the bifocal intraocular lens according to the present invention , how it functions , and how it differs from what has been previously employed can perhaps be best explained and understood by reference to the drawings . fig1 illustrates the front view of one preferred embodiment of an intraocular lens according to the present invention , generally designated by the numeral 10 . fig2 and 3 are a side and top cross - sectional view of the intraocular lens 10 as seen through lines ii -- ii , and iii -- iii , respectively . as seen in fig2 and 3 , the intraocular lens 10 is made up of an inner transparent wall 12 and an outer transparent wall 14 which define an internally closed space within the lens 10 . as further illustrated , this internally closed space comprises a centrally located refractive chamber 18 positioned above a liquid filled reservoir chamber 20 . refractive chamber 18 and reservoir chamber 20 are directly interconnected vertically by passages 22 . also , the upper edge of the refractive chamber 18 is connected to each side of the lower reservoir chamber 20 by a pair of vent tubes 24 and 26 which circumvent the refractive chamber 18 and the line of sight as explained later . vent tubes 24 and 26 are positioned within the lens 10 such that they are horizontally displaced away from the refractive chamber 18 . as further illustrated in fig1 the outer perimeter of the transparent walls are equipped , in this embodiment , with a pair of j - loop posterior attachment means 28 and 30 . it should be appreciated that the improved intaocular lens of the present invention can be employed with essentially any contemporary eye fastening mechanism or method . thus , it is contemplated that the intraocular lens can be used in conjunction with any appropriate anterior or posterior fastening means or medium as well as being attached to the iris by any of the methods well known in the art , and as such , geometric configurations , designs and structures other than the j - hook or j - loop should be considered equivalent for purposes of this invention . the intraocular lens 10 is intended to be surgically implanted into the human eye as a substitute for the natural crystalline lens . during implantation the refractive chamber 18 is aligned in the line of sight such that the light entering the eye passes through the central portion of the lens 10 . the central portion of the lens 10 consists of the lenticular portion of the intraocular lens and as such , has an appropriate optical grade anterior and posterior refractive surface 32 and 34 . in addition , the central lenticular portion of the intraocular lens contains the refractive chamber 18 inside the lens . this refractive chamber is essentially a hollow area with two additional optical grade refractive surfaces within the lens itself , an inner anterior and posterior surface 36 and 38 . it is the combination of these four refractive surfaces that establishes the refractive prescription of the lens . furthermore , and as illustrated in fig4 and 5 , the liquid reservoir 20 is filled , for far vision , with a liquid of predetermined refracrive index , while the refractive chamber 18 is filled with air or other inert vapor . thus , the volumes of the respective chambers 18 and 20 and liquid 40 are selected such that when the lens is in a vertical configuration associated with horizontal view , the liquid remains entirely within the lower reservoir 20 . as the angle of inclination of the line of sight tilts downward , the liquid previously in the lower chamber 20 flows into the refractive chamber 18 and in a similar manner , as the eye position returns to the horizontal sight , the liquid in the refractive chamber 18 drains back to the lower reservoir chamber 20 . in this manner , the refractive prescription of the lens will change by virtue of the presence or absence of the liquid in the line of sight ( i . e ., a liquid filled or empty refractive chamber 18 ). by preselecting the refractive index of the liquid and controlling the geometric contours and relative positions of the refractive surfaces , the intraocular lens can be tailored to the specific needs of the patient . in order to achieve the desired beneficial effects of the transfer of a refractive liquid in and out of the line of sight within the small geometric confines of an intraocular lens , it has been discovered that there must be connecting vent tubes between the refractive chamber and the reservoir . these vent tubes must be positioned such as to provide for rapid transfer of liquid in and out of the line of sight . in order to achieve this , the vertical tubes represent and can be envisioned as being the final element that completes a circular loop or pathway for fluid flow . as the liquid phase exits one chamber and enters the other chamber , the vent tubes are positioned such that the gaseous phase within the chamber being filled can be displaced through the vent tube back to the chamber that is emptying . this cyclic fluid pathway thus prevents localized vapor pockets that tend to resist the desired rapid liquid transfer from chamber to chamber . preferably , and as illustrated in the drawings , the vent tubes circumvent the central refractive chamber in a plane that is displaced horizontally from the refractive chamber . in this manner , the vent tubes assume a position displaced vertically over the chamber as the line of sight tilts downward . again , this feature insures the circulation of the gaseous phase through the vent tubes and as such , represents an aspect of the invention which could not be readily achieved in the previous differential contact lens of u . s . pat . no . 4 , 174 , 156 . in other words , because of the lenticular nature of the intraocular lens , the incorporation of vent tubes to complete a cyclic flow pathway to assist rapid liquid transfer is achieved . further , because of the lenticular of the intraocular lens , the reservoir chamber which is located inferiorly relative to the refractive chamber can advantageously be located posteriorly to the refractive chamber as illustrated in fig2 . because of this posterior relationship , the sensitivity of the fluid transfer from the reservoir chamber into the line of sight as a function of the motion of the eye turning downward is enhanced , thus again , insuring more rapid and abrupt change from a distant focal length to close vision . consequently , the intraocular lens of the present invention becomes a far more acceptable bifocal lens with a more rapid and more quickly induced transition between optical focal length options . fig6 and 8 illustrate an alternate preferred embodiment wherein the centrally located refractive chamber 42 is normally filled with the liquid when the line of sight is essentially horizontal and the reservoir chamber 44 is located directly above the refractive chamber 42 . again , the refractive chamber 42 and the reservoir chamber 44 are in direct fluid communication with each other by virtue of passages 46 and 48 and the lower edge of the refractive chamber 42 is connected to each side of the upper reservoir chamber 44 by a pair of vent tubes 50 and 52 which circumbent the refractive chamber 42 in the line of sight in a manner analogous to the previous preferred embodiment . the vent tubes 50 and 52 are again positioned within the lens such that they are horizontally displaced away from the refractive chamber 42 . a pair of anterior attachment loops 54 and 56 are mounted to the outer edge of the lens . the embodiment illustrated in fig6 through 8 performs in a manner somewhat analogous to that of the previous embodiment of fig1 through 3 , except the upper reservoir chamber 44 in this embodiment is filled , for far vision , with air or other suitable inert vapor and the refractive chamber 42 is filled with a liquid . as stated above , when the line of sight is essentially horizontal , the refractive chamber is filled with liquid . as the eye is turned downward , the liquid drains from the refractive chamber 42 into the reservoir chamber 44 . preferably , and as illustrated , the reservoir chamber 44 is anteriorly displaced relative to the refractive chamber 42 , thus taking advantage of the lenticular nature of the intraocular lens to enhance the sensitivity of the fluid transfer from one chamber to the next . also , it should be appreciated that the vent tubes 50 and 52 in this embodiment actually provide for the delivery of the liquid phase as opposed to a transfer of the gaseous phase in the other alternate embodiment . it is contemplated that the intraocular lens of the present invention can be manufactured out of any of the compositions known in the art and , as previously stated , implanted and fastened to the eye by any of the conventional methods and equipment . the actual construction of the lens will involve the precision manufacturing of two separate half lenses which are assembled into a single intraocular lens with the cavity between the halves subsequently being partially filled with the liquid and then sealed . in addition , the previously mentioned advantages associated with the rapid transfer of liquid in and out of the line of sight and resulting bifocal option , the intraocular lens of the present invention is further contemplated as being readily amenable to achieving neutral buoyancy by virtue of the presence of the partially filled internal space in the lens . having thus described and exemplified the preferred embodiments with a certain degree of particularity , it is manifest that many changes can be made within the details of the invention without departing from the spirit and scope of this invention . therefore , it is to be understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification , but is to be limited only by the scope of the attached claims , including the full range of equivalents to which each element thereof is entitled .
a bifocal intraocular lens consisting of an inner and outer transparent wall defining a centrally located refractive chamber , in the line of sight , and in fluid communication with a vertically positioned reservoir chamber , out of the line of sight , wherein vent tubes connect the remote edge of the refractive chamber to the vertically positioned reservoir chamber . such an intraocular lens is highly responsive to changes in the angle of inclination of sight by rapidly transferring a liquid of predetermined refractive index in and out of the refractive chamber , thus creating the bifocal effect .