News Column

Researchers Submit Patent Application, "Eye Surgery System and Method of Inserting an Intraocular Lens", for Approval

September 4, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors HAUGER, Christoph (Aalen, DE); SEESSELBERG, Markus (Aalen, DE); WETH, Christopher (Aalen, DE); WILZBACH, Marco (Stuttgart, DE), filed on February 6, 2014, was made available online on August 21, 2014.

The patent's assignee is Carl Zeiss AG.

News editors obtained the following quote from the background information supplied by the inventors: "The planning of a surgery for implanting an intraocular lens includes a selection of a suitable intraocular lens from a large number of different types and models of intraocular lenses available on the market. The different models of intraocular lenses may differ with respect to, for example, the refractive index of the lens material, the curvatures of the lens surfaces, the axial distance of the lens surfaces from each other, the diameter of the lens, the type of the haptics, and other properties. There are also different types of intraocular lenses, such as intraocular lenses having aspheric lens surfaces or having lens surfaces having free form surfaces without rotational symmetry, intraocular lenses providing zones with different refractive powers, and intraocular lenses including diffractive optical elements.

"The selection of the type and model of the intraocular lens to be implanted into a particular eye is commonly based on preoperative values determined from the eye, such as the visual defect, the curvature of the cornea, the distance between the corneal apex and the retina of the eye, i.e. the eye length, and the distance between the corneal apex of the eye and the crystalline lens, i.e. the anterior chamber length, and other suitable values. Heuristic formulas are typically used in order to determine properties of the intraocular lens based on one or more of the above preoperative values. Examples of such formulas include the Haigis formula, the Hoffer formula, the Holladay formula and the SRK/T formula.

"The selection of the type and model of the intraocular lens to be implanted into a particular eye does not always provide the desired result since the desired postoperative faculty of sight of the eye is not achieved subsequent to the surgery and after healing of incisions introduced into the cornea of the eye during the surgery."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present invention has been made in view of the above considerations.

"According to some embodiments, the invention provides a method of inserting an intraocular lens and an eye surgery system which can be used in such method in order to better achieve postoperative properties of the eye.

"According to some embodiments, a method of inserting an intraocular lens comprises: (1) determining at least the following preoperative values of an eye: (a) a value representing a curvature of a cornea of the eye, (b) a value representing a distance between a corneal apex of the eye and a retina of the eye, and (c1) a value representing a distance between the corneal apex of the eye and a crystalline lens of the eye; (2) selecting an intraocular lens based on the preoperative values; (5) inserting the intraocular lens into the eye; (6) determining at least the following intraoperative values of the eye: (c2) a value representing a distance between the corneal apex of the eye and the intraocular lens; (7) providing an eye model, wherein the eye model includes at least the following parameters: (a) a parameter representing a curvature of a cornea of the eye, (b) a parameter representing a distance between a corneal apex of the eye and a retina of the eye, (c2) a parameter representing a distance between the corneal apex of the eye and an intraocular lens; (d) a parameter representing a refractive power of the intraocular lens; (8) determining the second value representing a postoperative visual defect of the eye using the eye model, wherein: (a) the preoperative value representing the curvature of the cornea of the eye is assigned to the parameter of the eye model representing the curvature of the cornea of the eye, (b) the preoperative value representing the distance between the corneal apex of the eye and the retina of the eye is assigned to the parameter representing the distance between the corneal apex of the eye and the retina of the eye, and (c2) the intraoperative value representing the distance between the corneal apex of the eye and the intraocular lens is assigned to the parameter of the eye model representing the distance between the corneal apex of the eye and the intraocular lens; (d) a value determined based on the preoperative values or based on the selected intraocular lens is assigned to the parameter of the eye model representing the refractive power of the intraocular lens; (9) correcting the position and/or the orientation of the inserted intraocular lens or inserting a different intraocular lens based on the second value representing the postoperative visual defect of the eye.

"Both preoperatively determined values of the eye and intraoperatively determined values of the eye are used as parameters of the eye model, accordingly. The eye model is used to predict a postoperatively occurring visual defect of the eye. This prediction can be performed already during the surgery, i.e. the prediction is an intraoperative prediction such that further steps of the surgery can be planned, or an existing planning of steps of the surgery can be modified based on the intraoperatively determined postoperative visual defect of the eye. For example, the intraoperatively determined postoperative visual defect of the eye can be compared with a desired visual defect of the eye, in order to determine whether a position or an orientation of the currently inserted intraocular lens is correct or whether the selected and inserted intraocular lens should be replaced by a different intraocular lens.

"Changing of the orientation of the inserted intraocular lens can be in particular useful with intraocular lenses having an astigmatic power. The correcting of the position of the inserted intraocular lens can be performed in particular in such situations in which complications occurred when the intraocular lens was inserted into the capsular bag of the eye. Replacing of the inserted intraocular lens with a different intraocular lens will occur in particular in situations in which the selection of the inserted intraocular lens based on the preoperative values and the application of one of the empirical formulas was not successful due to particular properties of the eye of the patient under surgery.

"The values representing properties of the eye and the parameters of the eye model used in the method can be scalar values or tuples, wherein each tuple comprises plural scalar values. For example, the value representing the curvature of the cornea of the eye can be a radius of a sphere approximating the shape of the cornea of the eye. However, this value can also be the inverse of the radius of this sphere. Moreover, this value can be a tuple of two individual values representing the curvatures of the cornea measured in different planes. This can be in particular useful if the eye has an astigmatic visual defect. Moreover, the value representing the curvature of the cornea of the eye can be, for example, a tuple including plural coefficients resenting a Zernike polynomial representing an aspheric shape of the cornea up to a predetermined Zernike order in the usual manner.

"The value representing the distance between the corneal apex and the crystalline lens of the eye can be directly measured preoperatively, i.e. before performing the surgery. This value can be also obtained by subtracting the measured value of the distance between the crystalline lens and the retina of the eye from the measured distance between the corneal apex and the retina of the eye. Thus, also the tuple of the value of the distance between the corneal apex of the eye and the retina and the value of the distance between the crystalline lens and the retina of the eye is a value representing the distance between the corneal apex and the crystalline lens of the eye. Moreover, the value representing the distance between the corneal apex and the crystalline lens of the eye can be measured relative to the main plane of the crystalline lens, the apex of the front surface of the crystalline lens, the apex of the back surface of the crystalline lens or any other element of the lens which is physically present or is a mathematical construct based on the geometry of the crystalline lens.

"The eye model can be provided by plural possible methods. According to an exemplary method, the eye model is simulated using a computer and an optics software. Examples of such optics software include Code V, available from Synopsys, Inc., Pasadena, Calif., USA, and Zemax, obtainable from Radiant Zemax, LLC, Redmond, Wash., USA. Sets of parameters representing the optical properties of the simulated object, i.e. the eye, are typically supplied to the software in a suitable format. These parameters include, in particular, parameters representing the distances between interfaces, refractive indices of the materials provided between the interfaces and curvatures of the interfaces.

"Suitable models of the human eye have been developed. One example is the eye model of Gullstrand. Further background knowledge and details of useful eye models can be obtained from the articles by Yanqiao Huang and Duncan T. Moore, 'Human eye modeling using a single equation of gradient index crystalline lens for relaxed and accommodated states', Proc. SPIE 6342, International Optical Design Conference 2006; Jihong Feng; Hanyu Zhang; Xiaobing Wang; Aizhen Liu, 'Constructing a human eye model: The cornea shape effect on optical imaging for the human eyes', 3rd International Conference on Biomedical Engineering and Informatics (BMEI), 2010, vol. 1, no., pp. 171-173, 16-18 Oct. 2010; R. Navarro; J. Santamaria; J. Bescos, 'Accommodation-dependent model of the human eye with aspherics', Journal of the Optical Society of America A, Optics and image science September 1985, 2(8):1273-81; and Liou, H L, and N A Brennan, 'Anatomically accurate, finite model eye for optical modeling', Journal of the Optical Society of America A, 1997, 14, no. 8: 1684-1695.

"It is in particular possible to simulate the shape of the cornea of the eye using a finite element model before the shape of the cornea is inputted to the eye model. It is also possible that the calculation of the shape of the cornea using a finite element model is an intrinsic component of the eye model. An example of a finite element model simulating the shape of the cornea is illustrated in the article 'Lower- and higher-order aberrations predicted by an optomechanical model of arcuate keratotomy for astigmatism' by R. Navarro et al., J Cataract Refract Surg 2009; 35: 158-165. Using of such finite element model allows to take incisions into the cornea into account which are introduced into the cornea in order to insert surgical tools into the eye, to insert the intraocular lens into the eye, or which are introduced into the cornea in order to correct visual deficiencies.

"In the illustrated method, preoperatively determined values and intraoperatively determined values are assigned to the parameters of the eye model in order to determine and predict postoperative visual defects by performing calculations on the eye model. These calculations may include, for example, simulations, such as ray tracing.

"According to exemplary embodiments, the intraoperatively determined values of the eye also comprise a value determined by performing a wavefront measurement on the eye. Such value can be directly used to determine the visual defect during the surgery. Such value can also be used to verify the consistency of the currently used eye model, and it is also possible to modify parameters of the currently used eye model based on the value determined by the wavefront measurement. The wavefront measurement can be performed before and/or after the insertion of the intraocular lens.

"When the inserted intraocular lens has an astigmatic power, it can be advantageous if the intraoperatively determined values of the eye comprise a value obtained by performing a wavefront measurement on the eye. Values obtained by wavefront measurements readily allow to determine whether the orientation of the inserted intraocular lens is correct or should be changed.

"According to exemplary embodiments, the method further comprises: (3) applying an eye speculum to the eye before the intraocular lens is inserted into the eye, and (10) removing the eye speculum subsequent to the correcting of the position and/or the orientation of the inserted intraocular lens or subsequent to the inserting of the intraocular lens.

"The eye speculum is applied to the eye in order to maintain the eye open during the surgery. However, the eye speculum applies a certain pressure onto the cornea of the eye such that the shape of the cornea of the eye is distorted by the eye speculum. Such deformed cornea may result in that a wavefront measurement performed during the surgery detects a would-be visual defect of the eye which might result in unnecessary changes of the planning of the surgery. However, according to the illustrated method, such problems resulting from a distortion of the cornea from an applied eye speculum can be avoided since the preoperatively determined value of the curvature of the cornea is used as a parameter of the eye model for determining the postoperative visual defect of the eye.

"According to further exemplary embodiments, the method further comprises: (4) introducing at least one incision into the cornea of the eye, wherein the introducing of the incision may in particular occur before the intraocular lens is inserted into the eye, wherein the model of the eye further comprises the following parameter: (e) a parameter representing at least one of a position, an orientation and a length of the at least one incision in the cornea of the eye, and wherein (8) the determining of the value representing the postoperative visual defect of the eye includes (e) a value determined based on the at least one incision introduced into the eye is assigned to the parameter of the eye model representing the at least one of the position, the orientation and the length of the at least one incision in the cornea of the eye.

"An incision can be introduced into the cornea of the eye in order to insert surgical tools into the interior of the eye through the incision. The surgical tool can be, for example, an emulsifier used for removing the crystalline lens of the eye. An incision can be further introduced into the cornea of the eye in order to insert the intraocular lens into the eye. Such incisions are introduced into the cornea of the eye before the intraocular lens is inserted into the eye.

"Moreover, one or more incisions can be introduced into the cornea of the eye in order to change the curvature of the cornea of the eye for influencing the faculty of sight of the eye. Such incisions can be introduced into the eye before or subsequent to the insertion of the intraocular lens into the eye.

"According to exemplary embodiments, the eye model comprises a finite element model of the cornea of the eye as illustrated in the above mentioned article of R. Navarro et al.

"According to further exemplary embodiments, the method is performed such that (6) the following value is determined when the intraoperative values of the eye are determined: (f) a value representing a centration of the intraocular lens within the eye; wherein (7) the model of the eye comprises the following parameter: (f) a parameter representing a centration of the intraocular lens in the eye; and wherein (8) when the value representing the postoperative visual defect is determined, (f) the determined value representing the centration of the intraocular lens within the eye is assigned to the parameter of the eye model representing the centration of the intraocular lens within the eye.

"The value representing the centration of the intraocular lens within the eye can be, for example, a value defining a distance between the center of the intraocular lens from the optical axis of the eye and/or a value defining an orientation of a toric intraocular lens about the optical axis of the eye.

"According to further exemplary embodiments, a method of inserting an intraocular lens into an eye comprises: (1) determining preoperative values of an eye; (2) selecting an intraocular lens based on the preoperative values; (5) inserting the intraocular lens into the eye; (6) determining intraoperative values of the eye; (7) providing an eye model, wherein the eye model includes plural parameters; (8) determining the second value representing a postoperative visual defect of the eye using the eye model, wherein the preoperative values of the eye are assigned to a first subset of the plural parameters of the eye model and wherein the intraoperative values of the eye are assigned to a second subset of the plural parameters of the eye model, (9) correcting the position and/or the orientation of the inserted intraocular lens or inserting a different intraocular lens based on the value representing the postoperative visual defect of the eye.

"According to particular embodiments herein, the preoperative values comprise one or more values selected from the following values: (a) a value representing a curvature of a cornea of the eye, (b) a value representing a distance between a corneal apex of the eye and a retina of the eye, and (c1) a value representing a distance between the corneal apex of the eye and a crystalline lens of the eye.

"According to particular embodiments herein, the intraoperative values comprise one or more values selected from the following values: (a) a value representing a curvature of a cornea of the eye, (b) a value representing a distance between a corneal apex of the eye and a retina of the eye, (c2) a value representing a distance between the corneal apex of the eye and the intraocular lens, (e) a value representing at least one of a position, an orientation and a length of the at least one incision in the cornea of the eye, and (f) a value representing a centration of the intraocular lens within the eye.

"According to some embodiments of the method, a first eye model instance includes a representation of the cornea based on the intraoperative value representing the curvature of the cornea;

"wherein a second eye model instance includes a representation of the cornea based on the preoperative value representing the curvature of the cornea; wherein the determining of the intraoperative values includes a performing of a wavefront measurement for determining a first set of light rays outside of the eye; wherein the determining of the second value representing a postoperative visual defect of the eye comprises: calculating a second set of light rays inside the eye by extrapolating the light rays of the first set of light rays using the first eye model instance, calculating a third set of light rays outside the eye by extrapolating the light rays of the second set of light rays using the second eye model instance, and determining the second value representing a postoperative visual defect of the eye based on the third set of light rays.

"According to exemplary embodiments, an eye surgery system comprises

"a user interface; a measuring system configured to determine at least preoperative values and intraoperative values of an eye; a first computing module configured to determine a first value based on preoperative values, wherein the first value represents a property of an intraocular lens; a second computing module configured to determine a second value based on a simulation performed on an eye model, wherein the second value represents a postoperative visual defect of an eye, and wherein the eye model includes plural parameters; a controller configured (1) to receive preoperative values, (2) to trigger the first computing module to determine the first value representing the property of the intraocular lens, based on the preoperative values, (5) to trigger the user interface to display the first value representing the property of the intraocular lens, (6) to trigger the measuring system to determine intraoperative values, (8) to trigger the second computing module to determine the second value representing the postoperative visual defect of the eye, wherein the preoperative values of the eye are assigned to a first subset of the plural parameters and wherein the intraoperative values of the eye are assigned to a second subset of the plural parameters of the eye model, and (9) to trigger the user interface to display the second value representing the postoperative visual defect of the eye.

"The eye surgery system can be an integral system or a distributed system. When the eye surgery system is embodied as a distributed system, the measuring system for determining the preoperative values can be different from and located at a different site than the measuring system for determining the intraoperative values. Moreover, the controller can be embodied as a distributed system comprising plural components located at different sites, wherein the components are connected using suitable data connections, such as a computer network. The first computing module and the second computing module can be embodied as software modules running on one or more computers which can be integrated with the controller or located outside of the controller and connected with the controller via a suitable data connection.

"The first computing module can be configured, for example, to determine the first value representing the intraocular lens using the Haigis formula, the Hoffer formula, the Holladay formula, the SRK/T formula or other suitable computing methods. The first value representing the intraocular lens may include, for example, a refractive index lens of the intraocular lens, an identifier designating the material of which the lens of the intraocular lens is made, curvature of one or both surfaces of the intraocular lens and other data. The first value representing the intraocular lens may also include an identifier designating the type or model of the intraocular lens to be used, such as a trade name and a product designator under which the respective intraocular lens is available on the market.

"The second computing module can be configured to perform an optics software, such as Code V or Zemax. The second computing module can be further configured to run a finite element model simulating the shape of the cornea of the eye.

"According to further exemplary embodiments, the controller can be configured to wait for a predetermined user input via the user interface before the measuring system is triggered to determine the preoperative values, and/or wherein the controller is configured to wait for a predetermined user input via the user interface before the measuring system is triggered to determine the intraoperative values.

"According to further exemplary embodiments, the measuring system includes at least one of a keratoscope and an OCT measuring device for determining the value representing the curvature of the cornea of the eye.

"According to further exemplary embodiments, the measuring system comprises at least one of an OCT measuring device, an ultrasound measuring device and an interface measuring device for determining the value representing the distance between the corneal apex of the eye and the retina of the eye.

"According to further exemplary embodiments, the measuring system comprises at least one of an OCT measuring device and an interface measuring device for determining at least one of the value representing the distance between the corneal apex of the eye and the crystalline lens of the eye and/or the value representing the distance between the corneal apex of the eye and the intraocular lens.

"According to further exemplary embodiments, the measuring system comprises at least one of a wave front measuring device and an ametropia measuring device for determining the value representing the centration of the intraocular lens within the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

"The forgoing as well as other advantageous features of the disclosure will be more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. It is noted that not all possible embodiments necessarily exhibit each and every, or any, of the advantages identified herein.

"FIG. 1 is a schematic illustration of an eye surgery system according to an embodiment;

"FIG. 2 is a flowchart illustrating a method of inserting an intraocular lens into an eye, wherein the method can be performed using the eye surgery system shown in FIG. 1; and

"FIGS. 3A, 3B, 3C are schematic illustrations of an optical simulation using an eye model."

For additional information on this patent application, see: HAUGER, Christoph; SEESSELBERG, Markus; WETH, Christopher; WILZBACH, Marco. Eye Surgery System and Method of Inserting an Intraocular Lens. Filed February 6, 2014 and posted August 21, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1166&p=24&f=G&l=50&d=PG01&S1=20140814.PD.&OS=PD/20140814&RS=PD/20140814

Keywords for this news article include: Surgery, Software, Carl Zeiss AG, Medical Devices.

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