Preservative effect on epithelial barrier function measured with a novel technique.
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Adolescent↗
Biomedical subjects
J R Paugh
Publications and source records attributed to J R Paugh.
Ocular residence time of carboxymethylcellulose solutions.
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Adult↗
Rose bengal dye concentration and volume delivered via dye-impregnated paper strips.
PURPOSE: The technique of administration and the resulting volume and concentration of the dye delivered to the eye via dye-impregnated paper strips are not standardized or known. The purpose of this study was to use a standard technique for preparation of rose bengal dye from commercially available paper strips to determine the variability in concentration based upon soak time, and to determine the volume delivered by such a technique to a model eye. METHODS: Rose bengal filter paper strips were wetted for either 15, 30, or 45 s, and the resulting concentration of dye eluted was determined by spectrophotometry. With the same preparation technique and a 15-s soak time, the strip was applied to wetted filter paper, as a model for the moist surface of the eye. The volume of solution delivered was calculated by weight. RESULTS: Concentrations of rose bengal for the various soak times were: 15 s: 7.64 (+/- 1.11) by 10(-6) g/ml; 30 s: 9.70 (+/- 1.79) by 10(-6) g/ml; and 45 s: 10.27 (+/- 0.66) by 10(-6) g/ml. The volume delivered to the eye model with this technique was 17.43 microliters (+/- 3.09). CONCLUSIONS: The concentration of rose bengal dye delivered to the ocular surface by means of a wetted strip is relatively low and soak time/technique-dependent. This suggests a possibility that results in clinical studies with rose bengal strip application may be different than if controlled volume applications of commercially available 1% liquid rose bengal dye are used.
Cornea↗
A new method for determining corneal epithelial barrier to fluorescein in humans.
PURPOSE: To derive the value of corneal epithelial barrier to fluorescein in humans from experiments in which the fluorophore in instilled in a single drop. METHOD: A commercial scanning fluorophotometer, the Fluorotron Master, was used to scan through an anterior segment. It could not resolve the tear film from the cornea, but in the early stages of measurement, the tear component predominated. After 20 minutes, the remaining fluorescein was washed out of conjunctival sac, and the amount that penetrated into the cornea was estimated. Because the resolution was not sufficient to estimate the concentrations, the total masses in the tear film and in the cornea derived from the area under the profile were used to calculate the epithelial permeability. A value for the tear film thickness had to be assumed. RESULTS: The technique led to reproducible values for epithelial permeability-a range of 2:1 in a subject. High concentrations of fluorescein were required to achieve a sufficient penetration into the cornea, and this led to error in estimating the tear film concentration of the dye. A method is presented that corrects for this effect. For 17 normal subjects, the corrected permeability was 0.15 nm/second, and the tear turnover was 0.15/minute ( +/- 0.016, standard error.) CONCLUSIONS: This technique is convenient and yields two useful physiological parameters from a single clinical procedure. The permeability values are considerably higher than those found by previous workers, and the source of the discrepancy is discussed.
Absorption↗
Use of confocal microscopy to determine matrix and surface protein deposition profiles in hydrogel contact lenses.
We present a new method that combines protein-specific fluorescence staining with confocal microscopy to simultaneously measure matrix and surface protein deposits via optical sectioning of hydrogel contact lenses. Tetramethylrhodamine isothiocyanate (TRITC), Texas Red, fluorescein isothiocyanate (FITC), and fluorescein succinate were used to selectively react with the lysine residues of protein deposits for two lens types (etafilcon A [a 58% water, ionic lens] and polymacon [a 38% water, nonionic lens]). Because TRITC and Texas Red gave high levels of nonspecific staining, they were discontinued. Following exhaustive rinsing of lenses, central lens buttons were analyzed using a Bio-Rad MRC-500 laser scanning confocal microscope. Optical sections were made every 4 microns at 200x magnification, and the fluorescence signals were processed using image analysis software. The high water ionic material accumulated protein much more rapidly than the low water nonionic material. For a given lens type a correlation was observed between the wear time and the degree of protein deposition; however, we did observe significant inter-subject variations in total protein. From this preliminary work, we conclude that this confocal method is feasible and desirable for simultaneous determination of surface and matrix protein deposition.
Contact Lenses, Hydrophilic↗
Comparative study of two non-invasive tear film stability techniques.
This study was conducted to establish normative and comparative data from healthy subjects under uniform ambient conditions for two non-invasive tear breakup methods (the HIR-CAL grid-modified keratometer and the Mengher-Tonge xeroscope). The study also sought to establish the repeatability and inter-observer variability of the two methods. Forty-five subjects between the ages of 18 and 45 with no known dry eye conditions and with normal ocular health were assessed. Both methods were performed on one eye (both the eye and the first method of testing were randomly selected). On a direct comparison basis, we found that the keratometer method, as has been reported, yielded shorter (generalized sign rank test, n = 58 paired comparisons, p < 0.0001) non-invasive breakup times (NIBUTs) than the xeroscope (mean > or = 35.6 +/- 19.2 seconds and mean > or = 44.7 +/_ 16.3 seconds (mean +/- s.d.), respectively). The keratometer NIBUTs were longer than reported values. The different-day, same-subject repeatability of the NIBUTs as measured by both instruments was excellent. The inter-observer comparison indicated that examiner differences may exist, although the sample size for this assessment may have limited the strength of the comparison.
Adolescent↗
Equivalent oxygen percentage as a function of hydration in hydrogel lenses: an in vivo study.
Although many investigations have examined the parameters of hydrogel lens hydration loss, the in vivo effect (in humans) on lens oxygen behavior has not been characterized previously. Human subjects wore 2 different lenses (a thin, 38% water polymacon lens and a thin, 55% water bufilcon lens) for 5-min periods under either fully hydrated (i.e., with saline regularly applied to the lens) or partially hydrated (i.e., with "normal" wear of 1 blink every 5 s) conditions. An equivalent oxygen percentage (EOP) technique and a gravimetric method were used to determine lens oxygen behavior and hydration, respectively. The hydration results demonstrate that significant lens dehydration occurs during the partially hydrated (normal blink rate) condition compared to the in situ, fully hydrated situation. A corresponding, statistically significant diminution in oxygen equivalency was also observed.
Adult↗
Prevalence of Meibomian gland dysfunction.
This study was performed to determine the prevalence of Meibomian gland dysfunction (MGD) and to determine which patient profile factors might be associated with the syndrome. Patients were randomly selected, apparently normal patients presenting for routine vision examinations. Of the 398 patients for whom Meibomian gland expression was performed and a detailed history obtained, 155 patients or 38.9% exhibited MGD based on the principal clinical criterion of an absent or cloudy Meibomian gland secretion upon expression. Patient profile factors of gender, age, allergy occurrence, and contact lens wear were analyzed for correlation with MGD. Age was found to be the only significant correlating factor (positive correlation, p less than 0.0001).
Adolescent↗
Meibomian therapy in problematic contact lens wear.
Utilizing the principal diagnostic criterion of an absent or cloudy Meibomian gland secretion upon repeated expression, patients with Meibomian gland dysfunction (MGD) were selected to participate in a study of the efficacy of lid scrubs and massage in the treatment of MGD. Twenty-one patients with contact lens intolerance unrelated to lens, care system, or health factors were randomly assigned to treatment of one eye with common clinical therapy for MGD. After 2 weeks of treatment, gland expression, biomicroscopy, staining, comfort, and fluorescein breakup time were assessed in a masked manner. Analyzed using a paired-data t-test, the results indicated a significant increase in mean tear film breakup time (BUT) in the treated eye at follow-up compared to baseline (mean increase = 4.0 s, p = 0.0001). The control eye demonstrated no significant change (mean increase = 0.2 s, p = 0.5955). These objective results were corroborated by reports of improved subjective comfort with contact lens wear after therapy.
Adult↗
Reliability of corneal oxygen flux measurements.
Serial oxygen flux measurements were obtained from the same cornea of 5 human subjects after exposure to ambient air, a test gas mixture (2% oxygen, balance nitrogen) and 100% nitrogen at 2 individual measurement sessions. Analysis of variance (ANOVA) of the individual flux measurements for the test gas indicates that there were significant differences in corneal oxygen flux rates among subjects and sessions. Referencing the flux data for the test gas to the data for ambient air reduced the variability of data between sessions, although significant intersubject differences were still present. By referencing the flux data for the test gas to the concurrent air and nitrogen data, differences among subjects, as well as sessions, were reduced to the extent that they were not statistically significant. Standardization of data is important in the interpretation of corneal oxygen flux data so that intersubject and intersession differences can be minimized.
Air↗
Ocular response to hydrogen peroxide.
A controlled, randomized, double-masked study was conducted on eight human subjects to determine the threshold level of hydrogen peroxide, which is toxic when introduced into the eye via a high water content (75%; Durasoft 4) hydrogel contact lens. Subjective comfort, conjunctival hyperemia, corneal and conjunctival epithelial staining, and corneal oxygen uptake were assessed in response to 5-min wear of lenses that were presoaked in isotonic saline solutions of physiologic pH containing 0, 25, 50, 100, 200, 400, and 800 parts per million (ppm) hydrogen peroxide. Higher levels of hydrogen peroxide were associated with greater discomfort (p less than 0.05) and increased conjunctival hyperemia (p less than 0.001). The highest level of hydrogen peroxide tested (800 ppm) did not induce significant corneal or conjunctival epithelial staining or alter the corneal aerobic response. We conclude that residual concentrations of hydrogen peroxide in contact lens care systems should not exceed 100 ppm. Practitioners can use these data to estimate the level of residual hydrogen peroxide to which a patient may have been exposed upon lens application after neutralization.
Adult↗
Plus acceptance in hard contact lens wearers.
Hyperopes fitted with contact lenses often exhibit more plus acceptance compared to full spectacle correction beyond that accounted for by vertex distance considerations. The objective of this investigation was to attempt to identify the possible factors involved with this phenomenon. Eight hyperopes, one myope, and one control hyperope between 20 and 30 years of age were fitted with polymethyl methacrylate lenses, and over-refractions performed on different days with and without corneal anesthesia. The result was that every test hyperope accepted more plus without anesthetic than with anesthetic, by an average of 0.725 D, which was significant (p = 0.0000). One possible mechanism appears to be neurosensory feedback between corneal sensation and the level of accommodative tonus of the ciliary body.
Adult↗
Polymorphic corneal abnormalities.
Alterations of the deep corneal layers, which are manifest primarily as Hassall-Henle bodies in older patients, are a relatively frequent finding in the normal population. Changes which occur in Descemet's membrane and the endothelium earlier in life can be ascribed to various causes, including dystrophy, herpetic infections, and birth trauma. Six cases in which clear vesicles and scalloped lesions were found exclusively at the level of Descemet's membrane and the endothelium are reported. Although the polymorphic changes were in some cases extensive, visual acuity and, apparently, corneal physiology remained normal. The etiology for all cases was uncertain, but the evidence suggested a dystrophic origin or the occurrence of posterior corneal vesicles of a nonfamilial variety.
Adult↗
Is flatter and thinner always better?
In the current controversy regarding the relative importance of basecurve selection in hydrophilic lens design, one key to basecurve (bearing-relationship) predictability may lie in its subtle inter-action with another design parameter, lens thickness.
Contact Lenses, Hydrophilic↗