Field of the Invention

The invention relates to light-reactive ocular prosthetics. Background

Ocular prosthetics, or artificial eyes, are designed to aesthetically replace missing, damaged or underdeveloped eyes. Realism is a key consideration in the design of ocular prosthetics, as this benefits the confidence and comfort of the wearer. Ocular prosthetics are generally handmade and bespoke, a necessity brought about by the variation in form as a result of the varying needs of the wearer. Ocular prosthetics can however range in style from standard manufactured pieces that may be ordered remotely to pieces designed and handmade over the course of a number of consultations between the maker and the wearer. The resulting prosthetic can be extremely realistic, but problems remain in relation to how the prosthetic is used in practice. One such problem is that the prosthetic is inevitably fixed both in position and appearance. In varying light conditions a real eye will vary by its pupil varying in size. This can result in a user's real eye having a differently sized pupil to that of the prosthetic, which reduces the realism of the prosthesis. Light-reactive ocular prosthetic eyes have been proposed, for example by

Leuschner and Lapointe et al (see references 4 and 5), in which a liquid crystal display or light valve is used to simulate a varying pupil. These proposals may, however, result in additional problems such as a lack of contrast between the pupil and a surrounding iris, which can affect the realism of the resulting prosthetic, as well as the need to provide a complex array of addressable patterns to reproduce a pupil of appropriate size and shape, which may conflict with the need for a customised solution in each individual case. Other forms of light reactive ocular prostheses have been proposed, such as in US4332039 (reference 6) disclosing a magnetically-actuated pupil, in US6139577 and US6576013 (references 7 and 8), both of which disclose the use of a liquid crystal display, and in US5061279 (reference 9), disclosing the use of a photochromic pigment for simulating a dilating pupil.

It is an object of the invention to address one or more of the above problems. Summary of the Invention

In accordance with the invention there is provided an ocular prosthesis comprising an adjustable pupil, wherein the prosthesis is configured to apply a voltage across a pair of electrodes defining a lateral extent of the pupil to change the lateral extent of the electrodes, for example in response to a change in incident light intensity.

An advantage of the ocular prosthesis according to the invention is that a realistic pupil can be created that can be easily incorporated into a prosthesis that may be custom made for an individual.

The pupil may be configured such that an increased voltage applied across the pair of electrodes causes the lateral extent of the pupil to expand. The prosthesis thereby requires no applied signal when the pupil is to be in a contracted state, which would be a typical normal state in bright light, thereby saving on power requirements.

The electrodes are preferably disposed on opposing faces of an electroactive polymer film. The electroactive polymer film may be affixed to, and held in planar tension by, a surrounding support structure. The support structure may comprise a pair of rings affixed to opposing faces of an outer edge of the electroactive polymer film. The support structure may comprise a transparent, preferably curved, plate extending across a first face of the polymer film and pupil, and may comprise an iris image extending across a second opposing face of the polymer film and pupil, i.e. behind the pupil with the ocular prosthesis configured in use. The iris image may be applied to a face of a plate (preferably curved) extending across the second face of the polymer film. An advantage of using an electroactive polymer film is that a more realistic pupil and iris combination is made possible, since a realistic painted iris can be provided behind the film, which is typically transparent. Although the iris image will be fixed, the variable pupil created by the changing shape of the electrode on the polymer film creates a convincing illusion of a real varying pupil.

The prosthesis preferably comprises a controller and a light sensor connected to the controller, the controller configured to provide a voltage signal to apply the voltage across the pair of electrodes, the voltage signal being dependent upon incident light intensity falling on the light sensor. In preferred embodiments the prosthesis is self-contained, i.e. comprises all of the required components to respond to changes in light intensity without the need for external connections.

The prosthesis may further comprise a voltage transformer configured to transform the voltage signal from the controller and apply the voltage across the pair of electrodes. The transformer may be configured to apply a voltage of up to over 500V, and optionally up to 1.5 kV, across the pair of electrodes. The transformer may for example be a dc-dc transformer. Detailed Description

The invention is described in further detail below by way of example and with reference to the accompanying drawings, in which:

figure la is a schematic cross-sectional view of an artificial pupil for an ocular prosthesis according to an embodiment of the invention;

figure lb is a schematic cross-sectional view of the artificial pupil of figure la with a voltage applied;

figure 2a is a schematic plan view of the artificial pupil of figure la;

figure 2b is a schematic plan view of the artificial pupil of figure la with a voltage applied;

figure 3 is a schematic block diagram of the functional components making up an ocular prosthesis according to an embodiment of the invention;

figures 4a and 4b are an exploded schematic view and a side view of an exemplary embodiment of an artificial pupil and iris for an ocular prosthesis according to the invention;

figures 5a and 5b are photographs of an exemplary embodiment of an artificial pupil and iris constructed according to the illustrated embodiment of figure 4, with the pupil in a contracted state (figure 5a) and in a dilated state (figure 5b); and

figure 6 is an exploded view of an exemplary prototype ocular prosthesis. Exemplary embodiments of a light reactive ocular prosthesis according to the invention may use electroactive polymer technology to create the impression of a dilating and contracting pupil. Electroactive polymer (EAP) technology has applications in various fields, most notably in artificial muscle technology for use in force feedback applications such as 'soft' robotics [see reference 1 , and in particular chapter IV, in which various EAP materials and their applications are discussed] . As applied to ocular prostheses, the visual impression of dilation of a pupil can be achieved using this technology, using a technique similar to that of Rossiter et al [reference 2, which discloses the use of a 500 μιη thick circular biaxially prestrained polyacrylate film as a dielectric medium for mimicking a pigmented chromatophore sacculus] .

In applying EAP technology to the visual representation of a dilating or contracting pupil, a stretched, transparent elastomer film can be encapsulated under tension. The elastomer film may be encapsulated between two rings, which may be of the same size and thickness to avoid any distortion under tension. Once encapsulated, a circular film of a conductive paste is painted onto the transparent stretched elastomer, the paste representing the artificial pupil. When a high voltage (typically up to around 1.5 kV) is applied to the conductive paste across the elastomer film, the pupil will appear to dilate, as a result of the film being acted upon by Maxwell pressure [reference 3, which discloses fabrication and characteristics of spin coated dielectric films for use in stacked dielectric elastomer actuators] due to the application of an electric field. Altering the applied voltage, and therefore the applied electric field, allows the electrode to visually represent dilation and contraction of a pupil. A light sensor can be used in the prosthesis to detect ambient light conditions.

In exemplary embodiments the light sensor may be a light dependent resistor (LDR), or photoresistor. Other types of light sensors may alternatively be used such as a light sensitive diode (photodiode) or light sensitive transistor (phototransistor). A signal from the light sensor can be interpreted by a programmable micro-controller, which determines the voltage to be applied across the EAP film.

Figures la and lb, and figures 2a and 2b, illustrate schematically in cross- sectional view and plan view respectively various components of an exemplary ocular prosthesis making up a pupil assembly 100 for forming an artificial adjustable pupil 106. An elastomeric electroactive polymer film 101 is held in tension across a supporting structure in the form of a pair of rings 102a, 102b between which the film 101 is clamped. First and second electrodes 103a, 103b forming the pupil 106 are applied across opposing faces of the film 101. At least one of the electrodes 103a, 103b comprises a dark, preferably black, pigment (such as carbon black) for simulating the appearance of a pupil, and both electrodes 103a, 103b are sufficiently elastic or otherwise compliant to stretch and contract along with the underlying film 101. The electrodes 103a, 103b may for example comprise carbon grease, as disclosed by Rossiter et al. [reference 2] . Electrode traces 104a, 104b are applied across the opposing faces of the film 101 to connect the electrodes 103a, 103b to leads 105a, 105b across which a voltage may be applied. The electrode traces 104a, 104b may be pigmented differently to the electrodes 103a, 103b forming the pupil 106 so as to minimise their appearance in the prosthesis. The electrode traces 104a, 104b may for example be coloured to be similar to the surrounding iris, or may be made transparent. On application of a voltage across the leads 105a, 105b, the electroactive film

101 expands in the plane of the film, resulting in the electrodes 103a, 103b expanding along with the film and creating the appearance of the pupil 106 becoming dilated, as shown in the differences between figures la and lb and figures 2a and 2b. When the voltage is removed, the film returns to the unexpanded state and the pupil 106 contracts. A dilation/contraction of the pupil 106 can thereby be created that is controllable by the applied voltage.

Figure 3 illustrates in schematic block diagram form the functional components of an ocular prosthesis 300 comprising the pupil assembly 100 of figures 1 and 2. A microcontroller 301 , powered by a battery 302, receives a signal from a light sensor 303 and, in response to a detected amount of light, provides a signal to the leads of the pupil assembly 100. As the voltages required to cause the electroactive film will typically be very high, a transformer 304 is preferably provided to increase the voltage signal produced by the microcontroller 301 to a level that is sufficient to cause a response. If the detected amount of light is above a certain level, no signal will need to be applied to the pupil, which will be in contracted in its unactivated state. The prosthesis may therefore be configured to save on battery power by disabling the output signal to the pupil assembly when the detected amount of light exceeds a preset amount.

As an illustrative example, the input voltage to the micro-controller 301 provided by the battery 302 may be 5V, and the output voltage from the controller 301 may be increased by the transformer 304 to supply a voltage of up to 1.5 kV to the pupil assembly 100, with the maximum voltage corresponding to a maximum degree of dilation of the pupil 106. Figures 4a and 4b illustrate schematically an exploded view and side view of components making up an exemplary pupil assembly 400, in which the supporting structure for the elastomeric electroactive film 401 is provided by a pair of curved transparent plates or lenses 402a, 402b, which may be made of glass. An image representing the iris may be provided on one of the plates 402a, 402b, preferably the plate that is positioned behind the pupil 406 when assembled into the prosthesis. The artificial pupil and iris image is encapsulated between the two lenses 402a, 402b, which provides some refraction adding realism to the appearance of the pupil. The concave shape of the inside of the glass lenses allows the elastomer to flex when the pupil is dilated. The iris image may be painted on the concave surface of the lower lens, i. e. behind the pupil, thus preserving an important element of the hand-making process of ocular prosthetics. An exemplary embodiment of a pupil assembly 500 made according to that shown in figures 4a and 4b is shown in figures 5a and 5b, with figure 5a showing the pupil 506 in a contracted state and figure 5b with the pupil 506 in a dilated state. An iris image 508 is painted on to a plate behind the pupil 506, and a curved transparent plate or lens is provided in front of the pupil, serving to protect the electroactive polymer film as well as to prevent contact with the high voltage applied to the film and to provide a desired aesthetic appearance.

Figure 6 shows an exploded view of an exemplary prototype ocular prosthesis 600, showing the various components making up the device. The prosthesis 600 comprises a removable front casing 605 imitating the appearance of the sclera, and a rear casing 608 for housing the electronic components 607 including the controller, transformer and battery. A frontal encapsulating lens 601 covers the front of the prosthesis, behind which is provided a frontal lens 602 providing a refraction effect that adds to the realistic appearance of the artificial pupil. The artificial pupil assembly 603 is provided behind the frontal lenses 601 , 602, behind which is provided a rear encapsulating lens 604 having a curved lens carrying a painted image of the iris. A light dependent resistor 606 is provided for measuring ambient light conditions, from which the controller determines the voltage to be applied to the artificial pupil. Other embodiments are intentionally within the scope of the invention, which is defined by the appended claims.

References

1. Zhang R., "Development of Dielectric Elastomer Actuators and their Implementation in a Novel Force Feedback Interface" Doctor of Technical Sciences dissertation, Swiss Federal Institute Of Technology Zurich, 2007.

2. Rossiter J. et al., "Biomimetic chromatophores for camouflage and soft active surfaces", Bioinspiration & Biomimetics 7 (2012) 036009.

3. Lotz P. et al., "Dielectric Elastomer Actuators using improved Thin Film Processing and nanosized Particles" Electroactive Polymer Actuators and Devices (EAPAD) 2008, Proc. of SPIE Vol. 6927, 692723 (2008).

4. J. Lapointe et al., "An ocular prosthesis which reacts to light", Proc. SPIE 7885, Opthalmic Technologies XXI, 7885 12 (February 1 1 , 201 1); doi: 10. 1 17/12.874078

5. F.W. Leuschner, "Light-controlled pupil size for ocular prosthesis", Proc. SPIE 1644, Opthalmic Technologies II, 320 (August 14, 1992); doi: 10. 1 1 17/12. 137438

6. LaFuente, H., US Patent 4332039 ( 1982).

7. Schliepman, F. et al , US Patent 6139577 (2000).

8. Budman, F. et al., US Patent 6576013 (2003).

9. Friel, T., US Patent 5061279 ( 1991).