Madalena Lira

Adhesion of Pseudomonas aeruginosa and Staphylococcus epidermidis to silicone-hydrogel contact lenses.

Purpose. The purpose of this study is to compare the adhesion capabilities of the most important etiologic agents of microbial ocular infection to the recently available silicone–hydrogel lenses with those to a conventional hydrogel lens. Methods. In vitro static adhesion assays of Pseudomonas aeruginosa 10,145, Staphylococcus epidermidis 9142 (biofilm-positive), and 12,228 (biofilm-negative) to two extended-wear silicone–hydrogel lenses (balafilcon A and lotrafilcon A), a daily wear silicone–hydrogel lens (galyfilcon A) and a conventional hydrogel (etafilcon A) were performed. To interpret the adhesion results, lens surface relative hydrophobicity was assessed by water contact angle measurements. Results. P. aeruginosa and S. epidermidis 9142 exhibited greater adhesion capabilities to the extended wear silicone–hydrogel lenses than to the daily wear silicone– and conventional hydrogel lenses (p < 0.05). No statistical differences were found between the adhesion extent of these strains to galyfilcon A and etafilcon A. The biofilm negative strain of S. epidermidis adhered in larger extents to the silicone–hydrogel lenses than to the conventional hydrogel (p < 0.05), but in much lower amounts than the biofilm-positive strain. The water contact angle measurements revealed that the extended wear silicone–hydrogel lenses are hydrophobic, whereas the daily wear silicone– and conventional hydrogel lenses are hydrophilic. Conclusions. As a result of their hydrophobicity, the extended wear silicone–hydrogel lenses (lotrafilcon A and balafilcon A) may carry higher risk of microbial contamination than both the hydrophilic daily wear silicone–hydrogel lens, galyfilcon A and the conventional hydrogel lens, etafilcon A.

Biomechanical properties of the cornea measured by the Ocular Response Analyzer and their association with intraocular pressure and the central corneal curvature

Background:  The aim of this study was to investigate the biomechanical properties of the cornea and their association with intraocular pressure (IOP), central corneal thickness (CCT) and the central corneal radius of curvature (Rc).

Contact Lens Hydrophobicity and Roughness Effects on Bacterial Adhesion

Purpose. This study was designed to assess whether hydrogel contact lens (CL) surface hydrophobicity and roughness affect Staphylococcus epidermidis adhesion. Methods. Bacterial adhesion experiments were performed on two unworn silicone hydrogel and three unworn conventional hydrogel CLs using the S.epidermidis strain CECT 4184. Microbial colonization was assessed by conducting counts expressed as colony-forming units. CL hydrophobicity was determined through water contact angle measurements and the roughness parameters such as mean surface roughness (Ra), kurtosis (Rku), and skewness (Rsk) were determined through atomic force microscopy in Tapping Mode. Results. The conventional CLs showed similar water contact angles (p > 0.05) and were classified as hydrophilic. The silicone hydrogel CLs yielded hydrophobic contact angles with no significant differences between them (p > 0.05). The lenses with the highest (nelfilcon A and ocufilcon B) or lowest (comfilcon A and omafilcon A) Ra values displayed a lesser or greater extent of spikiness of their surfaces, respectively. All lenses showed a predominance of peaks (Rsk > 0) over troughs. S. epidermidis adhered more to the hydrophobic CLs (p < 0.05). Omafilcon A and comfilcon A, which showed the lowest Ra values among the hydrophilic and hydrophobic lenses, respectively, returned the lowest bacterial adhesion scores (p < 0.05). Conclusions. Our results suggest that more hydrophobic CLs are more prone to S. epidermidis adhesion. Although the Ra appears to be related to S. epidermidis adhesion, the influence of Rku and Rsk on this variable remains unclear.

Soft Contact Lens Surface Profile by Atomic Force Microscopy

Purpose. This study was designed to qualitatively and quantitatively characterize the surface morphology of four unworn conventional hydrogel contact lenses (omafilcon, hioxifilcon, nelfilcon A, and ocufilcon B) and two silicone-hydrogel contact lenses (senofilcon A and comfilcon A) without surface treatment. Methods. Surface roughness was assessed using atomic force microscopy in Tapping ModeTM to determine the representative roughness parameters mean surface roughness (Ra), mean square roughness (Rms), kurtosis (Rku), and skewness (Rsk). To date, these last two parameters have not been used to characterize contact lens surfaces. Rku provides information on the distribution of spikes above and below the mean line, and Rsk provides information about the asymmetric roughness of surfaces. The surface topography of the lenses was also mapped in detail. Results. In all the lenses, higher Ra and Rms values were obtained when larger surface areas were examined. The daily replacement contact lenses (nelfilcon A and ocufilcon B) showed the highest Ra and Rms values but according to their Rku scores, their surface profiles were less spiky than the remaining lenses. On the contrary, the lowest Ra and Rms values were recorded for comfilcon A and omafilcon A, which also exhibited the spikiest surface profiles. All the materials except the hioxifilcon showed a predominance of peaks (Rsk >0) over troughs. Conclusions. The shape parameters Rku and Rsk are useful for characterizing contact lens surfaces, because they provide different yet complementary information to that offered by Ra and Rms. Precise knowledge of the shape profile of a contact lens surface will give an idea of its susceptibility to deposit formation or colonization by microorganisms.

Bacterial adhesion to worn silicone hydrogel contact lenses

Purpose. The aim of this study was to, firstly, investigate whether silicone-hydrogel contact lenses (CL) are more or less susceptible to bacterial adhesion than conventional ones and, secondly, assess the influence of lens wear in the extent of bacterial adhesion. Four silicone-hydrogel CL (galyfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B) and one conventional hydrogel (etafilcon A) CL were tested. Methods. Bacterial adhesion experiments were performed on unworn and worn CL using the strain Staphylococcus epidermidis 9142. Worn lenses were obtained from a group of 31 subjects fitted with a silicone-hydrogel CL in one eye and a conventional hydrogel CL as contralateral pair. These lenses were used on a daily basis in combination with a multipurpose lens care solution. Adhesion assays were carried out in a parallel plate flow chamber, followed by image analysis. Hydrophobicity, roughness, and topography of the lenses surfaces were assessed through contact angle measurements and atomic force microscopy. Results. Unworn conventional and silicone-hydrogel CL were equally susceptible to bacterial adhesion of S. epidermidis. Conversely, worn conventional hydrogel (etafilcon A) were more prone to bacterial adhesion than worn silicone-hydrogel materials, which exhibited similar adhesion extents among them. The results also showed that the lens surface properties such as hydrophobicity, roughness, and surface topography changed during wear. The alteration of surface hydrophobicity of silicone and conventional hydrogel CL during wear had a great impact on lens bacterial adhesion susceptibility. Accordingly, balafilcon A becomes significantly less hydrophobic and less prone to bacterial adhesion after lens wear, whereas etafilcon A becomes more hydrophobic and also more susceptible to bacterial adhesion (p < 0.05). Conclusions. Worn silicone-hydrogel galyfilcon A, balafilcon A, lotrafilcon A, and lotrafilcon B are equally prone to microbial adhesion of S. epidermidis and generally less susceptible than the conventional hydrogel.

Refractive index and equilibrium water content of conventional and silicone hydrogel contact lenses

Purpose:  The purpose of the present study was to measure equilibrium water content (EWC) and refractive index of conventional and silicone hydrogel soft contact lenses (SCL) using a hand refractometer and an automated refractometer.

Clinical assessment of the lower tear meniscus height.

Purpose:  Different values of the lower tear meniscus height (TMH) can be obtained depending on the method and technique of measurement employed. This study aimed to assess (1) differences between the absolute (TMH‐A), reflex (TMH‐R) and fluorescein (TMH‐F) lower tear meniscus heights, (2) differences between the central (TMH‐R), nasal (TMH‐RN) and temporal (TMH‐RT) reflex lower tear meniscus heights and (3) the amount of fluorescein present in the lower tear meniscus, 5 min after fluorescein instillation (TMH‐FV).

Comparison of the VCTS-6500 and the CSV-1000 tests for visual contrast sensitivity testing.

The aim of this study was to analyze if differences exist between two available contrast sensitivity tests that use similar stimuli, specifically, the CSV-1000 (VectorVision, Greenville, OH)) and the VCTS-6500 (Vistech, Dayton, OH). Contrast sensitivity was measured on 105 healthy patients with ages ranged from 19 to 26 years with visual acuity of 20/25 or better. The tests were performed in the same room and contrast sensitivity was measured with the VCTS-6500 system and CSV-1000. For both tests, the spatial frequencies of 3, 6, 12 and 18 cycles per degree were recorded. Contrast sensitivity values were generally higher for the Vistech VCTS-6500 test being the difference statistically significant (p<0.001) for all the spatial frequencies. This difference was more significant for 3cpd spatial frequency and the two tests showed a better agreement for the 6cpd spatial frequency. Our results showed that there were significant differences between the VCTS-6500 and the CSV-1000 tests. Developments of some general recommendations or regulations in relation to clinical measurement of contrast sensitivity are necessary.

The effect of octylglucoside and sodium cholate in Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion to soft contact lenses

Purpose. In this study, the effect of the natural surfactants octylglucoside and sodium cholate in inhibiting Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion to conventional and silicone-hydrogel contact lenses (CL) was assessed. Hydrophobicity was also evaluated to conditioned and nonconditioned CL. Methods. The inhibiting effect of the tested surfactants was determined through “in vitro” adhesion studies to conditioned and nonconditioned CL followed by image acquisition and cell enumeration. Hydrophobicity was evaluated through contact angle measurements using the advancing type technique on air. Results. Sodium cholate exhibits a very low capability to inhibit microbial adhesion. Conversely, octylglucoside effectively inhibited microbial adhesion in both types of lenses. This surfactant exhibited an even greater performance than a multipurpose lens care solution used as control. Octylglucoside was the only tested surfactant able to lower the hydrophobicity of all CL, which can explain its high performance. Conclusions. The results obtained in this study point out the potential of octylglucoside as a conditioning agent to prevent microbial colonization.

Comparison of the tear film clinical parameters at two different times of the day

Purpose:  The aim of the present study was to analyse the quality and quantity of the tear film in a young, healthy and non‐contact lens‐wearing population with measurements taken in the morning and in the afternoon to establish if changes exist in these parameters.