OCULAR PROSTHESIS

Abstract: An ocular prosthesis (artificial eye) has representations of the pupil (6) and other parts of a natural eye visible through the corneal section (4) of the prosthesis. A display is associated with the representation of the pupil (6) and is to be differentially activated by incident light falling on the corneal section (4) of the prosthesis to create the impression that the pupil (6) dilates or contracts in changing light conditions. The display may be liquid crystal display and may be activated to cause one or more concentric rings to appear blackened around the representation of the pupil. The incident light may be measured by a photoelectric cell (8) housed within the prosthesis.

Description: OCULAR PROSTHESIS Field of Invention The invention relates to an ocular prosthesis or, as more commonly designated, an artifical eye. Background of the Invention Artifical eyes have been in use for many years. When a natural eye has been removed from the orbit (socket), it has been known to replace the natural eye in the orbit with an ocular prosthesis or artifical eye. An artifical eye has been made from a variety of materials and for many years glass was used. More recently, artifical eyes have been made from plastics material such as polymethyl methacrylate. An ocular prosthesis may take any of a variety of shapes. In one common form, it has been made somewhat in the shape of a hemisphere. The anterior part of the prosthesis presents a substantially hemispherical or domed surface which, when the prosthesis is properly positioned in the orbit, rests against the lining of the eyelids and usually permits normal opening and closing of the eyelids. That section of the anterior wall of the prosthesis which corresponds to the cornea of a natural eye is transparent and visible through the corneal section are representations of other parts of a natural eye (e.g. lens, iris, pupil, blood vessels, etc.). The posterior surface of the prosthesis may be somewhat flattened and non-planer and is shaped with the object of mating with the tissue defining the internal surfaces of the orbit so that the orbital muscles, which were effective to initiate and control movement of the natural eye, would also be effective to give similar movement to the prosthesis. One of the shortcomings of known artifical eyes resides in the fact that, as represented, the iris is fixed and thus the pupil of an artifical eye has not been able to dilate in the same manner as is the case with a natural eye. Therefore, known artifical eyes present a rather glassy stare. Although this disadvantage has long been widely recognised, a solution has not yet been found. Another shortcoming is that, because known artifical eyes are relatively heavy, the orbital muscles generally have not been effective to produce movement of the prosthesis similar to that of a natural eye. Description of the Invention It is a n object of the invention to make an artifical eye which will closely resemble a natural eye. It is another object of the invention to provide an artifical eye with a pupil which gives the appearance of changing in size in response to changing light conditions. According to the invention, an ocular prosthesis is formed with a substantially domed anterior external surface having a section thereof corresponding to the cornea of a natural eye, representations of the pupil and other parts of a natural eye visible through the corneal section of the prosthesis and a display associated with the representation of the pupil adapted to be differentially activated by incident light falling on the corneal section of the prosthesis to create the impression that the pupil dilates or contracts in changing light conditions. Preferably, the display is a liquid crystal display. As the pupil appears to change size simulating a dilating or contracting pupil, the ocular prosthesis of the invention is more animated than previously was the case. In its preferred form, it is an object of the invention to make an ocular prosthesis which is lighter that existing ones so that there will be greater movement of the prosthesis by the orbital muscles. This may be achieved by making the prosthesis substantially hollow. Brief Description of the Drawings Fig. 1 is a side sectional view of an ocular prosthesis according to one embodiment of the invention; Fig. 2 is a side view of the liquid crystal display apparatus which is positioned within the ocular prosthesis shown in Fig. 1; Fig. 3 is . an exploded isometric view showing parts of the liquid crystal display apparatus in greater detail; Fig. 4 is a view along 4-4 of Fig. 2; and Fig. 5 is a block diagram schematically illustrating how various parts co-operate. Detailed Description of the Embodiment The ocular prosthesis illustrated in Fig. 1 is formed with an anterior wall 1 and a posterior wall 2 with a hollow space 3 therebetween. The anterior wall 1 is shaped to provide a somewhat hemispherical or domed surface which, when the prosthesis is in position in the orbit, rests against the inner lining of the eyelids. The anterior wall 1 has a humped transparent section 4 which is visible between open eyelids and represents the cornea of a natural eye. All of the apparatus for simulating a dilating pupil is housed between anterior wall 1 and posterior wall 2. The anterior wall 1 and posterior wall 2 are normally attached to one another by way of a joint 5, which is preferably stepped, and the parts joined by a suitable adhesive. However, the walls may be separated should maintenance or adjustment be required to the apparatus housed therein. The apparatus for simulating a dilating pupil includes a liquid crystal display assembly 6 shown in block form in Fig. 1 and mounted immediately behind transparent corneal section 4. The liquid crystal display assembly 6 may have an axial bore 7 along which incident light falling on the corneal section 4 of the prosthesis may pass to be registered by a photoelectric cell 8. Photoelectric cell 8, which may be mounted at the back of liquid crystal display assembly 6, or in a cavity therein, is connected to a micro chip 9 which is powered by a battery 10. Micro chip 9 is in turn connected to liquid crystal display apparatus 6, prefer¬ ably by way of trimmer 11. The liquid crystal display assembly 6 preferably takes the form illustrated in Fig. 2, wherein the assembly 6 is rotated by 90°. When mounted within the prosthesis, the upper portion of assembly 6 is adjacent the corneal section 4. As shown in Fig. 2, a liquid crystal layer 16 is sandwiched between thin layers of indium tin oxide 17 and 18, which layers are transparent and conductive, and each comprises a plurality of discrete areas as is shown in Fig. 3. The liquid crystal layer 16 and the indium tin oxide layers 17 and 18 are in turn sandwiched between thin layers of glass 19 and 20. As shown, glass layers 19 and 20 are offset with respect to one another to provide access to the indium tin oxide layers 17 and 18. Representations of various parts of a natural eye are painted at 21 on the exposed surface of glass layer 19 and are visible through transparent corneal section 4. At the centre of the representation of the natural eye is a small black circular area depicting a contracted pupil as the pupil of a natural eye would appear in strong light ' conditions. Covering the painted representation is a clear layer 22 of polariser material. A similar polariser layer 23 is applied to the exposed surface of glass layer 20. Polariser layer 23 may be covered by an aluminised reflective layer 24. One or both polariser layers 22 and 23 may be omitted if a dichroic liquid crystal is employed. In this type of liquid crystal, a coloured dye is mixed with the liquid crystal. Fig. 3 is an exploded isometric view showing glass layer 19 with indium tin oxide layer 17 on its lower face and glass layer 20 with indium tin oxide layer 18 on its upper face. The liquid crystal layer is not shown. The indium tin oxide layer 17 has a central circular area 31 and concentric substantially annular areas 32, 33 and 34. Each of the areas 31, 32, 33 and 34 are separated from an adjacent area by a gap of approximately 3 to 4 microns. The indium tin oxide areas 31 to 34 are connected to indium tin oxide contact areas 35 to 38, respectively. References 41 to 48 indicate corresponding parts of indium tin oxide layer 18. When assembled, areas 31 to 34 are aligned with areas 41 to 44. In addition, central areas 31 and 41 are aligned with the small black circular painted area represent¬ ing a contracted pupil in the painted representation 21. The black painted pupil area is smaller than the areas 31 and 41 and appears to lie concentrically within those areas. Indium tin oxide contact areas 35 to 38 are displaced by 180° from the contact areas 45 to 48. As glass layers 19 and 20 are offset with respect to one another, all of the contact areas are exposed for access. Zebra strips 39 and 49 connect contacts 35 to 38 and 45 to 48 to contacts on printed circuit boards 40 and 50, respectively. A zebra strip is formed by vertically conductive elasto¬ meric sections separated by non-conductive elastomeric sections. The resulting sandwich has no conduction in the horizontal plane, only conduction in the vertical plane. Fig. 4 illustrates the manner in which indium tin oxide contacts 45 to 48 on glass layer 20 are connected via zebra strip 49 to contacts 51 to 54 on printed circuit board 50. Zebra strip 40 electrically connects contact 45 to 51, contact 46 to 52, contact 47 to 53 and contact 48 to 54. In Fig. 4, the contacts are shown spaced from the zebra strip for the sake of clarity. There is no electrical connection, for example, between contacts 45 and 52 or between contacts 45 and 46. Part of the printed circuit is shown on the upper face of printed circuit board 50. By way of this arrangement, areas 31 to 34 and 41 to 44 of indium tin oxide layers 17 and 18 may be energised with an alternating voltage that may take the form of a square wave of frequency 60Hz. When, for example, corresponding areas 31 and 41 are energised with the same alternating voltage, there will be no alternating electric field across the liquid crystal between areas 31 and 41 and hence no activation of the liquid crystal between areas 31 and 41. Energisation of layer 41 with an alternating voltage of the same frequency and amplitude, but of different phase, to that applied to area 31 will create an alternating electric field between areas 31 and 41, thus activating the liquid crystal between areas 31 and 41 only. Energisation of areas 32 and 42 in a similar manner will separately activate the liquid crystal between those layers and so on. Activation of the liquid crystal between corresponding areas in sequence may be effected by a series of voltage comparators comparing the output of the photoelectric cell with fixed voltages that may be internally generated by the integrated circuit or may be generated by the trimmer. Each voltage comparator may have a reference voltage corresponding to the voltage output of the photo¬ electric cell at certain light levels. When that light level is reached, the output voltage of the comparators may activate the liquid crystal between the appropriate corresponding areas 31 to 34 and 41 to 44, respectively. When the ocular prosthesis is being worn in strong light conditions, there will be no activation of the liquid crystal and only the painted pupil is visible through the transparent corneal section 4. Diminishing strength of light incident on corneal section 4 is registered by photoe'lectric cell 8 which sends a signal via micro chip 9, printed circuit boards 40 and 50, zebra strips 39 and 49 to the indium tin oxide layers 17 and 18 to cause activation of the liquid crystal between one or more of the corresponding areas 31 to 34 and 41 to 44, which appear blackened through the corneal section 4 of the prosthesis. This process is schematically illustrated in Fig. 5. At first, only liquid crystal between areas 31 and 32 is activated and appears blackened. This has the effect of simulating a dilating pupil as the size of the pupil appears to increase from that of the black painted area to that of areas 31 and 41. As t o the light deteriorates further, the liquid crystal between areas 32 and 42 is additionally activated simulating further dilation of the pupil. This process continues until all of the liquid crystal between the indium tin oxide layers is activated and appears blackened. This process thus gives the impression of a dilating pupil under decreasing light conditions. In increasing light conditions, the reverse process gives the impression of a contracting pupil. Trimmer 11 may be employed to vary the switching of the display rings to match the apparent dilation of the pupil of the prosthesis with the dilation of the pupil of the wearer's natural eye. Trimmer 20 may take the form of a tiny rheostat connected between micro chip 9 and printed circuit boards 40 and 50. The ocular prosthesis may be made by obtaining an impression of the patient's orbit and making a corresponding mould. The mould is divided into two portions, representing the anterior portion and the posterior wall. The apparatus . simulating a dilating pupil is positioned in the anterior portion of the mould together with a scleral mixture. When the anterior portion of the prosthesis is moulded, the apparatus for simulating the dilating pupil is moulded in position. The anterior portion of the pros¬ thesis is then hollowed out around the moulded-in apparatus to the required wall thickness. Suitable measures are taken during the moulding and/or hollowing steps so that there is access to various parts such as trimmer 11 and battery 10. The hollow space formed in the anterior portion of the prosthesis is made as large as possible thereby minimising the weight of the prosthesis. That, in turn, maximises the prospect that the orbital muscles will be able to move the prosthesis to the same extent as the move¬ ment of the wearer's natural eye. The posterior wall 2 of the prosthesis is preferably moulded to the desired wall thickness and does not have to be hollowed. Corresponding stepped ridges are cut around the perimeters of the two portions to facilitate joining and the two portions are attached together by means of an adhesive. The invention is not restricted to the preferred embodiment described in relation to the accompanying drawings. Many modifications will be apparent to the person skilled in the art without departing from the broad concept of the invention defined in the appended claims. For example, bore 7 may be omitted. Instead, the central portion of the painted area may be left unpainted to allow light to reach the photoelectric cell 8. In another embodiment, only one of the indium tin oxide layers 17 and 18 comprises discrete concentric areas, the other may be a continuous layer.

Claims: Claims. 1. An ocular prosthesis formed with a substantially domed anterior external surface having a section thereof corresponding to the cornea of a natural eye, representations of the pupil and other parts of a natural eye visible through the corneal section of the prosthesis and a display associated with the representation of the pupil adapted to be differentially activated by incident light falling on the corneal section of the prosthesis to create the impression that the pupil dilates or contracts in changing light conditions. 2. An ocular prosthesis as claimed in Claim 1, wherein the display is a liquid crystal display. 3. An ocular prosthesis as claimed in Claim 1 or 2, wherein differential activation of the display forms one or more concentric annular rings surrounding the representation of the pupil. 4. An ocular prosthesis as claimed in Claims 2 and 3, wherein the liquid crystal display is sandwiched between two layers of indium tin oxide, at least one of the layers comprising a plurality of discrete areas which may be differentially energised to activate the display. 5. An ocular prosthesis as claimed in Claim 3, wherein, commencing with the smallest ring, one or more rings are activated by diminishing incident light strength to simulate a dilating pupil. 6. An ocular prosthesis as claimed in any one of Claims 1 to 5 and including a photoelectric cell housed within the prosthesis to measure the incident light strength. 7. An ocular prosthesis as claimed in Claim 6, wherein signals from the photoelectric cell are passed via a micro chip to control the differential activation of the display. 8. An ocular prosthesis as claimed in any one of the preceding claims and including an adjustment means housed within the prosthesis whereby the apparent dilation of the pupil of the prosthesis may be matched with the dilation of the pupil of the wearer's natural eye. 9. An ocular prosthesis as claimed in any one of the preceding claims, wherein the prosthesis is made in two separable portions. 10. An ocular prosthesis as claimed in any one of the preceding claims, wherein the prosthesis is substantially hollow.

Inventors: SAUL IAIN GODFREY, TREFRY CLIFFORD ROY, SAUL, IAIN, GODFREY, TREFRY, CLIFFORD, ROY
Applicants: CONS TECHNOLOGY PTY LTD, OCULAR PROSTHETICS PTY LTD, TAYLOR & TREFRY PTY LTD
Application year: 1985
Main classification: A61F2
IPC codes: A61F2