The ARVO abstracts representing the work of innovators and researchers in the field of contact lenses this year appear to focus on: improved lens wettability and the attendant increased comfort; better elucidation of the safety of longer-term lens wear; and continued interest in the safety and effectiveness of cornea-shaping contact lenses as a refractive correction. Here are some studies that reflect those efforts.
Improved Wetting
Silicone hydrogel lens materials display different wettabilities depending on the type of surface modification technology and preconditioning solution. Alcon-affiliated researchers measured advancing contact angles in vitro as an indicator of silicone hydrogel lens wettability in the presence of artificial tear solutions, and studied lysozyme, albumin and mucin for their effect on the wettability of Acuvue Advance (AA), Focus N&D and O2 Optix lenses presoaked in three commercial multipurpose solutions, Opti-Free Express, ReNu MoistureLoc, AQuify used according to the manufacturers' listed regimen, and an investigational MPS.
Mucin and lysozyme had no effect on the contact angles of the lenses; albumin played an important role when lenses were preconditioned with particular surfactants. The effect of preconditioning the lenses in MPS showed different effects on the material wettabilities, possibly a reflection of the different polymers and surfactants in the marketed products and their interactions with the lens materials.906
Bausch & Lomb's ReNu with MoistureLoc may decrease the level of lost water in lenses worn by contact lens dry-eye subjects. Workers at B&L assessed whether changes in water content can be demonstrated in dry-eye subjects after wearing Acuvue 2 lenses soaked in B&L's ReNu with MoistureLoc, Alcon's Opti-Free Express, CIBA's AQuify, or AMO's Complete Moisture Plus multi-purpose solutions.
They enrolled 18, 20, and 20 dry-eye habitual soft spherical contact lens wearers all with a computer-based visual analog dryness score of 60 or less on a 100-point scale. Lenses were pre-treated in the four solutions in pre-treated lens cases. Each subject wore a test ReNu/ Acuvue 2 lens and a control solution/ Acuvue 2 lens on contralateral eyes for approximately an hour. Lenses were removed, weighed on an analytical balance, stored overnight under pressure at ambient temperature, and subsequently re-weighed.
In each of three studies, the test lenses exhibited statistically less mean relative percentage total water loss compared to the control lenses. The ReNu-soaked test lenses lost: 5.4 percent of their total water content vs. 7.6 percent lost by the Alcon Opti-Free Express soaked control lenses; 5.1 percent vs. 6.6 by the CIBA AQuify-soaked control lenses; and 5.7 percent vs. 6.8 percent for the AMO Complete Moisture Plus- soaked control lenses.922
Significant corneal staining can occur with certain lenses when used with certain multipurpose solutions, but this staining does not appear to influence comfort levels, an Alcon study finds. Even patients who experience good lens comfort should have a comprehensive slit-lamp examination to evaluate corneal staining. This is particularly relevant after two hours of lens wear.
| Several ARVO studies measured incidence of infiltrates, by lens type and mode of wear. |
Corneal staining occurred most frequently and at the greatest severity with RNU, and least with OFX. At all follow-up visits, COM and RNU showed more staining than OFX. Staining varied from a low-grade, micropunctate pattern to clinically significant diffuse staining requiring cessation of lens wear. Subjective comfort ratings decreased significantly from beginning to end of the day with no significant differences between the three regimens. There was no significant correlation between corneal staining and comfort at any time of the day.917
Materials and Ocular Health
Local contact lens-associated papillary conjunctivitis is more frequent in silicone hydrogel contact wear than in low-Dk lens wear, says another group at the University of New South Wales. At least 60 percent of eyes will have a recurrence of a CLPC event with silicone hydrogel extended wear.
In 10-year retrospective clinical trials in Australia and India, 1,894 subjects wore either low-Dk hydrogel lenses on a six-night schedule, or silicone hydrogel lenses on either a six- or 30-night EW schedule. The incidence of CLPC per 100 eye years (percent) for each lens type was determined for first events only, with CLPC classified by location of papillae. Papillae confined to less than two areas of the tarsal conjunctiva were classified as local, those spread over more than two areas, general.
The incidence of CLPC in low-Dk lens wearers was 3.9 per 100 eye years (r=2.9 to 5.0) and in silicone hydrogel lens wearers 5.2 per 100 eye years (r=4.3 to 6.2). There was a significantly greater incidence of local CLPC events (3.6 percent) compared to general events (0.7 percent in silicone hydrogel lenses), and a significantly greater incidence of general CLPC in low-Dk hydrogel lenses (3.4 percent) compared to local CLPC events (1.7 percent). Of all eyes, 63 percent had a recurrence of CLPC; 28 percent of eyes with prior CLPC events recurred as a general event, and 49 percent of eyes recurred as a local event with silicone hydrogel lens wear.2064
High-Dk silicone hydrogel lenses have been shown to significantly decrease the risk of hypoxic complications compared to traditional low-Dk hydrogels. A meta-analysis at Cleveland's Case Western Reserve University shows, however, that although silicone hydrogel lenses have the same overall risk for corneal infiltrates as hydrogel lenses, there is a greater risk for CLPC with silicone lenses.
The analysis reviewed 22 studies published or presented by November 2004 comprising 6,343 subjects and 12,139 eyes; 19 were prospective studies, and of these, 89 percent randomly assigned lenses. Follow-up ranged from four to 36 months, median=12 months. Infiltrates were defined as any occurrence of CLPU, CLARE, or IK, or as defined by a given study.
The probability of an event per 100 eyes in the traditional hydrogel group was 4.34 (r=2.68 to 6.94) for infiltrates and 2.24 (r=1.27 to 3.81) for CLPC. The pooled estimates of the occurrence of infiltrates were not significantly different for silicone hydrogel compared to hydrogel. There was an increased risk of CLPC in the silicone hydrogel group.2067
Wearers who sleep in contact lenses have a significantly higher incidence of severe keratitis, says a study in the United Kingdom and Australia. Silicone hydrogel lenses carry a five times lower risk of severe keratitis for extended wear compared with hydrogel lenses. Overall, morbidity (visual loss) is low. The study identified significant risk factors, though they are of little predictive value.
The 12-month, prospective, hospital-based epidemiological study scored the clinical severity of each presenting case of contact lens-associated keratitis, and documented the size and location of corneal infiltrates. The hospital catchment population, and the wearing modalities and lens types being used, were estimated from relevant demographic and market data.
Over 12 months, there were 38 cases of severe keratitis (SK, or microbial keratitis) and 80 cases of non-severe keratitis (NSK). The annual incidence (per 10,000 wearers) among contact lens wearers was 21.3 (17.8 to 25.5) for all forms of keratitis, 6.9 (5.0 to 9.4) for SK and 14.4 (11.6 to 18.0) for NSK. The incidence of SK stratified for wearing modality and lens type appears in Table 1. Corneal scrapes in 23 cases of SK found 43 percent were culture-positive, with P. aeruginosa the main pathogen in 30 percent of cases. More infiltrates occur in the peripheral cornea with DW hydrogel lenses, in the central cornea with DW hydrogel daily disposable lenses, and in the superior cornea with EW silicone hydrogel lenses. Peripheral infiltrates are less clinically severe. No patients suffered significant visual loss. Significant risk factors besides lens type/ modality were: gender; smoking; relevant eye and health problems; and season.927
|
Table 1. Incidence of Keratitis |
|
Lens Type |
Severe Keratitis |
Range Per 10,00 |
|
Daily wear rigid |
2.9 |
(0.8 to 10.4) |
|
DW hydrogel daily disposable |
4.9 |
(2.5 to 9.6) |
| DW hydrogel (excl. daily disposable |
6.4 |
(4.1 to 9.9) |
| DW silicone hydrogel |
0.0 |
(0.0 to 210.1) |
| Extended wear rigid |
0.0 |
(0.0 to 1,759) |
| EW hydrogel |
96.4 |
(37.5 to 245.2) |
| DW silicone hydrogel |
19.8 |
(6.7 to 58) |
Continuous wear may change the surface properties of silicone hydrogel lenses. Bacteria, except S. aureus, adhered in lower numbers and less tenaciously to worn lenses, based on work done at the University of Groningen, the Netherlands. Volunteers wore two pairs of either lotrafilcon A or balafilcon A silicone hydrogel lenses. The first pair was worn continuously for a week, the second for four weeks. One lens out of each pair was used for surface characterization, the other one for bacterial adhesion experiments. Lens surfaces were characterized by examination of their wettabililty, roughness and elemental composition. Adhesion of the hydrophilic Staphylococcus aureus 835 and hydrophobic P. aeruginosa #3 bacterial strains to a lens was studied using a parallel plate flow chamber.
Before use, the lotrafilcon A lens was rougher, was more wettable and had a higher susceptibility for S. aureus adhesion than the balafilcon A lens. After wear, both lens types became more and equally wettable, while differences in elemental surface composition decreased. S. aureus adhered more on worn balafilcon A lenses, while the opposite was seen for P. aeruginosa. The initial deposition rates of both bacteria to lotrafilcon A lenses decreased by wearing and were found to correlate with the surface roughness of worn lenses.930
In a similar study at U.K's Glasgow Caledonian University, Acanthamoeba showed a significantly higher affinity for worn second-generation silicone hydrogel lenses compared with unworn lenses, so patient wear may be considered a risk factor for this infection. However, as attachment to the worn second generation silicone hydrogels was similar to that of a worn conventional hydrogel, this new lens is at no more risk of promoting infection with Acanthamoeba than a conventional hydrogel.931
A CIBA-supported study assessed the one-year retention and disposition of wearers prescribed 30-night continuous wear of lotrafilcon A (Focus Night & Day, CIBA) lenses.
Of the enrolled cohort, 5,903 (94.5 percent) wearers completed final exit questionnaires and only 342 (5.5 percent) were lost to follow-up; 4,995 wearers (80 percent) completed the one-year period wearing lenses, and 908 (14.5 percent) discontinued wear of the study lenses. Of the reported events, 167 (2.7 percent) corneal infiltrates of varying severity have been confirmed in 158 wearers (2.5 percent).
At the 12-month survey 79.3 percent of wearers reported overnight wear of lenses for >21 nights in a row; 9.3 percent wore them one to two weeks in a row; 7.6 percent for one to six nights and 3.2 percent for daily wear only. This study suggests that patients adapt well to silicone hydrogel extended wear and stay with this mode of lens wear.2068
CRT
Various papers continue to show the effort to establish the safety of corneal reshaping, and measure and quantify the visual results.
A group at Germany's University of Tuebingen and University of Heidelberg pronounces overnight orthokeratology a very safe method for temporarily eliminating minor myopia. They evaluated Ortho-K for the treatment of myopia, as well as possible pathologic corneal alterations and changes in intraocular pressure.
Both eyes of 20 volunteers (mean age, 25.92 ±5.86) were fitted with Ortho-K lenses; the researchers recorded uncorrected visual acuity, refractive correction, corneal curvature and corneal changes, including measurements of corneal endothelial alterations. Six volunteers who wore glasses were controls. Both groups were free of eye disease or any pathological symptoms.
Before fitting the Ortho-K lenses, the wearing group had a mean spherical correction (OD/OS) of -2.06/-2.25 ±0.90/0.84 D, a mean uncorrected vision of 0.64 ±0.31 (LogMAR) and a mean central corneal radius of 7.78/7.77 ±0.31/0.30 mm. After one week of wearing contact lenses the majority had such a good response that no statistical difference in visual acuity between the two groups was detectable (the mean spherical correction was +0.14/-0.02 ±0.25/0.14 D; the mean uncorrected vision was -0.12 ±0.06; and the mean central corneal radius was 8.09/8.08 ±0.35/0.34 mm). Corneal irritations that occurred at the beginning of the study in the wearing group included corneal staining (40 percent, Grading scale 1.1), acute corneal edema (10 percent), and microcysts (5 percent). Problems with halos were frequently noticed (90 percent), but the wearers got accustomed to that. The study had a mean observation period of eight months. At that time no corneal edema was observed, and no corneal endothelial alterations, infectious corneal complications or IOP changes had occurred. Five volunteers discontinued the study from the wearing group.2054
Investigators at the University of New South Wales, Sydney, Australia, report that the use of high-Dk materials for overnight orthokeratology not only provides physiological advantages, but may also optimize clinical outcomes. The reason: High levels of overnight corneal edema appear to limit the clinical effects of overnight reverse-geometry lens wear, at least in the short term.
They fit 12 adult subjects (age 20 to 25) with reverse-geometry lenses for orthokeratology in both eyes. Subjects wore matched design lenses in Boston ES (nominal Dk/t=8) and Boston XO materials (nominal Dk/t=45) in the two eyes for eight hours overnight. A separate overnight trial was conducted to examine corneal changes in the absence of lens wear in the contralateral eye. The researchers measured LogMAR visual acuity, apical corneal radius and corneal eccentricity before and immediately after overnight lens wear, and monitored the overnight corneal edema response using optical pachymetry. Overnight central corneal edema averaged 11.5 ±5.8 percent in the ES-wearing and 3.3 ±3.7 percent in the XO lens-wearing eyes, respectively, compared to 2.4 ±2.1 percent with no lens wear. Despite the matched reverse-geometry lens designs, changes in unaided visual acuity and corneal topography were much less evident in the ES lens-wearing eyes compared to those wearing the XO material. No significant differences in clinical outcomes were found between ES lenses and no lens wear.2056
Dr. Key is in private practice and serves as the managing partner of Medical Center Ophthalmology LLP. He is a clinical professor of ophthalmology at the Baylor College of Medicine.
*Reference numbers noted as footnotes correspond to the abstract numbers in the 2005 ARVO program.
