WO2007098622A1

WO2007098622A1 - Spring-biased injector for an intraocular lens

Info

Publication number: WO2007098622A1
Application number: PCT/CH2007/000092
Authority: WO
Inventors: Rolf Meyer
Original assignee: Sdi Surgical Device International Gmbh
Priority date: 2006-02-28
Filing date: 2007-02-23
Publication date: 2007-09-07

Abstract

An insertion device for surgical implantation of an intraocular lens in the eye is disclosed. The device comprises a plunger (200) which is displaceable within a sleeve (110) for guided insertion of the lens. Biasing means with a varying spring constant, e.g. at least two springs (310, 320) acting in different phases of the stroke, are provided for generating a rearward biasing force. This improves the control of the insertion process for the surgeon.

Description

Spring-biased injector for an intraocular lens

Field of the invention

The present invention relates to an insertion device (injector) for surgical im- plantation of an intraocular lens in the eye.

Background of the invention

In cataract surgery, an opaque natural lens in a patient's eye is replaced by an artificial intraocular lens (IOL). In this procedure, the natural lens is first re- moved, usually by phacoemulsification. Then the artificial IOL is inserted. A variety of techniques can be used for the insertion step. Traditionally, the surgeon introduces the lens into the eye with the aid of surgical forceps. Alternatively, a specifically adapted insertion device (injector) may be used. Such a device generally comprises a sleeve and a plunger longitudinally displaceable within the sleeve for advancing an IOL in a deformed (e.g., rolled or folded) state through an opening in a small-diameter nozzle-like portion into the patient's eye, where the lens is then allowed to unfold. The nozzle portion, which is introduced into the eye through a small incision, often has a diameter of no more than 1.5 millimeters.

A variety of different injectors have become known in the art. In one example, the plunger is connected to the housing via a thread. The plunger is advanced longitudinally by rotating a proximal end of the plunger, the thread translating the rotation into a longitudinal displacement. While such a device indeed per- mits exact guiding of the plunger, the surgeon needs both hands for operating the device, and it is relatively difficult to hold the device straight during operation. Therefore, syringe-like injectors have been devised which permit one-hand operation. These devices comprise a slidable plunger which can be advanced by simply pushing on a proximal plunger head. In use, the surgeon holds the sleeve between his index finger and middle finger, while he presses the plunger head with the thumb of the same hand.

Correct insertion of an IOL into the eye is a very delicate operation requiring extremely fine control. In particular, it must be avoided that the surgeon "over- shoots", whereby the deformed lens would shoot out of the nozzle portion of the insertion device in an uncontrollable manner. For improving control, it has been proposed to provide a resistance force or rearward bias against the advancement of the plunger.

By the way of example, in US 6,059,791 , a coil-type spring is wrapped around a proximal portion of the plunger outside of the housing. In US 5,860,984, US 2004/0059343, US 6,251 ,114 and US 2002/0165610, a coil-type spring is wrapped around one of several different portions of the plunger within the housing.

In these arrangements, the biasing force is either present during the whole stroke (the stroke being defined as the movement of the plunger from a fully retracted position to a position at which the lens has exited the nozzle portion of the injector), or only during the very last phase of the stroke when the lens is about to exit the nozzle. The biasing force approximately follows a linear relationship between force and displacement, i.e., it follows Hooke's law F = kx, where x is plunger displacement or compression of the spring, F is the force exerted on the spring, and k is the so-called spring constant. In other words, the slope of the force-displacement relationship is approximately constant.

While such arrangements aid in providing better control of the device to the surgeon, control is not yet optimal. Summary of the invention

It is therefore an object of the present invention to provide an insertion device for surgical implantation of an intraocular lens in the eye which provides im- proved control to the surgeon.

According to a first aspect of the present invention, this object is achieved by an insertion device for surgical implantation of an intraocular lens in the eye with the features of claim 1.

In particular, a device is provided which comprises a housing comprising a sleeve and a lens-receiving portion for receiving an intraocular lens; a plunger manually displaceable in said sleeve, said plunger having a plunger tip for advancing said intraocular lens and having a proximal end

(plunger head) for manually displacing said plunger by pressing on the proximal end; and biasing means acting between said plunger and said housing to provide a rearward biasing force when said plunger is advanced forward by a sur- geon for advancing said intraocular lens, said biasing means having a force-displacement relationship with a slope that substantially changes in the course of advancing said plunger.

By providing biasing means having a significantly changing slope, the biasing forces can be better tailored to provide to the surgeon a clearer tactile feedback of the various phases of the stroke. The slope preferably increases during the stroke. It preferably increases by at least 50%, more preferably by at least 100% between the onset of action of the biasing means and the end of the stroke.

In one embodiment, the biasing means comprise at least one spring with a substantially nonlinear force-compression relationship. In other words, the biasing means comprise a spring whose spring constant changes with the degree of compression of the spring. Such a spring may, e.g., be manufactured from a wire whose thickness varies along the length of the spring. In an another embodiment, the spring may be a coiled spring whose outer diameter changes over the length of the spring, in particular, decreases from a first diameter at one end to a second diameter at the second end. The decrease may be linearly or may follow any other function, depending on the intended characteristics. Such a spring may have a constant thickness of the wire, or the wire may also vary of the length of the spring.

In another embodiment, the biasing means comprise a first spring and at least a second spring, possibly even three, four or more springs. These may readily be disposed in a manner to yield a force-displacement relationship with a slope that substantially changes in the course of advancing the plunger.

The force-displacement relationship can be adjusted by factors such as spring constant (for a nonlinear spring, spring constant as a function of compression), uncompressed length and maximum compression of each spring. By providing at least two springs, the rearward biasing force during the different phases of the stroke can be easily tailored to the needs of the surgeon. By the way of example, the first spring may act before the second spring begins to act, e.g., the first spring may act during the whole stroke, while the second spring may act only at the end of the stroke. Preferably, the first spring acts only from the point at which the plunger tip first touches the lens, while the second spring acts only during the last phase of the stroke in which the lens is about to exit the device.

The springs may be disposed in various locations. By the way of example, the first spring may be a coiled spring mounted on a portion of the plunger outside the housing. The second spring may then be a coiled spring mounted around the same plunger portion inside or around the first spring, or it might be mounted around a different portion of the plunger outside or inside the housing. Alternatively, both springs might be disposed inside the housing. It is also pos- sible to dispose at least one of the springs in a hollow portion of the plunger itself, preferably fully inside the plunger, such that the spring is only accessible through openings in the plunger wall. Many other combinations exist.

At least one of the springs may be preloaded, i.e., the spring already experiences a deviation from its unloaded, relaxed state before it starts to act on the plunger. The preloaded spring may be the first spring, a second or further spring or any combination of these. Advantageously, at least one preloaded spring starts to act on the plunger only in a phase of the stroke of the plunger when the lens is about to exit the device.

The nonlinear spring or the plurality of springs may be combined with a plunger guided in a ball-bearing assembly as well as with a plunger guided conventionally by a friction bearing or plain bearing. In addition or instead, one or more O- rings may be present for guiding the plunger.

According to a second aspect of the present invention, an insertion device for surgical implantation of an intraocular lens in the eye is provided which comprises - a housing comprising a sleeve and a lens-receiving portion for receiving an intraocular lens; a plunger manually displaceable within said sleeve, said plunger having a plunger tip for advancing said intraocular lens and having a proximal end or plunger head for manually displacing said plunger by pressing on the plunger head; a biasing means acting between said plunger and said housing for rear- wardly biasing said plunger when being advanced forward by a surgeon for inserting said intraocular lens into a patient's eye, wherein said biasing member is disposed in a manner to provide said biasing force substantially only during a predefined phase of advancing said plunger, said phase in normal operation extending from a first plunger position in which said plunger tip just begins to touch said intraocular lens to a second plunger position in which said intraocular lens has exited said device.

In this manner, the surgeon knows exactly when the plunger tip starts to touch the lens by starting to feel the biasing force from the biasing means, and the biasing means provides a biasing force exactly in that phase of the stroke in which the lens is actually forwarded in the injector. The biasing member preferably takes the form of at least one spring.

The invention further relates to corresponding methods of inserting an intraocu- lar lens in a patient's eye.

In particular, a method is proposed that comprises the steps of providing an insertion device comprising a housing with a sleeve and a lens-receiving portion for receiving an intraocular lens, said insertion de- vice further comprising a plunger manually displaceable within said sleeve, said plunger having a plunger tip for advancing said intraocular lens and having a proximal end or plunger head for manually advancing said plunger by pressing on the plunge head, said device further comprising a biasing member acting between said plunger and said housing for rear- wardly biasing said plunger; manually retracting said plunger into a substantially fully retracted position in preparation for an insertion stroke; providing said intraocular lens to said insertion device (e.g., by providing a cartridge containing the lens, or by inserting the lens directly into the suita- bly designed injector); in a first phase of the stroke, manually advancing said plunger by pressing with a finger, in particular, a thumb, on said plunger head, into a first partially retracted position in which said plunger tip first touches said intraocular lens, wherein no biasing force is exerted by the biasing member; - in a second phase of the stroke, further advancing said plunger to a second partially retracted position against the biasing force of said biasing member, thereby advancing said intraocular lens. By providing a biasing force from a biasing member such as a spring only when the plunger tip touches the lens, particularly good control is achieved when the lens is advanced in device. In a preferred embodiment, a second biasing mem- ber provides an additional biasing force at the end of the stroke.

Further advantageous embodiments are laid down in the dependent claims.

Brief description of the drawings The invention will be described in more detail in connection with exemplary embodiments illustrated in the drawings, in which Fig. 1 is a schematic partial view of an injector of the prior art;

Fig. 2 is a schematic diagram of force vs. displacement for an injector of the prior art; Fig. 3 is a perspective view of a first embodiment of an injector according to the present invention;

Fig. 4 is a side elevational view of the injector of Fig. 3;

Fig. 5 is a schematic diagram of force vs. displacement for the injector of

Fig. 3; Fig. 6 is a perspective view of a second embodiment of an injector according to the present invention;

Fig. 7 is a longitudinal section of the injector of Fig. 6;

Fig. 8 is a detail view of Fig. 7;

Fig. 9 is a schematic diagram of force vs. displacement for an injector having a pre-biased spring;

Fig. 10 is a schematic drawing of a first alternative arrangement of springs; Fig. 11 is a schematic drawing of a second alternative arrangement of springs; Fig. 12 is a schematic drawing of an injector having a non-linear spring;

Fig. 13 is a schematic diagram of force vs. displacement for an injector having a nonlinear spring; Fig. 14 is a schematic drawing of an injector having another alternative arrangement of springs; and Fig. 15 is a schematic diagram of force vs. displacement for the injector of

Fig. 14.

Detailed description of the invention

Fig. 1 shows a schematic drawing of an injector according to the prior art. The injector has a housing 100 which is only partly shown in Fig. 1. At its rear (proximal) end, the housing is closed by a closure cap 130. A plunger having a plunger rod 210 and a plunger head 230 is displaceable in a guided manner in the housing 100. Wrapped around a portion of the plunger rod outside the housing is a biasing spring 310. With one end, the spring is attached to the plunger head 230. When the plunger is now pushed into the housing, at some point the free end of the spring 310 will abut to the closure cap 130. If the plunger is ad- vanced further forward, the spring 310 is compressed between the closure cap 130 and the plunger head 230. In this manner, it exerts a rearward biasing force to the plunger relative to the housing.

The resulting relationship between plunger displacement x (in arbitrary units) and biasing force F (in arbitrary units) is illustrated in Fig. 2. During the initial phase of the stroke, the spring is yet uncompressed, and no biasing force acts. At position x = x1 , the spring starts to abut to the closure cap 130 and therefore starts to be compressed. The rearward force now rises in a linear manner with compression according to Hooke's law as follows: F - k(x- xX) , where the slope k is called the spring constant, until the spring is fully compressed at position x3.

Strictly speaking, Hooke's law only applies for ideal springs. For real-life springs, there may be small deviations from Hooke's law. However, even for a real-life spring, the relationship between force and compression is substantially linear to a reasonable approximation. Mathematically speaking, the derivative of force vs. displacement is approximately constant: dF/dx = k = const . While such a constantly rising biasing force may aid the surgeon in inserting an intraocular lens into a patient's eye with the prior-art injector, control is not perfect.

In order to improve control, the present invention suggests to provide biasing with a nonlinear force-displacement relationship. To this end, in a preferred embodiment, more than one spring is provided. A first embodiment of an injector 1 for an intraocular lens according to the present invention is shown in Figs. 3 and 4. The injector comprises a housing 100 in which a plunger 200 is guided for longitudinal displacement along the plunger axis 201.

The housing 100 comprises a sleeve 110 for guiding the plunger, merging into a housing front part 120. The housing 100, and in particular the sleeve 110, is preferably made from a corrosion-resistant and inert metal like titanium. How- ever, it may also be envisaged that the housing is manufactured from a high- strength plastic material. It may be manufactured in one part, or the front part 120 may be manufactured separate from the sleeve 110.

The housing front part 120 is adapted for receiving a lens cartridge (the car- tridge not being shown in the drawings). To this end, the front part 120 has a lateral window 121 and a pair of hooks 122 for holding the lens cartridge in the window 121 , such that the plunger tip 222 can enter a longitudinal through-bore of the lens cartridge when inserted in the window. The lens cartridge has a lens receiving section to be disposed in the region of the window 121 and a small- diameter nozzle portion which will extend beyond the front end of the front part

120. An intraocular lens provided in the lens receiving section of the cartridge may be pushed towards the nozzle portion and through an opening therein into a patient's eye by the action of the plunger 200. Depending on the type of lens cartridge, the lens is folded or rolled up during this process, or the lens may be already provided in a rolled-up or folded state in the lens receiving section.

A closure cap 130 is mounted on the rear (proximal) end of the sleeve 110. A finger support 131 in the form of two radial flanges is provided on the closure cap 130 or on the sleeve 110. The finger support 131 serves for supporting the index and middle finger when a surgeon grips the injector in a manner like a syringe.

The plunger 200 extends longitudinally through the sleeve 110. Its rear (proximal) end portion protrudes from the sleeve 110 through the closure cap 130. The plunger 200 comprises a cylindrical push rod 210 to whose front (distal) end a plunger needle 220 is releasably mounted. The rod and the needle may also be formed in one piece. The plunger needle 220 ends in a specifically shaped plunger tip 222 for pushing the lens through the nozzle portion of the cartridge into the patient's eye. At the rear end of the plunger, a plunger head 230 serving as a support for a surgeon's thumb is mounted on the push rod 210. In the present embodiment, the plunger head 230 is mounted on the push rod in a rotatable manner, allowing for rotation of the plunger head 230 around the plunger axis 201. While this is particularly advantageous in specific situations, the plunger head 230 may also be fixedly secured to the push rod 210 instead. An optional finger ring 240 is attached to the plunger head 230 for receiving the surgeon's thumb. This finger ring (handle ring) 240 provides im- proved guidance of the plunger 200 in the sleeve 110 and enables a quick release of the plunger 200 into its retracted position after insertion of the lens into the patient's eye. For further details and advantages of the finger ring, reference is made to U.S. patent application publication No. 2004/0097954, the contents of which are incorporated herein by reference in their entirety for teaching an injector having a finger ring.

In order to provide a rearward force (rearward bias) to the plunger when the same is advanced for insertion of a lens into a patient's eye, a first spring 310 and a second spring 320 are provided. Both springs are coil-type springs and are disposed around that portion of the plunger rod 210 that extends outside of the housing 100. With one end, each spring is fixed to the plunger head 230. The first spring 310 is longer and has a larger diameter than the second spring 320. It accommodates the second spring 320 in its inside. In order to avoid that the two springs get entangled, the two springs have opposite winding senses: The first spring 310 is a left-handed helix, while the second spring 320 is a right- handed helix. The first spring 310 has at its free end a ring-shaped stop 311 for abutting to the end face of the closure cap 130. The second spring 320 ends in a final turn 321 with close to zero pitch, this final turn likewise constituting a stop.

In operation of the device, a lens cartridge containing an intraocular lens for im- plantation is inserted into the cartridge window 121 of the housing front part 120 and secured there by the hooks 122. The surgeon holds the device by gripping the sleeve 110 between his index and middle fingers in a manner that these fingers rest in front of the finger support 131. The surgeon inserts the nozzle portion of the cartridge into an incision in the patient's eye and advances the plunger until the ring-shaped stop 311 abuts to the rear end of the closure cap 230. From this point, the surgeon receives a tactile feedback from the first spring 310 from which he knows that the plunger tip touches the lens. The surgeon then proceeds to advance the plunger further, thereby advancing the lens into the nozzle portion of the cartridge and compressing the first spring 310. Thus the first spring 310 exerts a rearward force to the plunger which increases with further advancement of the plunger. When the lens has been forwarded within the cartridge so far that is just about to exit the nozzle portion, the first spring 310 has been compressed so far that it has substantially the same length as the second spring 320. From this point on, the free end of the second spring 320 with stop 321 will abut to the right end of stop 311 , which in turn abuts to the right end of the closure cap 130. When the plunger is now advanced further, not only the first spring 310 is further compressed, but also the second spring 320 starts to be compressed. Thereby, the rearward biasing force is significantly increased, giving the surgeon a clear tactile feedback that the lens is now about to exit the nozzle.

In practice, it is very advantageous that the surgeon receives tactile feedback from the spring exactly when the plunger tip touches the lens for the first time, indicating that the critical phase of the stroke has begun. This advantage is independent of whether or not there is a second spring present, and whether or not the force-displacement relationship of the spring is linear. Prior-art embodi- ments of spring-biased injectors have missed this important point.

Fig. 5 shows a schematic diagram of the rearward biasing force F exerted by the springs vs. the amount of displacement x of the plunger starting from a fully retracted state. The resistance resulting from the lens being moved in the car- tridge is disregarded in Fig. 5, as this resistance depends on the type of lens, the type of cartridge, and it depends in a more complicated, but generally smooth and continuous manner on the displacement. In the initial phase of the stroke, before the plunger tip contacts the lens, none of the springs acts, and there is no biasing force up to a position x1. At this point, the first spring begins to act. Here, position x1 is chosen to be the plunger position at which the plunger tip first contacts the lens, but another point during the stroke might be chosen. Between points x1 and x2, the first spring is compressed. Its biasing force rises approximately in a linear manner upon advancing the plunger, according to Hooke's law F = k\ (x- x1) , where the slope or proportionality factor k1 is the spring constant of the first spring. At point x2, the second spring starts to be compressed. This leads to a sharp rise in the slope of the biasing force, as this force now not only results from compression of the first spring, but also of the second spring. The slope now is /c1 + /f2 , where k2 is the spring constant of the second spring. It is this sharp rise that provides tactile feedback to the sur- geon that the lens is about to exit the nozzle.

Overall, the relationship between force and displacement of the plunger therefore is non-linear. The slope of the curve describing force vs. displacement changes with displacement.

An alternative embodiment leading to a similar force-displacement relationship is shown in Figs. 6 to 8. In this embodiment, one of the springs is disposed in a hollow space within the plunger rod, while the other spring is wrapped around the plunger. An injector having a single spring disposed within the plunger is disclosed in European Patent Application EP 05 405 722.9 filed 23 December 2005. The contents of this application are incorporated herein by reference in their entirety for teaching a spring-biased insertion device for an intraocular lens whose spring is disposed inside the plunger rod. The embodiment of Figs. 6 to 8 will now be described in more detail. Similar parts carry the same reference signs as is Figs. 3 and 4.

As in the first embodiment, the injector of the embodiment of Figs. 6 and 7 comprises a housing 100 in which a plunger 200 is guided for longitudinal displacement along the plunger axis 201. The housing 100 again comprises a sleeve 110 for guiding the plunger, merging into a housing front part 120 adapted for receiving a lens cartridge. As in the first embodiment, a closure cap 130 is mounted on the rear (proximal) end of the sleeve 110. A finger support 131 is provided in one piece with the closure cap 130. The closure cap is mounted on the sleeve with the aid of a stud screw 134.

On the sleeve 110, an optional distance ring 140 is mounted, serving as a front limit stop for the surgeon's fingers. The ring 140 is secured on the sleeve in a releasable manner by a small stud screw 141 and is displaceable along the sleeve after loosening the screw 141 for adapting the distance between the finger support 131 and the ring 140, thereby adjusting the distance to the thickness of a surgeon's fingers.

Again, at the rear end of the plunger, a plunger head 230 serving as a support for a surgeon's thumb is mounted on the push rod 210, and an optional finger ring 240 is attached to the plunger head 230 for receiving the surgeon's thumb.

The plunger 200 is guided in the sleeve 110 with the aid of a ball-bearing assembly 270 disposed in the sleeve 110, i.e., in the rear part of the housing 100. The ball-bearing assembly 270 comprises a bushing for holding a plurality of _

14 balls distributed over the length and circumference of the bushing. These balls contact, on the outside of the bushing, the inner wall of the sleeve 110. On the inside of the bushing, the balls contact the outside surface of the push rod 210. In this way, the plunger 200 is guided in the sleeve 110 for longitudinal dis- placement with very little friction. It should be noted that in this configuration, the ball-bearing assembly 270 itself moves longitudinally in the sleeve 110 when the plunger 200 is displaced. By the way of example, when the plunger is displaced in the sleeve by two centimeters, the ball-bearing assembly is displaced by half this distance, i.e., by one centimeter. Instead, a different type of ball- bearing assembly may be used in which the ball-bearing assembly cannot move longitudinally in the sleeve. In this case, the balls of the ball-bearing assembly will not contact the inner surface of the sleeve. Further details and advantages of providing a ball-bearing assembly in the rear part of the housing are apparent from U.S. patent application publication No. 2003/0040755, the contents of which are incorporated herein by reference in their entirety for teaching the use of a ball bearing in an IOL insertion device. Instead of a ball-bearing assembly, another type of bearing, e.g., a plain (friction) bearing, may be employed. The plunger may instead be guided by one or more O-rings, or both a ball-bearing assembly and a conventional guidance means like a friction bearing or O-rings may be present.

In the present embodiment, the ball-bearing assembly further comprises a guide ball having a diameter which is larger than that of the bearing balls. A first guide groove is provided in the outer surface of the push rod, while a second guide groove is provided in the inside surface of the sleeve. The guide ball engages in both of these guide grooves, which serve as tracks for the guide ball during longitudinal displacement of the plunger. In this manner, the plunger is prevented from rotation around its axis, without adding any significant resistance force to the advancement of the plunger. In the present embodiment, the guide grooves are rectilinear. However, if it is desired to induce a controlled rotation of the plunger when the plunger is advanced longitudinally, one of both of the guide grooves may be curved, e.g., spiraled. While providing a guide ball in the bear- ing assembly that is guided in two complementary tracks is advantageous, other means for preventing uncontrolled rotation of the plunger may be employed, e.g., a single guide groove in the surface of the push rod into which engages a guide element, e.g., in the form of a pin or ball, held in the sleeve, where the guide element may be spring-biased, or in the form of a lug formed on the cap, extending into the guide groove.

A first coiled spring 330 is accommodated in a central, longitudinal bore (hollow space) 212 in a rear portion of the push rod 210. Two rectilinear, longitudinal slits provide lateral access to the bore 212. With its rear end, the spring 330 abuts to a ferrule 232 screwed into the rear end of the bore. The ferrule 232 thus serves as a proximal stop (rear limit stop) in the form of a rear/proximal spring seating for the spring 330. At the same time, the ferrule 232 serves for receiving the screw 233 with which the plunger head 230 is rotatably mounted on the push rod 210.

At its front end, the spring 330 abuts to a front (distal) spring seating 262. A pin 263 extends towards the rear end along the plunger axis from the spring seating 262 into the inside of the spring 330, preventing lateral movement of the spring 330. The front spring seating extends through the two lateral slits to the outside of the push rod 210. It is fixedly connected to a ring 261 surrounding the push rod. The ring 261 and the spring seating 262 together form a front limit stop (distal stop) 260.

A second coiled spring 340 is wrapped around the plunger rod 210. With its rear (proximal) end, it is connected to the plunger head 230. With its front (distal) end, it is connected to a ring 341 slidably mounted on the plunger rod 210.

In operation, the plunger is first brought into a fully retracted position. The lens cartridge is inserted into the window 121. The surgeon now pushes the plunger until the ring 261 abuts to the closure cap 130. The length of the first spring 330 is chosen such that in this position, the plunger tip just touches the lens in the cartridge for the first time. Thus, the surgeon receives tactile feedback that the lens is now being pushed forward in the cartridge. When the surgeon pushes the plunger further forward, ring 261 remains stationary with the housing 100, and the first spring 330 is compressed, exerting a linearly rising biasing force to the plunger. When the plunger is still further advanced, ring 261 will touch ring 341. The length of the second spring 340 is chosen such that this will occur when the lens is just about to exit the nozzle tip. From this position on, in addition to the first spring 330, also the second spring 340 starts to become compressed, as now both rings 261 and 341 are stationary with the housing. This manifests itself in an increase of the slope of the bias force, thus providing a tactile feedback to the surgeon that now the last phase of insertion of the lens has begun. Altogether, the overall relationship between biasing force and displacement is qualitatively the same as in Fig. 5.

In this embodiment, total compression of the springs is limited by the pin 263. Once the springs have been compressed so far that the free end of pin 263 touches ferrule 232, no more compression is possible. In this manner, a well defined end stop for the stroke of the plunger is provided.

The first spring 330 can already be preloaded (biased) in the fully retracted position of the plunger before being further compressed by advancing the plunger. To this end, the length of the uncompressed spring may be chosen larger than the distance available for the spring between the front and rear spring seatings in the configuration of Figs. 6 to 8. When the plunger is advanced beyond the point where the ring 261 first touches the closure cap 230, the resistance force sensed by the surgeon rises suddenly and distinctively by the action of the (preloaded) spring. The surgeon thus knows exactly and intuitively that he has reached that phase of the injection procedure where the lens is being advanced through the cartridge.

The corresponding force diagram is illustrated in Fig. 9, which shows a schematic diagram of biasing force F vs. displacement x during advancement of the plunger. When the plunger is advanced in the injector from a fully retracted position (x = 0 ), there is at first no biasing force. At position x = x1 , the plunger has been advanced to a partially retracted position where the ring 261 touches the rear of cap 230. When advancing the plunger further, the resistance force suddenly rises to the value given by the amount of preloading (bias) of the spring between seating 262 and ferrule 232. From there, the biasing force from the first spring rises approximately in a linear manner upon further advancing the plunger, according to Hooke's law. At position x = x2 , the second spring 340 starts to act. At position x = x3, pin 263 touches ferrule 232, and the plunger cannot be advanced further. By a proper choice of the spring constants and of the initial compression of the first spring, both the initial resistance force beyond point x = x1 and the slopes of the increase of the force with displacement can be easily adjusted to individual needs. Such force characteristics may also be achieved when the spring is disposed in other locations, e.g., around the plunger, as long as the spring is already preloaded (pre-biased) in the fully retracted position of the plunger and is further compressed only by advancing the plunger beyond a partially retracted position.

In addition to the already described configurations, a large variety of different ways of disposing the first and second spring are possible. By the way of example, Fig. 10 shows an embodiment in which the second (shorter) spring 360 surrounds the first (longer) spring 350, both springs being disposed around the plunger rod.

Fig. 11 shows an embodiment in which two springs 370, 380 are disposed in a series configuration end-to-end around the plunger rod. In this embodiment, once the free end of spring 370 touches the closure cap 130, both springs start to be compressed. As the spring constant k1 of spring 370 is smaller than spring constant k.2 of spring 380, spring 370 will be compressed more easily than spring 380. The effective spring constant k of the combination of springs is approximately k = /c1 -/c2/(/c1 + /c2) < /c1. At some point of the stroke, there will be a position of the plunger at which spring 370 is already fully compressed while spring 380 is still only partially compressed. From this point on, it will only be spring 380 that acts with its spring constant k2. Altogether, the resulting relationship between force and displacement is again qualitatively similar to that of Fig. 5.

The springs may be disposed in different places. By the way of example, at least one of the springs may be disposed in the inside of housing 100, e.g., in the hollow space 112 towards the front of sleeve 110 in Fig. 7. A first stop for such a spring can easily be provided in the form of a flange in the inside of housing front part 120, while a second stop would then be constituted by the ring with which plunger needle 220 is mounted to plunger rod 210.

In alternative embodiments, more than two springs are provided, e.g., three or four springs. By the way of example, one spring might be provided inside the housing, at least one spring around the plunger and one spring inside the plunger.

Instead of providing a plurality of springs, it is also possible to provide a single biasing member which has a nonlinear force-displacement relationship. An ex- ample would be a spring whose spring constant varies along the length of the spring. Conceptually, such a spring would be similar to the situation in Fig. 11. However, the variation of biasing force with displacement/compression can be tailored to be much smoother than for separate springs, if this is desired. As another example, Fig. 12 shows an embodiment of an injector having a coiled (helical) spring which is wound from a wire with uniform thickness and with constant pitch, but whose outer diameter decreases over its length, giving the spring an overall essentially conical shape. Fig. 13 shows a diagram of force vs. displacement for a spring whose wire thickness rises linearly along the length of the spring or whose outer diameter decreases linearly along the length of the spring, leading to a roughly quadratic rise in force. Other embodiments of nonlinear springs are of course possible, including springs with non-uniform pitch. Instead of coiled springs, any other type of spring may be used, including cantilever springs or combinations of different spring types. The spring might also be constituted by a piece of resilient material, e.g., rubber etc, which provides an elastic biasing force against the advancement of the plunger.

Instead of compression springs, at least one spring exerting a tension force might be employed. In this case, e.g., one spring may be provided in a hollow space of the plunger which would extend into the inside of the housing, and the spring would be fixedly connected between a proximal stop which may come into abutment with the housing and a distal stop fixedly connected with the plunger. On pushing the plunger into the housing, the spring would then be ten- sioned.

Still another embodiment is illustrated in Fig. 14. A first spring 310 and a second spring 320 are both mounted on a plunger 210 for compression between a plunger head 230 and a closure cap 130 of an injector housing 100. The first spring 310 is longer and has a larger diameter than the second spring 320. It accommodates the second spring 320 in its inside. Insofar, the embodiment of Fig. 14 is similar to the embodiment of Figs. 3 and 4. While in the embodiment of Fig. 14 the springs are wound in the same sense, it is of course possible to wind the in opposite senses.

The first spring 310 has at its distal end a ring-shaped stop 311 for abutting to the end face of the closure cap 130. Likewise, the second spring 320 has at its distal end a ring-shaped stop 321. The plunger 210 has a longitudinal slit 211, similar to the embodiment of Figs. 7 and 8, which is, however, shorter than in the former embodiment. A pin extends laterally through the ring-shaped stop 321 and through the slit 211 , connecting two diametrically opposite sides of the ring-shaped stop 321 through the slit. In this manner, the movement of the ring- shaped stop 321 relative to the plunger is limited between the rear (proximal) end and the front (distal) end of the slit. The position of the distal end of the slit is chosen such that the inner (second) spring 320 is pre-compressed by the stop 321 when the pin abuts to the distal end of the slit. In this manner, the inner spring is preloaded, while the outer spring is unloaded in a fully retracted position of the plunger 210.

This leads to a diagram of force vs. displacement as it is sketched diagrammati- cally in Fig. 15. When the plunger is advanced in the injector from a fully retracted position ( x = 0 ), there is at first no biasing force. At position x = x1 , the plunger has been advanced to a partially retracted position where the ring- shaped stop 311 of the first spring 310 touches the rear of cap 230. When advancing the plunger further, the first spring 310 starts to be compressed. The compression force rises from zero approximately in a linear manner upon further advancing the plunger, according to Hooke's law. At position x = x2 , the stop 321 of the inner (second) spring abuts to the cap 130 or to the stop 310 of the first spring. From this point on, the second (inner) spring 320 starts to be compressed further, beyond the amount by which it is already pre-compressed (preloaded). This leads to a sudden, sharp rise in force by the amount of the preloading of the second spring. At position x = x3 , the pin extending through the slit 211 touches the rear (proximal) end of the slit, and the plunger cannot be advanced further. By a proper choice of the spring constants and of the initial compression of the second spring, the force characteristics can be easily tailored to individual needs. As already stated for the other embodiments, such a force characteristics may also be achieved when the second spring is disposed in other locations, e.g., inside the plunger or inside the housing, as long as the second spring is already preloaded (pre-biased) in the fully retracted position of the plunger and is further compressed only by advancing the plunger beyond a partially retracted position.

Advantageously, the plunger position x = x2 at which the second spring first starts to act against the forward movement of the plunger is chosen such that it corresponds to the position in which the lens is just about to exit the nozzle tip of the injector. In this manner, a very distinct tactile feedback is provided to the surgeon that this crucial point in the injection process has been reached.

It will be appreciated that the foregoing description refers to specific embodiments and is to be understood as not limiting the invention. In particular, many more modifications are possible without leaving the scope of the present invention. In particular, it will be apparent that springs of various different types, e.g., linear or nonlinear, coiled or otherwise constructed etc., can be used, that such springs can be disposed in various different locations, e.g., wound around the plunger inside or outside the housing or disposed in the plunger, that such springs can be combined in various combinations, and that any of these springs may be preloaded or fully relaxed in a fully extended position of the plunger, without leaving the scope of the present invention.

List of reference symbols

X Displacement x1 First position x2 Second position x3 Third (final) position

F Force (in arbitrary units)

1 Injector

100 Housing

110 Sleeve

112 Hollow region

120 Front part

121 Window for cartridge

122 Hook

130 Cap

131 Finger support

132 Opening

133 Groove

140 Distance ring 141 Screw (stud)

200 Plunger

201 Plunger axis

210 Plunger rod

211 Longitudinal slit

212 Bore

220 Plunger needle

222 Plunger tip

230 Plunger head

231 Thumb support

232 Ferrule

233 Screw

240 Finger ring

250 Spring

260 Distal stop assembly

261 Ring

262 Spring seating

263 Pin

270 Ball bearing assembly

310 First spring

320 Second spring

330 First spring

340 Second spring

350 First spring

360 Second spring

370 First spring

380 Second spring

390 Non-linear spring

Claims

Patent claims

1. An insertion device for guided insertion of an intraocular lens into a pa- tient's eye, said device comprising a housing (100) comprising a sleeve (110) and a lens-receiving portion (120) for receiving an intraocular lens; a plunger (200) manually displaceable in said sleeve (110), said plunger (200) having a plunger tip (222) for advancing said intraocular lens; and a biasing means (310, 320; 330, 340; 350, 360; 370, 380; 390) acting between said plunger (200) and said housing (100) to provide a rearward biasing force when said plunger (200) is advanced forward for inserting said intraocular lens, said biasing means having a force- displacement relationship with a slope that substantially changes in the course of advancing said plunger (200).

2. The device of claim 1 , wherein said biasing means (310, 320; 330, 340; 350, 360; 370, 380; 390) is disposed in a manner to provide said bias- ing force substantially only during a predefined phase of advancing said plunger (200) forward, said phase in normal operation extending from a first plunger position (x1 ) in which said plunger tip just begins to touch said intraocular lens to a second plunger position (x3) in which said intraocular lens has exited said device.

3. The device of claim 1 or 2, wherein said biasing means comprises a nonlinear spring (390) having a substantially nonlinear force- compression relationship.

4. The device of claim 3, wherein said nonlinear spring (390) is a coiled spring of predetermined length wound from a wire having a thickness which varies over the length of the spring.

5. The device. of claim 3, wherein said nonlinear spring (390) is a coiled spring of predetermined length being wound in a manner that the outer diameter of the spring substantially changes over the length of the spring.

6. The device of one of claims 1 to 5, wherein the biasing means comprises a first spring (310; 330; 350; 370) and at least a second spring (320; 340; 360; 380).

7. The device of claim 6, wherein said first and second springs are disposed in a manner such that said second spring (320; 340; 360; 380) acts only after the first spring (310; 330; 350; 370) has begun to act when said plunger (200) is advanced forward.

8. The device of claim 6 or 7 wherein said first and second springs are coiled springs.

9. The device of claim 8, wherein said first and second springs are dis- posed around a plunger portion outside said housing (100).

10. The device of claim 8 or 9, wherein said second spring (320) is disposed inside said first spring (310).

11. The device of claim 8 or 9, wherein said second spring (360) is disposed around said first spring (350).

12. The device of claim 8 or 9, wherein said first spring (370) and said second spring (380) are disposed in a series configuration.

13. The device of one of claims 8 to 12, wherein said second spring (320) and said first spring (310) have opposite winding senses.

14. The device of one of claims 6 to 13, wherein at least one of said first spring and said second spring is disposed inside said housing (100).

15. The device of one of claims 6 to 14, wherein at least one of said first spring and said second spring is disposed in a hollow space within said plunger (200).

16. The device of one of claims 6 to 15, wherein at least one of said first spring and said second spring is preloaded in a fully retracted position of said plunger (200).

17. An insertion device for guided insertion of an intraocular lens into a patient's eye, said device comprising a housing (100) comprising a sleeve (110) and a lens-receiving portion (120) for receiving an intraocular lens; a plunger (200) manually displaceable within said sleeve (110), said plunger (200) having a plunger tip (222) for advancing said intraocular lens; a biasing means (310, 320; 330, 340; 350, 360; 370, 380; 390) acting between said plunger (200) and said housing (100) for rear- wardly biasing said plunger when being advanced forward by a surgeon for inserting said intraocular lens into a patient's eye, wherein said biasing means is disposed in a manner to provide said biasing force sub- stantially only during a predefined phase of advancing said plunger

(200), said phase in normal operation extending from a first plunger position (x1 ) in which said plunger tip just begins to touch said intraocular lens to a second plunger position (x3) in which said intraocular lens has exited said device.

18. A method of inserting an intraocular lens into a patient's eye, said method comprising the steps of providing an insertion device comprising a housing with a sleeve and a lens-receiving portion for receiving an intraocular lens, said insertion device further comprising a plunger manually displaceable within said sleeve, said plunger having a plunger tip for advancing said in- traocular lens and having a plunger head, said device further comprising a biasing member acting between said plunger and said housing for rearwardly biasing said plunger; manually retracting said plunger into a substantially fully retracted position in preparation for an insertion stroke; providing said intraocular lens to said insertion device (e.g., by providing a cartridge containing the lens, or by inserting the lens directly into the suitably designed injector); in a first phase of the stroke, manually advancing said plunger by pressing with a finger, in particular, a thumb, on said plunger head, to a first partially retracted position in which said plunger tip first touches said intraocular lens, wherein no biasing force is exerted by the biasing member; in a second phase of the stroke, further advancing said plunger beyond said first partially retracted position against the biasing force of said biasing member, thereby advancing said intraocular lens.

19. The method of claim 18, further comprising the step of, in a third phase towards the end of the stroke, manually advancing said plunger beyond a second partially retracted position against a further biasing force of an additional biasing member.