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At least 55 records · Page 3Linked to original sources
PubMed1990

Are hard lenses superior to soft? Arguments in favor of hard lenses.

The overriding consideration in choosing between soft contact lenses (SCLs) and rigid gas-permeable (RGP) lenses is the severity of the changes each induces in the corneal epithelium, endothelium, and conjunctival structures. Lens-related epithelial changes are largely the consequence of relative oxygen deprivation and consequent corneal edema. Factors such as lower oxygen transmissibility, minimal tear exchange capacity, and large diameters may explain why SCL wearers show a higher rate of corneal infiltrates, sterile ulcers, and irregular staining patterns than users of RGP lenses. The greater association of hydrogels with infectious keratitis may reflect their tendency to accumulate proteinaceous deposits, harbor bacteria in the polymer matrix, and resist easy disinfection. SCL wear has been linked to endothelial polymegethism, a largely irreversible condition that may cause more rapid corneal swelling and slower deswelling after periods of hypoxic stress. Among the conjunctival problems more often seen in SCL wearers are superficial neovascularization, contact lens-related superior limbic keratoconjunctivitis, and giant papillary conjunctivitis. Mechanical irritation from large-diameter lenses, a tendency to build up mucoproteinaceous deposits, corneal draping, and hypersensitivity to preservatives in SCL care products may play a role in these problems.

Conjunctival Diseases↗
PubMed1995

Disposable contact lenses and bacterial adhesion. In vitro comparison between ionic/high-water-content and non-ionic/low-water-content lenses.

An in vitro quantitative study of the adhesion of a Staphylococcus aureus strain to two types of disposable contact lenses has been carried out. The first type was an ionic/high-water-content (I-HWC) lens (42% Etafilcon A, 58% water) and the second was a non-ionic/low-water-content (Nl-LWC) lens (61.4% poly(2-hydroxyethyl methacrylate), 38.6% water). Adhesion to the two lens types was evaluated both in basic conditions and after treatment with lysozyme. The results showed that I-HWC lenses are more prone to Staphylococcus aureus adhesion than NI-LWC lenses, both untreated (+15.4%) and treated with lysozyme (+20.5%). Lysozyme increased bacterial adhesion by 30.5% on the lenses with lower water content, and by 36.3% on those with higher water content.

Bacterial Adhesion↗
PubMed2004

Opacification of hydrophilic MemoryLens U940A intraocular lenses: analysis of 2 explanted lenses.

PURPOSE: To determine the rate of opacification of hydrophilic MemoryLens U940A intraocular lenses (IOLs) (Mentor Ophthalmics, Inc.) in the given cohort and perform a histopathological and spectrophotometer analysis of 2 explanted opacified IOLs. SETTING: Ophthalmology Department, Faculty Hospital, Nitra, Slovakia. METHOD: This retrospective study comprised 182 patients (205 eyes) who had implantation of a MemoryLens U940A IOL from June 1997 to June 2000. The patients were examined using a slitlamp to detect the presence of IOL opacification. In 4 cases, the lenses were explanted because of significant opacification and patient-reported problems; 2 lenses were provided for further analysis. One unused reference MemoryLens U940A IOL was also evaluated. All IOL were stained with von Kossa to determine the presence of calcium in the opacification. To confirm the components presence of an ultraviolet (UV) absorber, the IOLs were examined with an Avatar 330 Fourier transfer infrared (IR) spectroscope and a UV visible spectrophotometer (Philips). The IR spectrums for the IOL were identified using an IR spectrum atlas. The opacified IOLs, reference IOL, and the IOL packaging were further examined to determine the presence of silicone. RESULTS: Various amounts of opacification were found on the MemoryLens U940A IOL in 30 eyes (30 patients) (14.63%). Two explanted IOLs were positive for von Kossa staining, proving the presence of calcium deposits; the reference lens staining was negative. Spectrophotometry showed that the reference IOL and opacified IOLs were of the same polymer. The presence of the UV absorber on the benzophenone base was seen in the reference lens but not the opacified IOLs. In contrast, an increased concentration of low-molecular-weight components generated during the degradation of the polymer was present in the opacified lenses. The white cover pf the IOL is of polydimethyl siloxane, a silicone rubber. However, no silicone rubber was present in any examined lens, perhaps because the IOLs were in contact with alcohol during the histopathologic examination. CONCLUSIONS: The results indicate opacification of the hydrophilic MemoryLens U940A was caused by premature consumption of the UV absorber in the polymer component of the IOLs optic, with a subsequent degradation of the polymer. Whether silicone from the white cover led to the IOL opacification, as reported with other types of hydrophilic IOLs, could not be confirmed.

Aged↗
PubMed2003

Kersley lecture: eye believe in contact lenses: contact lenses and/or refractive surgery.

PURPOSE: Media publicity has made patients increasingly aware that surgical vision correction is available. This article gives an overview on refractive surgery and contact lenses. METHODS: Contact lens and refractive surgery possibilities are highlighted for patients with myopia, hyperopia, astigmatism, presbyopia, aphakia, and keratoconus. Therapeutic, pediatric, and cosmetic indications are discussed. RESULTS: Refractive surgery is beneficial for low refractive errors. The use of contact lenses is mandatory in cases of monovision and strabismus before refractive surgery and beneficial for therapeutic use postoperatively. CONCLUSION: Although many patients are always best corrected with contact lenses, only the right synergism of contact lenses and refractive surgery will benefit patients.

Contact Lenses↗
PubMed1991

Use of high-density vitreous substitutes in the removal of posteriorly dislocated lenses or intraocular lenses.

We successfully used high-density vitreous substitutes to remove four dislocated crystalline lenses and three dislocated intraocular lenses (IOLs) from the vitreous cavity. Fluorosilicone oil (300 cs) was used to remove the four lenses and one of the IOLs. Perfluorophenanthrene (Vitreon) was used to remove the other two dislocated IOLs. The dislocated lenses or IOLs were floated by the high-density vitreous substitutes and removed safely without damaging the retina; there were no intraoperative complications. Postoperative residual fluorosilicone oil droplets were found in one case.

Adult↗
PubMed1977

Iridocapsular lenses versus iris-clip lenses: comparison of the results and complications of 100 of each.

The results and complications of implantation of 100 iridocapsular and 100 iris-clip lenses are evaluated. The follow-up period for the first group varied from one to 25 months (mean 12 months) and from one to 43 months (mean 27 months) for the second group. I performed all of the operations and most of the follow-up examinations. Of the patients with iridocapsular lenses, 86 percent and of those with iris-clip lenses, 87 percent obtained a visual acuity of 0.5 (6/12) or better. Binocular vision, positive depth perception, and a small degree of aniseikonia (3% or less) are evident optical benefits. The complicatioons most frequently necessitating a second operation were retained lens material (17%) and repositioning the pseudophakos (6%) in the iridocapsular group. The four-loop lenses caused fewer problems; in one case, posterior luxation necessitated its removal.

Adolescent↗
PubMed2001

Clinical performance of polynomial lenses versus tri-curve lenses. I: initial comfort.

Twenty-two subjects were asked to wear custom-made polynomial back surface design rigid gas permeable (RGP) lenses and conventional tri-curve RGP lenses to compare the initial comfort provided by the two lens designs monocularly and binocularly. Polynomial lenses, based on tri-curve lens fittings, did not provide better initial comfort than tri-curve lenses. The results seem to indicate that an aspheric back surface alone may not play a very important role in the initial comfort of RGP lens wear. The method used to derive the specifications of the polynomial surface may, however, need further modifications to improve its accuracy.

Journal Article↗
PubMed2002

Do specially designed visual display unit lenses create increased postural load compared with single-vision lenses during visual display unit work?

Three different types of spectacle lenses, specially designed for visual display unit (VDU) work, were compared with single-vision lenses regarding postural load. The different corrections effect on postural load was measured by using electromyography. Muscle loads were recorded from the trapezius muscle and the infraspinatus muscle. Continuous measurements of body posture were measured by using three dual axis inclinometers attached to the head, back, and upper arm. No significant differences were found between the single-vision lenses and the specially designed VDU lenses regarding muscle load. Small differences were found regarding the head angle. The study concludes that these new lens designs create interesting opportunities for the optometrist to optimize the visual conditions for VDU workers.

Arm↗
PubMed1992

Studies on human lenses: II. Distribution and solubility of fluorescent pigments in cataractous and non-cataractous lenses of Indian origin.

Fluorometric studies of cataractous and non-cataractous human lenses were carried out to study the emission characteristics and the distribution and solubility of lenticular pigments. Most of the detected fluorophores were well distributed over the cortical and nuclear portion of the lens. The decrease in solubility of proteins with aging and cataract formation is concomitant with increasing photolysis of tryptophan. However, this is likely a phenomenon independent of the photochemical transformations of the lens proteins. The number of emitting species in the diseased lenses are higher than in the normal mature lenses. A species emitting around 375 or 388 nm is of particular interest (lambda cx 330 nm) in that the emission characteristics of this fluorophore resemble kynurenic acid which has a high photosensitizing efficiency. The concentration of fluorescent pigments in the lenses of Indian origin is significantly high. The intense pigmentation could be attributed largely to the formation of photoproducts in the absence of normal endogenous antioxidant accumulation that is dependent on nutrition standard. If, indeed, any of these fluorescent pigments, because of their photosensitizing ability, are responsible for lenticular opacity, it is not the abundance of sunlight alone but also malnutrition that could account for the high incidence of cataract in India.

Adult↗
PubMed2002

Quantitative performance of bifocal and multifocal intraocular lenses in a model eye: point spread function in multifocal intraocular lenses.

OBJECTIVE: To compare the optical properties of bifocal diffractive and multifocal refractive intraocular lenses. METHODS: A model eye with a pupil 4.5 mm in diameter was used to determine the point spread function (PSF) of the distance focus and near focus of a diffractive bifocal intraocular lens (IOL) (model 811E; Pharmacia Inc, Columbus, Ohio) and of a refractive multifocal IOL (model SA40N; Allergan Optical Inc, Irvine, Calif) to compare them with PSFs of foci of corresponding monofocal lenses. For interpreting the PSFs the through focus response, the modulation transfer function, and the Strehl ratio were evaluated. RESULTS: The intensity of the distance focus of the bifocal diffractive lens reached 58.5% and the near focus attained 42.7% of the intensity of a corresponding monofocal lens. The maximal halo intensity surrounding both foci was approximately 4.5%. The distance peak of the refractive multifocal IOL was 73.4% and the near peak 25.1% of a corresponding monofocal lens. The out-of-focus image overlaying the distance focus of the refractive multifocal IOL was approximately 3% of the light intensity of the distance focus, whereas the PSF of the near focus of the multifocal IOL is substantially affected by out-of-focus images. The computed modulation transfer functions show better results for the monofocal lenses, similar results for the tested distance foci, and clear advantages for the bifocal diffractive near focus. CONCLUSIONS: Modulation transfer functions reveal comparable properties for distance vision and a superiority of the bifocal diffractive lens over the refractive multifocal lens for near vision.

Eye↗
PubMed2005

[Intraocular lenses for the correction of refraction errors. Part 1: phakic anterior chamber lenses].

In this overview, the current status of intraocular lens surgery to correct refractive error is reviewed. The interventions are divided into additive surgery with intraocular lens implantation without extraction of the crystalline lens (phakic intraocular lens, PIOL) or the removal of the crystalline lens with implantation of an IOL (refractive lens exchange, RLE). Phakic IOLs are constructed as angle-supported or iris-fixated anterior chamber lenses and posterior chamber lenses that are fixated in the ciliary sulcus. The implantation of phakic IOLs has been demonstrated to be an effective, safe, predictable and stable procedure to correct higher refractive errors. Complications are rare and differ for the three types of PIOL; for anterior chamber lenses these are mainly pupil ovalization and endothelial cell loss.

Anterior Chamber↗
PubMed2005

[Intraocular lenses for the correction of refraction errors. Part II. Phakic posterior chamber lenses and refractive lens exchange with posterior chamber lens implantation].

In this overview, the current status of intraocular lens surgery to correct refractive error is reviewed. The interventions are divided into additive surgery with intraocular lens implantation without extraction of the crystalline lens (phakic intraocular lens, PIOL) or removal of the crystalline lens with implantation of an IOL (refractive lens exchange, RLE). Phakic IOLs are constructed as angle-supported or iris-fixated anterior chamber lenses and posterior chamber lenses which are fixated in the ciliary sulcus. The implantation of phakic IOLs has been demonstrated to be an effective, safe, predictable and stable procedure to correct higher refractive errors. Complications are rare and differ for the three types of PIOL; for posterior chamber lenses these are mainly cataract formation and pigment dispersion. RLE is preferable in cases of high ametropia in which the natural lens has lost its accommodative effect. The main complications for myopic RLA include retinal detachment, while hyperopic refractive lens exchange may be associated with surgical problems in the narrower anterior eye segment.

Humans↗
PubMed2006

Calculated tear oxygen tension under contact lenses offering resistance in series: piggyback and scleral lenses.

BACKGROUND: Models of oxygen delivery to the cornea with contact lens wear have considered the customary situation of one lens being worn on the cornea. However, two lenses, such as a rigid lens piggybacked on a soft lens, may be worn by patients with special ocular and visual needs. This paper extends existing single lens models to circumstances where two lenses offer resistance to oxygen in series. METHODS: Theoretical oxygen tensions are calculated for tear layers trapped beneath piggyback contact lens systems (and scleral lenses) and the anterior corneal surface with a simple single chamber corneal model using a personal computer software spreadsheet. RESULTS: Acceptable values are anticipated for contact lens materials of modern oxygen permeability values of approximately 60-100 Fatt Dk units under open eye conditions. CONCLUSIONS: The results of this spreadsheet model of oxygen supply to the anterior corneal surface offer a useful guide to clinicians concerned about providing their patients with physiologically acceptable piggyback lens systems.

Contact Lenses↗
PubMed1994

Are there acceptable anterior chamber intraocular lenses for clinical use in the 1990s? An analysis of 4104 explanted anterior chamber intraocular lenses.

PURPOSE: The authors pose the question as to whether there are any anterior chamber intraocular lenses (AC IOLs) acceptable for clinical use in the 1990s. METHODS: Data on the incidence and types of complications of 4104 AC IOLs that were submitted to the Center for IOL Research from 1982 to 1993 were retrieved from the laboratory database and analyzed using cumulative frequency calculations and the chi-square test. Normalized explantation rates were related to implantation rates that were derived from market-share analysis. RESULTS: Of 4104 explanted IOLs, 50% were closed-loop designs (n = 2095/4104); 26% (1100/4104) were miscellaneous, older designs; and 22% (919/4104) were open-loop lenses. The most important complications were corneal pathology (2065/4104) and inflammation (1370/4104). Closed-loop designs were responsible for almost 80% of corneal pathology, with an increasing complication rate with ongoing implant duration (P < 0.0001). Open-loop AC IOLs showed, in relation to their normalized rate of implantation, a significantly lower rate of complications and explantations (P < 0.01). CONCLUSION: Complication rates of flexible, open-loop AC IOLs are much lower than previously assumed. They should be distinguished clearly from most older AC IOL designs. Consideration of these lenses as an alternative to sutured posterior chamber IOLs for secondary or exchange implantation may be warranted for selected clinical indications. They also could provide an alternative to the aphakic spectacle rehabilitation program in developing countries, which will have a positive impact on the overwhelming backlog of patients with cataract in the underprivileged world.

Anterior Chamber↗
PubMed1993

Unwanted optical images with narrow profile intraocular lenses compared with conventional intraocular lenses.

About 35% of intraocular lenses now implanted in the United States are narrow profile lenses, measuring on the average 5.0 mm by 6.0 mm. This study sought to determine whether these lenses cause unwanted optical images with a decrease in the quality of vision. Seventy-five eyes with a 5.0 mm x 6.0 mm intraocular lens (IOL) were compared with 75 eyes with a 6.5 mm IOL. All patients had capsulorhexis, phacoemulsification, and capsular fixation of the IOL. There was no statistically significant difference in unwanted visual images (16% and 20%, respectively), ability to drive at night (79% and 69%), or patient satisfaction. Careful patient selection is, however, important.

Aged↗
PubMed1994

Neodymium:YAG laser damage on silicone intraocular lenses. A comparison of lesions on explanted lenses and experimentally produced lesions.

In this study we examined 17 explanted silicone intraocular lenses (IOLs) (two one-piece, 15 three-piece) that had evidence of neodymium:YAG (Nd:YAG) laser damage. The majority of lenses (47.1%) had been explanted because of persistent pigment deposits and chronic inflammation. Decentration or IOL dislocation had occurred with 29.4% of lenses. All 17 patients had had Nd:YAG laser posterior capsulectomy, anterior surface polishing, or both; treatments ranged from one to 13 times. By both clinical and gross examination, the laser lesions appeared dark. This was misinterpreted by some opthalmologists as pigment deposits and some patients had additional Nd:YAG laser treatment, which increased the severity of the laser damage. The mean depth of laser damage on the IOLs was 143 +/- 113.4 microns. It was between 51 and 175 microns in approximately 61.0% and deeper than 300 microns (maximum 660 microns) in 9.3%. We compared the explanted IOLs with silicone IOLs that were experimentally damaged using standard power levels from 0.3 to 3.0 mJ and different focal areas. The appearance of the experimentally induced laser burns was equivalent to that on the explanted IOLs, especially the dark laser pits. Since the laser lesions may resemble pigment deposits on slitlamp examination, we recommend careful examination of patients prior to planned laser therapy.

Cataract Extraction↗
PubMed2003

Menicon Z 30-day continuous wear lenses: a clinical comparison to Acuvue 7-day extended wear lenses.

PURPOSE: To establish equivalent safety and efficacy of the clinical performance of a novel hyper-O2 transmissible rigid gas-permeable (RGP) lens (Menicon Z, tisilfocon A) when worn continuously for 30 days (29 nights) when compared with a conventional control hydrogel lens (Acuvue; etafilcon A) worn for 7 days (6 nights). METHODS: This study was a prospective, open-label, 24-center, concurrent, cohort-controlled clinical trial. This abbreviated report will focus on the length of wear achieved, slitlamp findings, and adverse event rates. RESULTS: Two-thirds (66.5%) of patients wearing the RGP lens achieved greater than or equal to 22 nights of continuous wear; slitlamp observations revealed two categories of findings: those associated with lens modality and those with lens wearing time. Adverse events were mostly associated with foreign body abrasions for RGP lenses, whereas the hydrogel lens showed a higher number of bacterial infections. CONCLUSION: The results of this study revealed some interesting differences in the classification and severity of findings. The results demonstrate that the continuous wear of Menicon Z (tisilfocon A) RGP lenses for up to 30 nights is a safe and equivalent alternative to 7-day (6 nights) hydrogel wear lenses.

Adult↗
PubMed2003

Comparing goblet cell densities in patients wearing disposable hydrogel contact lenses versus silicone hydrogel contact lenses in an extended-wear modality.

PURPOSE: The current study evaluates the response of the ocular surface to extended contact lens wear by comparing a new silicone hydrogel lens to an ACUVUE 2 lens. METHODS: Twenty subjects with an average age of 28 years were randomly assigned to a fitting with ACUVUE 2 or PureVision lenses. Ocular surface assessment by impression cytology was performed at baseline and for the 6 months after initiation of lens wear. RESULTS: Although goblet cell density significantly increased with wear time, no statistically significant difference was observed between the contact lens groups. The average baseline goblet cell percentages were as follows: ACUVUE 2 group, 1.44; PureVision group, 1.11. The 6-month averages were as follows: ACUVUE 2 group, 3.16; PureVision group, 2.22. CONCLUSIONS: It appears that silicone hydrogel lenses may be slightly less irritating to the ocular surface than lenses not containing silicone. This could be a promising indicator for successful 30-day continuous wear.

Adult↗