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PubMedDate not supplied

Kinetic visual disturbances with contact lenses.

Kinetic (variable) visual disturbances in contact lens wearers may be generated optically or mechanically. These disturbances are categorized in two groups: 1) those affecting both phakic and aphakic contact lens wearers; and 2) those peculiar to aphakic patients. Within each category disturbances vary with the types of lens used. In this review, the optical and mechanical bases for the various problems are discussed, as are possible solutions. It is emphasized that the ophthalmologist prescribing contact lenses should be aware of the patient's work hazards and requirements, and weigh the advantages and disadvantages of contact lenses. For example, is the patient exposed to high temperatures, heavy or fast-moving equipment, altered barometric conditions, etc.? Is physical exertion required? Employers and fellow workers should be aware of the contact lens wearers in their work force.

Aphakia, Postcataract↗
PubMed2003

On- and off-eye spherical aberration of soft contact lenses and consequent changes of effective lens power.

BACKGROUND: Soft contact lenses produce a significant level of spherical aberration affecting their power on-eye. A simple model assuming that a thin soft contact lens aligns to the cornea predicts that these effects are similar on-eye and off-eye. METHODS: The wavefront aberration for 17 eyes and 33 soft contact lenses on-eye was measured with a Shack-Hartmann wavefront sensor. The Zernike coefficients describing the on-eye spherical aberration of the soft contact lens were compared with off-eye ray-tracing results. Paraxial and effective lens power changes were determined. RESULTS: The model predicts the on-eye spherical aberration of soft contact lenses closely. The resulting power change for a +/- 7.00 D spherical soft contact lens is +/- 0.5 D for a 6-mm pupil diameter and +/- 0.1 D for a 3-mm pupil diameter. Power change is negligible for soft contact lenses corrected for off-eye spherical aberration. CONCLUSIONS: For thin soft contact lenses, the level of spherical aberration and the consequent power change is similar on-eye and off-eye. Soft contact lenses corrected for spherical aberration in air will be expected to be aberration-free on-eye and produce only negligibly small power changes. For soft contact lenses without aberration correction, for higher levels of ametropia and large pupils, the soft contact lens power should be determined with trial lenses with their power and p value similar to the prescribed lens. The benefit of soft contact lenses corrected for spherical aberration depends on the level of ocular spherical aberration.

Adult↗
PubMed2004

In vivo confocal microscopy: increased conjunctival or episcleral leukocyte adhesion in patients who wear contact lenses with lower oxygen permeability (Dk) values.

PURPOSE: Contact lens wear is known to threaten the health of the ocular surface. In vivo confocal microscopy (IVCM) to visualize leukocyte rolling and extravasation in inflammation was recently described. We tested the hypothesis that contact lens wear is associated with measurable inflammation in superficial vessels. METHODS: Leukocyte rolling and sticking (hallmarks of the inflammatory process) were recorded by IVCM. IVCM was performed on conjunctival or episcleral blood vessels bilaterally on 55 contact lens wearers (15 male, 40 female) and 22 non-contact lens wearers (8 male, 14 female). Data were analyzed in 2 ways. Considering each vessel as an independent variable resulted in 132 analyzable vessel segments (13 daily disposable contact lenses, 67 traditional contact lenses, 14 rigid gas-permeable lenses, and 38 controls). Considering each subject as an independent variable resulted in analyzable data for 47 subjects (5 daily disposable contact lens wearers, 22 traditional contact lens wearers, 5 rigid contact lens wearers, and 15 control patients). Free-flowing, sticking, and rolling cells were counted in the vessels. Multiple parameters including mean flow velocity, shear rate, rolling cells/mm/min, and sticking cells/mm were calculated. RESULTS: We found no significant difference in leukocyte adhesion between control patients and patients wearing daily disposable, traditional disposable, or rigid gas-permeable lenses in both types of statistical analyses. However, the data regarding vessel segments as an independent variable show that there were more rolling cells in patients who wore contact lenses with oxygen permeability values (Dk) less than 10 as compared to those who wore contact lenses with oxygen permeability values greater than 16 (P < 0.01) or compared to controls (P < 0.01). CONCLUSION: IVCM is a novel, powerful technique to recognize a critical but subclinical component of inflammation. Although our data indicate that contact lens wear does not markedly increase rolling and sticking of leukocytes in conjunctival or episcleral vessels, there may be subclinical inflammation in association with lenses with the lowest oxygen permeability.

Adult↗
PubMed1993

Heparin inhibits Pseudomonas adherence to soft contact lenses.

Adherence of bacteria to the surface of contact lenses may play an important role in contact lens intolerance and corneal infections. To decrease the capability of bacteria to adhere to contact lenses we incubated two types of soft contact lenses with two strains of Pseudomonas aeruginosa (serotypes 0:11 and 0:8) at a concentration of 5 x 10(7) c.f.u./ml for 12 hours. When heparin was added to the medium at a concentration of 1000 IU/ml the numbers of bacteria adhering to the contact lenses were significantly fewer than in the controls (p < 0.005). Our results suggest that heparin, either included in contact lens solutions or bonded to the surface of the contact lens, may decrease contact-lens-related morbidity.

Bacterial Adhesion↗
PubMed1997

Mesopic vision in myopia corrected by photorefractive keratectomy, soft contact lenses, and spectacles.

PURPOSE: To evaluate contrast vision and glare sensitivity under mesopic conditions in eyes having uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia and in eyes corrected by disposable soft contact lenses, soft contact lenses, and spectacles. SETTING: Division of Experimental Ophthalmic Surgery, University of Tübingen, Germany. METHODS: The Mesoptometer II test was used to evaluate mesopic vision (glare sensitivity and contrast vision) in 28 eyes of 14 patients wearing disposable soft contact lenses, 20 eyes of 10 patients wearing soft contact lenses, 39 eyes of 20 patients wearing spectacles, 30 eyes of 15 emmetropic patients, and 33 eyes of 22 patients after PRK with 5.0 mm optical zone. Follow-up was between 15 and 60 months after PRK (mean 34.5 months). RESULTS: The guidelines of the German Ophthalmologic Society state that patients must recognize Mesoptometer II contrast levels of 1:5 or better with and without glare to meet the minimum legal night-driving standards for private cars. All eyes with disposable soft contact lenses and soft contact lenses, all emmetropic eyes, and 38 eyes corrected by spectacles recognized contrast levels of 1:5 or better without glare. In contrast, 18 eyes in the PRK group were unable to recognize contrast level 1:5 without glare. With glare, 1 eye in the disposable soft contact lens group, 1 in the soft contact lens group, and 7 with spectacles were unable to recognize the 1:5 contrast level. All emmetropic eyes recognized contrast levels of 1:5 or better; 22 PRK eyes were unable to recognize contrast level 1:5 with glare. CONCLUSION: Myopic PRK may lead to long-term impairment of mesopic vision, while soft contact lens use does not seem to markedly influence mesopic vision in eyes with low to moderate myopia.

Adolescent↗
PubMed2003

Effects of contact lenses on corneal thickness and corneal curvature during usage.

PURPOSE: To investigate the effects of contact lenses on corneal thickness and curvature. METHODS: Eighty-four eyes of 45 patients (26 female and 19 male) wearing contact lens for the first time with a median age of 23.04 +/- 7.2 years (range, 15-44 years) were included in the study. After all patients had undergone a routine ophthalmic examination, corneal thickness measurements in nine regions and corneal topography were performed before wearing contact lenses and after 1 month, 6 months, and 12 months. Patients were classified into three groups according to duration of wear. Groups were also classified into two subgroups according to the lens type (rigid gas-permeable and soft contact lenses). RESULTS: Mean visual acuity was 0.82 +/- 0.26 with spectacles and 0.92 +/- 0.26 with contact lenses. At the end of 1 month, statistically significant corneal thinning and thickening were noted in different regions in group 1. In group 2, statistically significant corneal thinning was noted in all regions with soft contact lenses and rigid gas-permeable contact lenses except in the inferior temporal region at the end of 6 months. In group 3, corneal thinning was noted in all regions with soft contact lenses and rigid gas-permeable contact lenses. This corneal thinning was statistically significant in all regions with the soft contact lenses except in the inferior nasal region and with rigid gas-permeable contact lenses except in the central region. When corneal curvatures were examined, corneal flattening was seen in groups 1 and 2. In group 3, corneal steepening was noted. CONCLUSIONS: Soft contact lenses and rigid gas-permeable contact lenses cause corneal thickening and corneal flattening in the first months, but they cause corneal thinning and corneal steepening with time. These alterations can be evaluated as evidence that contact lenses negatively influence corneal physiology.

Adolescent↗
PubMed2001

Adhesion of tear proteins to contact lenses and vials.

Tear-protein adhesion to contact lenses contributes to lens contamination and deterioration, and depends primarily on the type of contact-lens material used. Adhesion of tear proteins to contact lenses and glass vials was examined using spectrophotometry, hydrophobic-interaction HPLC and bicinchoninic acid (BCA) protein assay. Using spectrophotometry at 280 nm, vials containing two proteins (lysozyme and milk lipocalin) at three different concentrations were examined for changes in their protein concentrations over a 3-week period. Vials containing 5.0 mg/ml lysozyme lost about one-third of their protein (P<0.005), while vials containing 5.0 mg/ml milk lipocalin lost two-thirds of their protein (P<0.01). Conversely, vials containing 1.0 mg/ml lysozyme lost two-thirds of their protein (P<0.005), while vials containing 1.0 mg/ml milk lipocalin lost one-third of their protein (P>0.05). Subsequently, lysozyme deposition on both glass vials and contact lenses was monitored for 5 days using spectrophotometry, to determine lysozyme content in the vials, and HPLC, to determine lysozyme deposition on contact lenses stored in the same vials. This experiment indicated considerable variation in lysozyme deposition on vials and contact lenses, with vial deposition remaining relatively constant (P>0.05) while lens deposition decreased and then increased (P<0.05). Finally, the same experiment was repeated, monitoring lysozyme deposition using the BCA assay. This experiment yielded the most consistent results, with lysozyme deposition on vials continuing throughout the 5 day experiment (P<0.05), while deposition on lenses again decreased and then increased, although to a much lesser extent than in the previous experiment (P>0.05).

Animals↗
PubMed1999

Biconcave contact lenses: a critical analysis of their optical properties.

BACKGROUND AND OBJECTIVE: The purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid. MATERIALS AND METHODS: The optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrand's model of the human eye. RESULTS: The performance of biconcave contact lenses represents a compromise between that of Goldmann's and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power. CONCLUSIONS: Biconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.

Contact Lenses↗
PubMedDate not supplied

[Use of contact lenses in progressive myopia].

Effects of contact lenses on clinical refraction and vision function were examined in patients with progressive myopia. A total of 535 patients were examined; contact lens correction was employed in 385 of these, 150 ones wearing spectacles have made up the reference group; the follow-up period was up to 5 years. Refraction remained unchanged by the end of the follow-up in 73.2 percent of patients using contact lenses, whereas in the reference group this value has made up 10.8 percent. The stabilizing action of contact lenses is explained mainly by improved function of the accommodation system of the eye, weakened in progressive myopia, and by improved quality of the retinal image.

Accommodation, Ocular↗
PubMed2006

[Practical measures. Contact lenses after glaucoma surgery].

New soft therapeutic contact lenses after glaucoma surgery provide good results, both in terms of tolerance and efficacy (60% pressure increase in a personal series of ten patients with the Trabeculens contact lens). Indicated for moderate immediate postoperative leakage, their use remains transitory and they should be removed as soon as intraocular pressure is (rapidly) corrected. After glaucoma surgery, wearing contact lenses can be discussed if there are no contraindications and 6-12 months after the intervention in a compliant patient. Evaluation of the risk-benefit ratio is important. Gas-permeable, small-diatmeter hard contact lenses, bi- or trifocal spherical or posterior toric - the most stable - should be favored. Soft contact lenses can also be used, but because of their presence on the conjunctiva, notably in the filtration zone, they are less frequently recommended. Contact lens wear should in all cases be strictly limited to the daytime.

Contact Lenses, Hydrophilic↗
PubMed1991

The application of disposable contact lenses in the Navy.

With the recent advent of disposable contact lenses, many of the problems which have been hindering the military application of contact lenses have been overcome. Fifty-five myopic naval personnel with no previous contact lens experience were put through a three-week study using these contact lenses. The aim was to test the feasibility of supplying bespectacled myopic seamen with contact lenses at the outset of operational missions. Seven developed conjunctival injection which caused them to discontinue contact lens wear. Of the remaining 48, however, a vast majority showed preference for contact lenses when compared to spectacles in the work environments that they were exposed to. With contact lenses, 95.8% had comparable or better vision during the day and 85.4% during the night. No serious ocular complications were noted and only minor findings were detected in the 96 eyes at the end of three weeks of contact lens wear.

Contact Lenses↗
PubMed1989

Visual performance with aspheric rigid contact lenses.

Single vision aspheric contact lens designs may be able to enhance visual performance by controlling spherical aberration. In this study, we have compared the visual performance provided by two front surface aspheric rigid contact lenses with that of a spherical rigid contact lens and spectacle correction. These 4 corrections were worn by ten subjects while visual acuity was determined as a function of aperture size. The possibility that front surface aspheric lens designs may enhance visual performance was confirmed, although individual subjects varied significantly in this visual response. Contributions to the visual performance, other than contact lens surface shape, may include lens position and stability.

Adult↗
PubMed1997

[Contact lenses. Infections and hygiene].

BACKGROUND: Contact lens wearers are subject to increased risk of infection, and an attempt was made to determine which factors cause the overproportional risk of infection? PATIENTS: The aim of this paper is to explain with appropriate bibliographic support why people who wear contact lenses are at risk of infection. RESULTS: The relative risk of keratitis is a function of the lens material and the wearing time of the contact lenses. Extended wear of hydrogel lenses is associated with an overproportional risk of infection. According to the literature, the frequency of complications in contact lens wearers generally is the result of poor hygiene in 66% of the cases. The general lack of hygiene among contact lens wearers must, therefore, be regarded as one cause among pathophysiological mechanisms of the eye. The microbial spectrum favors gram-negative bacteria living in a wet environment such as Pseudomonas, Serratia and parasites like Acanthamoeba. CONCLUSION: The specific spectrum of pathogens and new problem organisms not only challenge the fitter but also the manufacturers to adapt hygiene (sanitary) measures and products to the new development. Disposable contact lens systems are the first step, but they do not solve all the problems of contact lens wearers. Therefore, the importance of contact lens hygiene must be especially emphasized when the ophthalmologist is giving instructions to the patient. On the other hand, hygiene should also not be neglected by the contact lens fitters since it is part of the whole problem.

Contact Lens Solutions↗
PubMed1977

In-office measurement of soft contact lenses.

The dimensions of soft contact lenses cannot be measured by methods used for hard lenses, so new techniques have had to be devised. This paper introduces standards and tolerances for the measurement of soft contact lenses. Previous methods of measuring these lenses are reviewed, and 2 new methods are described for measuring thickness and diameter. Instrument errors and the reliability of these methods are assessed.

Contact Lenses, Hydrophilic↗
PubMed1997

The use of disposable contact lenses as therapeutic lenses.

PURPOSE: To evaluate the efficacy of Acuvue contact lenses as a therapeutic contact lens in 33 patients with noninfectious corneal disorders. METHODS: We fit 33 patients (21 female, 12 male) with Acuvue contact lenses. Patients were seen in follow-up at 24 hours, 4 days, 15 days, and then monthly. Contact lenses were replaced weekly. Ocular signs and symptoms related to lens tolerance were recorded at each follow-up visit. RESULTS: Twenty-six patients (79%) improved or remained asymptomatic. Seven patients (21%) were discontinued due to complications, intolerance, or poor fit. In the majority of patients (79%), the Acuvue lens was tolerated and was beneficial in the treatment of corneal disease. CONCLUSIONS: The Acuvue contact lens can be effectively utilized as a therapeutic contact lens.

Adolescent↗
PubMed1982

Flexure and residual astigmatism with cellulose acetate buterate (CAB) contact lenses on toric corneas.

Thin contact lenses flex on toric corneas, thus changing the residual astigmatism. Our study evaluated the flexure and induced astigmatism of CABCURVE cellulose acetate buterate (CAB) contact lenses on toric corneas and compared the results with those found for polymethyl methacrylate (PMMA) and Polycon lenses. Ten subjects (20 eyes) with corneal toricities ranging from 1.12 to 3.12 D wore six CABCURVE lenses with center thicknesses from 0.10 to 0.20 mm. Flexure and induced residual astigmatism were measured on all corneas with all lenses in a double-masked fashion. We found that all the CABCURVE lenses flexed on the toric corneas and altered residual astigmatism. Both flexure and induced residual astigmatism increased as center thickness decreased, and were greater than with PMMA or Polycon lenses of similar dimensions. These findings should be considered when deciding which lens type to fit on patients with toric corneas.

Adult↗
PubMed1998

Reactive oxygen species (ROS) generated by xanthine oxidase in the corneal epithelium and their potential participation in the damage of the corneal epithelium after prolonged use of contact lenses in rabbits.

Prolonged use of contact lenses (for 14 days) evoked an imbalance between the activity of xanthine oxidase (an enzyme belonging to reactive oxygen species-generating oxidases) and catalase (an enzyme belonging to reactive oxygen species-scavenging oxidases) in the corneal epithelium of rabbits. The activity of catalase decreased, while xanthine oxidase activity was very high. Of other enzymes studied in the corneal epithelium, the activities of xanthine oxidoreductase, glucoso-6-phosphate dehydrogenase and succinate dehydrogenase were decreased. In contrast, the activities of lactate dehydrogenase and lysosomal hydrolases (acid beta-galactosidase, dipeptidyl peptidase II) were increased and appeared in animals sacrificed immediately after contact lens removal. In rabbits sacrificed later (after 1 h), an additional increase of lactate dehydrogenase and lysosomal hydrolase activities developed in the superficial layers of the corneal epithelium. Catalase supplementation during use of contact lenses prevented both the significant decrease of catalase activity in the corneal epithelium and the development of additional epithelial damage. In contrast, topical treatment with 3-aminotriazole (an inhibitor of catalase) resulted in the nearly complete loss of catalase activity in the corneal epithelium and the appearance of more serious epithelial damage. We conclude that ROS generated by xanthine oxidase induce additional damage of the corneal epithelium related to the use of contact lenses.

Animals↗
PubMed1985

Soft bifocal contact lenses for patients with nearpoint asthenopia.

Bifocal contact lenses have generally been considered solely for the presbyopic population. However, pre-presbyopic individuals with accommodative or vergence disorders who respond favorably to plus lenses at near may be good candidates for bifocal contact lenses. A group of ten non-presbyopic patients who manifest accommodative dysfunctions or near point esophoria were fit with the Ciba BI-SOFT contact lenses. Nearpoint accommodative and vergence findings were evaluated through both near point plus spectacle lenses and the bifocal soft lenses. Results indicate that the BI-SOFT bifocal contact lens was effective in changing the near point visual posture. However, poor distance vision acuity due to ghost images reduced the subjective success rate of the BI-SOFT lens on this non-presbyopic population.

Adult↗