0000000000019303
AUTHOR
José B. Almeida
Microscopic observation of unworn siloxane-hydrogel soft contact lenses by atomic force microscopy
In the present study, samples of lotrafilcon A, balafilcon A, and galyfilcon A contact lenses were observed by atomic force microscopy (AFM) in tapping mode at areas ranging from 0.25 to 400 m2. Mean roughness (Ra), root-mean-square roughness (Rms) and maximum roughness (Rmax) in nanometers were obtained for the three lens materials at different magnifications. The three contact lenses showed significantly different surface topography. However, roughness values were dependent of the surface area to be analyzed. For a 1 m2 area, statistics revealed a significantly more irregular surface of balafilcon A (Ra = 6.44 nm; Rms = 8.30 nm; Rmax = 96.82 nm) compared with lotrafilcon A (Ra = 2.40 nm; …
Dynamic in vitro dehydration patterns of unworn and worn silicone hydrogel contact lenses.
Purpose: To evaluate the effect of wear on dynamic in vitro dehydration of silicone hydrogel (Si-Hi) contact lens (CL) using a previously described gravimetric procedure. Methods: Five different silicone hydrogel (Si-Hi) contact lenses (CL) were evaluated after being worn by patients under daily wear conditions for 15 days to 1 month. Lenses were conditioned and disinfected with a multipurpose solution after each day of wear. Lenses were left to dehydrate in an analytical balance under controlled conditions of temperature and relative humidity and the results compared with data from new lens samples of the same power and material. Several quantitative parameters were obtained and compared b…
Refractive index and equilibrium water content of conventional and silicone hydrogel contact lenses
Prova tipográfica (In Press)
Qualitative and quantitative characterization of the in vitro dehydration process of hydrogel contact lenses
Purpose: To investigate the in vitro dehydration process of conventional hydrogel and silicone-hydrogel contact lens materials. Methods: Eight conventional hydrogel and five silicone-hydrogel contact lenses were dehydrated under controlled environmental conditions on an analytical balance. Data were taken at 1-min intervals and dehydration curves of cumulative dehydration (CD), valid dehydration (VD), and dehydration rate (DR) were obtained. Several quantitative descriptors of the dehydration process were obtained by further processing of the information. Results: Duration of phase I (r 2 5 0.921), CD at end of phase I (r 2 5 0.971), time to achieve a DR of � 1%/min (r 2 5 0.946) were stron…
Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses
Abstract: Purpose. To evaluate the qualitative and quantitative topographic changes in the surface of worn contact lenses (CLs) of different materials using atomic force microscopy (AFM). Methods. The topography of five different CL materials was evaluated withAFM over a surface of 25 lm2 according to previously published experimental setup. Average roughness (Ra) and root mean square (Rms) values were obtained for unworn and worn samples. Results. The Ra value increased for balafilcon A (11.62–13.68 nm for unworn and worn samples, respectively), lotrafilcon A (3.67–15.01 nm for unworn and worn samples, respectively), lotrafilcon B (4.08–8.42 nm for unworn and worn samples, respectively), g…
Equivalences between refractive index and equilibrium water content of conventional and silicone hydrogel soft contact lenses from automated and manual refractometry
PURPOSE: The purpose of the present study was to develop mathematical relationships that allow obtaining equilibrium water content and refractive index of conventional and silicone hydrogel soft contact lenses from refractive index measures obtained with automated refractometry or equilibrium water content measures derived from manual refractometry, respectively. METHODS: Twelve HEMA-based hydrogels of different hydration and four siloxane-based polymers were assayed. A manual refractometer and a digital refractometer were used. Polynomial models obtained from the sucrose curves of equilibrium water content against refractive index and vice-versa were used either considering the whole range…
Oxygen Transmissibility of Piggyback Systems With Conventional Soft and Silicone Hydrogel Contact Lenses
To investigate the apparent oxygen transmissibility of various piggyback systems using conventional and silicone hydrogel soft contact lenses of different water content and permeability, rigid poly(methyl methacrylate), and rigid gas-permeable lenses of medium, high, and ultrahigh oxygen permeability. The aim of the study was to establish which material (rigid or hydrogel) is more representative of the resulting oxygen performance of piggyback systems. METHODS: The apparent oxygen transmissibility of 66 piggyback systems was measured with an electrochemical method. Eighteen of these combinations involved the use of silicone hydrogel contact lenses currently available. One hyperpermeable rig…
Technical note: a comparison of central and peripheral intraocular pressure using rebound tonometry
Purpose: To compare central and peripheral intraocular pressure (IOP) readings obtained with rebound tonometry.Methods: Intraocular pressure was measured on the right eye of 153 patients (65 males, 88 females), aged from 21 to 85 years (mean +/- S.D., 55.5 +/- 15.2 years) with the ICare rebound tonometer at centre, and 2 mm from the limbus (in the nasal and temporal regions along the 0-180O corneal meridian).Results: Intraocular pressure values obtained with the ICare were 14.9 +/- 2.8; 14.1 +/- 2.5 and 14.5 +/- 2.7 mmHg at centre, nasal and temporal corneal locations, respectively. On average, nasal and temporal IOP readings were 0.75 and 0.37 mmHg lower than the central reading (p 0.05, r…
Microscopic observations of superficial ultrastructure of unworn siloxane-hydrogel contact lenses by cryo-scanning electron microscopy
The purpose of this study was to analyze three commercial siloxane-hydrogel contact lens materials, lotrafilcon A, balafilcon A, and galyfilcon A, by cryogenic scanning electron microscopy (cryoSEM). The fully hydrated lenses were frozen in slush liquid nitrogen and qualitatively observed in a cryogenic scanning electron microscope. The superficial ultrastructure of the siloxane-hydrogels was observed at the areas where the lens fractured during sample cryogenic preparation. There are qualitative differences among the three examined materials in the complex polymer network structure existing between the outer layer and the underlying polymer. CryoSEM, although destructive, is a useful tool …