Abstract:
An improved method and subconjunctival device for causing the eye to focus on a near object. The device automatically changes the focal length of the eye in response to a changing of the length of the medial rectus muscle or the inferior rectus muscle so that the eye can focus on a near object. The device is powered by a rechargeable battery and includes an electrode for stimulating the ciliary muscle as the length of the medial rectus muscle or the inferior rectus muscle changes.

Description:
RELATED PATENT APPLICATIONS 
     This patent application is a continuation in part of U.S. patent application Ser. No. 09/176,673, filed Oct. 21, 1998, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an improved method and apparatus for assisting an eye to focus on an object, and more particularly to an improved method and an apparatus that is implanted in the body. 
     BACKGROUND OF THE INVENTION 
     It is well known that an aging lens precludes or diminishes a person&#39;s capacity to focus on near objects. Focus is accomplished by changing the curvature of the lens and the angular relation of the eyes to each other in accordance with the distance of the observed object to the eye. 
     The change in curvature of the lens, called “Accommodation” is controlled by the circular fibers of the ciliary muscle which is an annulus that is connected to the lens by the zonules. When the ciliary muscle is relaxed, the lens is flattened, i.e., it has less curvature. Thus, distant objects are in focus. 
     On the other hand, contraction of the ciliary muscle will cause the zonules to relax and the lens to thicken, i.e., it has more curvature, thereby shortening its focal distance to accommodate the viewing of a near object. 
     Accommodation causes the angular relation of the eyes to change such as by rotating them inwardly so that they turn toward the near object and so that they turn down. The inward rotation which is caused by the medial rectus muscles is called “Convergence.” The downward turning which is caused by the inferior rectus muscles does not have a specific name. 
     The amount of Convergence caused by an Accommodating lens is called the Accommodation—Convergence Ratio:          A                 C     A                          
     where Accommodation is measured in diopters and Convergence is measured in meter angles (m.a.). 
     The Accommodation—Convergence Ratio which is about 4:1 is constant throughout life. 
     On the other hand, when the medial rectus muscle causes the eye to turn toward a near object, the lens accommodates a given amount. This is the Convergence—Accommodation Ratio: 
     
       
         C/A 
       
     
     The Convergence—Accommodation Ratio varies over a lifetime. For young people, the ratio is about 4 m.a. per diopter. However, as a result of ageing the lens gradually becomes less elastic and the ciliary muscle weakens so that the ciliary muscle is not strong enough to cause the lens to adequately accommodate so that when the eyes converge 4 m.a., the accommodation is less than one diopter and there is a failure to focus. The reduction of the ability of the lens to accommodate is called presbyopia. 
     Therefore, as a person ages, more stimulation must be applied to the ciliary muscle so that it can contract and maintain the 1:4 ratio. 
     As explained in Kamerling U.S. Pat. No. 4,603,697, which issued Aug. 5, 1986, the content of which is hereby incorporated in its entirety by reference, the inability of the eye to focus on near objects can be compensated for by the use of an implanted electrode that can assist the eye to maintain focus. The electrode stimulates the ciliary muscle to constrict and thereby thicken the lens to increase its curvature so that it focuses on a near object thereby keeping the presbyopes in focus. 
     The system described in the Kamerling patent relies upon an external or internal source of power which must be energized to stimulate the ciliary muscle. That patent discloses that the stimulation can be achieved by using radio signals which are detected by an antenna. 
     It would be desirable if the lens could be automatically focused without external stimulation when a person changes the focus to read or see a near object. 
     SUMMARY OF THE INVENTION 
     Thus, with the foregoing in mind, the invention relates to a method for enabling the eye to focus on a near object comprising the step of applying an electrical stimulation to the ciliary muscle in response to a change in the length of the medial rectus muscle or the inferior rectus muscle. 
     In another aspect the invention relates to a device for enabling the eye to focus on an object. The device comprises an electrode for electrically stimulating the ciliary muscle to change the focus of the eye. It also includes another implanted means for generating an electrical signal in response to the movement of the medial rectus muscle or the inferior rectus muscle, a battery, and electrical connectors for connecting the battery, electrode and movement sensor. 
    
    
     DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic drawing of a device constructed in accordance with the invention. 
     FIG. 2A is a front schematic view of the eye showing a sensor constructed in accordance with the invention connected to the medial rectus muscle. 
     FIG. 2B is a front schematic view of the eye showing a sensor constructed in accordance with the invention connected to the inferior rectus muscle. 
     FIG. 3 is a graph showing the ratio of voltage signals necessary to accomplish the result of the invention as a person ages. 
     FIG. 4 is a section of the eye showing the electrode inserted in the ciliary muscle in accordance with the present invention. 
     FIG. 5 is a section of the eye showing the electrode inserted over the sclera adjacent the ciliary muscle in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a device  10  constructed in accordance with a presently preferred form of the invention is seen to include an electrode  14  which is connected by thin wires  16  and  18  to an implanted rechargeable battery  24 , a movement sensor  28  and a micro-chip  30 . 
     As will be explained more completely, the rechargeable battery  24  supplies a minute voltage signal to the electrode  14  by way of the micro-chip  30  when the movement sensor  28  detects a change in the length of the medial rectus muscle. 
     Referring to the FIGS. 2A and 2B, it can be seen that the motion sensor  28  is connected to the medial rectus muscle  34  (FIG. 2A) or the inferior rectus muscle  36  (FIG.  2 B). The electrode  14  is inserted into the ciliary muscle  40 . 
     As is well understood, when a person tries to view a near object, the medial rectus muscle  34  and the inferior rectus muscle  36  of each eye shortens slightly as the eyes turn in toward the object and down while the lens  48  thickens to increase its curvature and shorten its focal length. 
     In accordance with the invention and as seen in FIGS. 2A,  2 B and  3 , the change in length of the medial rectus muscle  34  or inferior rectus muscle  36  is detected by the sensor  28  which sends a first low voltage signal A (FIG. 3) which is proportional to the change in medial rectus  34  or inferior rectus  36  length to electrode  14  through the micro-chip  30 . 
     The micro-chip  30  includes a circuit (not shown) that emits a second low voltage signal B which is proportional to the first low voltage signal to stimulate ciliary muscle  40  and cause it to contract. 
     The contracted ciliary muscle  40  will consequently thicken the lens  48  in proportion to the change in length of the medial rectus muscle  34 . Therefore, the focal length of the lens  48  is shortened and the near object is brought into focus for viewing. 
     When the object is removed, the medial rectus muscle  34  and inferior rectus muscle  36  relaxes, the first low voltage signal A is reduced, the ciliary muscle  40  ceases to be stimulated and the lens  48  flattens to permit viewing of distant objects. 
     The ratio of the second low voltage signal emitted by the micro-chip B for a given first low voltage signal A is built into the micro-chip  30  and is based on the amount of stimulation needed by the ciliary muscle. This can be determined individually for each person after examination. In the alternative it can be approximated by relying on the person&#39;s age since rate at which Accommodation—Convergence Ratio deviates from the 4:1 ratio as a person ages is known. 
     Further, as the person ages and the ciliary muscle  40  continue to weaken and the elasticity of the lens  48  continues to decrease, the amount of stimulation that the ciliary muscle  40  will require to thicken the lens  48  an amount sufficient to bring an object into focus will increase. Therefore, for given change in length of the medial rectus muscle  34  or inferior rectus muscle  36 , and a corresponding first low voltage signal A that the change in length causes, the second low voltage signal emitted by the micro-chip  30  will have to be greater as that person ages to maintain the Accommodation—Convergence Ratio at 4:1 as seen in FIG. 3 at B′ and B″. 
     The ratio of the second low voltage signal B, B′ or B″ to the first low voltage signal A necessary to accommodate the weakening of the ciliary muscle and loss of elasticity of the lens can be increased by simply replacing the micro-chip  30  with one that has the preferred voltage signal ratio built into it, or the micro-chip may be remotely reprogrammed to provide the desired second low voltage signal B, B′ or B″ in response to a given first low voltage signal A. 
     In its presently preferred form, the device  10  is contained entirely within the body. The electrode  14  can be inserted into the ciliary muscle as seen in FIG. 4 or the sclera adjacent the ciliary muscle as seen in FIG.  5 . Hence, there are no antennae, electrodes, connecters or any other part extending through the skin. 
     The rechargeable battery  24  is recharged transcutaneously from time to time by magnetic induction in a manner similar to that describe in U.S. Pat. No. 5,411,537 or through a series resonant circuit such as that described in U.S. Pat. No. 5,279,292, or other similar suitable electromagnetic recharging device  54 . It will be apparent when the rechargeable battery  24  requires recharging since this will be detected by the diminution and ultimate inability of the eyes to focus on near objects. 
     The electrode  14  of the device  10  may be surgically inserted by performing a limbal peritomy, pulling back a conjunctival tenons flap, grasping the wires  16  and  18  and the electrode  14  and inserting them through the sclera of the eye so that the electrode extends preferably into the circular fibers of the ciliary muscle  40  as seen in FIG. 4 approximately 4 millimeters behind the limbus, and then closing the conjunctiva with sutures. While insertion into the circular fibers of the ciliary muscle is preferred, the electrode could be inserted into the longitudinal fibers without impairing the operability of the device. 
     The rechargeable battery  24  and micro-chip  30  may be implanted subconjunctivally in which case the wires  16  and  18  can run subconjunctivally to the electrode  14 . 
     Still further, the motion sensor  28  which may be comprised of a very thin wire can be sutured directly into or hooked onto the medial rectus muscle  34  or inferior rectus muscle  36  so that its length changes in accordance with the movement of that muscle, thereby varying the low voltage signal A applied to the micro-chip  30  and the low voltage signal B applied to the electrode  14 . 
     The ratio of object distance to change of length of the medial rectus muscle, i.e., Convergence, is incorporated into the Accommodation—Convergence Ratio and hence is well known by those skilled in the art. Similarly, ratio of object distance to change of length of the inferior rectus muscle, is well known by those skilled in the art. Accordingly, it is a relatively straightforward process to calibrate the micro-chip  30  so that constriction of the ciliary muscle  40  and the consequent reduction in the focal length of the eye is proportional to the change in length of the medial rectus muscle  34  or the inferior rectus muscle  36 . 
     When the device  10  is installed, the patient will be essentially unaware of its presence since it will operate to bring the lens  48  into focus automatically in response to the movement of the medial rectus or inferior muscles  34  and  36  of each eye. 
     The only time that the device will require attention would be when the rechargeable battery  24  requires recharging, which can be accomplished by a suitable battery recharger  54 , or when the micro-chip  30  is replaced or reprogrammed. 
     While the invention has been described with respect to one presently preferred embodiment, it is apparent that other forms of embodiments will be obvious to those skilled in the art in view of the foregoing description. Thus, the scope of the invention should not be limited by that description, but, rather, only by the scope of the appended claims.