Vision prosthesis

A vision prosthesis includes a lens having an index of refraction that varies in response to a focusing stimulus. An actuator in communication with the lens provides the focusing stimulus on the basis of a range estimate from a rangefinder. A controller coupled to the rangefinder and to the actuator causes the actuator to generate a focusing stimulus on the basis of the range estimate.

FIELD OF INVENTION

This invention relates to a vision prosthesis, and in particular, to prosthetic lenses.

BACKGROUND

In the course of daily life, one typically regards objects located at different distances from the eye. To selectively focus on such objects, the focal length of the eye's lens must change. In a healthy eye, this is achieved through the contraction of a ciliary muscle that is mechanically coupled to the lens. To the extent that the ciliary muscle contracts, it deforms the lens. This deformation changes the focal length of the lens. By selectively deforming the lens in this manner, it becomes possible to focus on objects that are at different distances from the eye. This process of selectively focusing on objects at different distances is referred to as “accommodation”.

As a person ages, the lens loses plasticity. As a result, it becomes increasingly difficult to deform the lens sufficiently to focus on objects at different distances. To compensate for this loss of function, it is necessary to provide different optical corrections for focusing on objects at different distances.

One approach to applying different optical corrections is to carry different pairs of glasses and to swap glasses as the need arises. For example, one might carry reading glasses for reading and a separate pair of distance glasses for driving. This is inconvenient both because of the need to carry more than one pair of glasses and because of the need to swap glasses frequently.

Bifocal lenses assist accommodation by integrating two different optical corrections onto the same lens. The lower part of the lens is ground to provide a correction suitable for reading or other close-up work while the remainder of the lens is ground to provide a correction for distance vision. To regard an object, a wearer of a bifocal lens need only maneuver the head so that rays extending between the object-of-regard and the pupil pass through that portion of the bifocal lens having an optical correction appropriate for the range to that object.

The concept of a bifocal lens, in which different optical corrections are integrated into the same lens, has been generalized to include trifocal lenses, in which three different optical corrections are integrated into the same lens, and continuous gradient lenses in which a continuum of optical corrections are integrated into the same lens. However, just as in the case of bifocal lenses, optical correction for different ranges of distance using these multifocal lenses relies extensively on relative motion between the pupil and the lens.

Once a lens is implanted in the eye, the lens and the pupil move together as a unit. Thus, no matter how the patient's head is tilted, rays extending between the object-of-regard and the pupil cannot be made to pass through a selected portion of the implanted lens. As a result, multifocal lenses are generally unsuitable for intraocular implantation because once the lens is implanted into the eye, there can be no longer be relative motion between the lens and the pupil.

A lens suitable for intraocular implantation is therefore generally restricted to being a single focus lens. Such a lens can provide optical correction for only a single range of distances. A patient who has had such a lens implanted into the eye must therefore continue to wear glasses to provide optical corrections for those distances that are not accommodated by the intraocular lens.

SUMMARY

The invention provides a vision prosthesis for restoring a patient's ability to focus on objects at different distances. The vision prosthesis includes a lens whose focal length can automatically be changed, and a rangefinder coupled to that lens for estimating the range to an object that the patient wishes to focus on.

In one embodiment, the variable-focus lens of the vision prosthesis has an index of refraction that varies in response to a focusing stimulus. An actuator in communication with the lens provides the necessary focusing stimulus on the basis of a range estimate from the rangefinder. A controller coupled to the rangefinder and to the actuator causes the actuator to generate a focusing stimulus on the basis of this range estimate.

Because it is the index of refraction that is changed, the vision prosthesis provides control over the focal length of the lens without the need to mechanically move the lens or any portions thereof. The vision prosthesis thus provides a lens of variable focal length with no moving parts and without the complexity and excessive power consumption associated with a moveable system.

The lens of the vision prosthesis can be adapted for implantation in an eye of a phakic or an aphakic human patient. Alternatively, the lens, and its associated electronics, can be worn outside the patient on, for example, an eyeglass frame.

When implanted in the eye, the lens can be disposed at a variety of locations, such as the anterior chamber, the posterior chamber, the lens bag, or the cornea. To ease the implantation process and to minimize the extent of the incision required, the lens can be a foldable lens having a tendency to spring back into an unfolded state.

In one embodiment of the vision prosthesis, the lens includes a chamber containing a nematic liquid crystal or other material that has a changeable index of refraction. A nematic liquid crystal has an index of refraction that changes in response to an applied electromagnetic field. This change in the index of refraction results in a change in the focal length of the lens.

The actuator for the lens can include a variable voltage source and one or more electrodes coupled to both the variable voltage source and the lens. Alternatively, the actuator can include a variable current source and one or more coils coupled to the variable current source and to the lens. In either case, the actuator generates a field, an electric field in the former case and a magnetic field in the latter case, that can interact with the nematic liquid crystal to selectively alter its index of refraction.

The index of refraction of the lens need not be spatially uniform. By providing a plurality of actuating elements coupled to different local regions of the lens, the index of refraction can be varied at those local regions. This enables the lens to have an effective optical shape that is largely independent of its physical shape. A convex lens can be created, for example, by applying a stronger electric field to the central portion of a planar chamber filled with nematic liquid crystal than to the periphery. This changes the index of refraction at the center more than at the periphery. A lens having a spatially non-uniform index of refraction can be implemented by providing a plurality of electrodes disposed at different portions of the lens. In one aspect of the invention, these electrodes are concentric electrodes. In such a case, the index of refraction can be made a function of distance from the center of the lens.

In an alternative embodiment, the index of refraction can be made a function of more than one spatial variable. For example, the electrodes can be distributed in a two-dimensional grid on the surface of the lens. Such a grid can be a polar grid or a rectilinear grid. Its primary function would be to correct wavefront aberrations present in the eye due to abnormalities in the cornea, the lens, and the ocular media.

An advantage of a lens having planar chamber as described above is that such a lens can be made thin enough to be implanted in very small spaces within the eye. For example, a lens in which first and second planar sides are separated by a gap smaller than the separation between the lens bag in an eye and the iris in the eye can be implanted in the posterior chamber of the eye.

In some cases, it may not be possible to vary the index of refraction sufficiently to correct the patient's vision. In such cases, the lens can include one or more lens elements that can be moved so as to bring an image into focus. Such a lens also includes a motor to move the lens elements.

Alternatively, the lens can have a baseline curvature and also be filled with nematic crystal or a material having an index of refraction that can be changed. The baseline curvature can be used to perform a gross correction that can be fine-tuned by locally varying the index of refraction of the lens material.

In one embodiment of the vision prosthesis, the rangefinder includes a transducer for detecting a stimulus from an anatomic structure in an eye, the stimulus being indicative of a range to the object-of-regard. The transducer can be a pressure transducer for detecting contraction of a muscle, such as a piezoelectric element that generates a voltage in response to contraction of the muscle. Alternatively, the transducer can be an electromyograph for detecting electrical activity associated with contraction of the muscle.

The stimulus detected by the transducer can come from the activities or states of one or more anatomical structures within the eye. These activities or states include: contraction of a ciliary muscle, tension in a zonule, mechanical disturbance of a lens bag, contraction of a rectus muscle, and dilation of an iris.

The rangefinder of the vision prosthesis does not, however, have to rely on the operation of any structure in eye to estimate a distance to an object. For example, the rangefinder can also include an autofocus system. One example of an autofocus system includes: an infrared transmitter for illuminating an object with an infrared beam; an infrared receiver for receiving a reflected beam from the object, and a processor coupled to the infrared receiver for estimating a range to the object on the basis of the reflected beam. However, other autofocusing systems can readily be adapted for the use in the vision prosthesis.

To assist the autofocus system in achieving and maintaining focus, it is often desirable to include a feedback loop coupled to the autofocus system. One example of a feedback loop includes first and second lenslets posterior to the lens. Each lenslet is in optical communication with an associated photodetector posterior to that lenslet. The distance between the lenslet and its associated photodetector is between the focal lengths of the two lenslets.

Regardless of the type of rangefinder, it is useful to provide an optional manual focusing control for enabling a patient to fine tune focusing of the lens. A manual focusing control enables the patient to correct compensate for minor inaccuracies in the signal provided by the automatic focusing system. With a manual focusing control, the rangefinder can in fact be dispensed with. Thus, in yet another embodiment of the invention, the apparatus includes a manual focusing control instead of a rangefinder.

These and other features and advantages of the invention will be apparent from the following detailed description and the accompanying figures, in which:

DETAILED DESCRIPTION

FIG. 1shows a block diagram of a vision prosthesis10having a lens12whose index of refraction can be made to vary in response to a focusing signal provided to the lens12by an actuator14. The lens12directs light through a nematic liquid-crystal whose index of refraction varies in response to an applied electric field. The actuator14includes one or more electrodes in electrical communication with the lens12. However, the lens12can also direct light through a material whose index of refraction varies in response to an applied magnetic field. In this case, the actuator14is a magnetic field source, such as a current-carrying coil, in magnetic communication with the lens12.

Throughout this specification, the terms “lens” and “intraocular lens” refer to the prosthetic lens that is part of the vision prosthesis10. The lens that is an anatomical structure within the eye is referred to as the “natural lens”.

The nature of the focusing signal provided by the actuator14controls the extent to which the index of refraction is changed. The actuator14generates a focusing signal in response to instructions from a controller16in communication with the actuator14.

The controller16is typically a microcontroller having instructions encoded therein. These instructions can be implemented as software or firmware. However, the instructions can also be encoded directly in hardware in, for example, an application-specific integrated circuit. The instructions provided to the microcontroller include instructions for receiving, from a rangefinder18, data indicative of the distance to an object-of-regard, and instructions for processing that data to obtain a focusing signal. The focusing signal alters the lens' index of refraction to focus an image of the object-of-regard on the retina.

The rangefinder18typically includes a transducer19for detecting a stimulus from which a range to an object can be inferred. The signal generated by the transducer19often requires amplification before it is of sufficient power to provide to the controller16. Additionally, the signal may require some preliminary signal conditioning. Accordingly, in addition to a transducer19, the rangefinder18includes an amplifier21to amplify the signal, an A/D converter23to sample the resultant amplified signal, and a digital signal processor25to receive the sampled signal. The output of the digital signal processor25is provided to the controller16.

A power source20supplies power to the controller16, the range finder18, and the actuator14. A single power source20can provide power to all three components. However, the vision prosthesis10can also include a separate power source20for any combination of those components that require power.

1.1 Lens and Actuator

In one embodiment of the vision prosthesis10, the lens12is an intraocular lens. The intraocular lens12can be implanted into an aphakic patient, as shown inFIG. 2, in which case it can be implanted into the lens-bag22from which the patient's natural lens has been removed. Alternatively, the intraocular lens12can be implanted into a phakic patient, in which case it can be implanted into the posterior chamber24, between the iris26and the patient's natural lens28, as shown inFIG. 3. With the intraocular lens12implanted in the posterior chamber24, the haptic30of the lens12rests in the sulcus32. The intraocular lens12can also be implanted in the anterior chamber34, as shown inFIG. 4, or in the cornea36, as shown inFIG. 5.

Preferably, the lens12is a foldable lens having a tendency to spring back to its unfolded position. Such a lens12can be inserted through a small incision, maneuvered into the desired location, and released. Once released, the lens12springs back to its unfolded position.

In one embodiment of the lens12, shown in exploded view inFIG. 6, first and second curved chambers38a,38bfilled with nematic liquid-crystal are separated by a transparent plate40. In this embodiment, the actuator14includes a variable voltage source41connected to two transparent electrodes42a,42bdisposed on an outer surface of each curved chamber38a,38b. The variable voltage source41generates a variable voltage in response to instructions from the controller16. First and second transparent outer layers44a,44bcover the first and second electrodes42a,42brespectively.

When the variable voltage source41applies a voltage, the first and second electrodes42a,42bimpose an electric field in the nematic liquid-crystal. This electric field tends to reorient the directors of the nematic liquid-crystal, thereby changing its index of refraction. A lens assembly of this type is described fully in U.S. Pat. No. 4,190,330, the contents of which are herein incorporated by reference.

In another embodiment, shown inFIG. 7A, the lens12includes a thin chamber46filled with nematic liquid-crystal and the actuator14includes a variable voltage source48and first and second sets50a,50bof electrodes52a–cdisposed on opposed planar surfaces of the thin chamber46. Each of the electrodes52a–cis individually addressable by the controller16. A voltage maintained across a electrode52aform the first set50aand a corresponding electrode from the second set50bresults in an electric field across a local zone of the nematic liquid-crystal adjacent to those electrodes. This electric field reorients the directors, and hence alters the index of refraction, within that zone. As a result, the index of refraction can be made to vary at different points of the lens12.

FIG. 7Ashows a lens assembly having concentric electrodes52a–c. A lens assembly of this type is described fully in U.S. Pat. No. 4,466,703, the contents of which are herein incorporated by reference. In this embodiment, the index of refraction can be altered as a function of distance from the center of the lens12. However, individually addressable electrodes52a–ccan also be arranged in a two-dimensional array on the surface of the lens12. When this is the case, the index of refraction can be varied as a function of two spatial variables. The grid of electrodes52a–ccan be a polar grid, as shown inFIG. 7A, or a rectilinear grid, as shown inFIG. 7B. The electrodes52a–ccan be distributed uniformly on the grid, or they can be distributed more sparsely in certain regions of the lens12and more densely in other regions of the lens12.

Because of its thin planar structure, a lens12of the type shown inFIG. 6is particularly suitable for implantation in constricted spaces, such as in the posterior chamber24of a phakic patient, as shown inFIG. 3.

In another embodiment, the lens12includes a chamber filled with a nematic liquid-crystal and the actuator14is a current-carrying coil that generates a magnetic field. In this embodiment, the controller16causes current to flow in the coil. This current supports a magnetic field that reorients the directors in the nematic liquid-crystal. This results in a change in the liquid crystal's index of refraction.

The extent to which the index of refraction of a nematic liquid crystal can be changed is limited. Once all the directors in the nematic liquid crystal have been polarized, increasing the magnitude of the imposed electric field has no further effect. A nematic liquid crystal in this state is said to be saturated. To change the focal length beyond the point at which the nematic crystal is saturated, a lens12can also include one or more lens elements that are moved relative to each other by micromechanical motors.

Alternatively, the lens can have a baseline curvature that and also be filled with nematic crystal. The baseline curvature can be used to perform a gross correction that can be fine-tuned by locally varying the index of refraction of the lens material.

In another embodiment, the lens is made up of a multiplicity of lenslets, as shown inFIG. 7B, each of which has its own baseline curvature and each of which is filled with nematic crystal. An individually addressable electrode is then connected to each of the lenslets. In this embodiment, both the lens curvature and the index of refraction can be varied locally and can be varied as a function of two spatial variables.

In a normal eye, contraction of a ciliary muscle54is transmitted to the natural lens28by zonules56extending between the ciliary muscle54and the lens-bag22. When the object-of-regard is nearby, the ciliary muscle54contracts, thereby deforming the natural lens28so as to bring an image of the object into focus on the retina. When the object-of-regard is distant, the ciliary muscle54relaxes, thereby restoring the natural lens28to a shape that brings distant objects into focus on the retina. The activity of the ciliary muscle54thus provides an indication of the range to an object-of-regard.

For an intraocular lens12, the transducer19of the rangefinder18can be a transducer for detecting contraction of the ciliary muscle54. In one embodiment, the rangefinder18can include a pressure transducer that detects the mechanical activity of the ciliary muscle54. A pressure transducer coupled to the ciliary muscle54can be a piezoelectric device that deforms, and hence generates a voltage, in response to contraction of the ciliary muscle54. In another embodiment, the transducer can include an electromyograph for detecting electrical activity within the ciliary muscle54.

As noted above, the activity of the ciliary muscle54is transmitted to the natural lens28by zonules56extending between the ciliary muscle54and the lens-bag22. Both the tension in the zonules56and the resulting mechanical disturbance of the lens-bag22can be also be used as indicators of the distance to the object-of-regard. In recognition of this, the rangefinder18can also include a tension measuring transducer in communication with the zonules56or a motion sensing transducer in communication with the lens-bag22. These sensors can likewise be piezoelectric devices that generate a voltage in response to mechanical stimuli.

The activity of the rectus muscles58can also be used to infer the distance to an object-of-regard. For example, a contraction of the rectus muscles58that would cause the eye to converge medially can suggest that the object-of-regard is nearby, whereas contraction of the rectus muscles58that would cause the eye to gaze forward might suggest that the object-of-regard is distant. The rangefinder18can thus include a transducer that responds to either mechanical motion of the rectus muscles58or to the electrical activity that triggers that mechanical motion.

It is also known that when a person intends to focus on a nearby object, the iris26contracts the pupil60. Another embodiment of the rangefinder18relies on this contraction to provide information indicative of the distance to the object-of-regard. In this embodiment, the rangefinder18includes a transducer, similar to that described above in connection with the range finder18that uses ciliary muscle or rectus muscle activity, to estimate the distance to the object-of-regard. Additionally, since contraction of the pupil60diminishes the light incident on the lens12, the transducer19of the rangefinder18can include a photodetector for detecting this change in the light.

The foregoing embodiments of the rangefinder18are intended to be implanted into a patient, where they can be coupled to the anatomical structures of the eye. This configuration, in which the dynamic properties of one or more anatomical structures of the eye are used to infer the distance to an object-of-regard, is advantageous because those properties are under the patient's control. As a result, the patient can, to a certain extent, provide feedback to the rangefinder18by controlling those dynamic properties. For example, where the rangefinder18includes a transducer responsive to the ciliary muscle54, the patient can control the index of refraction of the intraocular lens12by appropriately contracting or relaxing the ciliary muscle54.

Other embodiments of the rangefinder18can provide an estimate of the range without relying on stimuli from anatomic structures of the eye. For example, a rangefinder18similar to that used in an auto-focus camera can be implanted. An example of such a rangefinder18is one that transmits a beam of infrared radiation, detects a reflected beam, and estimates range on the basis of that reflected beam. The output of the rangefinder18can then be communicated to the actuator14. Since a rangefinder18of this type does not rely on stimuli from anatomic structures of the eye, it need not be implanted in the eye at all. Instead, it can be worn on an eyeglass frame or even hand-held and pointed at objects of regard. In such a case, the signal from the rangefinder18can be communicated to the actuator14either by a wire connected to an implanted actuator14or by a wireless link.

A rangefinder18that does not rely on stimuli from an anatomic structure within the eye no longer enjoys feedback from the patient. As a result, it is desirable to provide a feedback mechanism to enhance the range-finder's ability to achieve and maintain focus on an object-of-regard.

In a feedback mechanism as shown inFIG. 8, first and second lenslets62a,62bare disposed posterior to the intraocular lens12. The first and second lenslets62a,62bare preferably disposed near the periphery of the intraocular lens12to avoid interfering with the patient's vision. A first photodetector64ais disposed at a selected distance posterior to the first lenslet62a, and a second photodetector64bis disposed at the same selected distance posterior to the second lenslet62b. The focal length of the first lenslet62ais slightly greater than the selected distance, whereas the focal length of the second lenslet62bis slightly less than the selected distance.

The outputs of the first and second photodetectors64a,64bare connected to a differencing element66that evaluates the difference between their output. This difference is provided to the digital signal processor25. When the output of the differencing element66is zero, the intraocular lens12is in focus. When the output of the differencing element66is non-zero, the sign of the output identifies whether the focal length of the intraocular lens12needs to be increased or decreased, and the magnitude of the output determines the extent to which the focal length of the intraocular lens12needs to change to bring the lens12into focus. A feedback mechanism of this type is disclosed in U.S. Pat. No. 4,309,603, the contents of which are herein incorporated by reference.

In any of the above embodiments of the rangefinder18, a manual control can also be provided to enable a patient to fine-tune the focusing signal. The digital signal processor25can then use any correction provided by the user to calibrate the range estimates provided by the rangefinder18so that the next time that that range estimate is received, the focusing signal provided by the digital signal processor25will no longer need fine-tuning by the patient. This results in a self-calibrating vision prosthesis10.

The choice of which of the above range-finders is to be used depends on the particular application. For example, a lens12implanted in the posterior chamber24has ready access to the ciliary muscle54near the haptic30of the lens12. Under these circumstances, a rangefinder that detects ciliary muscle activity is a suitable choice. A lens12implanted in the anterior chamber34is conveniently located relative to the iris26but cannot easily be coupled to the ciliary muscle54. Hence, under these circumstances, a rangefinder that detects contraction of the iris26is a suitable choice. A lens12implanted in the cornea36is conveniently located relative to the rectus muscles58. Hence, under these circumstances, a rangefinder that detects contraction of the rectus muscles58is a suitable choice. In the case of an aphakic patient, in which the natural lens28in the lens-bag22has been replaced by an intraocular lens12, a rangefinder that detects zonule tension or mechanical disturbances of the lens-bag22is a suitable choice. In patients having a loss of function in any of the foregoing anatomical structures, a rangefinder that incorporates an automatic focusing system similar to that used in an autofocus camera is a suitable choice.

1.3 Power Source

As noted above, the controller16, the rangefinder18, and the actuator14shown inFIG. 1require a power source20. In one embodiment, the power source20can be an implanted battery68. The battery68can be implanted in any convenient location, such as under the conjunctiva70in the Therron's capsule, or within the sclera. Unless it is rechargeable in situ, such a power source20will periodically require replacement.

In another embodiment, the power source20can be a photovoltaic cell72implanted in a portion of the eye that receives sufficient light to power the vision prosthesis10. The photovoltaic cell72can be mounted on a peripheral portion of the lens12where it will receive adequate light without interfering excessively with vision. Alternatively, the photovoltaic cell72can be implanted within the cornea36, where it will receive considerably more light. When implanted into the cornea36, the photovoltaic cell72can take the form of an annulus or a portion of an annulus centered at the center of the cornea36. This configuration avoids excessive interference with the patient's vision while providing sufficient area for collection of light.

Power generated by such a photovoltaic cell72can also be used to recharge a battery68, thereby enabling the vision prosthesis10to operate under low-light conditions. The use of a photovoltaic cell as a power source20eliminates the need for the patient to undergo the invasive procedure of replacing an implanted battery68.

The choice of a power source20depends in part on the relative locations of the components that are to be supplied with power and the ease with which connections can be made to those components. When the lens12is implanted in the cornea36, for example, the associated electronics are likely to be accessible to a photovoltaic cell72also implanted in the cornea36. In addition, a rechargeable subconjunctival battery68is also easily accessible to the photovoltaic cell72. The disposition of one or more photovoltaic cells72in an annular region at the periphery of the cornea36maximizes the exposure of the photovoltaic cells72to ambient light.

When the lens12is implanted in the anterior chamber34, one or more photovoltaic cells72are arranged in an annular region on the periphery of the lens12. This reduces interference with the patient's vision while providing sufficient area for exposure to ambient light. For a lens12implanted in the anterior chamber34, a rechargeable battery68implanted beneath the conjunctiva70continues to be conveniently located relative to the photovoltaic cells72.

When the lens12is implanted in the posterior chamber24, one or more photovoltaic cells72can be arranged in an annular region of the lens12. However, in this case, the periphery of the lens12is often shaded by the iris26as it contracts to narrow the pupil60. Because of this, photovoltaic cells72disposed around the periphery of the lens12may receive insufficient light to power the various other components of the vision prosthesis10. As a result, it becomes preferable to dispose the photovoltaic cells72in an annular region having radius small enough to ensure adequate lighting but large enough to avoid excessive interference with the patient's vision.

The lens12inFIG. 1need not be an intraocular lens. In an alternative embodiment, shown inFIG. 9, the vision prosthesis10, including the lens12, is mounted on a frame74and worn in the manner of conventional eyeglasses. This embodiment largely eliminates those constraints on the size and location of the power source20that are imposed by the relative inaccessibility of the various anatomical structures of the eye as well as by the limited volume surrounding them.

In the embodiment shown inFIG. 9, the rangefinder18is typically of the type used in an autofocus camera together with the two-lenslet feedback mechanism described above in connection with the intraocular vision prosthesis10. The lens12, its associated actuator14, and the power source20can be selected from any of the types already described above in connection with the intraocular embodiment of the vision prosthesis10.