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.

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.

Methods: Sixteen SCL were used in this study including 12 conventional SCL not containing siloxane moieties (equilibrium water content (EWC) range: 38.6-74%) and the four silicone hydrogel based contact lenses currently available (WC range: 24-47%).

Oxygen transmissibility of piggyback systems with conventional soft and silicone hydrogel contact lenses.

Purpose: 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.

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 microm2. Mean roughness (Ra), root-mean-square roughness (Rms) and maximum roughness (Rmax) in nanometers were obtained for the three lens materials at different magnifications.

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.

pH stability of ophthalmic solutions.

Background: In this study, we evaluated the pH value of 17 ophthalmic solutions, and we investigated whether the pH of these solutions changed over time after the bottle was opened.

Methods: Fifteen bottles of each type of solution were chosen at random from different production lots. A 0.

Porous structure of Purevision versus Focus Night&Day and conventional hydrogel contact lenses.

The surface and bulk structures of hydrogel contact lenses that contain siloxane moieties, Purevisiontrade mark (balafilcon A) and Focus(R)Night&Daytrade mark (lotrafilcon A), were investigated. Standard hydrogel lenses of low (Seequence(R)), medium (Acuvue(R)), and high water content (Precision UV(R)) were used as controls. All the lenses were dehydrated in a series of ethanol solutions of increased concentration, critical-point dried in CO(2), and sputter coated with gold/palladium before they were examined by scanning electron microscopy.