Test Lens Research Articles

An evaluation of 1-day disposable contact lens wear in a population of allergy sufferers

Purpose: This was a multi-site, 128-subject, bilateral crossover study to evaluate subjective comfort and slit-lamp findings with 1-day disposable contact lenses in a population of allergy sufferers during periods when allergen levels were elevated. Methods: The study involved 1-month of single-use daily wear with a 1-day disposable test lens ( 1· DAY ACUVUE ® Brand Contact Lenses, Johnson & Johnson Vision Care) and 1-month of daily wear with subjects’ habitual lenses replaced to their usual replacement schedule. Pollen and mould counts were obtained for each site 1 week prior to the study and twice weekly throughout the study period. Subjective comfort and slit-lamp findings were recorded at baseline and after 1-month’s wear of each modality. Results: Sixty-seven percent of subjects agreed that the 1-day disposable lenses provided improved comfort when compared to the lenses they wore prior to the study, compared with 18% agreeing that the new pair of habitual lenses provided improved comfort. The 1-day disposable lenses showed greater improvement in slit-lamp findings from baseline than new habitual lenses. Conclusion: The use of 1-day disposable lenses is an effective strategy for managing allergy-suffering contact lens wearers.

Surface treatment or material characteristic: the reason for the high level of Acanthamoeba attachment to silicone hydrogel contact lenses.

To determine the reason for the high level of attachment of Acanthamebic to silicone hydrogel (SH) contact lenses. The effect surface treatment has on attachment is determined using silicone elastomer (SE) lenses. All test lenses were unworn. SH (PureVision), conventional hydrogel (Acuvue), treated SE (Silsoft), and untreated SE (Silsoft) lens quarters were incubated for 90 min with plate-cultured Acanthamoeba castellanii trophozoites. After incubation and rinsing, the trophozoites attached to one surface of each quarter were counted by direct light microscopy. Sixteen replicates were performed for each lens type. Logarithmic transformation of data allowed the use of parametric analysis of variance. Lens polymer had a significant effect on attachment (P<0.001), with higher numbers of trophozoites attaching to the SH and SE (treated and untreated) lenses as compared with the conventional hydrogel. No significant difference in attachment was detected between the SH and SE (treated and untreated) lenses. Acanthamoeba attachment to the SH lens was significantly greater than to the conventional hydrogel. The similarity in attachment to surface-treated and non-surface-treated SE lenses suggests that the increased attachment found with the SH lens may be an inherent characteristic of the polymer rather than an effect of the surface treatment procedure. It is possible that SH lenses are at greater risk of promoting Acanthamoeba infection if exposed to the organism because of the enhanced attachment characteristic of this new material.

Limitations of the Shack–Hartmann sensor for testing optical aspherics

Aspheric lenses and surfaces are increasingly used in modern high-quality optics. Therefore, new measuring methods for an accurate quantification of these aspheres are also necessary. The current approach to quantify aspheres is to apply null systems such as computer-generated holograms as a part of a null lens in a interferometer. An alternative to this method is the Shack–Hartmann wavefront sensor. The dynamic range of this sensor can be adjusted by the optical parameters of the applied microlens array. Hence, large wavefront aberrations can be measured directly without a null lens. However, there are basic limitations in the dynamic range of a Shack–Hartmann sensor (SHS) depending on the curvature of the incident wavefront. In this paper, an analytical expression to determine the strongest wavefront curvature which can be measured with a defined microlens array of an SHS is derived. It allows to calculate the microlens parameters required to measure the wavefront of a test lens. Particularly, the influence of rotational symmetric aspherical wavefront shapes to the dynamic range of an SHS has been studied. A comparison between interferometry and the SHS has been accomplished. Numerical solutions using scalar diffraction theory illustrate the analytical predictions.

Effect of eyelid closure and overnight contact lens wear on viability of surface epithelial cells in rabbit cornea.

To determine the effects of open, closed eye, and overnight contact lens wear on homeostatic epithelial surface cell death in the rabbit cornea. One eye of each rabbit was either closed by eyelid suture or fitted with one of the following test contact lenses: (1) low Dk/t rigid gas permeable (RGP) lens, (2) hyper Dk/t RGP lens, (3) hyper Dk/t soft lens. The other eye served as a control. After 24 hours, whole corneas were carefully excised and immediately stained with a calcein-acetoxymethyl ester-ethidium homodimer viability assay to quantify the number of nonviable surface epithelial cells. In addition, exfoliated corneal epithelial cells were collected with an eye irrigation chamber to determine cell viability. In the normal cornea, open-eye conditions showed significantly more nonviable surface cells in the central cornea than in the periphery (p < 0.05). Overnight wear of all test lenses and eyelid closure induced significant decreases in the number of nonviable cells on the central corneal surface compared with controls (p < 0.05). All exfoliated corneal epithelial cells collected by eye irrigation were nonviable. In the rabbit model, overnight contact lens wear significantly downregulated spontaneous epithelial surface cell death independent of lens rigidity or material oxygen transmissibility. These effects were similar to eyelid closure without lens wear. Taken together, these results suggest that eyelid closure and the physical presence of the contact lens may protect against the shear stress forces exerted by eyelid blinking, which are believed to cause central surface cell death and subsequent exfoliation.

Adaptive effects of 30-night wear of hyper-O 2 transmissible contact lenses on bacterial binding and corneal epithelium : A 1-year clinical trial

Objective To determine effects of lens type and oxygen transmissibility on human corneal epithelium during extended wear (EW). Design Prospective, randomized, double-masked, single-center, parallel treatment groups, 1-year clinical trial. Participants One hundred seventy-eight patients completed the study: (1) high-O 2 soft lens (6-night [N] EW) (n = 27); (2) hyper-O 2 soft lens (6N-EW, n = 33) or (30N-EW, n = 66); and (3) hyper-O 2 rigid gas-permeable lens (RGP) (30N-EW, n = 52). Intervention Irrigation chamber to collect exfoliated corneal surface cells, confocal microscopy, and tear collection at baseline, 1, 3, 6, 9, 12 months of EW. Main outcome measures (1) Pseudomonas aeruginosa (PA) binding to exfoliated corneal surface cells; (2) central epithelial thickness; (3) superficial epithelial cell area; (4) epithelial surface cell exfoliation; and (5) tear lactate dehydrogenase. Results Quantitative evidence demonstrated increased binding of PA to human exfoliated corneal epithelial cells during the first 3 months of soft lens EW; the control high-O 2 test lens showed significantly higher bacterial binding ( P < 0.05). Binding activity gradually decreased thereafter and returned to baseline after 9 and 12 months. The corneal epithelium demonstrated enlargement of surface cell size, thinning of central epithelium, and a significant decrease in surface cell shedding ( P < 0.05). Remarkably, there was subsequent partial adaptive recovery in cell shedding and epithelial thickness but not surface cell size. There was no significant difference between 6N and 30N continuous wear of the hyper-O 2 soft lens for all outcome measures. Importantly, hyper-O 2 RGP lens wear did not show significantly increased PA binding during 1 year. Conclusions This study establishes three important new findings: (1) hyper-O 2 soft lens EW produces significantly less PA binding than the lower O 2 soft lens with no significant difference in PA binding with 6N versus 30N EW of the hyper-O 2 soft lens; (2) there is a remarkable adaptive recovery after 6 months with all soft lens wear with gradual return to prelens PA binding levels and partial recovery of other outcome measures for all test lenses EW except surface cell size; (3) 30N EW of the hyper-O 2 RGP lens produced no significant increases in PA binding over 1 year. Taken together, these results suggest that introduction of new hyper-O 2 transmissible lens materials into clinical use may offer safer EW, and future epidemiologic studies of ulcerative infectious keratitis should consider both lens type and time in lens EW in any incidence/risk analysis.

Evaluation of Glutaraldehyde and Povidone Iodine for Sterilization of Wide-Field Contact Vitrectomy Lenses

Wide-field vitrectomy contact lenses are currently sterilized with ethylene oxide gas, and other lenses with autoclaving. To maintain a large inventory or possibly run the risk of loss of lens quality with repeated autoclaving, glutaraldehyde 2% and povidone iodine 5% solution were evaluated as possible sterilizing agents. Ethylene oxide presterilized lenses were contaminated with known concentrations (10(5) organisms/mL) of bacteria (S. epidemidis, P. aeruginosa, B. subtilis), and fungi (A. flavus, C. albicans) for 5 minutes. The test lenses were treated with glutaraldehyde or povidone iodine for 5, 10, 30, 60, and 120 minutes, and controls with sterilized water for a similar duration. Following treatment, both test and control lenses were sampled with sterile cotton swabs. The swabs were cultured for bacteria (tryptone soya broth 48 hours), and fungi (Saubourd's dextrose broth 5 days). The culture was negative for both glutaraldehyde- and povidone iodine-treated lenses against all organisms at all time points except B subtilis, which needed 120 minutes treatment. Two hours contact time with glutaraldehyde 2% or providone iodine 5% can sterilize vitrectomy contact lenses against common bacteria and fungi without affecting lens quality.

The performance of two different hydrogel lenses in symptomatic dry-eye contact lens patients

Twenty percent of contact lens patients exhibit dry-eye symptoms. The purpose of this study was to determine if either of two innovative lens designs would perform better for these patients than their habitual lenses. The sample consisted of 10 symptomatic soft contact lens patients. Each patient was dispensed one pair of study lenses: one B&L Soflens 66 and one Proclear Compatibles. All patients completed symptom surveys on their habitual lenses and the test lenses. Data were analyzed with the Student t-test. Both the Soflens 66 and Compatibles provided fewer symptoms than the patients’ habitual lenses (p < 0.005). Results suggest newer lens designs may provide greater comfort for symptomatic patients.

Interferometric focal length measurement of power-distributed lenses

An interferometric method for measuring the focal length of power-distributed lenses is described. The test lens is illuminated by a regular pitch interferometric pattern produced by a reflective diffraction grating interferometer. In order to measure the focal length, a CCD camera digitizes the image of the pattern magnified by the lens, and fast Fourier transformed to reconstruct the phase modulo 2π along each row. The change in spatial frequency is determined by unwrapping the phase along each row of the digitized imaged pattern. The technique is used for measuring the focal length distribution inside the progression corridor of both positive and negative progressive lenses.

Focal-length measurement by multiple-beam shearing interferometry

The application of multiple-beam shearing interferometry to lens focal-length measurement is described. A coated shearing plate interferometer was used in transmission to produce sharp multiple-beam fringes that rotate as the collimation of the incoming wave front from the lens under test changes. The test lens was used to collimate light from a point source that was translated longitudinally, and the focal length was determined from the rate of rotation of the fringes as the source moved. This method is simple, accurate, and lends itself to automatic determination of focal length.

Characterization of test lenses for calibration of focimeters

The problem of characterizing test lenses for the calibration of focimeters is analysed. The uncertainty budget is discussed in view of complying with ISO recommendations. The most relevant quantity to be measured is the radius of curvature of lens refracting surfaces. Practical considerations on the required measuring capabilities are given.

Spatial filtration of fringe-shift interferograms in double-exposure recording of gabor holograms. II

We analyze the conditions for formation in diffusely scattered fields of a fringe-shift hologram characterizing spherical aberration of a positive test lens or objective with spatial filtration of the diffraction field performed at the recovery of a double-exposure Gabor hologram.

Analysis of moiré fringes for measuring the focal length of lenses

We describe a technique based on fast Fourier transform and least-squares fit for automated analysis of moiré fringe patterns for accurately measuring the focal length of lenses. An interference fringe pattern is produced by a reflective diffraction grating interferometer and illuminates the test lens. Moiré fringes are generated by digitally superimposing the magnified fringe pattern imaged by the lens on the interference fringe pattern without the test lens. We analyze two common ways to generate the digital moiré effect: multiplication and subtraction with successive rectification of the two digitally stored intensity distributions, and we show that in the latter case by means of the described technique it is possible to determine the moiré spatial frequency by a simple and fully automated procedure.

A new approach to high accuracy measurement of the focal lengths of lenses using a digital Fourier transform

A new approach is proposed for measuring the focal length of a lens. The lens is illuminated by an interference pattern with a regular pitch produced by an interferometer that uses a reflective grating. The focal length is determined by measuring the number of fringes falling inside a fixed aperture both with and without the test lens inserted in the set-up. To measure the number of fringes, three images of the interference pattern are digitized by a CCD camera. A one-dimensional FFT algorithm is applied to the digitized image to reconstruct the phase modulo 2π along each row. The phase is unwrapped along each row and averaged to calculate the number of fringes that fall inside the aperture of 512 pixels. This technique is alternative to methods based on the moiré effect and a higher accuracy is obtainable. The focal lengths of both positive and negative lenses have been measured.

Menadione-induced oxidative stress accelerates onset of Emory mouse cataract in vivo

PURPOSE. We evaluated the effect of the free-radical generator, menadione, on the time of occurrence of cataract in the Emory mouse, a model for human cataract. Concomitant experiments were done to compare production and level of reactive metabolites of oxygen in the Emory mouse and its cataract resistant (CR) genetic control. METHODS. Test and control mice were fed both a normal diet and a diet supplemented with menadione, and the lenses were evaluated for the time of occurrence of cataract and the level of membrane ATPases. Effects of menadione were determined on incubated lenses of Emory and CR mice, assaying reactive species of oxygen, levels of antioxidant enzymes, and formation of the lipid peroxidation product, malondialdehyde. RESULTS. Systemic administration of menadione markedly accelerated the onset of Emory mouse cataract, and decreased ATPase activities suggested oxidative damage to membrane proteins. Cumulative levels of O 2 · -, H 2 O 2, ·OH and malondial-dehyde were significantly higher than controls in the lenses incubated in the presence of menadione, showing that it generates oxidative stress. However, [GSH] in lenses decreased equally in test and control mice. The observed increases in catalase and glutathione peroxidase activities in the test lenses indicated an early protective response to oxidative insult. CONCLUSIONS. Acceleration by menadione of the appearance of cataract in the Emory mouse demonstrates that oxidative stress is a risk factor in late-onset cataract. This quinone caused a greater increase in the production and levels of reactive metabolites of oxygen in Emory mice than in CR mice, indicative of a higher susceptibility of the former to oxidative insult.

Reflective grating interferometer for measuring the focal length of a lens by digital moiré effect

A new technique is proposed, based on digital moiré effects, for measuring the focal length of a lens. The test lens is illuminated by a variable pitch interference pattern produced by an interferometer which makes use of a reflective diffraction grating. Moiré fringes are generated by digitally adding the magnified images produced by the lens on the original interference pattern. The focal length of the lens can be determined by counting the number of moiré fringes. This technique is suitable for measuring both long and short focal length lenses. The focal lengths of both positive and negative lenses were experimentally measured.

Effects of hydrogel lens transmissibility profiles on local corneal swelling during eye closure.

To develop a unified model for describing the relations among local and regional contact lens transmissibility, topographical corneal location, and lens-induced corneal swelling under the closed eye. Thirteen adult male subjects, all adapted to daily wear of hydrogel lenses, wore a series of hydrogel lenses under patched eyes for 4 h. Corneal swelling was determined using an optical pachometer for five sites along the vertical meridian of test corneas. Four of the test conditions involved approximately uniform (no lens or parallel lenses) oxygen barriers over the central 8 mm of the cornea. Four additional sessions involved test lenses of -6, -3, +3, and +6 D, all having a center thickness of 0.2 mm. For the uniform barrier conditions, corneal swelling followed a similar pattern at all sites. Swelling was greatest centrally and least at the most peripheral, 7 mm, chord. The swelling vs. lens thickness response could be closely described by a third-order polynomial. Swelling with nonuniform thickness lenses at all sites showed evidence of small thickness averaging effects. Average central corneal swelling under the nonuniform lenses could be estimated from the polynomial function by averaging lens thickness over 5.5 to 6.75 mm for minus lenses and approximately 7.75 mm for plus lenses. The corneal swelling response to closed eye wear of hydrogel lenses follows a well ordered course over the central 7 mm. Over the same topographical area, the degree of swelling is influenced by both local and regional lens thickness profiles.

Multiple-beam lateral shear interferometry for optical testing

Lateral shear interferometry is used to obtain the lateral aberrations of a lens. The zeroth-order fringe in an interferogram obtained from a wedge-plate lateral shear interferometer, however, directly displays the lateral aberration curve of a test lens. Nevertheless, the intensity distribution, is cosinusoidal. Multiple-beam interferometry results in sharpened fringes; hence the multiple-beam wedge-plate shear interferometer displays the lateral aberration curve of a lens sharply, provided the shear is small. For large shear, some new artifacts appear in the interferogram, which are also explained.

Modified integrated optic Fresnal lens for waveguide-to-fiber coupling

The traditional design procedure for the waveguide Fresnel lens was carried over from those of bulk optics and micro-optics. In this design it is assumed that the lens thickness is negligibly small with respect to the focal length. This criterion does not hold for many integrated optic devices, in particular those with small mode-index modulations and long wavelengths. Under these conditions, the focal properties of the lens become unpredictable and the lens efficiency is reduced, both of which severely limit the usefulness of the lens as a waveguide-to-fiber coupler. To correct for this shortcoming, the standard Fresnel lens design procedure was modified to acocunt for the thickness of the lens explicitly. Both the standard and the modified Fresnel lens designs are outlined. A comparison of the limitations of the two lenses predicts better performance for the modified Fresnel lens. This is supported through computersimulation results for a pair of test lenses.

Measuring the focal length of optical systems by grating shearing interferometry

Using grating shearing interferometry, a new and simple technique to measure the effective focal length of optical systems is described. The diffraction pattern of a phase grating positioned at the focal point of the lens under test is evaluated for this purpose. The relative lateral shift between the undiffracted zero order and the diffracted first orders caused by the grating is measured. By utilizing knowledge of the wavelength of light, the grating period, and the diameter of an aperture stop placed in front of the test lens, we can determine the effective focal length of the test lens. Results of measurements are presented and compared with calculated values. The dependence of the focal length on the wavelength of the light is shown by using two laser sources of different wavelengths. An analysis of the measurement accuracy is given.

Determination of focal length of convex lenses using Newton's method

The conventional Newton's method can be applied for the measurement of focal lengths of convex lenses. The advantages of this method are that it does not require the location of the principal points of the test lens for the measurement of focal length and it can be applied to the thin as well as thick lenses. But the Newton's method suffers from some of the inherent errors introduced due to systematic errors such as bench correction error and depth of focus of the optical components involved in the measurements of distances. Therefore, some modifications in this method have been suggested and the method in its modified version is applied to find out the focal length of a convex lens with better accuracies. In the suggested improvements, the use of a sufficiently illuminated target in place of cross-slit, and the travelling microscopes in place of screen, reduced the inaccuracies introduced because of the bench error and the depth of focus of the optical components involved.