Patent CA-1340128-E (CA)
Title: Deformable-elastic intraocular lens
Inventor: GUPTA AMITAVA
IPC: A61L27/16
Filed: 1988-09-16
Granted: 1998-11-17
Abstract: Generally speaking, the present invention comprises an IOL having a deformable-elastic transparent lens body of crosslinked acrylic material having a tensile strength sufficient to resist deformation after implantation into the eye as by forces exerted by growing tissue around the IOL; a flexibility as measured by elongation at break sufficient to allow the lens body to be readily folded, rolled or otherwise deformed to a low profile condition for implantation through a small incision into the eye; an elastic memory which enables the folded lens body to naturally and at a controlled rate return to its original shape and optical resolution without damaging or otherwise traumatizing eye tissue; and a low-tack surface which will not stick to surgical instruments used to hold and guide the lens body during insertion and positioning within the eye.  In particular, the crosslinked acrylic material comprises copolymers of methacrylate and acrylate esters which are relatively hard and relatively soft at body temperature, crosslinked with a diacrylate ester to produce an acrylic material having a substantially tack-free surface, a crosslink density between 0.5 x 10 -1  and 1.5 x 10 -1 moles per liter, a glass transition temperature in the range of -30 to 25°C, a tensile modulus in the range of 1000 to 3000 psi and an elongation at break of between 100 and 300%.     Such a lens body is easily folded, rolled or otherwise deformed into a low profile for insertion through a small incision and after insertion will naturally return to its original optical resolution at a slow controlled rate in between 20 and 180 seconds even if the lens body has been deformed to a low profile condition for an extended period of time.  The slow return allows the surgeon adequate time to locate the folded IOL in the eye before the lens body returns to its original shape and resolution and insures that the unfolding of the lens will not damage or otherwise traumatize ocular tissue.   Furthermore, a lens body of the foregoing material and composition possesses a desired tensile strength to resist deformation in response to forces exerted by tissue growing around the implanted lens body thereby maintaining the desired optical characteristics and resolution of the lens body.   Preferably, in the formation of the deformable-elastic acrylic material,  the copolymers of methacrylate and acrylate esters are mixed at approximately a 45 to 55 weight percent ratio and the relatively hard methacrylate ester is a fluoroacrylate.  The fluoroacrylate functions as a surface energy lowering agent as well as a monomer providing long term stable inertness and tensile strength to the polymer without adversely effecting the pliancy of the resulting material.  In this regard, the fluoroacrylate is present in a concentration range by weight of between 5 and 25% and preferably is trifluoro ethyl methacrylate.   Also in the preferred formulation of  the crosslinked acrylic, the mixture of the copolymers is partially polymerized prior to chemical  crosslinking with  diacrylate  ester  in a concentration range of between 0.5 and 3.0 percent by weight.    The resulting crosslinked acrylic material may be molded and formed into lens bodies machined to have the desired optical characteristics and resolution with haptics extending therefrom either integral with or separately attached to the lens body.  Preferably, the crosslinked acrylic material formed according to the present invention is machined and otherwise processed at low temperatures in the range of -80 to -10°C and preferably at -60°C.   In particular, during cutting the lens body is maintained at a temperature below its Beta-relaxation temperature where the material is even harder than at its glass transition temperature.