The present invention is directed to an ophthalmic lens mold. More specifically, the invention is directed to an improved ophthalmic lens mold.
The circumferential edge of an ophthalmic lens, e.g., contact lens or intraocular lens, is critical in that irregularities in this edge can cause discomfort to the eye and/or to the eyelid as it passes over the edge. It is also important that the edge create a smooth transition as the eyelid moves from the eye to the lens to prevent unwanted lens movement.
Ophthalmic lenses are often made by cast molding, in which a monomer material is deposited in a cavity defined between optical surfaces of opposing halves of a lens mold. Great care is taken in some mold designs to create a knife edge about one of the mold's optical surfaces to precisely form the critical contact lens edge when the mold halves are brought together.
In another arrangement, a mask that is opaque to ultraviolet light is deposited on one of the mold halves about its optical zone to block UV light during curing of the contact lens. The edge of the mask defines the edge of an area in the mold cavity in which monomer can be polymerized and, therefore, forms the ophthalmic lens edge.
Referring to FIG. 1, a contact lens mold 10 includes a back curve mold half 12 and a front curve mold half 14 defining respective optical surfaces 16 and 18. Mold halves 12 and 14 are secured in a mold tray (not shown) and brought together, as indicated by arrow 20, so that a mold cavity is defined between surfaces 16 and 18 into which a monomer material is deposited to form a contact lens.
Referring also to FIG. 2, back curve mold 12 includes a transparent core, e.g.,quartz core, 22 surrounded by a metal sleeve 24. An opaque mask, e.g., a metallic mask, 26 is deposited about optical surface 16 and forms an edge 28 thereabout. Front curve mold 14 includes another tranparent core surrounded by a metallic sleeve.
When monomer is deposited into the mold cavity, collimated ultraviolet light is directed through the back of mold half 12. The transparent core passes the light to an area of the mold cavity bounded by a cylinder defined by edge 28, thereby curing the monomer in this area. The mask, however, is opaque to ultraviolet light, and monomer radially outward of the area defined by edge 28 does not cure. The UV light is collimated, and there is a precise transition from cured to uncured material at the cylindrical boundary, which therefore determines the edge of the molded contact lens. The unpolymerized material may be rinsed away upon separation of the mold halves.