| abstract |
Improvements in the O'Driscoll et al. U.S. Pat. No. 3,700,761 composition consisting of regulating critical proportions of PVP, HEMA, MA, EDMA, Water and the first and second stage initiators for producing hydrophilic lens blanks from which reproducible and predictable hydrated lenses are obtained with ratios of acceptance of 95 - 98%, to dimensional standards between the grinding dry and hydrated wet states and with ratios of resisting dimensional change in wet storage of upwards of ninety five percent. Compositions lying outside of the critical ranges of proportions provide lenses which are unpredictable (90% rejection) drift in size and do not provide reproducibility between dry and wet states and thereby create fitting problems. Critical ratios of MA to EDMA lying between 2.5/3.2 at 15% PVP content down to 1/1 at 28% PVP content provide reproducibility and predictability dry-to-wet and the optimum ratio is 1.5/0.7 at 20% PVP (reagents containing less than 1% water). Further improvement is made in the method of casting and cutting of U.S. Pat. No. 3,700,761, in which there is used a disposable mold of Teflon, high-density polyethylene or of RTV Silicone material with break-away curved bottom which is discarded to provide a convex surface requiring no cutting thereby eliminating many cutting and grinding steps on the conventional hard-lens lathe. Water-soluble medicaments as in U.S. Pat. No. 3,700,761 can be added to precision-cut eye bandages by dissolving in H2O and adding a total of 5% H2O to HEMA or the medicament can be used in eye drops, the bandage with 5% added containing 65% H2O instead of 60%. |