a light adjustable lens ( lal ) comprises four distinct chemical entities or components . the first component is the matrix polymer that gives the lens its basic shape , refractive index , and material properties . the second component is known as the macromer and is , by design , chemically similar to the matrix polymer . one difference between the two is the presence of photopolymerizable end groups on the macromer such that the application of the appropriate frequency of light will cause the macromer molecules to form chemical bonds between each other . the third component is the photoinitiator that absorbs the applied incoming light ( 365 nm ) and initiates polymerization of the macromer . the fourth component of the lal is a uv absorbing molecule that protects that retina from ambient uv irradiation . the mechanism upon which the lal technology is based is depicted graphically in fig1 . application of light to - the lal will cause the photopolymerized macromers in the irradiated region to form an interpenetrating network within the target area of the lens . this action produces a change in the chemical potential between the irradiated and unirradiated regions of the lens . to reestablish thermodynamic equilibrium , macromers in the unirradiated portion of the lens will diffuse into the irradiated region producing a swelling in the irradiated region that effects a change in the lens curvature . as an example , if the central portion of the lens is irradiated and the outside portion is left nonirradiated , unreacted macromer diffuses into the center portion causing an increase in the lens power and a hyperopic shift . likewise , by irradiating the outer periphery of the lens , macromer migrates outward causing a decrease in the lens power and a myopic correction . by controlling the irradiation dosage ( i . e ., beam intensity and duration ), spatial intensity profile , and target area , physical changes in the radius of curvature of the lens surface are achieved , thus modifying the refractive power of an implanted lal to either add or subtract spherical power , adjust along toric axes , or correct higher order aberrations . note that multiple zones may be irradiated to form a multi - focus lens , e . g . a bulls eye lens . once the appropriate power adjustment is achieved , the entire lens is irradiated to polymerize the remaining unreacted macromer to prevent any additional change in lens power . by irradiating the entire lens , macromer diffusion is prevented , thus no change in lens power results . this second irradiation procedure is referred to as “ lock - in ”. the lal of fig1 requires the application of uv - a light ( i . e . 365 nm ) to initiate the photopolymerization process . the natural human optical media are transmissive in the uv - a wavelength range . according to published results and experiments performed at calhoun vision , inc . ( pasadena , calif .) the natural human cornea transmits around 50 % of the incident light at 365 nm . in addition , measurements of human aqueous and vitreous indicate that greater then 90 % of the light at 365 nm is transmitted , so that some of the 365 nm light once inside the eye will reach the retina . uv - a is considered to cause negative photochemical effects to the human retina like dyschromatopsia (“ blue cone knock out ”). in order to avoid phototoxic effects , several international standardization committees ( e . g . icnirp ) have defined wavelength specific maximum permissible retinal exposure values ( mpe ). clinical trials using the lal technology indicate that even at doses significantly below the given limit values , patients perceive disturbed color vision for a couple of days post irradiation . due to the fact that the lens body is homogeneously formed of photosensitive material , a comprehensive lock - in of the entire lens is required to stabilize its refractive properties . failure to do so , may result in unintended power changes by exposing the eye to ambient source of uv , e . g . sunlight . the requirement that the lal is locked - in up to the outer edges causes the major disadvantage with regard to uv safety . in theory , the lock - in intensity pattern matches exactly the diameter of the lal . therefore , the entire beam is refracted into the lal and absorbed within the material according to lambert - beers law . however , a minor , nonabsorbed portion of the beam is still transmitted trough the lal and forms a resulting intensity pattern at the retina . one embodiment of the invention reduces the amount of uva light striking the retina . this embodiment involves a new lens molding technique that allows a thin ( 50 - 100 μm ), highly absorbing uv layer to be attached to the posterior surface of the lal . an example of such a lens is shown in fig2 a - 2c . fig2 a depicts a rear elevational view of lens 10 , where the rear side of the lens includes a uv absorbing layer 11 . a particularly useful class of uv - absorbing compounds that comprise the uv absorbing layer is selected from compounds having the following formula or structure : wherein each x is independently selected from the group consisting of h , halogen , alkyl , hydroxyl , amino , carboxyl ; each r 1 is independently selected from the group consisting of h , alkyl , substituted alkyl , alkoxy , substituted alkoxy , hydroxyl , amino and carboxyl ; r 2 contains a vinyl moiety ; m is an integer from 1 - 3 ; and n is an integer from 1 - 4 . the preferred uv - absorbing compounds absorb uv light strongly in the range 300 nm to 400 nm , and exhibit reduced absorption at wavelengths higher than about 400 nm . the amount of uv absorber required to give the desired amount absorption is dependent upon the specific uv absorber , its concentration in the layer , and its optical path length . the lens 10 comprises a light adjustable region 12 , and haptics 13 . fig2 b depicts a sectional view of lens 10 of fig2 a along line a - a . fig2 c depicts a sectional view of lens 10 of fig2 a along line b - b . the majority of the uv radiation applied to the lal during the lock - in process is absorbed by the lens lock - in process . the remaining fraction of the incident radiation depends on the absorption coefficient of the material of the bulk lens portion 12 and absorbing layer 11 , as well as the individually traveled optical path length . fig3 depicts a graph of the retinal dose versus the lens absorption . line 31 illustrates the dependency of the retinal dose on the optical path length of the lens . as expected , increasing the optical path length of the lens causes the retinal dose to decrease exponentially . the reduction in light at the retina is accomplished by increasing the lal thickness , e . g . portion 12 and / or increasing the backing layer thickness , e . g . layer 11 . the remaining retinal intensity can be theoretically decreased by several magnitudes by this approach , as the convergence of line 31 of fig3 indicates . the previous discussion considered an idealized case where the lock - in beam is the same size as the lal ( e . g . 6 mm ), the beam is focused in the central volume of the lal , and that the irradiating beam is aligned exactly to the lal in the x and y planes . however , in clinical practice the above assumptions are not necessarily valid due to diameter manufacturing tolerances of individual lals and variation in patient anterior chamber depth ( acd ) that cause slight variation in the magnification of the lock - in beam at the lal . these two factors can conspire together to make the lal smaller than the incident beam , which will permit rays at the edge of the lal to pass unattenuated to the retina as illustrated in fig4 . in fig4 , spill over light 41 from the lock - in process passes to the retina 42 . also illustrated in fig4 is another factor that contributes to unattenuated light passing around the lal to the retina , which is a patient &# 39 ; s natural saccadic eye motion 43 during the treatment procedure . this motion will cause both temporal defocus and decentration of the beam at the lal . the magnitude of the temporal spillover depends on the patient / physician individual motion statistics . thus , increasing the thickness or increasing the absorption coefficient of the uv absorbing back layer to decrease the dose at the retina may not be sufficient to drop the dose at the retina below levels that will produce erythropsia in a majority of the patients . another embodiment of the invention is an uv blocking safety rim . this rim significantly enhances uv safety for patients , and does not require in - vivo lock - in . the rim also does not act as a diffusion reservoir of unpolymerized macromers . the rim further prevents cells from migrating to the back of the lal , leading to an improved pco rate . the pco rate can be significantly reduced using sharp - edged lens designs that involve certain pressure to the posterior capsule . the additional uv safety rim may be advantageously shaped in the form of a sharp edge design of particular angulations . another embodiment of the invention involves using a uv - light blocking rim around the lal . an example of this embodiment is shown in fig5 a . this example lens 50 includes rim 51 , will reduce or prevent light spill over from eye movements and / or lens size variation . fig5 b depicts a sectional view of lens 50 of fig5 a along line a - a . fig5 c depicts a sectional view of lens 50 of fig5 a along line b - b . to determine a diameter of this uv blocking rim , the amplitude of eye motion was measured for a series of patients with an implanted lal during their respective treatment procedures . a statistical analysis of this motion data indicates that 90 % of all patient lens motion was within 230 μm of alignment . therefore , designing an outer uv absorbing rim that has a radius of 250 μm on each side should reduce greater than 90 % of the spill over contribution . one embodiment of the uv blocking rim may have the rim material be transparent , and include a layer of material to the front side and / or back side of the rim , which is fully opaque in uv light and visible light , for example a black or colour pigmented layer as in lens 81 of fig8 a . another embodiment of the uv blocking rim may have the rim material be transparent in uv and visible light , and include surface modifications , such as frosting , blazed / nonblazed diffractive structures that direct the light outward in the peripheral retina , prisms , nonblazed wedge structures or other types of blazed wedge structures to the front side and / or back side of the rim , for example lens 82 of fig8 b . these modifications refract or scatter the unwanted light from the light path . a further embodiment of the uv blocking rim may have the rim material be clear in visible light and be highly absorbing in uv light , for example lens 83 of fig8 c . one type of material is the same material used as the uv layer 11 . the rim may be photo - locked prior to implantation or as part of the manufacturing cycle . a still further embodiment may have the rim comprise opaque material the blocks both uv and visible light , such as lens 84 of fig8 d . the different edge designs of fig8 a - 8d avoid or minimize visible stray light and glare at large pupil dilations . furthermore , another embodiment may involve modifications in the refractive index such as creating gradient index optical surface or regular phase gratings in the material portion of the rim , for example as shown in fig9 a and 9b . in fig9 a , the rim portion 92 with an internal phase grating is integral with the backing layer 91 . in this embodiment , rim portion 92 may comprise the same material as layer 91 . in fig9 b , the rim portion 92 with an internal phase grating is separate from the backing layer 91 . in this embodiment , rim portion 92 may comprise the same material as layer 91 or a different material . the implementation of the refractive index gradients is arranged in such a way as to direct the majority of radiation into the peripheral retina ( well outside the macula ) while also avoiding the creation of regions of peak irradiance in these peripheral regions . another embodiment of the invention is an uv blocking safety rim that is not limited to the iol material or its derivatives and is accomplished by creating particularly shaped uv - blocking haptics and / or haptic joints , for example as shown in fig1 a and 10b . in fig1 a , the dual piece haptics 103 include the uv blocking area 101 . in fig1 b , the single piece haptics 104 include the uv blocking area 102 . lens 50 of fig5 a may be produced by prelocking of the uv - backing layer during manufacturing process . the backing layer could be entirely locked in after molding . the bulk will be molded onto the inactive backing in a second step . moderate heat will be applied afterwards to allow thermal healing of the interface . the fully polymerized backing layer could potentially prevent diffusion of macromers into it . fig6 a and 6b depict alternative embodiments of the lens . in fig6 a , the uv layer 61 is substantially uniform in thickness . in fig6 b , the uv layer 62 varies in thickness , for example layer 62 may be thicker where layer 12 is thinner . this will even out the uv blocking of the layers 12 and 62 . fig7 depicts another embodiment of the invention . in fig5 a - 5c , and 6 a - 6 b , rim 51 is separate from layer 11 . in fig7 , rim portion 71 is integral with layer 72 . in this embodiment , rim portion 71 may comprise the same material as layer 72 . note that the haptics shown in various embodiments are not limited to c - loop configuration , as other types may be used . a blocking layer may be positioned between layer 11 and layer 12 and / or between layer 12 and rim 51 to ensure that no unpolymerized macromer can diffuse in or out of the layer 12 and / or rim 51 . alternatively , materials may be chosen for the different layers whose chemical structure prevents the macromer from diffusion ( i . e . steric hindrance ). note that the lens shape may be flattened in the annular area 14 in order to provide sufficient edge thickness for joining the bulk lens with the haptics . the transition from the flattened area to the lens body can be shaped differently . fig5 a includes a sharp edge resulting from basic joining of the geometries ; however fig6 b discloses a smooth transition with a radius r t & gt ;& gt ; 0 . this configuration helps to reduce the risk of pco ( posterior capsular opacification ) by forming a tight contact interface between the posterior capsule which prevents epithelial cells from migrating onto the posterior lens surface . another embodiment has the layer 11 and rim 51 comprised of the same photo - active material . this material has high uv - blocking capabilities that is accomplished either through absorption of optical radiation or reflective properties . this layer 11 is extended towards the edges to form the safety rim 51 . the use of the same material composition as used in the backing layer requires that the rim also needs to be photolocked since this rim will act as a reservoir of unpolymerized macromers which may cause unintended power changes in the future . although the present invention and its advantages have been described in detail , it should be understood that various changes , substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims . moreover , the scope of the present application is not intended to be limited to the particular embodiments of the process , machine , manufacture , composition of matter , means , methods and steps described in the specification . as one of ordinary skill in the art will readily appreciate from the disclosure of the present invention , processes , machines , manufacture , compositions of matter , means , methods , or steps , presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention . accordingly , the appended claims are intended to include within their scope such processes , machines , manufacture , compositions of matter , means , methods , or steps .
embodiments of the invention involve intraocular lenses that are light adjustable to change a focal length of the lens after it has been implanted into a person or animal . the lens includes a layer of uv absorbent material located on a rear side , which is the side facing a retina . the lens may comprise a uv reducing rim that surrounds a peripheral portion of the lens , and reduces or blocks uv light from striking the retina .