high-Dk Lenses Research Articles

Evaluation of the effect of the sagittal height of soft contact lenses on corneal topography after 4 h and 8 h of wear

Purpose To evaluate modifications of corneal topography following four and eight hours wear of high DK lenses.

Evaluation of the effect of the sagittal height of soft contact lenses on corneal topography after 4 h and 8 h of wear

Purpose To evaluate modifications of corneal topography following four and eight hours wear of high DK lenses.

Corneal thickness after overnight wear of an intraocular pressure fluctuation contact lens sensor

To assess the effect of overnight wear of a contact lens-based sensor (CLS) for monitoring of 24-hr intraocular pressure (IOP) fluctuations on central corneal thickness (CCT). Changes in the CCT, mid-peripheral corneal thickness and central corneal radius (CCR) during overnight CLS wear in 20 eligible patients with ocular hypertension or established glaucoma were prospectively studied using ultrasound pachymetry and topography. Corneal thickness and CCR changes were evaluated from pre-to-postsleep, with the fellow eye as control. Paired t-test or Wilcoxon signed-rank test was used as appropriate and with α = 0.05. Relationship between the IOP profile recorded by the CLS and the pre-to-postsleep corneal thickness differences was assessed using the Spearman correlation coefficient. After CLS wear, mean CCT had changed from 523 to 537 μm (p = 0.015) in the study eye and from 518 to 522 (p = 0.206) in the fellow eye (n = 15). There was no difference in CCT change between eyes (p = 0.075). There were no statistically significant changes in horizontal or vertical CCR in either eye (p > 0.05 for all). No correlation was found between the pre-to-postsleep differences in the CLS signal and the pre-to-postsleep differences in ultrasound CCT measurements (p = 0.974). The continuous IOP monitoring does not appear to be affected by differences in corneal thickness that occur during overnight CLS wear, although the CLS did induce some corneal swelling. This effect was not statistically significantly different from the control eye and does not seem to influence the CLS IOP profile.

Corneal Erosions, Bacterial Contamination of Contact Lenses, and Microbial Keratitis

To estimate the rate of corneal erosion coupled with gram-negative bacterial contamination of contact lenses and compare this with the rate of microbial keratitis (MK) with contact lenses. The rate of corneal erosion and contact lens contamination by gram-negative bacteria were calculated from several prospective trials. These rates were used to calculate the theoretical rate of corneal erosion happening at the same time as wearing a contact lens contaminated with gram-negative bacteria. This theoretical rate was then compared with the rates of MK reported in various epidemiological and clinical trials. Corneal erosions were more frequent during extended wear (0.6-2.6% of visits) compared with daily wear (0.01-0.05% of visits). No corneal erosions were observed for lenses worn on a daily disposable basis. Contamination rates for lenses worn on a daily disposable basis were the lowest (2.4%), whereas they were the highest for low Dk lenses worn on an extended wear basis (7.1%). The estimated rate of corneal erosions occurring at the same time as wearing lenses contaminated with gram-negative bacteria was the lowest during daily wear of low Dk lenses (1.56/10,000 [95% CI: 0.23-10.57]) and the highest during extended wear of high Dk lenses (38.55/10,000 [95% CI: 24.77-60.04]). These rates were similar in magnitude to the rates reported for MK of different hydrogel lenses worn on differing wear schedules. The coincidence of corneal erosions during lens wear with gram-negative bacterial contamination of lenses may account for the relative incidence of MK during lens wear with different lens materials and modes of use.

Lipophilic versus hydrodynamic modes of uptake and release by contact lenses of active entities used in multipurpose solutions

To determine if the silicone-type components of new high Dk lens materials contribute significantly to uptake and/or release of two common antimicrobial agents, myristamidopropyl dimethylamine (Aldox) and poly[hexamethylene biguanide hydrochloride] (PHMB), found in multipurpose solutions. Five commercial contact lenses were cycled in lens cases in a PHMB- and an Aldox-containing MPS. Single-cycle soaks (6, 16 or 64h) and multi-cycle soaks (6, 16, 142 and 48h) were used to assess kinetics and saturation effects of uptake. Lens capacity for uptake of each entity was determined using a semi-saturation model. Release kinetics was assessed for these semi-saturated lenses (100-mL MPS-soaked) in 2mL of a tear mimic fluid. Lenses that exhibited low uptake in a single cycle (with 3mL of MPS) became saturated within approximately 3 cycles. PHMB uptake was highest with non-silicone hydrogel (non-SiHy) and/or ionic lenses (approximately 70% depletion in 16h). PHMB uptake by non-ionic SiHy lenses was low (<40% depletion in a single 3-mL soak of 64h). Aldox uptake was highest for all SiHy lenses (approximately 80% depletion in 16h). PHMB uptake capacity was highest by ionic and non-SiHy lenses, while Aldox uptake capacity was much higher with all SiHy lenses than with any non-SiHy lens. The slower desorption of PHMB (t(1/2)= approximately 120min) compared to Aldox (t(1/2)= approximately 20min) may partially explain observed higher staining after 2-4h with PHMB products used with some lenses, whereas any clinical effects from Aldox would be expected to manifest soon after insertion.

Investigation of posterior corneal curvature in CL-induced corneal swelling

To evaluate Orbscan II measurements without contact lens (CL) removal to monitor in vivo posterior corneal curvature in CL (hypoxia)-induced corneal swelling during extended wear (EW). Orbscan II corneal topographer was used to measure posterior corneal curvature 1 week before CL wearing and during 1 week of EW. Central corneal thickness (CCT) was also measured during the 2-week study with OCT to determine the corneal swelling percentage. High Dk (lotrafilcon A) and low Dk (etafilcon A) soft CL were randomly fitted in EW in the right and left eyes of 20 subjects with normal ocular health. Orbscan and OCT were also performed without CL removal after 3 and 7 days of wear. Low Dk lenses induced significantly higher corneal swelling (2.41+/-2.65%), as compared to the high Dk lenses (0.17+/-2.28%; P<0.05 repeated measures ANOVA (Re-ANOVA and paired t-test) measures with OCT. The low Dk lens induced a significantly posterior corneal flattening compared to the high Dk lens (0.036+/-0.06mm versus 0.006+/-0.04mm; P<0.05 Re-ANOVA and paired t-test). High repeatability for Orbscan-measured posterior best fit sphere (BFS) radii with (r(2)=0.15, 95% limits of agreement (LoA)=0.10 to -0.06) and without (r(2)=0.00, 95% LoA=0.08 to -0.08) CL removal was also observed and suggest that posterior corneal changes was not due to Orbscan variability. Orbscan is a non-invasive and reproducible technique to evaluate and monitoring posterior corneal curvature in vivo in CL (hypoxia)-induced corneal swelling during EW.

Rat Silicone Hydrogel Contact Lens Model: Effects of High- Versus Low-Dk Lens Wear

This study used a rat contact lens (CL) model to test if high- versus low-Dk lens wear caused changes in (1) conjunctival Langerhans cell (LC) number or location; (2) Bcl-2 expression; and (3) infection risk. Female, Lewis rats wore a high- or low-Dk CL continuously for 2 weeks. Afterward, corneas were harvested and processed for ADPase activity to identify LCs, for immunostaining and for real time-polymerase chain reaction. Contact lens-wearing rats also were challenged with Pseudomonas aeruginosa by placing a bacterial-soaked CL on the eye followed by topical delivery of bacteria. After 48 hrs, slit lamp examination and real time-polymerase chain reaction were used to evaluate the corneal response. Conjunctival LC were significantly increased after low- versus high-Dk CL wear (P<0.0001). In contrast, conjunctival LC in non-lens wearing rats was not significantly different from the high-Dk lens wearing group. Bcl-2 mRNA levels were significantly decreased in low- versus high-Dk CL wearing rats, while Bax, FasL, caspase 3, and caspase 9 levels were unchanged. Immunostaining for Bcl-2 showed fewer positively stained epithelial cells in the low- versus high-Dk lens wearing group. After bacterial challenge, 30% of low- versus none of the high-Dk CL wearing corneas became infected and showed increased mRNA levels for several proinflammatory cytokines/chemokines, inducible nitric oxide synthase and matrix metalloproteinase-9. Low- versus high-Dk or non-CL wear led to an increased number of conjunctival LC, decreased Bcl-2 levels, and increased the risk of bacterial infection.

The effect of long-term wear of soft lenses of low and high oxygen transmissibility on the corneal epithelium

To measure the effects of long-term wear of soft lenses of low and high oxygen transmissibility (Dk) on basal epithelial appearance and epithelial thickness. Sixty-three subjects were enrolled in a cross-sectional study. Seventeen high Dk lens wearers and 24 low Dk lens wearers who had worn lenses on an extended wear basis for more than 3 years (range: 3-22) were compared to a group of 22 age-matched subjects who had never worn contact lenses. Cell regularity and the intensity of light backscattered by the basal epithelium were assessed using confocal microscopy. Epithelial thickness was measured at the centre and at four peripheral locations using modified optical pachometry. Epithelial basal cells appeared less regular in low Dk lens wearers than high Dk wearers or controls (Mann-Whitney U-test, P=0.001). The intensity of backscattered light did not differ across groups (Kruskal-Wallis test, P=0.37). Low Dk wearers had the thinnest epithelium (46 (10) microm), followed by high Dk wearers (54 (14) microm) and controls (58 (9) microm; ANOVA, P<or=0.006). Topographical position did not affect epithelial thickness (ANOVA, P=0.10). Visible alterations to the basal epithelial cells can only be detected in long-term extended wearers of low Dk soft lenses. Extended wear of high Dk soft lenses results in topographically uniform epithelial thinning that is significantly less than the thinning seen with low Dk lenses. Confirmation of these findings using groups with evenly matched duration of lens wear is required.

Rigid Gas-Permeable Contact Lens Base Curve Radius and Transmissibility Effects on Corneal Oxygen Uptake

The purpose of this study is to determine the effects of rigid gas-permeable contact lens thickness, base curve radius, and material permeability on corneal hypoxic stress. Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the right eye of 10 human subjects for the normal open eye (air) and after 5 minutes of static wear of rigid contact lenses of four cornea-to-contact lens base curve fitting relationships: 0.2 mm steeper-than-K (STK), 0.1 mm STK, on K, and 0.1 mm flatter-than-K (FTK). There were also four materials (polymethylmethacrylate [Dk=0], lotifocon B [OP-2, Dk=15.9], lotifocon A [OP-3, Dk=30], lotifocon C [OP-6; Dk=60]) and three center thicknesses (0.14, 0.28, and 0.53 mm for the OP-6 lenses and 0.14 mm for all other materials) with all other parameters being constant. Each subject participated in two identical sessions. A repeated-measures analysis of variance was performed to compare the mean response across lens materials/thicknesses and the four curvature values. Significant differences were found only for lens material/thickness (p<0.0001). Although OP-2 and OP-6 (0.53 mm) were manufactured to have the same Dk/t, post hoc comparisons showed that the oxygen uptake rate with OP-6 (0.53 mm) was significantly lower. The same is also true for OP-3 and OP-6 (0.28 mm), with OP-6 (0.28 mm) having a significantly lower oxygen uptake rate. In contrast to past studies with PMMA, cornea-to-contact lens base curve fitting relationship, with the lens materials and designs studied here, did not affect corneal hypoxic stress, and thick, high Dk lenses resulted in less change in corneal response than did thin, lower Dk lenses of the same Dk/t. This is attributed to the lens reservoir effect that has been previously described.

Corneal hypoxia secondary to contact lenses: the effect of high-Dk lenses

Contact lenses made from materials of low-oxygen permeability (Dk) do not meet the oxygen requirements of the cornea for overnight wear. Long-term extended wear of these lenses results in chronic changes to all layers of the cornea, many of which are associated with hypoxia. High-Dk silicone hydrogel and gas permeable lenses are now available for 30-night continuous wear. The high-oxygen transmissibilities of these lenses have enabled the development of a successful continuous wear modality by eliminating the hypoxic effects of long-term wear. Presently, the focus is on improving lens performance by developing lenses that are more biocompatible, provide greater comfort, and maintain a stable tear film without inflammatory or mechanically induced adverse events.

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.

The evolution in therapeutic contact lenses.

Therapeutic soft contact lenses were first approved in the 1970s, but the variety of available materials and parameters continues to evolve. Currently, the armamentarium of therapeutic contact lenses allows the clinician to select lenses that not only protect the corneal surface but also assist in modulation of the healing process. This article summarizes the available contact lenses, the conditions most amenable to treatment, and the decision-making process that allows optimal selection of a therapeutic contact lens for a specific patient. Many of the hydrophilic soft contact lenses used for cosmetic correction are not approved for therapeutic use but have been used in an off-label manner as therapeutic lenses. Communicating with the patient is important when recommending the use of a therapeutic contact lens, explaining the goals of therapy, warning about the risks contingent upon contact lens use, and determining whether the lens is being used in an off-label fashion. The advances in contact lens technology have opened new options for use of therapeutic contact lenses. With a new generation of high-Dk lenses whose makers promise fewer limiting problems of vascularization and infection, the utility of the older, traditional therapeutic lenses can be enhanced and the more selective application of individual lenses can be permitted. By considering the healing objectives of the particular treatment plan for a specific patient, greater control of the endpoint and timeframe of therapy is now possible.

The ocular response to extended wear of a high Dk silicone hydrogel contact lens

Purpose: A four‐month extended wear clinical trial was conducted to compare die ocular effects of a high Dk Balafilcon A silicone hydrogel lens and a low Dk HEMA 38.6 per cent H2O soft lens. Method: Twenty‐four subjects who were adapted to daily wear of soft lenses wore a high Dk lens in one eye and a low Dk HEMA lens in the other eye for four months on an extended wear basis after one week of daily wear. Thirteen progress evaluations were conducted using standard clinical procedures. Results: Eighteen subjects (75 per cent) completed the study. The high Dk lens induced significantly less bulbar and limbal injection and corneal vascularisation dian the low Dk HEMA lens (p < 0.05). Epithelial microcysts were observed only in the eyes wearing the low Dk lens. A significant increase in myopia was found in die eyes wearing die low Dk HEMA lens (mean = 0.50 D, p < 0.01) compared to die insignificant myopic increase of 0.06 D in the eyes wearing the high Dk lens. Three subjects developed small infiltrates in the high Dk lens wearing eyes and significantly more post‐lens debris was observed under the high Dk lens. Six subjects developed papillary conjunctivitis in die eye wearing silicone hydrogel lenses but only two of those were discontinued from the study. Conclusion: No hypoxia‐related effects were observed with extended wear of the high Dk Balafilcon A silicone hydrogel lens.

Comparison of changes in corneal thickness under low Dk and high Dk rigid contact lenses

In a randomised study, the relation between corneal thickness changes and Dk value of rigid gas permeable contact lenses was investigated in 10 volunteers. Each volunteer was fitted with lenses of different Dk values in each eye. A low Dk lens ( Dk15) was fitted on one eye of each subject and a high Dk lens ( Dk125) on the contralateral eye. After 2 months the reverse was done. After another 2 months, the lenses were again exchanged for the first pair. After each change corneal thickness was measured. A non-significant trend in corneal thickness was found in 13 of the 20 eyes. We conclude that for daily wear use the lower Dk materials meet corneal requirement.

The patient's first impressions of high-Dk RGP lenses

The patient's first impressions of high-Dk RGP lenses

Corneal endothelial cell morphology under permanent wear of rigid contact lenses

The influence of the permanent wear of rigid high Dk-lenses (nominal Dk 71 or 92) with elliptical geometry on the corneal endothelium was assessed. For this purpose the endothelium of 16 patients was compared by specular microscopy before and after the permanent wear. The wearing time of the lenses varied between 7 and 24 months. Computerized morphometric analysis of the photographs revealed that the variability in cell size (polymegathism) and in cell shape (pleomorphism) did not change during the wearing period. It is suggested that this is due to the high gas-permeability and the elliptical geometry of the contact lenses.

Clinical evaluation of various contact lenses from the incidence of complications

The case histories of 87,765 patients (173,891 eyes) were examined to learn the actual state of complications with ocular pain, caused by wearing different types of contact lenses. The incidence of complications for each particular type of contact lens was 4.9% for PMMA lenses, 2.2% for LOW Dk lenses, 0.9% for HIGH Dk lenses and 3.3% for HEMA lenses. The incidence of emergency cases was also in the same order: 1.30%, 0.33%, 0.16% and 0.47%, respectively. In the group of hard type lenses, the results corresponded well to the level of oxygen tension on the cornea under each contact lens. In addition to ocular pain, epiphora was next most common subjective complaint for PMMA lenses and injection was for the other lenses. Complications caused by the HEMA lenses required significantly longer periods for healing than those caused by hard type lenses.