Extended-wear Lenses Research Articles

An Early Assessment of Silicone Hydrogel Safety: Pearls and Pitfalls, and Current Status

The contact lens industry has evolved and now provides many choices, including continuous wear, overnight orthokeratology, frequent-replacement lenses, daily-disposable lenses, and many alternatives in systems of care and maintenance. Epidemiologic studies to date have shown that how a lens is worn, particularly if worn overnight, can increase the risk of microbial keratitis. However, the risk of silicone hydrogel contact lenses worn on a continuous-wear basis has been evaluated only recently. This article summarizes the recent research data on extended-wear silicone hydrogel lenses and discusses the challenges of early evaluations of silicone hydrogel lens safety. Finally, the relevance of this information is discussed to practitioners and contact lens wearers making choices about the risks and benefits of different products and how they are used.

Risk of Corneal Inflammatory Events with Silicone Hydrogel and Low Dk Hydrogel Extended Contact Lens Wear: A Meta-Analysis

High Dk silicone hydrogel (SH) lenses have been shown to significantly decrease the risk of hypoxic complications compared to traditional low Dk hydrogels. However, the risks of inflammatory complications with SH compared to low Dk lenses are not as clear. A meta-analysis was performed to combine the relevant literature to evaluate the risks of corneal inflammatory events in users of SH and low Dk hydrogel extended wear lenses. A systematic search was conducted using online databases, unpublished meeting abstracts, and retrieval of other cited references presented or published between 1990 and February 2006. Each study was evaluated for quality in terms of the research question, and these quality assessments were used to determine which studies should be used in subgroup analyses. A generalized linear mixed model framework with an underlying Poisson distribution for the occurrence of events was employed to combine information from the included studies. Twenty-three studies published or presented on either or both arms by February 2006 were selected for analysis. A total of 9,336 subjects and 18,537 eyes comprised the entire sample. Seven studies were published in the 1990s. Eighteen studies (78%) were prospective, and 11 (48%) used randomization. The follow-up ranged from 4 to 36 months, with a median of 12 months. The rates of infiltrates for low Dk hydrogels and SH lenses were 7.7 (2.2, 26.7) and 14.4 (4.3, 48.2) per 100 eye-years, respectively. In the subset of five best quality studies, the unadjusted risk ratio for corneal inflammatory events for SH lenses compared to low Dk lenses was 2.18 (p < 0.005). Across studies, adjusted risk ratios ranged from 2.18 to 2.23 (p < 0.05), with strong confounding between material and length of wear. Based on published or presented studies between 1991 and 2006, there is approximately a twofold higher risk for corneal inflammatory events in users of SH lenses when typically worn for up to 30 days extended wear when compared with low Dk extended wear lenses when typically worn for 7 days extended wear. The increased risk cannot be definitively linked to SH lens materials because the effect of material on outcome is confounded by length of wear.

Contact lens‐related corneal ulcers requiring hospitalization: A 7‐year retrospective study in Belgium

To evaluate the clinical and epidemiological aspects of contact lens-related infectious corneal ulcers requiring hospitalization. A retrospective analysis was performed on the files of patients hospitalized for contact lens-induced corneal ulcer in the eight Belgian university hospitals over a 7-year period (January 1997 to December 2003). Diagnoses for all hospitalized patients are obligatorily registered using the ICD-9 code. A total of 107 patients with contact lens-related corneal ulcers were documented: the number increased from five in 1997 to 22 in 2003. A total of 99 subjects used soft contact lenses, of whom nine used disposables, 73 planned replacement and 17 conventional lenses. Only six patients used extended wear lenses. Three patients used daily disposable lenses. The most frequently cultured organisms were Pseudomonas and other Gram-negative germs (70%) and Acanthamoeba (16%). The majority (77%) of the corneal ulcerations were centrally located and resulted in an average visual loss of four lines. During the study period, the number of patients hospitalized rose, which is only partially explained by the increasing prevalence of lens wearers: 3.5% and 6.5% of the Belgian population used lenses in 1995 and 2003, respectively. These factual data highlight the need for improvements in patient education.

A Review of the Holden–Mertz Criteria for Critical Oxygen Transmission

Holden and Mertz established the foundations for the new generation of silicone hydrogel contact lenses for daily and extended wear in 1984. Absence of lens-induced corneal swelling was their premise and although this was possible with daily wear, the goal with extended wear seemed almost impossible because of the limitation of hydrogel materials. Experience with extended and daily wear of disposable contact lenses during the last 2 decades and, more recently, with silicone hydrogels has led to the reconsideration of the validity of the findings of Holden and Mertz. A pivotal influence on the Holden and Mertz critical Dk/t value for closed-eye lens wear was exerted by two numbers: the no-lens wear corneal edema level (4%) and the silicone lens data point (Dk/t of 182x10, closed-eye edema level of 2.6%). Subsequent publications appear to give a more accurate assessment of the no-lens closed-eye corneal edema level, and there are also more recent measurements of silicone hydrogel lens Dk/t and corneal edema responses. It now appears that the Holden and Mertz criteria for extended-wear critical Dk/t should be revised upwards to at least 125x10.

Bacterial Transmission from Contact Lenses to Porcine Corneas: An Ex Vivo Study

To quantify the transmission to ex vivo porcine eyes of Staphylococcus aureus 835 and Pseudomonas aeruginosa 3 from three types of contact lenses-one daily wear and two extended wear-differing in hydrophobicity and roughness. One daily wear lens (etafilcon) and two extended-wear lenses (one lotrafilcon A and one balafilcon A) were inoculated in a bacterial suspension for 30 minutes and then placed on ex vivo porcine eyes. After 16 hours of contact between lens and eye, confocal laser scanning microscopy was used to determine the number of bacteria on the lens and cornea for the calculation of transmission percentages. Transmission percentages were significantly different for both bacterial strains from an etafilcon A lens and balafilcon A lens (P = 0.006 and 0.04, respectively). Percentages varied from 51% to 68% for the hydrophobic P. aeruginosa and from 54% to 82% for the hydrophilic S. aureus strain, depending on the contact lens involved. Both strains were transferred the least from the most hydrophilic and roughest lens made of lotrafilcon A, although the difference was only statistically significant for S. aureus. Bacterial transmission to the porcine cornea differed in the various types of contact lenses and was least in the hydrophilic and rough lens type.

Dispersion of microemulsion drops in HEMA hydrogel: a potential ophthalmic drug delivery vehicle

Approximately 90% of all ophthalmic drug formulations are now applied as eye-drops. While eye-drops are convenient and well accepted by patients, about 95% of the drug contained in the drops is lost due to absorption through the conjunctiva or through the tear drainage. A major fraction of the drug eventually enters the blood stream and may cause side effects. The drug loss and the side effects can be minimized by using disposable soft contact lenses for ophthalmic drug delivery. The essential idea is to encapsulate the ophthalmic drug formulations in nanoparticles, and disperse these drug-laden particles in the lens material. Upon insertion into the eye, the lens will slowly release the drug into the pre lens (the film between the air and the lens) and the post-lens (the film between the cornea and the lens) tear films, and thus provide drug delivery for extended periods of time. This paper focuses on dispersing stabilized microemulsion drops in poly-2-hydroxyethyl methacrylate (p-HEMA) hydrogels. The results of this study show that the p-HEMA gels loaded with a microemulsion that is stabilized with a silica shell are transparent and that these gels release drugs for a period of over 8 days. Contact lenses made of microemulsion-laden gels are expected to deliver drugs at therapeutic levels for a few days. The delivery rates can be tailored by controlling the particle and the drug loading. It may be possible to use this system for both therapeutic drug delivery to eyes and the provision of lubricants to alleviate eye problems prevalent in extended lens wear.

Ulcerative keratitis in contact lens wearers.

To determine the clinical microbiological characteristics of corneal ulcers in contact lens wearers. A retrospective study of 23 patients admitted to our department with contact lens-related corneal ulcers during a 43-month period. Detailed demographic data, the type of contact lens, duration of lens wear, and wearing schedule were derived from a self-administered questionnaire. The severity of the ulcer; cultures of corneal scrapings, storage solutions, and contact lenses; treatment; and final outcome were evaluated. Of the 86 cases of ulcerative keratitis admitted during the study period, 23 (26.74%) were attributed to contact lens use. Most patients were young women from urban areas. All of them were using soft contact lenses for 3 days to 20 years. Five patients used daily-wear lenses as extended-wear lenses. Most ulcers (47.82%) were mild; 30.43% were moderate; and 21.47% were severe. Corneal scrapings for cultures were obtained in 15 of the cases and were positive in 10 (43.47%) of them, whereas in 33.33% of the culture-positive storage solutions and in 66.67% of the culture-positive contact lenses, corneal scrapings were negative. Pseudomonas aeruginosa was the most frequent isolated pathogen (60%). The final visual acuity was 20/40 or better in 60.87% of the cases. Contact lens use is an important risk factor for the development of ulcerative keratitis, with P. aeruginosa remaining the predominant pathogen. It seems important to culture contact lenses and contact lens storage solutions, in addition to the corneal scrapings, and the role of initial therapy for the corneal ulcers remains important.

Effects of Extended-Wear Soft Contact Lenses on the Ocular Surface and Central Corneal Thickness

Purpose: New contact lens materials with high oxygen permeability are said to be convenient for the extended-wear (EW) schedule. We evaluated the short-term effect of EW soft contact lens usage on ocular surface and central corneal thickness. Patients and Methods: Fifty-two eyes of 26 patients were included in the study. Sixteen of the patients used the high oxygen-permeable lenses for a 30-day extended-wear schedule (group I). Ten patients used the lenses on a daily wear basis (DW, group II). All patients were evaluated for visual acuity and central corneal thickness by corneal and conjunctival biomicroscopy, Schirmer and tear break-up time (BUT) tests. Impression cytology was performed in the superior/temporal, inferior/nasal quadrants of the conjunctiva, 1 mm from the limbus, with cellulose acetate filter paper. The specimens were graded under light microscopy according to Nelson’s classification. Results: Three patients in the EW group were excluded from the study as they discontinued lens usage due to slight discomfort and hyperemia. Biomicroscopic findings and tear function tests indicated no increased pathological results. Central corneal thickness decreased from 554 ± 9.55 to 546 ± 9.30 µm (mean ± SEM) in the EW group (p = 0.002), whereas no significant change occurred in the DW group. Cytological evaluation of the EW group showed an 88% increase in metaplasia (p = 0.007), especially close to the limbal areas and in the superior quadrants; this ratio was 30% in the DW group. Snake-like chromatin changes were found to be increased, from 4 to 6 patients, in the EW group while it remained the same in the DW group (p > 0.05). Individual comparisons of the initial and final pathological conditions of the ocular surfaces in the two groups showed that there was an increase in pathology in the EW group while there was no significant difference in the DW group. Conclusions: On a 30-day extended-wear basis with high oxygen-permeable lenses, the possible development and increase of conjunctival cytologic changes secondary to mechanical trauma is one of the main remaining problems. Conjunctival and related immunologic pathologies should not be overlooked when prescribing an extended-wear lens schedule.

Corneal variations produced by soft extended-wear contact lenses

Using keratometry, we evaluated corneal variations due to use of soft extended-wear contact lenses. Fifty subjects were fitted with either PureVision contact lenses (36% hydration) or Focus Night&Day contact lenses (24% hydration). Results showed decreased horizontal and vertical corneal curvature radii at 0° and 90° 1 day after lens fitting. Variations in corneal curvature radius were greater with these extended-wear lenses than with other types of soft contact lenses.

Perspectives on the Pill: An Essay Review

1FDA History Office, HFC‐24, Room 13‐51, Rockville, MD. E-mail: sjunod@ora.fda.gov

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Bacterial colonization of disposable soft contact lenses is greater during corneal infiltrative events than during asymptomatic extended lens wear.

Microorganisms, especially gram-negative bacteria, are considered to play a role in the etiology of certain corneal infiltrative events (CIEs) observed during soft contact lens wear. This study explored the possibility of microbial colonization of soft contact lenses as a risk factor leading to CIEs. In a clinical trial conducted from March 1993 to January 1996, 330 subjects wore disposable soft contact lenses on a 6-night extended-wear and disposal schedule. During this period, 4,321 lenses (118 during CIEs; 4,203 during asymptomatic lens wear) were recovered aseptically and analyzed for microbial colonization. A greater percentage of lenses were free from microbial colonization during asymptomatic wear than during CIEs (42 versus 23%; P < 0.0001). The incidence of gram-positive bacteria, gram-negative bacteria and fungi was greater during CIEs than during asymptomatic lens wear (P < 0.05). During asymptomatic lens wear, gram-positive bacteria were isolated most frequently and were usually normal external ocular microbiota. Of the gram-positive bacteria, the incidence of Streptococcus pneumoniae was greater during CIE than during asymptomatic wear (7.6 versus 0.6%; P < 0. 0001). While gram-negative bacteria were seen in few cases during asymptomatic wear, their incidence during CIE in comparison to asymptomatic wear was substantial and significant (23.7 versus 3.8%; P < 0.0001). Also, the level of colonization was high. Of CIEs, events of microbial keratitis, contact lens acute red eye, and asymptomatic infiltrative keratitis were associated with lens colonization with gram-negative bacteria or S. pneumoniae. Colonization of soft contact lenses with pathogenic bacteria, especially gram-negative bacteria and S. pneumoniae, appears to be a significant risk factor leading to CIE.

Trends in Australian contact lens prescribing 2000

Background:This study was conducted to ascertain current modes of contact lens prescribing in Australia. Methods:One thousand questionnaires were randomly distributed to proportionate samples of optometrists in each state of Australia. The profession fits the majority of contact lenses in Australia and the sample represents 55 per cent of all optometrists. We requested details of the first 10 patients fitted with contact lenses after receipt of the questionnaire. Results:We received 224 completed questionnaires, detailing contact lens fits to 2,230 patients. The mean age of the patient group was 32.3 ± 12.9 years and 65 per cent of these were female. Sixty per cent of patients were existing wearers, the remainder being new fits. The data indicated that 94 per cent of new fits were with soft lenses, of which six per cent were for extended wear. For refits 83 per cent were soft lenses and 24 per cent were extended wear. It was clear that the lens of first choice was mid‐water‐content (52 per cent of all soft lens fits). Only nine per cent of all soft fits were for lenses which were not replaced on a planned basis. The majority of rigid lenses were prescribed using mid‐Dk materials (71 per cent). Analysis of solution prescribing indicates that multipurpose products were the most common regimens for planned replacement soft lenses. The percentage of hydrogen peroxide prescribed increased as lens replacement became less frequent. Conclusions:Non‐planned replacement lenses are now rarely prescribed to patients. Extended wear lenses and rigid lenses are prescribed more to existing contact lens wearers. The impact of multifocal lens designs on contact lens prescribing is very small, namely, five per cent of soft contact lenses and eight per cent of rigid lenses, despite 20 per cent of patients being over 45 years of age.

Proposed performance criteria for extended wear contact lenses

The introduction of silicone-hydrogel materials has changed expectations for the response to contact lenses used in extended wear. In keeping with this technology shift, we have re-evaluated the criteria by which practitioners judge the performance of extended wear lenses. Attendees at the 1999 Annual Clinical Conference of the British Contact Lens Association were surveyed. The proportion of respondents who considered it appropriate to fit selected patients with conventional, disposable and silicone-hydrogel soft lenses for extended wear was 63%, 67% and 86%, respectively. Only 11% of respondents did not fit extended wear because of personal experience with infectious keratitis, and over 50% relied on educators' advice in avoiding this practice. Fifteen per cent of practitioners reported fitting extended wear on occasions. Ninety-five per cent of respondents thought that the relative risk of infectious keratitis with daily wear compared with no lens wear should be ten or less, which was reduced to 60% when it was revealed that the current relative risk is estimated to be 60. A strong preference for a relative risk of infection with extended wear compared to daily wear of less than five times was indicated, which is consistent with current estimates. A minority of respondents were prepared to accept an overnight oedema level of over 6% with extended wear, although silicone-hydrogel materials have been shown to induce less than 4%. A wide variety of microcyst responses were considered reasonable, with many respondents accepting up to 40 per cornea; again, this result contrasted with early research data suggesting a level of 10 microcysts or less occurring with silicone-hydrogel materials. Interpretation of these findings has led us to the following proposals for safe extended wear: (i) extended wear fitting should preferably be done with silicone-hydrogel materials, rather than conventional hydrogels, where the available parameter ranges overlap; (ii) the relative risk of corneal infection with extended wear compared to daily wear should be two to five times, providing the relative risk of daily wear compared to the no lens wear'situation is reduced to 20 times, and (iii) extended wear lenses should produce an average of no more than 4% overnight oedema and no more than 10 microcysts per eye in the long term.

Extended-wear contact lenses, microbial keratitis, and public health

Extended-wear soft contact lenses (lenses worn continuously for more than 24 h and in many cases for 1–4 weeks) are being relaunched in several countries. This move follows a decade of their restriction by licensing authorities and by contact-lens practitioners because the incidence of microbial keratitis is greater with extended-wear than with daily-wear, soft hydrogel lenses.1,2 Why are extended-wear lenses being revisited and what might be the implications for public health?

The temporal correlation of elevated tear IgE levels with the onset of symptoms in patients wearing daily-wear and extended-wear contact lenses

Fourteen patients wearing a disposable contact lens as a daily-wear lens in one eye and as an extended-wear lens in the other eye had tear immunoglobulin (Ig)E levels measured at a baseline visit and at 13 follow-up visits over a 31-day period. Multivariate regression analyses were performed for tear IgE levels against numerous independent variables, including a history of allergies and the level and progression of various symptoms. Although there was a significantly higher level of symptoms in the extended-wear vs. the daily-wear eyes ( p = 0.05), no significant difference in tear IgE levels between the extended-wear and daily-wear eyes was observed. However, tear IgE levels were consistently higher in allergic patients vs. nonallergic patients ( p = 0.02), regardless of the wearing type. A simultaneous bilateral elevation in the tear IgE levels had a 100% correlation with patients reporting a positive history of environmental allergies. Periodic lag analysis revealed that increased symptoms in the extended-wear eyes correlated ( p = 0.003) with elevated tear IgE levels three periods (6.5 days) prior. This pilot study suggests a potential predictive value for tear IgE with regard to contact lens symptomatology. It also revealed a strong correlation between a history of allergies and elevated tear IgE in all types of contact lens wearers.

Immunoglobulin A antibodies against Pseudomonas aeruginosa in the tear fluid of contact lens wearers

Purpose. Pseudomonas aeruginosa is the most important cause of contact lens-associated ulcerative keratitis, especially for those who use extended-wear lenses. Until now, the presence of specific anti-P. aeruginosa immunoglobulin A (IgA) antibodies in the tears of contact lens wearers has not been investigated and is the purpose of the current study. Methods. The levels of specific IgA antibodies against P. aeruginosa and total secretory IgA (sIgA) concentrations were measured in tears of various groups of contact lens and non-contact lens wearers using enzyme-linked immunosorbent assays. Contact lens groups were divided into the following categories: daily-wear rigid gas-permeable lenses (n = 23), daily-wear soft lenses (n = 22), extended-wear soft lenses (n = 17), and non-contact lens wearers (n = 23). As a positive control group, we tested tears obtained from patients with cystic fibrosis (n = 5) because the respiratory tract of these persons often are colonized by P. aeruginosa. Results. The percentage of nonresponders (<15 U/ml) varied between 9% in daily-wear rigid gas-permeable contact lens users to 23% in daily-wear soft contact lens users. The percentage of nonresponders in controls was 13%. The frequency of nonresponders was not significantly different among the different groups tested. All patients with cystic fibrosis showed a very high anti-P. aeruginosa IgA response in their tears. When analyzing the mean anti-P. aeruginosa IgA response, a significandy lower level was found in extended-wear contact lens users (38 U/ml) compared to non-contact lens wearers (82 U/ml). Total s-IgA levels in die tears of the various groups tested were not significandy different. Conclusions. A substantial number of persons in the population of contact lens wearers tested lack detectable IgA antibodies against P. aeruginosa in their tears and may be susceptible to P. aeruginosa keratitis if die physiological condition of dieir cornea is compromised. Invest Ophthalmol Vis Sci. 1996; 37:2081-2088.

Trends in Contact Lens-Associated Corneal Ulcers

Charts of 320 patients with corneal ulcers seen on the Cornea Service of Wills Eye Hospital from July 1, 1992, to June 30, 1995, were reviewed retrospectively. Of these cases, 96 (30%) were associated with contact lens use. Ulcers in contact lens users accounted for 36% of cases in the last 6 months of 1992 and all of 1993, 20% of cases in 1994, and 29% in the first 6 months of 1995. The contact lenses most commonly associated with ulcers were disposable extended-wear lenses. They were used in 33% of contact lens-associated ulcers in 1992, 27% in 1993, 39% in 1994, and 44% in 1995. Pseudomonas was the predominant organism prior to 1993 (1-4). From 1993 to 1995, however, the number of Pseudomonas ulcers steadily decreased. Two or three Acanthamoeba infections continue to be treated each year. There has been a significant decrease in the number of contact lens-related ulcers treated at our institution compared with previous years (p < 0.01) (3, 4).

Biofilms in device-related infections

The use of various medical devices including indwelling vascular catheters, cardiac pacemakers, prosthetic heart valves, chronic ambulatory peritoneal dialysis catheters and prosthetic joints has greatly facilitated the management of serious medical and surgical illness. However, the successful development of synthetic materials and introduction of these artificial devices into various body systems has been accompanied by the ability of microorganism to adhere to these devices in the environment of biofilms that protect them from the activity of antimicrobial agents and from host defense mechanisms. A number of host, biomaterial and microbial factors are unique to the initiation, persistence and treatment failures of device-related infections. Intravascular catheters are the most common devices used in clinical practice and interactions associated with these devices are the leading cause of nosocomial bacteremias. The infections associated with these devices include insertion site infection, septic thrombophlebitis, septicemia, endocarditis and metastatic abscesses. Other important device-related infections include infections of vascular prostheses, intracardiac prostheses, total artificial hearts, indwelling urinary catheters, orthopedic prostheses, endotracheal tubes and extended wear lenses. The diagnosis and management of biofilm-associated infections remain difficult but critical issues. Appropriate antimicrobial therapy is often not effective in eradicating these infections and the removal of the device becomes necessary. Several improved diagnostic and therapeutic modalities have been reported in recent experimental studies. The clinical usefulness of these strategies remains to be determined.

Contact lens wear by hospital health care staff: is there cause for concern?

Microbial keratitis can occur in association with contact lens wear. The absolute risk of infection is low but may be enhanced as a consequence of increased exposure to potentially pathogenic microbes in a hospital setting. There is variation in risk depending on type of lens worn and its modality of use. Extended-wear lenses carry the greatest risk. Pseudomonas aeruginosa and Acanthamoeba are causes of potentially devastating ocular infections in contact lens wearers. The risk of these infections could be reduced by fastidious hygiene practice. Hydrogen peroxide disinfection is recommended when a storage case is included in the care regimen. This should be cleaned thoroughly and dried prior to disinfection and never exposed to tap water. Daily wear of one-day ‘disposable’ soft contact lenses or use of rigid gas permeable lenses is recommended for hospital staff. Contact lenses should be removed immediately and discarded or disinfected if the eye becomes contaminated and/or use of an eyewash is required.