| Intraocular lens -> Monitor Keywords |
|
|
  Intraocular lensUSPTO Application #: 20060167545Title: Intraocular lens Abstract: The Invention concerns an intraocular lens with negative spherical aberration and a method of determining the refractive power of intraocular lenses. In the environment of immersion medium the intraocular lens refracts an incoming wave with an elliptically oblongly curved wave front into an outgoing wave with a substantially spherical wave front. (end of abstract) Agent: Crowell & Moring LLP Intellectual Property Group - Washington, DC, US Inventors: Werner Fiala, Christine Kreiner USPTO Applicaton #: 20060167545 - Class: 623006230 (USPTO) Related Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Eye Prosthesis (e.g., Lens Or Corneal Implant, Or Artificial Eye, Etc.), Intraocular Lens, Aspheric Lens The Patent Description & Claims data below is from USPTO Patent Application 20060167545. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention concerns an intraocular lens (IOL) and a method of determining the imaging properties of intraocular lenses. [0002] Lenses of that kind are known. The topology of conventional intraocular lenses generally involves spherical curved surfaces whose imaging properties however are not ideally suited to producing an image on the retina of the human eye. Known methods of determining the imaging properties of intraocular lenses therefore presuppose basically spherically curved surfaces. [0003] The object of the invention is to provide an intraocular lens whose imaging properties produce an image of improved quality on the retina. A further object of the invention is to provide a method of determining the imaging properties of the intraocular lens, which method provides reliable results independently of the topological nature of the lens. [0004] According to the invention that object is attained by an intraocular lens with negative spherical aberration. Conventional, spherically curved intraocular lenses of positive refractive power have a positive spherical aberration, that is to say they refract an incoming wave with a plane wave front into an outgoing wave with an elliptically oblongly curved wave front. The focus of such a lens is accordingly not punctiform. In comparison the intraocular lens according to the invention is preferably of such a configuration that, in the environment of immersion medium, in particular the in vivo environment (refractive index 1.336) in the eye it refracts an incoming wave with an elliptically oblongly curved wave front into an outgoing wave with a wave front which is substantially spherical. In that way the imaging properties of the cornea of the eye, which is in front of the IOL, are better taken into consideration and the effect is that more accurate focusing on the retina is possible. [0005] Such imaging properties are preferably achieved by the refractive index and the curvature of the lens surfaces being so selected that the lens at the centre has a refractive power D of greater than or equal to +3. dioptres (dpt) in the immersion medium and that in the environment of air an incoming wave with a substantially plane wave front is refracted into an outgoing wave with a hyperbolic wave front. [0006] The shape of the curvature of the wave fronts and also the curvature of the lens surfaces can be described by the following function: y.sup.2=px-(1+asph)x.sup.2 (1) wherein x coincides with the direction of light propagation or the lens thickness, y specifies the direction perpendicular thereto, radially outwardly with respect to the lens centre, p is any parameter and asph is so-called asphericity, that is to say a measurement in respect of the deviation of the curvature of the lens surface from a spherical shape. The shape of the lens surface or wave front is shown in section for different asphericities in FIG. 1. With an asphericity of greater than 0 the equation accordingly describes an ellipse whose minor axis in the x-direction (illustrated on an extended scale) is less than that in the y-direction (oblong). If the asphericity is equal to 0, a circle is described. If it is between 0 and -1 (in each case excluding the limit values), an ellipse is described, whose major axis in the x-direction is greater than that in the y-direction (prolong). If the asphericity is -1 then equation (1) describes a parabola and if its value is less than -1 it then describes a hyperbola. [0007] Preferably the hyperbolic wave front of a wave produced from an incoming plane wave by the lens according to the invention has an asphericity (asph.sub.OUT) of less than or equal to -1. Also the intraocular lens preferably has at least one convexly curved surface whose curvature is of an asphericity (asph.sub.L) of less than or equal to -1. [0008] The invention is described in greater detail hereinafter by means of embodiments by way of example with reference to the Figures in which: [0009] FIG. 1 shows a view of the curvature of a curve described by equation (1) for various asphericity values, [0010] FIG. 2 shows a diagram of the asphericity of an outgoing wave for various topographical asphericities of the cornea with a corneal refractive power at the centre of 40 dioptres, [0011] FIG. 3 shows a diagram of the asphericity of an outgoing wave for various topographical asphericities of the cornea with a corneal refractive power at the centre of 50 dioptres, [0012] FIG. 4 shows a diagram of the negative asphericity of the surface of a first embodiment of the IOL according to the invention for the conversion of a spherical wave into another spherical wave and the negative asphericity of an outgoing wave measured in air and in the immersion medium in each case in dependence on the refractive power of the lens, [0013] FIG. 5 shows a diagram of the negative asphericity of the surface of a second embodiment of the IOL according to the invention for the conversion of an aspherical wave into a spherical wave and the negative asphericity of an outgoing wave measured in air and in the immersion medium in each case in dependence on the refractive power of the lens, [0014] FIG. 6 is a diagrammatic view of a measuring apparatus for determining the waveform of the outgoing wave refracted by an IOL with incoming radiation of plane waves, [0015] FIG. 7 shows a diagrammatic cross-section through a third embodiment of the IOL according to the invention, [0016] FIG. 8 shows the wave front of an outgoing wave from the IOL shown in FIG. 7 in comparison with an outgoing wave from a lens with spherical surfaces measured in air, and [0017] FIG. 9 shows the wave front of an outgoing wave from the IOL shown in FIG. 7 in comparison with an outgoing wave from a lens with spherical surfaces measured in the immersion medium. [0018] The imaging conditions taken into account in relation to the IOL according to the invention, in the human eye, are investigated hereinafter. As is known the cornea has a refractive index of about 1.37 topographically it essentially represents an aspheroidal dish. It has a negligibly slight influence on refraction of an incoming wave. Refraction of the incident light depends rather on the one hand on the curvature which is predetermined by the topography of the cornea but on the other hand on the refractive index of the immersion medium behind the cornea (aqueous humour). As is known, that has a refractive index of 1.336. The topography of the cornea is characterised by the asphericity (asph.sub.c), for which the literature specifies values of asph.sub.c=-0.26.+-.0.18 (Kiely et al, in G Smith et al, Vision Research 41, 2001, 235-43) and asph.sub.c=-0.18.+-.0.15 (Guillon et al, loc. cit.). In accordance with those literature values it can be assumed that the cornea of the human eye is generally elliptically curved. For the following considerations, a value range of asph.sub.c=-0.56 to 0 is therefore assumed for the asphericity of the cornea, in order to ensure that practically all human cornea asphericities occurring in nature are embraced. In that respect it is to be observed that the upper limit value (asph.sub.c=0) corresponds to a cornea with spherical curvature. [0019] In addition the topography of the cornea is characterised by its surface refractive power at the centre point, that is to say on the optical axis. A range of 40 to 50 dioptres (dpt) is assumed for that purpose, whereby the range of the surface refractive power of the cornea, which actually occurs in nature and which in accordance with knowledge at the present time is at 43 dpt as an average value, is masked both towards higher and also lower values. [0020] FIGS. 2 and 3 show the asphericity (asph.sub.IN) of a wave refracted by the cornea or the immersion medium, on the incidence of a plane wave, that is to say a wave with a plane wave front, like for example light which is emitted by a point at an infinitely far distance. That depends on the topographical asphericity of the cornea and the spacing of the apex of the wave front from the apex of the cornea (abscissa value). The spacing between the centre of the intraocular lens and the front apex point of the cornea in the human eye, which is between a minimum of 3 mm and a maximum of 6 mm, is taken as the basis for the range of that value. FIG. 2 specifies the conditions in the case of a cornea with a central surface refractive power of 40 dpt. It can be seen therefrom that the asphericity of the refracted wave front which impinges on the intraocular lens ranges between the limit value asph.sub.IN=0 with a topographical asphericity of the cornea asph.sub.C=-0.56 and the limit value asph.sub.IN=10.8 with a topographical asphericity asph.sub.C=0. On the basis of a central surface refractive power of the cornea of 50 dpt, see FIG. 3, the asphericity of the refracted wave front asph.sub.IN impinging on the intraocular lens is between 0 and +11.4. Overall therefore it can be established that the asphericity of that wave front is always in the last-mentioned range, and the wave front is therefore either spherical (asph.sub.IN=0) or otherwise always elliptically oblongly curved (asph.sub.IN>0). In other words the cornea has a positive spherical aberration as it refracts the beams at the edge more greatly than those at the centre. Based on that realisation therefore an IOL with negative spherical aberration is required in order to refract the aspherical wave coming from the cornea so as to achieve improved image formation on the retina of the eye. [0021] Preferably the IOL according to the invention is so designed that, in the environment of immersion medium, an incoming wave with an elliptically oblongly curved wave front is refracted into an outgoing wave with a substantially spherical wave front, wherein the refractive power of the IOL is to be so selected in dependence on the eye of the patient that the centre of the outgoing waves is on the retina of the eye. [0022] The IOL according to the invention can assume various configurations: in accordance with a first embodiment, at its centre, in the environment of the immersion medium, it has a refractive power D.sub.I of at least +3 dpt and the refractive power decreases towards the edge of the lens. In addition by way of example a refractive index of 1.46, a lens diameter of 6 mm and an axis-parallel edge thickness of 0.25 mm is assumed to apply. [0023] FIG. 4 shows the required negative asphericity of the surfaces (asph.sub.L) of a first, biconvex, symmetrical embodiment of the IOL according to the invention for the conversion of an incoming wave with a spherical wave front (asph.sub.IN=0, that is to say for the extreme case of a topographical asphericity of the cornea, which is to be expected as a minimum, of -0.56) into an outgoing wave with an also spherical wave front (asph.sub.OUT=0). The asphericity of the surfaces of the IOL depends on the central surface refractive power of the IOL in the immersion medium. The configuration is shown in the lower curve (open circles). [0024] In addition FIG. 4 (open triangles) shows the configuration of the negative asphericity of the wave front of the outgoing wave which is produced by a corresponding IOL in the immersion medium if the incoming wave has a plane wave front. The upper curve in FIG. 4 (open squares) shows the negative asphericity of the wave front of an outgoing wave which is produced by the same lens measured in air when a wave with a plane wave front is incident. Continue reading... Full patent description for Intraocular lens Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Intraocular lens patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Intraocular lens or other areas of interest. ### Previous Patent Application: Tissue shaping device Next Patent Application: Leg prosthesis system and method Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Intraocular lens patent info. IP-related news and info Results in 1.89565 seconds Other interesting Feshpatents.com categories: Computers: Graphics , I/O , Processors , Dyn. Storage , Static Storage , Printers |
||
