Corneal edema with hydrogel lenses and eye closure: effect of oxygen transmissibility

Several investigators have reported that significant corneal edema develops when daily wear hydrogel lenses are worn with the eyes closed. The amount of edema that develops when extended wear hydrogel lenses are worn with eye closure is not well documented. This study compared the amount of corneal edema that developed when subjects wore one daily wear lens with the edema that developed when they wore three lens types designed for extended wear. The daily wear lens was the U3 series Bausch & Lomb Soflens contact lens. The extended wear lenses were the Cooper Permalens, the Soft Lens Hydrocurve II 55 lens, and the Sauflon PW lens. The five subjects developed only small amounts of corneal edema when they wore the four lens types under opened-eye conditions but they developed significant amounts of corneal edema when they wore the four lens types for 3-hr periods with eye closure. The amount of corneal edema correlated well with the oxygen transmissibility (DK/L) of the study lenses. The results can be used to predict the amount of corneal edema that the average patient will develop initially when wearing a hydrogel lens of known water content or oxygen permeability (DK) and thickness (L) under opened and closed-eye conditions.

Corneal edema with hydrogel lenses and eye closure: effects of lens thickness

Subjects wore hydrogel lenses of two different thicknesses (0.07 mm and 0.18 mm) on one eye and no lens on the other eye during 3-hour periods of eye closure. They developed more corneal edema (12.7%) with the thicker lenses than with the thinner lenses (7.9%) and more corneal edema with the thinner lenses than with no lens (0.9%). The results suggest that hydrogel lens thickness would have to be less than 20 nm to reduce corneal edema to levels that develop when the eyes are closed without a contact lens.

Investigations on the association of phosphatidylserine synthase with the ribosomal component from Escherichia coli

The CDP-1,2-diacyl-sn-glycerol (CDP-diacylglycerol):L-serine O-phosphatidyltransferase (EC 2.7.8.8, phosphatidylserine synthase) of Escherichia coli is the first enzyme in the pathway committed to the biosynthesis of the major lipid in E. coli, phosphatidylethanolamine. The enzyme is unique among the phospholipid biosynthetic enzymes due to its high affinity for ribosomes in crude extracts. We report here investigations which define the nature of this in vitro affinity for ribosomes. Phosphatidylserine synthase can be dissociated from ribosomes in the presence of various inorganic salts at high ionic strength. Dissociation was also brought about by cellular levels of the polyamine spermidine. These results suggest the interaction of the enzyme with ribosomes in vitro is primarily ionic in nature, and polyamines may prevent this interaction in vivo. In the presence of nonionic detergent-lipid substrate mixed micelles under assay conditions the enzyme is also dissociated from ribosomes. Dissociation does not occur in the presence of detergent alone or in the presence of lipids which are not substrates or products of the enzyme. This dissociation by lipid substrate indicates the enzyme is not associated with ribosomes during catalysis.