FIELD OF THE INVENTION

The invention relates generally to the field of ocular prosthetics, more specifically the invention relates to a device for adjusting "apparent" pupil size.

BACKGROUND OF THE INVENTION

Prosthetic eyes have existed for a long time because accidents and illnesses sometimes require eyes to be removed. With prosthetic eyes of the prior art, an observer can easily notice the presence of the prosthesis because pupil size does not vary with ambient light conditions. Increased realism of a prosthetic eye is desired by the monocularist.

Danz (US Pat. No. 4,272,910) describes a fixed iris image within the body of an artificial eye. The image has a central dark portion simulating a pupil in a bright light condition. An annular ring of electrooptically sensitive material such as liquid crystal display (LCD) material is placed in front of the iris and concentrically surrounding the pupil simulating central dark portion. The outer diameter of the ring is selected to simulate the diameter of a pupil in a less than bright environment. The annular ring is normally transparent. When a photoelectric sensor detects a light level below a fixed threshold, a battery excites an annular ring to make the pupil appear to dilate.

Schleipman et al. in U.S. Pat. No. 6,139,577 also uses a series of concentric rings of LCD material to simulate a range of dilation and contraction of a pupil. In their device, a pixelated iris image is created from a digital photograph of a desired natural iris by removing a number of pixels to provide clear non-image areas. As concentric rings of the LCD are selectively activated and darkened, the portions of the pixilated iris with the activated LCD behind will appear as a pupil of various degrees of dilation. The prosthetic eye of Schleipman has holes in the iris image because the LCD is located behind the iris. Furthermore, it requires a

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RECTIFIED SHEET (RULE 91.1) battery for function. The important drawback associated with using a battery is the replacement of the battery. Indeed, the smaller and lighter the battery (which are important characteristics), the more often replacement is required.

Budman (US Pat. No. 6,576,013) also teaches memory-stored iris image and a battery for powering the iris image and the apparent of pupil contraction-dilation. Additional power may be provided by a solar device coupled to power source. Light sensor, itself maybe a solar device in which case it may provide a dual function of detecting ambient light level and providing electrical power. Budman suggests that a solar cell can be provided as an additional source of energy to complement battery power but does not exclude a battery due to electrical requirements that cannot be satisfied by small solar cell having a surface area allowing it to fit behind the pupil opening.

To our knowledge, none of the prior art prosthetic eyes having a variable pupil have been successful in providing a functional, low cost, long service life prosthetic.

SUMMARY OF THE INVENTION

It is an object to provide a device that requires very little electrical energy for operation and is inexpensive and simple to manufacture. Furthermore, a prosthetic eye according to the present invention would be self-sufficient in terms of energy and would not require a battery for function.

It is therefore an object of the present invention to provide a prosthetic eye with a dynamic pupil that reacts to light in a natural way. Applicants have discovered that it is possible to make an eye prosthesis having an adjustable pupil that appears to constrict/dilate naturally as a function of light conditions that uses photovoltaic cells to power and control directly. The prosthesis of the present invention does not require a battery because it uses a passive electronic circuit powered by a photovoltaic cell used to control one or more liquid crystal pixels arranged around the pupil. The photovoltaic cell is located at the center of an iris

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RECTIFIED SHEET (RULE 91.1) behind the one or more liquid crystal cell. In the prosthetic eye of the present invention, the photovoltaic cell acts as a photodetector and battery, thereby simplifying the device, minimizing the cost and limiting the weight of such a device. It is another object of the present to provide a prosthetic eye device comprising an iris having an aperture in its center; the aperture defining a pupil; a photovoltaic cell having a surface area located within or corresponding to a surface area of the pupil; wherein the photovoltaic cell is located at or behind the iris; one or more liquid crystal cell in front of the iris, the liquid crystal cell activation for simulating variations in pupil diameter; an electronic circuit that receives electrical potential from the photovoltaic cell and activates the one or more liquid crystal cells; wherein an apparent pupil size varies inversely with light intensity.

In some embodiment of the device, the liquid crystal cells are disposed as concentric rings around the pupil and a passive electronic circuit can activate the liquid crystal cells from an outer concentric ring to an inner concentric ring as a function of increasing light intensity.

In other embodiments, the liquid crystal cell has a variable thickness (and therefore resistance) in order to control electrical potential required for responding to light.

Yet other embodiments of the present invention will provide a serrated inner side of said liquid crystal cell for increased pupil realism.

The prosthetic eye of the present invention can be used in the manufacturing toys with realistic eye where pupil diameter varies as a function of light conditions.

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RECTIFIED SHEET (RULE 91.1) BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by way of the following detailed description of embodiments of the invention with reference to the appended drawings, in which: Figure 1 shows a liquid crystal cell (a) without potential applied where the iris image appears black and (b) with potential applied where the iris image is seen in reflection.

Figure 2 shows a cross-sectional view through an ocular prosthesis with proposed dynamic LCD iris/pupil. Figure 3 illustrates a passive voltage circuit for controlling apparent pupil diameter where each ring shaped liquid crystal pixel is a capacitor.

Figure 4 shows a graphical simulation of the on-off thresholds for the passive circuit of Fig. 3. Each line shows the potential applied to each LC pixel as a function of illumination of the SC. The long dashed line is the potential across a LC pixel in series with 3 diodes, which is in the ON state under a high light ambient (VSC = 4.9V). Small dashed line: 2 diodes, ON at medium light (VSC = 4.3V). Solid line: 1 diode, ON at lower light (VSC = 3.7V for R1=10kO. VSC = 3.4V if R1=100MO).

Figure 5 illustrates different iris images for a prosthetic eye. Figure 6 shows a standard voltage photovoltaic cell array design for mass production.

Figure 7 shows a high voltage photovoltaic cell array design for mass production.

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RECTIFIED SHEET (RULE 91.1) Figure 8 (a-d) shows iris images with different pupil sizes through the LC cell surviving the ocular prosthesis manufacturing process.

Figure 9a shows a photograph of a real light iris under high ambient light, fig. 9b shows the same image as (a) with a 50% transmission polarizer, fig. 9c shows the same image under a 70% transmission polarizer, fig. 9d shows a 20% lighter image under a 70% transmission polarizer. Figs. 9b-d show simulations with the liquid crystal cells in the OFF state.

Figure 10 is a schematic representation of a variable thickness design for controlling "apparent" pupil diameter. DETAILED DESCRIPTION OF THE INVENTION

The realism of an ocular prosthesis is limited by the immobility of the pupil. Applicant's solution is to use a liquid crystal display to vary the pupil size as a function of the ambient light. Several liquid crystal cells were fabricated and tested for survivability through the ocular prosthesis manufacturing process. The dynamic pupil is controlled by a novel and entirely autonomous, self-powered passive electronic circuit using a photovoltaic cell. The photovoltaic cell size matches the minimum opening of the pupil.

The first LCD surviving the rugged conditions of the ocular prosthesis manufacturing steps and an entirely passive circuit controlling the pupil have been demonstrated for the first time. A design for a complete prosthesis with a dynamic pupil has been proposed. Finally, a standard device for the mass production of ocular prostheses is presented.

Applicants have shown that a practical solution for an autonomous self-powered dynamic pupil is possible, given the constraints of size, fabrication process, weight, cost and manufacturability on a mass scale. Applicants envisage that the LCD could be mass produced, and only the final steps for the integration of the

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RECTIFIED SHEET (RULE 91.1) iris matched to a patient would be necessary prior to assembly using standard manufacturing materials and processing steps for the production of the prosthesis. Applicants believe the dynamic pupil ocular prosthesis will have a positive impact on the self-worth and quality of life of patients. The realism of an ocular prosthesis is limited by the inability of the artificial pupil to react to light. This has a negative impact on patients who have received a single prosthetic implant to replace an eye. A good proposed solution to the problem is to use LCD technology as a color spatial light modulator to control the pupil size. Up to now, very few reports have been made but no successful result has been put forward. The principal problem is that the LCD does not survive the rugged conditions of the ocular prosthesis manufacturing process.

The first LCD surviving the ocular prosthetic manufacturing steps and an entirely passive circuit to control the pupil diameter is herein demonstrated. A few micrometers square integrated circuit (IC) chip, including the passive circuit and a photovoltaic cell (PC), is proposed, with the liquid crystal (LC) cell to constitute a standard device for the mass production of ocular prostheses. The integrated chip, which controls the pupil size via the LC cell, is autonomous and powered by the PC alone.

There is a requirement in Ophthalmology for a prosthetic iris which is self- accommodating, to improve the quality of life of patients who have lost an eye. The present invention addresses this need by exploring a solution based on LCD. The proposed solution is to use a small LCD, positioned over an iris image, in which ring shaped pixels will appear black or transparent depending of the ambient light, to simulate the dynamic pupil. A liquid crystal cell, see Fig. 1A, is made of two indium tin oxide (ITO) coated (c) glass plates (b) with the LC (e) between the two plates. In Fig. 1A, light enters the LC cell from the right and is horizontally polarized by the polarizer (a). The light passes the glass substrate (b), the transparent ITO electrode (c) and the

RECTIFIED SHEET (RULE 91.1) orientation layer (g). The rod-like LC molecules (e) have the property to align themselves together and using the transparent orientation layer (g), make the helicoidally shape (e) shown in the figure. Without the potential applied, when the light passes through the LC medium, the polarized light rotates by 90° to become vertically polarized due to the birefringence in the LC. The sequence layers on the rear glass plate are identical to the entry surfaces, and vertically polarized light is blocked by the second polarizer, which allows only the horizontally polarized light through. The image of the iris is placed in contact with the rear exit glass plate. No light is reflected and therefore the image of the iris appears black. In fig. 1 B, under an applied electric field, the positive dielectric anisotropy LC (h) aligns with the direction of the electric field, therefore leaves the polarization of the light unchanged and the light passes through the LC cell. The iris image is thus reflected, passes a second time through the LC cell and is therefore seen in reflection. Using this concept, the passage of the light may be controlled through the LC cell. To simulate a dynamic pupil, ITO electrodes are designed to be concentric annular in shape.

Figure 2 shows a schematic of the dynamic pupil in an ocular prosthesis using Applicants design of the LC cell. Applicants add a specially designed PC, so that dynamic control of the pupil can be implemented. The silicon (or thin-film, polymer, or other) PC, lies behind the iris and has a diameter of the minimum opening of the pupil. The intensity of the ambient light is detected by the PC, which generates the potential needed to switch the ring shaped LC pixels. In order that the light level may be detected, a simple and novel level selector circuit is added for switching the different ring shaped LC pixels, as shown in Fig. 3, which are controlled on the basis of the level of the ambient light.

To operate the dynamic pupil, the LC needs a minimum electric field Emin to obtain a good molecular alignment. The potential required is then V = Emind, where d is the distance between the two LCD electrodes. To minimize the potential and the cost of the ocular prosthesis, a minimum distance, about dmin =

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RECTIFIED SHEET (RULE 91.1) 3.2 μιη ³ must be chosen for the LC used in Applicants experiments. Furthermore, the static LCD requires almost no current, and a potential at the minimum distance dmin is approximately 2-3 V. The current is determined by the leakage through the high resistivity LC cell and the speed of switch-on. As both these can be very low, the power requirements are almost negligible, requiring no power supply. Thus it is important to have a control mechanism which is passive and consumes a minimum of power to control the pupil. Using a novel passive circuit connected to the concentric ring electrodes and the PC with several discrete sections in series, each with a potential of 0.7V, the correct potential can be easily achieved to operate the LCD making the dynamic pupil autonomous under daylight conditions when it is most needed. An implanted rechargeable battery is not desirable as it requires periodic replacement owing to limited lifetimes, adds to cost, and increases the mass, which poses other problems of prosthesis droop. Thus Applicants system solves important issues by reducing not only the cost and long term management, but also the stringent weight requirements.

Fig. 3 shows the schematic of the passive electric circuit components required for the electrical operating principle of the dynamic pupil. The indium tin oxide (ITO) electrodes are transparent. When there is low light, the potential is also low and the LC cell is not operated at all, and thus the entire LC cell is left in the OFF state, by using parallel polarizers, and is therefore seen as black. The light is blocked so that the pupil appears large.

Each ring shaped electrode acts like a capacitor (C1 , C2 and C3). An electrode will let the light from the iris image to pass through it when the applied potential is around 3V or more. A diode drops the potential by around 0.5V depending of the diode type and the current. To operate the largest diameter electrode, the interconnected photovoltaic cells must generate 3V + 0.5V = 3.5V, which lets the light pass through. With more light, the PC must generate 3 + 0.5 χ n V, to operate the n ^th ring electrode to make the pupil appear smaller. Without the resistance connected, there is no current flow as the LC electrodes operate as

RECTIFIED SHEET (RULE 91.1) capacitors. With a current close to zero, the diode potential drop is also close to zero and all the pixels remain in the ON state for practically the same illumination; however, with the resistors in place, the potential drop increases sequentially operating the electrodes in sequence, with increasing illumination. This circuit is very flexible and can be adjusted for most pupils which react differently under illumination. The number of interconnected PCs, the diode type and the number of diodes may be changed simply to simulate a patient's pupil. Fig. 4 presents a simulation of this circuit. (C1 = C2 = C3 = 1.1 nF, R1 = R2 = R3 = 10kQ and VD = 0.5V) The adjustability of the pupil is determined by the band-gap of the diode. However, the resistors can be changed to fine tune the output voltage. For example, if the patient's pupil reacts under lower light, one can increase the resistor in parallel with the larger pupil pixel (R1 = 100ΜΩ, requiring a current of <100nA, easily obtained from small PCs). The simulation in fig. 4 shows that the large pupil pixel curve shifts to the left.

High voltage photovoltaic cell (PC). Under a constant illumination on its exposed surface, a PC generates a constant power P=IV. As the proposed application does not need substantial current I, the PC can be modified to maximize the voltage V. Fig. 6 shows the design of such PC. The PC can be sectioned and by interconnecting them in series, the voltage is multiplied (Fig. 7). This concept is well known and can generate higher voltages than the single cell, and the device needs with a PC size equal to the minimum diameter of the pupil (~3mm). Using this concept, the device can be self-powered and autonomous. The PC can generate enough current to operate the device. Firstly, in the dark it does not need any illumination and the pixels remain in the OFF state. Typically, an office has an ambient light level of around 320 lux and in a darker room,

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RECTIFIED SHEET (RULE 91.1) around 50 lux. As an estimate, using only half this light level (25 lux) for switching ON the largest ring-shaped pixel, each one of the 9 PCs in series will receive about P = 37nW on its 1mm square surface (237nW under full illumination). For a typical multiple-junction PC, the quantum efficiency η is more than 60% and the conversion efficiency p is more than 15%. The current generated by the PC is then I = ηρΡ = 4nA. 3V is required to operate the first pixel, which may be achieved with a resistor R = V / 1 = 750ΜΩ. Therefore, the device should operate using resistors of between 500-750 ΜΩ.

Each year, thousands of people lose an eye. A mass produced and inexpensive solution which would fit the requirements for many patients, is highly advantageous and desirable. The minimum and maximum size of the human pupil is about the same for all human beings assuming they do not have an iris disease. The pupil diameter variation under light is also close to being the same for everyone. Fig. 5 shows the design of a iris images which could be integrated into ocular prosthesis.

The circuit components (diodes and resistors) must be chosen to well represent the patient's average pupil diameter variation. After mass production, each device can be easily modified to accommodate the patient's pupil using a well- known technology: resistors laser trimming. By trimming the resistors, their resistance can be tuned and therefore the light intensity needed to vary the pupil diameter changed, as explained before. Choosing the number of electrode rings can also fine tune the graded opening of the pupil as a function of the ambient light conditions to provide a more natural appearance. Applicants believe that 3 or 4 rings should suffice for a good appearance. Note that the integrated IC chip can be fabricated directly into the back surface of the PC wafer.

To demonstrate the principle of simulating pupil dilation, a simple LCD sample with ring shaped ITO electrodes was fabricated and operation of the pupil was confirmed, showing the dark LCD in low light conditions and the transparent LCD under high ambient light conditions. In the final prosthetic eye, an iris image

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RECTIFIED SHEET (RULE 91.1) would be behind the LC cell and the photovoltaic cell would become the minimum opening of the black colored pupil. This handmade LC cell, which is a working adjustable pupil, survived heating to 120°C for 1.5 hour.

To Applicant's knowledge, this is the first LC cell surviving the ocular prosthesis manufacturing process. To test the survivability of LC cells for processing at high temperatures and pressures, a number of LC cells were fabricated in Applicants laboratory. Different dimensions were used to test the robustness and the functioning of the cell after processing. The liquid crystals chosen (MLC-6647 from MERCK) for Applicants' application are rod-like shape in the nematic phase, which are the most widely used in the LCD applications, but specially selected for their wide operating temperature range. As the cell is only a few microns thick the volume of the LC required to operate the device is tiny (< 0.5pL) and is therefore very low cost, as is true for most LCDs. Due to the high pressure in the encapsulation process, thin glass cover plates were found to curve and generate fringes in the one-inch square or larger LC cells. Applicants found that LC cells of dimensions 25 χ 25mm square for example, required a minimum glass plate thickness of approximately 1 mm. Having proved this requirement, cell used for the evaluation were samples from LC-TEC (FOS-25 x 30-TN-W), which were 25 x 30 mm with a total thickness of for the assembled cell of 2.4 mm, including the glass plates.

A standard approach was used to manufacture a test device. The first step for the ocular prosthesis manufacturing process is to encase it in wax. Ocularists use their own specific recipes for the fabrication of the prosthesis, but there are many similarities. A stone/plaster mould of the LC cell with wax is made to accommodate extra space for the acrylic to surround the device.

The composition of the ocular prosthesis is a mix of poly(methyl methacrylate)/methyl methacrylate monomer (PMMA/MMA). The liquid MMA monomer is added and mixed in a glass jar with PMMA clear polymer with a

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RECTIFIED SHEET (RULE 91.1) proportion of polymer: 3.5 to monomer: 1 by weight. The acrylic preparation is mixed occasionally for uniformity and left to rest until it achieves dough consistency, within 20-30 minutes, depending of the ambient temperature (faster when the temperature is higher). Once the mould has hardened, it is opened and the LCD with wax is removed and cleaned of any wax residues. Once the acrylic dough mix is ready, the LCD is surrounded with the mix, so that is totally encapsulated. The encapsulated LCD is placed in the mould, which is assembled together and placed under pressure using a clamp. The whole assembly is placed in a high pressure heat-curing unit set initially at 3 bar, for 30 minutes at 105°C and then 30 minutes at 120°C. After this curing process, the pressure is released and the mould is immersed in tap water to cool. The mould is opened and the device is taken out of the mould and then hand polished with various fine abrasives to make it clear and examined for transparency and clarity, To Applicants knowledge, the is the first LCD to survive the ocular prosthesis manufacturing steps.

Considering that the ocular prostheses are approximately 10 mm thick depending on the implant, the 2.4 mm thick LCD can be easily integrated. Applicants used a 25 x 30 mm LC cell because it was commercially available (LC-TEC courtesy) but smaller LC cells more appropriate for the iris size of about 13mm diameter are being addressed. Currently, Applicants do not envisage a reduction in the thickness of the glass cell, however, for smaller diameters, a thinner glass could be used. Also note that all electronic components require almost no space, as these can simply be made into a single integrated circuit chip measuring much less than one mm square. However, with thinner glass cells, transparent spacers must be inserted between the two glass plates in the center of the cell to ensure that the plates do not collapse at high pressures, although smaller diameters will help eliminate this requirement. In Applicants case, the transparent supports in the middle of the LCD will not affect the system because the light does not need to be switched in the smallest pupil size area. Moreover, lack of polarizers in that

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RECTIFIED SHEET (RULE 91.1) region would give more light to the PC, which would simulate the pupil color quite well.

Four iris images Figs. 8(a-d) having survived the ocular prosthesis manufacturing steps are seen through the encapsulated LCD display discussed above. These images are the final result after adding the ring shaped ITO etching patterns (fig. 3), inside ON/OFF cells. The pupil size follows the size of the healthy eye, as shown in Groot S G D, Gebhard J W. Pupil size as determined by adapting luminance. J. Opt. Soc. 1952; 42: 492-495, where the best relation between the diameter of the human pupil and the intensity of the incident light is: log D = 0.8558 - 0.000401 (log B + 8.1) ³

Where D is the diameter of the pupil in millimeters and B is the luminance of the visual field in millilamberts. However, age, eye color, sex, drugs administered, ametropia, pathological conditions and the stimulus field of the patient affect the pupil size. Applicant's proposal is to photograph the patient's eye under different light intensity conditions and to fabricate concentric ring electrodes on a backdrop of this painted iris.

The polarizers used in the LCD cut out a significant percentage of incident light. The important factor to note is that despite the reduction in the transmitted light, it appears that there is little difference in the rendition and in the visibility of the iris in Fig. 8 (a-d) with different pupil sizes through the LC cell surviving the ocular prosthesis manufacturing process. However, the image through the LCD shown in figs. 8 (a-d) is initially a lighter one. It is clear that it would be difficult to make an LCD dynamic iris similar to a very light color iris, as shown in figs. 9 (a-d). Fig. 9a is a real iris viewed under high ambient light. The objective would be to make a similar image with polarizer. Fig. 9b is the same iris image under a 50% transmission polarizer. The difference between those two pictures is easily notable even if the black of the pupil LC pixel is perfect. Figures 9c and 9d are

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RECTIFIED SHEET (RULE 91.1) under a 70% transmission polarizer but fig. 9d uses a 20% lighter image. The result gets closer to the first real iris (fig. 9a) but the demarcation between the small pupil (LC cell) and the ring LC pixel may be just noticeable. This problem may be solved by changing or removing the polarizer over the smallest pupil diameter as the light does not need to be switched in that region.

On the other hand, a dark eye, which is the most common in the world, would be relatively easy using a lighter image under the LCD. Polarizers with a transmission of over 35%, which are easily available, would be necessary to obtain a good contrast. Using a less efficient polarizer, which has poor extinction, would give better transmission in the ON state. In the OFF state, the poorer extinction would be complimented by the dark background of the silicon substrate. The silicon photovoltaic cell proposed here would help to emulate a perfectly black pupil despite the reduced transmission through the polarizers. The polarizers must be selected appropriately depending on the colour of the iris. With a dark iris, for example, a poor polarizer may be used, resulting in a better contrast and a near black pupil.

Finally, another demonstration of the working principle of the passive circuit was performed using a clock LCD. In the dark, none of the pixels operate, and as the light level increased monotonically, the pixels turned on gradually until (not shown). Nine tiny interconnected photovoltaic cells are used in series to power the LCD. More than nine photovoltaic cells in series could be used for delivering a potential higher than that required for this experiment . The size of the passive circuit is less than 8mm diameter and will be hidden by the image of the iris in the final ocular prosthesis (or integrated into the silicon cell), once fully integrated. There were crossed polarizers on the LCD used in this experiment.

With respect to manufacturing a prosthesis of the present invention, the liquid crystal cell and photovoltaic (PC) can be provided as a kit and assembled as a unit for use in manufacturing a prosthetic by combining it with an iris image and a prosthetic base in order to mold them together into a prosthetic. The base can be

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RECTIFIED SHEET (RULE 91.1) the part that can holds the LC assembly and the iris image in position and the finished prosthetic could mate with an ocular implant.

Another approach for varying the "apparent" pupil 60 size as a function of light intensity is shown in Fig. 10. This embodiment requires only one liquid crystal cell where activation of specific liquid crystals is a function of cell thickness. For example, if the cell becomes thicker from the outer periphery to its center (i.e. dome-shaped), a low level light condition will generate a low electrical potential from the photovoltaic cell and be enough to activate those liquid crystals on the outer periphery due to the lower resistance in this area of the cell. Increased lighting would therefore cause a gradual decrease in the apparent pupil 60 size and vice-versa. Fig. 10 schematizes an average light intensity required to activate liquid crystals where the vertical axis represents light intensity. It will be understood that the dome shape makes for a multiple of rings of different activation energy (61 and 62). In order to simplify the drawing however, only two thicknesses are depicted. One of the advantages of this embodiment is the more natural pupil 60 size transition periods. Transitions are continuous rather than discrete, as is the case with multiple concentric rings.

It will be understood that solar cell and photovoltaic cell are used interchangeably. Furthermore, it will be understood that liquid crystal cell and indium tin oxide (ITO) electrode are interchangeable for the purpose of varying an apparent pupil diameter.

The iris of the present invention can be disc-shaped and have an aperture in its center for the photovoltaic cell (PC). However, it is also possible to have an iris that is manufactured to have a PC in its center. In this specific case, the PC acts as the pupil can be manufactured as an integral part of the iris. It is also possible to have the iris design painted or attached to the underside of the of the liquid crystal cell electrode.

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RECTIFIED SHEET (RULE 91.1) The term "corresponding to" should be understood as meaning essentially corresponding to. For example, a pupil is generally round and a photovoltaic cell is generally square or rectangular in shape. If the square PC fits into the round pupil area taking up essentially the available space, the PC should be understood as corresponding to the pupil area.

The circuit is shown throughout the application as functioning with a direct current (DC) but it should be understood that the circuit can also be adapted to function with an alternate current (AC) source.

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RECTIFIED SHEET (RULE 91.1)