normal corneas and (2) patients who have keratoconus. METHODS: In study 1, 26 patients were fitted with cosmetic contact lenses. In 13 patients, the first rigid gas permeable lens was chosen on the basis of corneal topography using the EyeSys videokeratoscope and contact lens software version 2.11w. Thirteen control patients were fitted with rigid gas permeable contact lenses by means of diagnostic contact lenses. The number of parameter changes required in each group to reach the best fit were compared. In study 2, the records of 28 patients (41 eyes) with keratoconus who had been successfully fit with rigid gas permeable lenses were reviewed. Topographic analysis using the EyeSys videokeratoscope was conducted. The following 8 data points were analyzed: maximum dioptric curvature with respect to the central visual axis, the power at the visual axis (VK), the average keratometry readings within the 3-mm zone, the average flat K at 3-mm central and 5-mm paracentral regions, and the K reading at 1.5, 2.0, and 2.5 mm superior to the visual axis. RESULTS: Study 1: In 10 eyes (38%) fitted with cosmetic contact lenses utilizing corneal topography and the EyeSys contact lens program, the first lens chosen by the computer program was correct with no additional changes in lens parameters required. In the other 16 eyes, 21 parameter changes were required. In the control group, 14 eyes (53%) required no additional change in parameters from the original contact lens that was fitted using diagnostic lenses. In the other 12 eyes, 12 parameter changes were required. Study 2: In the keratoconus group, of the 9 measurements analyzed, the final base curve of patients' rigid gas permeable lenses was correlated most closely with the average flat corneal curvature at the 3-mm central zone. CONCLUSION: Study 1: In fitting cosmetic rigid gas permeable contact lenses, the videokeratoscope with the EyeSys software 2.11w contact lens program proved to be inferior to diagnostic lenses in selecting the final correct contact lens parameters. However, it may be useful in selecting an initial diagnostic lens with which to begin rigid gas permeable fitting. Study 2: In patients with irregular corneas such as keratoconus, corneal topography is helpful in determining the initial base curve of the contact lens. In patients with keratoconus, it appears to be the average flat corneal curvature at the 3.0-mm zone.

Contact Lenses↗
PubMed1991

[Contact lenses--possibilities, problems and hazards].

Because use of contact lenses has become more common, knowledge of the basics is necessary. The most important kinds and materials of contact lenses, the indications for their application, and especially the important complications are illustrated by some clinical examples. Some simple first-aid measures are presented.

Adult↗
PubMed1992

A European fitting philosophy for aspheric, high-Dk RGP contact lenses.

Microbial keratitis, the most serious complication of contact lens wear, is most frequently associated with soft contact lenses. Rigid gas permeable (RGP) lens wearers are less often affected. Increased use of high-Dk RGP lenses could reduce the number of cases of microbial keratitis. In Europe, aspheric high-Dk RGP lenses are very popular. This article presents practical guidelines for computer-aided fitting of aspheric RGP lenses. Base curve selection using the keratometer to determine the corneal topography is described. This method, which is inexpensive and time-saving, is suitable for fitting cosmetic contact lenses or lenses used in treating such corneal pathology as keratoconus.

Contact Lenses↗
PubMed1997

Multifocal contact lenses--look again!

In this study aspheric progressive simultaneous vision multifocal contact lenses demonstrated up to 1.8 lines of lost distance visual acuity, reduction in distance and near stereoacuity, and mild to moderate difficulties with night driving, ghost images, haloes and glare. These deficits, which can be minimized with certain designs and lighting conditions, seem to be well tolerated by highly motivated young presbyopes. Combining different styles of multifocal contact lenses in the two eyes simultaneously may be another method of further improving performance. Depending on the design, the performance of these lenses approaches that of spectacle correction in terms of contrast sensitivity and near visual acuity, the latter being important to this population. Both test lenses proved easy to fit based on the manufacturer's recommendations alone. Although multifocal contact lenses may not be suitable for people whose occupations require precise distance visual acuity and stereopsis, our results suggest that they may be an acceptable alternative for a substantial proportion of presbyopes who desire the convenience, performance and improved cosmesis of contact lenses.

Adult↗
PubMed1991

Virucidal efficacy of various lens cleaning and disinfecting solutions on HIV-I contaminated contact lenses.

The virucidal efficacy of various commercially available contact lens care cleaning regimens on human immunodeficiency virus (HIV-1) contaminated contact lenses using either cursory or meticulous cleaning with a rubber policeman was evaluated. Levels of infectious HIV-1 remaining on individual contact lenses were determined by cultivating the lenses with target HUT-78 cells and subsequently analyzing the cultures for the production of HIV-1 p24 by antigen capture and for HIV-1 gag gene DNA content by the polymerase chain reaction. The data indicate that most of the lens care regimens tested, when coupled with meticulous rubbing, were capable of safely decontaminating the contact lenses, that is, they reduce the amount of infectious HIV-1 on the lenses by greater than a 10 log concentration (10(-10], relative to standard controls. Most tested lens care regimens, if properly followed, would virtually eliminate any chance of the lens serving as a vector for HIV.

Contact Lenses, Hydrophilic↗
PubMed1989

[Possibility of the survival of free-living amoebae which cause keratitis in decontamination solutions used for the maintenance of contact lenses].

Because Acanthamoeba keratitis associated with contact lenses were described, several solutions used in stationary eye wash stations were contaminated by free-living amoebae. 0.9% sodium chloride rinsing solutions allowed cyst and trophozoite growth and only one solution for decontamination using hydrogen peroxide led to rapid elimination of cysts and trophozoites. Antiseptic solutions containing ammonium derivatives or chlorhexidine killed only trophozoites. Because of the constant contamination of tap water with Acanthamoeba cysts resistant to chlorine, the prevention of amoebic keratitis in wearers of contact lenses needs: use of sterile solutions for decontamination or rinsing, choice, if possible, of oxidizing solutions, suppression of tap water for rinsing.

Acanthamoeba↗
PubMed2006

Imprinted soft contact lenses as norfloxacin delivery systems.

Soft contact lenses are receiving an increasing attention not only for correcting mild ametropia but also as drug delivery devices. To provide poly(hydroxyethyl methacrylate), PHEMA, lenses with the ability to load norfloxacin (NRF) and to control its release, functional monomers were carefully chosen and then spatially ordered applying the molecular imprinting technology. Isothermal titration calorimetry (ITC) studies revealed that maximum binding interaction between NRF and acrylic acid (AA) occurs at a 1:1, and that the process saturates at 1:4 molar ratio. Hydrogels were synthesized using different NRF:AA molar ratios (1:2 to 1:16), at two fix AA total concentrations (100 and 200 mM), and using moulds of different thicknesses (0.4 and 0.9 mm). The cross-linker molar concentration was 1.6 times that of AA. Control (non-imprinted) hydrogels were prepared similarly but with the omission of NRF. All hydrogels showed a similar degree of swelling (55%) and, once hydrated, presented adequate optical and viscoelastic properties. After immersion in 0.025, 0.050 and 0.10 mM drug solutions, imprinted hydrogels loaded greater amounts of NRF than the non-imprinted ones. Imprinted hydrogels synthesized using NRF:AA 1:3 and 1:4 molar ratios showed the greatest ability to control the release process, sustaining it for more than 24 h. These results prove that ITC is a useful tool for the optimization of the structure of the imprinted cavities in order to obtain efficient therapeutic soft contact lenses.

Acrylates↗
PubMed2003

Therapeutic contact lenses: the role of high-Dk lenses.

Currently, the armamentarium of contact lenses that can be used for therapeutic effect provides a wider selection of lenses than ever before. If the therapeutic goal is protection and healing of the corneal epithelium, epithelial or stromal edema is best avoided, and the selection of a high-Dk silicone hydrogel (balafilcon A, lotrafilcon A) lens or a very thin membrane-type lens (crofilcon) is the best choice. If the goal is surface protection as well as stimulation of stromal wound vascularization, selection of a low-water content, thick, hydrophilic lens is the better option. If the patient is prone to lens loss or requires frequent replacement of the therapeutic lens, a prudent economic decision is to select a daily disposable moderate-water content lens. Specific circumstances may mandate the selection of a specific therapeutic lens. Patients with a prior history of active giant papillary conjunctivitis may be better served by the use of a crofilcon glyceryl methacrylate lens, which has a lower incidence of this complication. Patients who have dry eye may benefit from a higher-water content lens if adequate unpreserved tear supplementation is provided with or without punctal occlusion. The options when selecting a therapeutic contact lens are wider than ever before. Although the new generation of high-Dk lenses promises fewer limiting problems of vascularization and infection, one can use the older traditional therapeutic lenses when induced vascularization of the cornea is needed or when an economic necessity exists. Not all of the available lenses are FDA approved for therapeutic use, and such wear is an off-label use. The patient should be informed of the goal of therapy as well as the benefits and risks of therapeutic contact lenses.

Contact Lenses↗
PubMed1980

The use of contact lenses in wet or damp environments.

The adhesion between the eye and a contact lens was recorded when influenced by water with varying salt concentrations. Both active removal and spontaneous loss of hard and soft contact lenses applied to the eye were investigated. In environments with saline less than 9 0/00 the risk of a soft contact lens falling out from the eye is almost negligible. In environments with saline greater than or equal to 9 0/00 the risk increase since adhesion in active removal decreased considerably. In reality, based upon the investigations of spontaneous loss of contact lenses in an underwater environment, well fitted soft lenses still do not however fall out of the eye. It should therefore be possible to use well fitted soft contact lenses without any significant risk even in working conditions which may include splashing of water upon the eye and regardless of the various salt concentrations of naturally occurring water in Sweden. For hard contact lenses, independent of salt concentration, adhesion in the underwater environment is extremely low and such lenses cannot therefore be used on an unprotected eye in conjunction with, for example, swimming. The risk of them falling out under splashing with water upon the eye is clearly greater than for soft lenses.

Adhesiveness↗
PubMedDate not supplied

[Perceptions of ophthalmologists regarding teaching models applied to contact lenses].

PURPOSE: To identify perceptions regarding teaching models applied to contact lenses. METHODS: A transversal study in a readily accessible sample consisting of ophthalmologists (n=39) was performed by applying a questionnaire. RESULTS: The sample consisted of 39 ophthalmologists, 51.3% males and 48.7% females. Regarding frequency prior to courses on contact lenses, 28.2% reported only one course; 25.6% two courses; 5.1% three courses; 2.6% five courses and 2.6% more than 10 courses. 23.1% never attended contact lens courses and 12.8% did not answer the questionnaire. On comparison of previous knowledge with that acquired by the offered course, 59.0% declared that they increased their knowledge a lot; 33.3% reported median increase; 2.6% little increase and 5.1% did not answer. As concerns training in contact lenses, 66.7% answered that they never had any training; 30.7% answered affirmatively and 2.6% did not answer. Among those who had training, 75% declared it was good; 16.7%, very good and 8.3%, regular. CONCLUSION: The offered teaching model for contact lenses was considered very valuable, increasing a great deal of knowledge in most subjects.

Contact Lenses↗
PubMed2006

A comparison of wavefront aberrations in eyes wearing different types of soft contact lenses.

PURPOSE: The purpose of this study is to investigate the optical quality of eyes wearing different types of soft contact lenses (sCLs) using wavefront aberrometry. METHOD: A psychophysical aberrometer (WFA1000B; BriteEye, SuZhou, China) was used to measure wavefront aberrations for 56 eyes of 28 subjects under four conditions: 1) without contact lenses (non-CL), 2) with lathe-cut contact lenses (lathe-cut CL; Shuliang, Weicon Optics, Shanghai, China), 3) with cast-molded contact lenses (cast-molded CL; Vistavue, J&J Vision Care, U.S.), and 4) with spun-cast contact lenses (spun-cast CL; Lanfenzhiji, Justcome Optics, Beijing, China). The three types of sCLs were made from different materials and lens design. The root mean square (RMS) values of the wavefront aberrations and individual Zernike aberrations were calculated and compared among the CL-wearing conditions. RESULTS: Astigmatism was not significantly changed by any of the three soft contact lenses when compared with the non-CL condition. However, a significant difference in the RMS values of higher-order aberrations was observed between the lens types (F=8.29, p<0.0001). Induced higher-order aberrations were found for both the cast-molded CL and the spun-cast CL conditions. There were significant differences in the aberrations in each of the higher orders between the CL conditions (F=3.77, p=0.011 for third order; F=5.31, p=0.002 for fourth order; F=13.86, p<0.0001 for fifth and higher orders). More higher-order Zernike aberrations such as coma and spherical aberration were induced by cast-molded CLs and/or the spun-cast CLs. CONCLUSION: Wavefront aberrations in the eyes with soft contact lenses vary from one individual lens type to another. Although the variation in wavefront aberrations could be attributed to the differences in the methods of manufacture, influences from other factors such as the lens material and lens design could not be excluded and deserve further investigation.

Adult↗
PubMed1997

[What is the role of contact lenses within the scope of electronystagmography?].

BACKGROUND: During electronystagmography it is necessary to correct detective vision for calibration, smooth pursuit, and saccadic eye movements. Therefore more and more people use contact lenses instead of normal glasses. Given the lack of detailed information about this phenomenon, in the current literature we decided to investigate the influence of soft contact lenses on electronystagmography. The aim of this study was to find out differences in the results of electronystagmography between using glasses or contact lenses. METHODS: Our investigation involved 20 vestibular healthy human subjects with myopia. In the first part of the examination they used their contact lenses and in the second part they were wearing normal glasses. After measuring the calibration potential we wanted to see if contact lenses would increase the rate of artifacts in the electronystagmogram. Then we attempted to determine whether contact lenses would an influence on the registration of the optokinetic nystagmus. Induced saccadic eye movements were recorded and analysed. RESULTS: Contact lenses had a negative influence neither on the calibration potential nor on the rate of artifacts. The latency of the saccadic eye movements also showed no differences between both parts of this investigation. Only the velocity of the saccades and the gain value during the optokinetic test were reduced when glasses were used. CONCLUSIONS: Contact lenses may stimulate the secretory function of the lacrimal gland and thus decrease friction forces. It is also possible that the reduced image size produced or the reduction-effect of minus by glasses in near sighted persons negatively influences eyeball velocity. In summary, our study demonstrates that contact lenses do not have a negative influence on electronystagmography. Therefore electronystagmographic studies of patients with contact lenses are permissible for purposes of documenting a medical opinion.

Adult↗