Effects of refrigeration on daily microbial bioburden of hydrogel lenses

Microbial bioburden of contact lenses was evaluated in connection with lens care by refrigeration. Subjects wore new hydrogel contact lenses for approximately 8 hours. The microbial bioburden initially and after an overnight refrigeration of the lens was evaluated with the use of viable counts on three different media. No major changes in viable counts were observed resulting from this method of storage. Scanning electron microscopy indicated the presence of foreign material on both new and worn lenses, presumed to be debris from lens manufacture and mucoid deposits from daily wear. Microbial colonization was not apparent and single bacterial cells could not be discerned on the micrographs.

Validity of optical pachometry measurements made with contact lenses in situ

Traditionally changes in corneal thickness associated with contact lens wear have been measured with optical pachometers after the lenses are removed from the cornea. In studies of corneal response to the extended wearing of hydrogel and silicone elastomer contact lenses, optical pachometry measurements may be improved by uninterrupted lens wear during the measurements. Using four flexible lens types differing in design and thickness, a single observer made pachometric measurements both with and without the lenses in place on eight subjects. This study demonstrates that valid and reliable measures of corneal thickness may be made without removing flexible lenses from the eye.

Comparison of oxygen tension measurement methodologies: further studies

The oxygen quantifying techniques of Hill and Rasson and Fatt have been compared by Roscoe and Wilson, who have also derived an "average" equivalent oxygen percentage (EOP) calibration equation. This study provides additional data which support their conclusions. Eight subjects wore three different hydrogel contact lens types of various center thicknesses and oxygen transmissibilities. Open-eyelid oxygen polarographic data were taken for each of these lenses worn by the subjects. The "average" EOP calibration equation was used to calculate the EOP values. The relation between center thickness and the ratio of the oxygen tension values derived by the two methods agrees relatively well with that found previously.

Optical pachometry measurements: reliability and variability

Polymethyl methacrylate (PMMA) lenses of known thickness were measured by one investigator with a pachometer. This experienced pachometrist held variation in thickness measurements to within 1% over time. The measurements were repeatable with a SD less than 1%. The data indicate that measured corneal thickness changes should be greater than 1 to 2% to be considered true changes in thickness.

Myofibrillar protein degradation after eccentric exercise

Male rats were run downhill for 90 minutes (nonexhaustive). Following the exercise, muscle protein degradation was increased, as determined by urinary 3-methylhistidine. However, minimal changes were observed in the relative percentage of the minor myofibrillar proteins and in the protease calcium activated factor in the long head of the triceps brachii muscle (eccentrically exercised) following the exercise bout.

Corneal thickness changes associated with daily and extended contact lens wear

Human corneal thickness was measured during daily wear of hydrogel contact lenses and then during the initial 2 weeks extended wear of hyper-thin (0.035 mm), low water content (38.6%), hydrogel lenses (polymacon). Results show that subjects wearing standard thickness (0.12 mm) and ultra-thin (0.07 mm) hydrogel lenses of low water content for daily wear will exhibit a diurnal swelling of the cornea. Subjects wearing hyper-thin (0.035 mm) low minus power hydrogel contact lenses of low water content for extended wear will exhibit overnight (closed eye) swelling of the cornea followed by a deswelling throughout the day (open eye). The degree of swelling and deswelling can vary greatly among individual subjects.