Patent Publication Number: US-9408747-B2

Title: Planning system and procedure for eye surgery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/723,900 and German Patent Application No. DE 10 2012 022 080.4, filed Nov. 8, 2012, which are hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The invention relates to a planning system for generating control data for a treatment device that creates at least one incision surface in the cornea using a laser apparatus. The invention also relates to a treatment device having a planning system of the above-mentioned type. 
     The invention also relates to a method for generating control data for a treatment device that creates at least one incision surface in the cornea using a laser apparatus. 
     Finally, the invention likewise relates to a method for eye surgery, whereby at least one incision surface is created by means of a treatment device in the cornea using a laser apparatus. 
     The state of the art comprises a wide variety of treatment methods with the objective of performing refractive correction of the human eye. The objective of the operation methods is to systematically reshape the cornea in order to influence the light refraction in the eye. Various operation methods are used for this purpose. The most widespread nowadays is the so-called Laser-Assisted In Situ Keratomileusis, also abbreviated LASIK. In this procedure, first of all, a flap is cut from the surface of the cornea on one side and folded back. This flap can be cut by means of a mechanical microkeratome or else by means of a so-called laser keratome of the type sold, for example, by Intralase Corp. of Irvine, Calif., United States. Once the flap has been cut and folded back, the LASIK surgery provides for the use of an excimer laser that ablates the cornea tissue underneath the flap that has been exposed in this manner. After the volume located underneath the surface of the cornea has been vaporized in this manner, the cornea flap is folded back into its original position. 
     The use of a laser keratome to expose the flap is advantageous in comparison to employing a mechanical blade since the geometrical precision is improved and the frequency of clinically relevant complications is diminished. In particular, the flap can be created with a much more constant thickness by using laser radiation. Moreover, the edge of the incision is precisely shaped, reducing the risk of healing problems due to this boundary surface that is left over after the operation. However, a drawback of this method is that two different treatment devices have to be used, namely, the laser keratome that exposes the flap and the laser that vaporizes the cornea tissue. 
     These drawbacks are overcome with a method that was recently implemented by Carl Zeiss Meditec AG and that is abbreviated as FLEx. This method for lenticule extraction employs a short-pulse laser, preferably a femtosecond laser, to create an incision geometry in the cornea, separating a cornea volume (so-called lenticule) in the cornea. This volume is then removed manually by the surgeon after the flap covering the lenticule has been folded back. The advantage of this method is, for one thing, that the quality of the incision is further improved by using a femtosecond laser. Secondly, only a single treatment device is needed; the excimer laser is no longer used. 
     A refinement of the FLEx method is referred to in the literature as the SMILE (Small Incision Lenticule Extraction) method in which no flap is created but rather only a small opening incision that serves to access the lenticule located beneath the so-called cap. The separated lenticule is removed through this small opening incision, as a result of which the biomechanical integrity of the anterior cornea is less affected than in the LASIK, FLEx or PRK (photorefractive keratectomy) methods. Moreover, in this manner, fewer superficial nerve fibers in the cornea are cut and this has been proven to be advantageous when it comes to the restoration of the original sensitivity of the surface of the cornea. As a result, the symptom of dry eyes that often has to be treated after a LASIK procedure is often less severe and less protracted. Other complications after LASIK, which usually have to do with the flap (e.g. folds, epithelial ingrowth in the flap bed) occur less often in procedures without a flap. 
     When incision surfaces are made in the cornea by means of laser radiation, the optical radiation effect is normally utilized in that a photodisruption is created by means of individual optical pulses whose duration can be between about 100 fs and 100 ns. It is also a known procedure to apply individual pulses whose energy lies below a threshold value for a photodisruption into the tissue or material with such an overlap that this also achieves a material or tissue separation. This concept for creating an incision in the cornea tissue allows a wide variety of incisions. 
     With the SMILE method known so far, the opening incision is made in such a way that its diameter corresponds to the diameter of the cap incision. 
     For clinical reasons, it can be advantageous for the diameter of the cap incision to be selected much larger than that of the lenticule incision. In this case, it is more difficult to access the lenticule. One possibility to make a subsequent correction that might become necessary is to retrace the opening incision very precisely again and to expand it to form a conventional flap incision. Subsequently, the flap is folded back and a conventional treatment is performed with an excimer laser. If the opening incision is not retraced again, tissue residues (loose cornea constituents) could occur, which impair the vision. 
     SUMMARY 
     In an embodiment, the present invention provides a planning system for generating control data for a treatment device for eye surgery that creates at least two incision surfaces in the cornea using a laser apparatus. The planning system includes a computation device configured to specify the cornea incision surfaces based on data of a refractive correction. The cornea incision surfaces include an access incision and a cap incision, with the access incision having a smaller diameter than the cap incision. The computation device being configured to generate a control data record for the cornea incision surfaces for purposes of controlling the laser apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  shows a schematic representation of a treatment device with a planning system for a treatment to carry out a refractive correction by means of eye surgery, 
         FIG. 2  shows a schematic representation of the effect of the laser radiation that is used in the treatment device of  FIG. 1 , 
         FIG. 3  shows another schematic representation of the treatment device shown in  FIG. 1  for the application of the laser radiation, 
         FIG. 4  shows a schematic sectional view through the cornea in order to illustrate the removal of the cornea volume in conjunction with the refractive correction by means of eye surgery, 
         FIG. 5  shows a schematic representation of the structure of the treatment device shown in  FIG. 1 , with special reference to the planning system that is present there, 
         FIGS. 6  A and B show a schematic view of a SMILE lenticule geometry according to the state of the art, 
         FIGS. 7  A and B show a schematic representation of a SMILE incision geometry according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the present invention is to provide a planning system for generating control data, a treatment device for refraction-correcting eye surgery as well as a method for generating control data for such a treatment device, which ensures an optimal positioning of the incision to access the lenticule. 
     This is achieved according to embodiments of the invention with a planning system of the above-mentioned type, which has computation means for specifying a cornea incision surface, whereby the computation means specifies the access incision in such a way that it has a smaller diameter than the cap incision. 
     In another embodiment, the invention provides a treatment device having a laser apparatus that cuts at least one incision surface in the cornea using laser radiation on the basis of control data, and having a planning system of the above-mentioned type for generating the control data, whereby the planning system specifies the access incision in such a way that it has a smaller diameter than the cap incision. 
     Finally, another embodiment of the invention provides a method for generating control data according to the above-mentioned type, comprising the following steps: generating a control data record for the cornea incision surface for purposes of controlling the laser apparatus, whereby the planning system specifies the access incision in such a way that it has a smaller diameter than the cap incision. 
     In an embodiment, the invention provides a method comprising the following steps: generating a control data record for the cornea incision surface, transmitting the control data to the treatment device, and creating the incision surfaces by controlling the laser apparatus on the basis of the control data record, whereby, when the control data record is generated, the incision surface is specified in such a way that it has a smaller diameter than the cap incision. 
     The cap incision, i.e. the incision that runs largely parallel to the surface of the cornea, is selected to be larger than the diameter of the lenticule. Moreover, according to the invention, an opening incision or access incision is created whose position is between the edge of the cap incision and the edge of the lenticule incision. This access incision can preferably be shaped like a circular segment or a strip. 
     Hence, if needed at a later point in time, a flap can be created by making another opening incision on the periphery of the cap incision, without having to take the first opening incision into account. 
     It goes without saying that the features that were mentioned above and that will still be explained below can be used not only in the combinations given but also in other combinations or on their own, without departing from the scope of the present invention. 
     A treatment device for eye surgery is shown in  FIG. 1  and designated by the general reference numeral  1 . The treatment device  1  is configured to create laser incisions in the eye  2  of a patient  3 . For this purpose, the treatment device  1  has a laser apparatus  4  that emits a laser beam  6  from a laser source  5  and that focuses this laser beam  6  as a focused beam  7  into the eye  2  or the cornea. Preferably, the laser beam  6  is a pulsed laser with a wavelength between 300 nanometers and 10 micrometers. Moreover, the pulse length of the laser beam  6  is in the range between 1 femtosecond and 100 nanoseconds, whereby pulse repetition rates of 50 kHz to 5000 kHz and pulse energies between 0.01 microjoule and 0.01 millijoule are possible. The treatment device  1  thus makes an incision surface in the cornea of the eye  2  by deflecting the pulsed laser radiation. For this reason, a scanner  8  as well as a radiation intensity modulator  9  are also provided in the laser apparatus  4  or in its laser source  5 . 
     The patient  3  lies on a table  10  that can be adjusted in three spatial directions in order to suitably orient the eye  2  with respect to the incident laser beam  6 . In a preferred set-up, the table  10  can be adjusted by a motor. 
     The regulation can especially be carried out by a control unit  11  that fundamentally controls the operation of the treatment device  1  and, for this purpose, is in communication with the treatment device via suitable data connections, for example, connection lines  12 . Of course, this communication can also be achieved by other modalities, for example, via optical conductors or wirelessly. The control unit  11  performs the appropriate settings, the time control of the treatment device  1 , especially of the laser apparatus  4 , and thus effectuates corresponding functions of the treatment device  1 . 
     The treatment device  1  also has a fixation device  15  that fixes the position of the cornea of the eye  2  relative to the laser apparatus  4 . This fixation device  15  can comprise a known contact glass  45  against which the cornea of the eye is secured by means of negative pressure and that gives the cornea the desired geometric shape. Such contact glasses are known to the person skilled in the art, for example, from German patent application DE 10 2005 040338 A1. The disclosed content of this publication is encompassed in its entirety here, insofar as the description comprises a model of the possible contact glass  45  for the treatment device  1 . 
     The treatment device  1  also has a camera (not shown here) that can take a picture of the cornea  17  through the contact glass  45 . In this context, the illumination for the camera can be in the visible as well as in the infrared light spectrum. 
     The control unit  11  of the treatment device  1  also has a planning system  16  that will be explained in greater detail below. 
       FIG. 2  schematically shows the mode of operation of the incident laser beam  6 . The laser beam  6  is focused and, as the focused laser beam  7 , it strikes the cornea  17  of the eye  2 . A schematically drawn lens  18  is provided for purposes of focusing. In the cornea  17 , this lens brings about a focus in which the laser radiation energy density is so high that, in combination with the pulse length of the pulsed laser radiation  6 , a non-linear effect occurs in the cornea  17 . For example, each pulse of the pulsed laser radiation  6  in the focus  19  can generate a photodisruption in the cornea  17  which, in turn, initiates a plasma bubble only schematically shown in  FIG. 2 . When the plasma bubble is formed, the tissue layer separation comprises a larger region than the focus  19 , even though the conditions for generating the photodisruption are only achieved in the focus  19 . In order for a photodisruption to be generated by each laser pulse, the energy density, i.e. the fluence of the laser radiation, has to be above a certain, pulse-length-dependent threshold value. The person skilled in the art is familiar with this situation, for example, from DE 69500997 T2, a translation from a European patent. As an alternative, a tissue separating effect can also be attained by pulsed laser radiation in that several laser radiation pulses are emitted in a given range, whereby the focal spots overlap. Then several laser radiation pulses work together to achieve a tissue-separating effect. The type of tissue separation that the treatment device  1  uses, however, is not relevant for the description below; all that is relevant is that an incision is made in the cornea  17  of the eye  2 . 
     In order to perform refractive correction by means of eye surgery, the laser radiation  6  removes a cornea volume from a region inside the cornea  17  in that tissue layers that isolate the cornea volume are separated there and then permit the cornea volume to be removed. In order to isolate the cornea volume that is to be removed, for instance, when applying pulsed laser radiation, the position of the focus  17  of the focused laser radiation  7  in the cornea  17  is adjusted. This is shown schematically in  FIG. 3 . The refractive properties of the cornea  17  are systematically changed by the removal of the volume so as to attain the envisaged refractive correction. The volume is thus usually lenticular and is referred to as a lenticule. 
       FIG. 3  shows the elements of the treatment device  1  only to the extent that they are needed for purposes of elucidating the creation of the incision surface. The laser beam  6 , as already mentioned, is bundled in a focus  19  in the cornea  17 , and the position of the focus  19  in the cornea is adjusted to that, in order to make the incision surface, focusing energy from laser radiation pulses is applied to the tissue of the cornea  17  in various places. The laser radiation  6  is preferably provided in the form of pulsed radiation by the laser source  5 . The scanner  8  is structured in two parts in the set-up shown in  FIG. 3  and it consists of an xy-scanner  8   a  that, in one variant, is implemented by two essentially orthogonally deflecting galvanometer mirrors. The scanner  8   a  two-dimensionally deflects the laser beam  6  stemming from the laser source  5 , so that a deflected laser beam  20  is present downstream from the scanner  9 . The scanner  8   a  thus brings about an adjustment of the position of the focus  19  essentially perpendicular to the main direction of incidence of the laser beam  6  in the cornea  17 . In order to adjust the depth position, the scanner  8  has, aside from the xy-scanner  8   a , also a z-scanner  8   b  that is configured, for example, as an adjustable telescope is changed. The z-scanner  8   b  ensures that the z-position of the focus  19  is changed, i.e. its position on the optical axis of incidence. The z-scanner  8   b  can be installed upstream or downstream from the xy-scanner  8   a.    
     The association of the individual coordinates with the spatial directions is not essential for the operating principle of the treatment device  1  nor, by the same token, is the fact that the scanner  8   a  deflects around axes that are at a right angle to each other. Rather, any scanner can be used that is capable of adjusting the focus  19  in a plane that does not encompass the axis of incidence of the optical radiation. Moreover, any desired non-Cartesian coordinate system can be employed for purposes of deflecting or regulating the position of the focus  19 . Examples of this are spherical coordinates or cylindrical coordinates. The position of the focus  19  is controlled by means of the scanners  8   a ,  8   b  under actuation by the control unit  11  that establishes the appropriate settings of the laser source  5 , of the modulator  9  (not shown in  FIG. 3 ), and of the scanner  8 . The control unit  11  ensures proper operation of the laser source  5  as well as the three-dimensionally focus adjustment described here by way of example, so that ultimately, an incision surface is created that isolates a specific cornea volume that is to be removed for purposes of refractive correction. 
     The control unit  11  functions in accordance with control data that is prescribed as target points for the focus adjustment, for example, in the case of the laser apparatus  4  described here merely by way of an example. As a rule, the control data is compiled in a control data record. This results in geometric specifications as a pattern for the incision surface that is to be created, for example, the coordinates of the target points. In this embodiment, the control data record then also contains concrete place values for the focus adjustment mechanism, e.g. for the scanner  8 . 
     The creation of the incision surface by means of the treatment device  1  is shown in  FIG. 4  by way of an example. A cornea volume  21  in the cornea  17  is isolated by adjusting the focus  19  in which the focused beam  7  is bundled. For this purpose, incision surfaces are created that are configured here by way of an example as an anterior flap, or anterior cap, incision surface  22  and as a posterior lenticule incision surface  23 . These terms are to be understood merely by way of examples and serve to establish the link to the conventional Lasik or Flex method for which the treatment device  1 , as already explained, is likewise configured. Here, the only essential aspect is that the incision surfaces  22  and  23  as well as the encircling edge incision  25  that brings the incision surfaces  22  and  23  together at their edges have to be capable of isolating the cornea volume  21 . Moreover, through an opening incision  24 , a cornea flap that delimits the cornea volume  21  on the anterior side can be folded back so that the cornea volume  21  can be removed. 
     As an alternative and in a way that is essential for the present invention, it is possible to employ the SMILE method, whereby the cornea volume  21  is removed through a small opening incision as is described in German patent application DE 10 2007 019813 A1. The disclosed content of this publication is incorporated in its entirety here. 
       FIG. 5  schematically shows the treatment device  1  and it is on this basis that the significance of the planning system  16  will be described in greater detail. In this variant, the treatment device  1  has at least two units or modules. The already described laser apparatus  4  emits the laser beam  6  onto the eye  2 . The operation of the laser apparatus  4 , as already described, takes place fully automatically by means of the control unit  11 , that is to say, in response to an appropriate starting signal, the laser apparatus  4  starts to generate and deflect the laser beam  6 , creating incision surfaces in this process that are structured in the manner already described. The laser apparatus  5  receives the control signals needed for the operation from the control unit  11 , which has previously been provided with the applicable control data. This is done by means of the planning system  16 , which is shown in  FIG. 5  merely by way of example as a component of the control unit  11 . Of course, the planning system  16  can also be configured on its own and can communicate with the control unit  11  via a hard-wired or wireless connection. The only essential aspect is that an appropriate data transmission channel has to be provided between the planning system  16  and the control unit  11 . 
     The planning system  16  generates a control data record that is made available to the control unit  11  in order to perform the refractive correction by means of eye surgery. Here, the planning system uses measured data about the cornea of the eye. In the embodiment described here, this data comes from a measuring device  28  that has previously measured the eye  2  of the patient. Of course, the measuring device  28  can be configured and can transmit the applicable data to the interface  29  of the planning system  16  in any desired manner. 
     The planning system now assists the operator of the treatment device  1  in defining the incision surface for isolating the cornea volume  21 . This can go as far as being a fully automatic definition of the incision surfaces, which can be carried out, for example, in that, on the basis of the measured data, the planning system  16  specifies the cornea volume  21  that is to be removed, then defines its boundary surfaces as incision surfaces, and generates appropriate control data for the control unit  11 . At the other end of the degree of automation, the planning system  16  can have input means where a user enters the incision surfaces in the form of geometric parameters, and the like. Intermediate stages involve proposals for the incision surfaces that the planning system  16  generates automatically and that can be modified by an operator. Fundamentally, all of the concepts that were already explained above in the more general description part can be used in the planning system  16 . 
     In order to carry out a treatment, the planning system  16  generates control data for creating the incision surface, and this data is then used in the treatment device  1 . 
       FIG. 6 a    shows a schematic representation of a cornea cross section according to the state of the art using a SMILE method for illustrating the geometric situation. The cornea  17  has an anterior cap incision  22  with an opening incision  26 . The posterior lenticule incision  23  isolates the lenticule volume  21 , which can be removed through the opening incision  26 . If the need arises to perform a second refractive treatment, it is not possible to once again remove a lenticule. Rather, in such a case, the opening incision  26  is expanded along the periphery of the cap incision  22  to form a flap by means of which the conventional Lasik method can then be carried out with an excimer laser. However, for this purpose, the opening incision  26  has to be retraced very precisely, since otherwise, an unwanted isolation of cornea tissues between the original opening incision and the flap incision can occur, as a result of which the vision is severely impaired. 
       FIG. 7 a    shows a schematic representation according to the invention. The cap incision  22  and the lenticule incision  23  correspond to the situation already shown in  FIG. 6 a   . The opening incision  26  is now positioned between the periphery of the cap incision  22  and the lenticule edge incision  25 . In this manner, the lenticule  21  can still be removed through the opening incision  26 , but when a flap is cut along the periphery of the cap incision  22 , a sufficient distance from the opening incision  26  is maintained so that no cornea tissue is inadvertently isolated. 
       FIG. 7 b    shows a top view of the cornea depicted in  FIG. 7 a   . The distance between the cap incision  22 , or the lenticule edge incision  25 , and the opening incision is approximately 1 mm to 2 mm in order to ensure adequate stability of the flap. 
     It should be additionally pointed out that, of course, the treatment device  1  or the planning system  16  are also capable of concretely implementing the method described in general terms above. 
     Another embodiment of the planning system is in the form of a computer program or of an appropriate data medium with a computer program that implements the planning system on an appropriate computer, so that the measured data is input via suitable data transmission means to the computer and the control data is transmitted from this computer to the control unit  11 , for which purpose, once again, data transmission means known to the person skilled in the art are employed here. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B.” Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise.