PLANNING METHODS AND DEVICES FOR PRECISELY CHANGING A REFRACTIVE INDEX

Abstract

Planning methods and a planning device for generating control data for a control unit of a laser treatment device for changing a refractive index in the treatment zone of a transparent organic material, a laser treatment device, and a computer program product. The invention facilitates precise correction of the refractive index and thus adjusts the previously planned profile of the refractive index in the transparent organic material region to be treated during the treatment. Even highly locally limited refractive index variations are correctable. Data describing the actual behavior of the indicator structure in the examination zone are considered, and control data is output to the control unit at specified intervals during the treatment of the material in the treatment zone, wherein the last described behavior of the indicator structure in the examination zone is constantly used as new actual behavior of the indicator structure to ascertain the control data.

Claims

1.-22. (canceled)

23. A planning method to generate control data for a control unit of a laser processing apparatus utilized in a surgical procedure to change a refractive index in a processing zone of a transparent organic or inorganic material, the method comprising: characterizing an actual behavior of an indicator structure in an examination zone arranged in an optical path downstream of a processing zone of the transparent organic or inorganic material transilluminated by examination radiation; defining a target behavior of the indicator structure in the examination zone; determining a change profile of the refractive index in the processing zone from the difference between actual behavior of the indicator structure in the examination zone and the target behavior of the indicator structure in the examination zone; determining a scanning pattern of focal spots of pulsed processing laser radiation of the laser processing apparatus for processing the transparent organic or inorganic material in the processing zone to implement the change profile of the refractive index in the processing zone; determining control data for the control unit of the laser processing apparatus for implementing the scanning pattern; and repeating aforementioned steps iteratively at predetermined intervals, wherein the characterization of the actual behavior of the indicator structure in the examination zone implemented most recently is always adopted as a new actual behavior.

24. The planning method as claimed in claim 23, further comprising determining a target distribution of the refractive index in a processing zone from the target behavior of the indicator structure in the examination zone and determining an actual distribution of the refractive index in the processing zone from the actual behavior of the indicator structure in the examination zone.

25. The planning method as claimed in claim 23, further comprising using indicator structures in a plurality of examination zones for characterizing the actual behavior and for defining the target behavior, wherein: the examination zones are arranged in the optical path upstream and downstream of the processing zone, and further comprising comparing a behavior of an upstream indicator structure in an examination zone upstream of the processing zone to behavior of a downstream indicator structure in an examination zone downstream of the processing zone, and/or comparing a behavior of an indicator structure in an examination zone arranged in the optical path downstream of the processing zone but not downstream of a region of the processing zone processed by application of the scanning pattern of focal spots to the behavior of an indicator structure downstream of the region of the processing zone processed by use of the scanning pattern.

26. The planning method as claimed in claim 23, further comprising taking into account the influence of at least one zone which represents a distorting transmitting medium in the optical path of the examination radiation.

27. The planning method as claimed in claim 23, further comprising making use of the pulsed processing laser radiation of the laser processing apparatus, at least one examination radiation from the range between x-ray radiation via the range of visible light and microwave radiation up to ultrasound for characterizing the actual behavior or both, and choosing at least one of the following processes for detection purposes: interferometric detection including optical coherence tomography (OCT) and a phase-sensitive OCT, confocal detection; fundus camera recordings, refractometric measurement, wavefront measurement and ultrasound imaging.

28. (canceled)

29. The planning method as claimed in claim 23, further comprising determining the scanning pattern of focal spots for implementing the change profile of the refractive index such that at least some of the processing zone is swept-over multiple times by the pulsed processing laser radiation.

30. The planning method as claimed in claim 23, wherein the control data comprise at least one of target coordinates of the focal spots, a pulse energy of the pulsed processing laser radiation and a processing time.

31. The planning method as claimed in claim 30, further comprising determining only a subset of the target coordinates of the focal spots in the processing zone and interpolating further target coordinates between two target coordinates of this subset.

32. The planning method as claimed in claim 23, further comprising using a closed loop for tracking a change in the refractive index in the processing zone and completing the closed loop when the target behavior of the indicator structure and hence the desired change profile of the refractive index is implemented.

33. The planning method as claimed in claim 23, wherein the transparent organic or inorganic material to be processed comprises a tissue of a patient's eye; and wherein the processing zone is arranged in at least one of the following regions of the patient's eye: a cornea, a natural lens or an intraocular lens, and/or wherein the examination zone is arranged in the retina of the patient's eye.

34. The planning method as claimed in claim 23, wherein the processing zone is arranged in at least one of the following regions of the patient's eye: a cornea, a natural lens or an intraocular lens, and/or wherein the examination zone is arranged in the retina of the patient's eye.

35. A planning device to generate control data for a control unit of a laser processing apparatus to change a refractive index in a processing zone of a transparent organic or inorganic material, the laser processing apparatus comprising: a laser device with a laser source that generates pulsed processing laser radiation; a focusing apparatus that focuses the pulsed processing laser radiation at a focus in the processing zone; a scanning apparatus that scans the focus of the pulsed processing laser radiation in the processing zone of the transparent organic or inorganic material; and an examination apparatus that detects examination radiation to characterize an actual behavior of an indicator structure in an examination zone using a detection apparatus, wherein the planning device comprises an interface that supplies data from the examination apparatus and an interface that transmits control data to the control unit of the laser processing apparatus, and wherein the planning device is configured: to record the actual behavior of the indicator structure in the examination zone arranged in an optical path downstream of the processing zone of the transparent organic or inorganic material transilluminated by the examination radiation, to define a target behavior of the indicator structure in the examination zone, to determine a change profile of the refractive index in the processing zone from the difference between the actual behavior and the target behavior of the indicator structure in the examination zone, to determine a scanning pattern of focal spots of the pulsed processing laser radiation for processing the transparent organic or inorganic material in the processing zone for implementing the change profile of the refractive index in the processing zone, and to establish the control data for the control unit of the laser processing apparatus therefrom, wherein the planning device is furthermore configured to, at predetermined intervals during the processing of the transparent organic or inorganic material in the processing zone, supply data from the examination apparatus, the data describing the actual behavior of the indicator structure, and configured to transmit control data to the control unit of the laser processing apparatus, wherein most recently described behavior of the indicator structure in the examination zone is always adopted as new actual behavior of the indicator structure for the purposes of ascertaining the control data.

36. The planning device as claimed in claim 35, furthermore configured to determine a target distribution of the refractive index in a processing zone from the target behavior of the indicator structure in the examination zone and an actual distribution of the refractive index in the processing zone from the actual behavior of the indicator structure in the examination zone.

37. The planning device as claimed in claim 35, furthermore configured to record the actual behavior of indicator structures in a plurality of examination zones and use these to define the target behavior, wherein at least one of the plurality of examination zones is arranged in the optical path upstream and downstream of the processing zone, and a behavior of an indicator structure in an examination zone upstream of the processing zone is compared to the behavior of the indicator structure in an examination zone downstream of the processing zone, and a behavior of an indicator structure in an examination zone arranged in the optical path downstream of the processing zone but not downstream of a region of the processing zone processed by use of the scanning pattern of focal spots is compared to the behavior of an indicator structure downstream of the region of the processing zone processed by the use of the scanning pattern.

38. The planning device as claimed in claim 35, furthermore configured to take account of influence of at least one zone which represents a distorting transmitting medium in the optical path of the examination radiation.

39. The planning device as claimed in claim 35, wherein, for characterizing the actual behavior of the indicator structure, use is made of at least one of the pulsed processing laser radiation of the laser processing apparatus and at least one examination radiation from the range between x-ray radiation via the range of visible light and microwave radiation up to ultrasound, and wherein one of the following apparatuses is chosen for detection purposes: an interferometer including optical coherence tomography (OCT) and a phase-sensitive OCT; a confocal detector, a fundus camera, a refractometer, a wavefront measuring device and an ultrasound imaging system.

40. (canceled)

41. The planning device as claimed in claim 35, furthermore configured to determine the scanning pattern of focal spots to implement the change profile of the refractive index such that at least some of the processing zone is swept-over multiple times by the pulsed processing laser radiation.

42. The planning device as claimed in claim 35, wherein the control data comprise at least one of target coordinates of the focal spots, a pulse energy of the pulsed processing laser radiation and a processing time.

43. (canceled)

44. The planning device as claimed in claim 35, wherein the transparent organic or inorganic material to be processed comprises a tissue of a patient's eye; and wherein the processing zone is arranged in at least one of the following regions of the patient's eye: a cornea, a natural lens or an intraocular lens, and/or wherein the examination zone is arranged in the retina of the patient's eye.

45. (canceled)

46. A laser processing apparatus for processing a transparent organic or inorganic material, comprising a laser device with a laser source for generating pulsed processing laser radiation; a focusing apparatus for focusing the pulsed processing laser radiation on a focus in the processing zone; a scanning apparatus for scanning the focus of the pulsed processing laser radiation in the processing zone of the transparent organic or inorganic material; an examination apparatus which detects examination radiation for characterizing an actual behavior of an indicator structure in an examination zone using a detection apparatus, a control unit for controlling the laser processing apparatus by means of control data, and a planning device for generating control data for the control unit, as claimed in claim 35.

47. A computer program product with program code which, when executed on a computer, carries out the planning method for generating control data for a control unit of a laser processing apparatus for changing a refractive index in a processing zone of a transparent organic or inorganic material as claimed in claim 23.

48. A computer program product with program code which is readable on a planning device for generating control data for a control unit of a laser processing apparatus for changing a refractive index in a processing zone of the transparent organic or inorganic material as claimed in claim 35, including by a processor of such a planning device, and which, when executed by the planning device, generates control data in order to operate the laser processing apparatus.

49.-50. (canceled)

51. A method for changing a refractive index in a transparent organic or inorganic material, comprising: generating control data for a laser processing apparatus for changing the refractive index using a planning method as claimed in claim 23, and processing the transparent organic or inorganic material, including a tissue of a patient's eye, by the laser processing apparatus with the aid of the control data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The present invention shall now be explained in more detail on the basis of example embodiments. In the figures:

[0084] FIGS. 1a and 1b depict the principle of a laser-induced change in the refractive index (LIRIC) in a patient's eye according to the prior art, in a region of the cornea 4 or in an intraocular lens 5, as described above;

[0085] FIG. 2 depicts the diagram of a laser processing apparatus having a first planning device according to the invention;

[0086] FIG. 3 depicts the diagram of a further laser processing apparatus according to the invention having a second planning device according to the invention, in which in particular the laser device is explained in more detail and the examination apparatus is also physically integrated;

[0087] FIG. 4 depicts a schematic planning set up according to the invention for LIRIC processing of a region of the cornea for the purposes of obtaining a desired change in the optical path of a patient's eye, and FIG. 4a in turn shows an excerpt of FIG. 4 in the form of a real image representation of a very specific measurement set up; and

[0088] FIG. 5 depicts a schematic planning set up according to the invention for an LIRIC treatment of a transparent floater in the vitreous humor.

DETAILED DESCRIPTION

[0089] FIG. 2 schematically depicts a laser processing apparatus 1 having a first planning device P according to the invention. In this variant, it has at least two devices or modules. A laser device L emits pulsed and focused processing laser radiation 2 toward the patient's eye 3. Here, the operation of the laser device L is implemented in fully automated fashion, that is to say the laser device L starts the deflection of the processing laser radiation 2 following an appropriate start signal and in the process generates modified regions in a processing zone 17 of a transparent organic or inorganic material. In its use as an ophthalmological laser processing apparatus 1, it generates modified regions in a processing zone 17 of a patient's eye, for example in the cornea 16, the natural lens or in the vitreous humor 6 of the patient's eye 3, but also in an artificial intraocular lens 5 in the patient's eye 3. The refractive index of the transparent organic or inorganic material is altered in these modified regions of the processing zone 17 as a result of the action of the processing laser radiation 2. The control data required for the operation are received by the laser device L in advance as a control data record from a planning device P via communication paths not denoted in any more detail, such as control lines, for example. Naturally, the communication can also be implemented in wireless fashion. As an alternative to direct communication, it is also possible to arrange the planning device P in spatially separated fashion from the laser unit L and to provide a corresponding data transmission channel. The transmission is for example implemented prior to the operation of the laser device L.

[0090] For example, the control data record is transmitted to the laser device L of the laser processing apparatus 1 via an interface S2 of the planning device P and, according to another example, an operation of the laser device L is blocked until a valid control data record is present at the laser device L. A valid control data record can be a control data record that, in principle, is suitable for use with the laser device L of the laser processing apparatus 1. However, additionally, the validity can also be linked to further tests being passed, for example whether specifications about the laser processing apparatus 1, e.g., an appliance serial number, or about the patient, e.g., a patient identification number, which are additionally stored in the control data record, correspond to other specifications that, for example, were read at the laser processing apparatus 1 or entered separately, as soon as the patient is in the correct position for the operation of the laser device L.

[0091] The planning device P produces the control data or the control data record, which is made available to the laser device L for implementing the operation, from the supplied data. Firstly, these are characterization data, which were ascertained by use of an examination apparatus Musing examination radiation 27for the patient's eye 3 to be treated and which are supplied via an interface S1 for supplying characterization data from the planning device P. In particular, these are data from the characterization of an actual behavior of an indicator structure 18 in an examination zone 16 of the patient's eye 3, said data providing information about a processing zone 17 transilluminated in the process by the examination radiation 27, the pulsed and focused processing laser radiation 2 being intended to act, acting or having acted in said zone.

[0092] Further, target data are supplied via a further interface S1 and these contain a target behavior of the indicator structure 18 in the examination zone 17, with a (two- or three-dimensional) change profile of the refractive index in the processing zone 17 then being determined from the difference of the actual behavior and the target behavior of the indicator structure 18 in the examination zone 16. In this example embodiment, they are transmitted in automatic or manual fashion via an input device E to the planning device P by way of the interface S1.

[0093] In the present example embodiment, the characterization data originate from a separate examination apparatus M, which communicates with the planning device P of the laser processing apparatus 1. A direct radio or wired link of the examination apparatus M to the laser processing apparatus 1 in respect of the data transmission, which can be used in one variant for example, is advantageous in that the use of incorrect characterization data is excluded with the greatest possible reliability.

[0094] The control data generated by the planning device P determine the scanning pattern 15 of the focus 14 of the laser device L in a tissue or in a structure of the patient's eye 3, the control data rendering the laser processing apparatus 1 controllable in such a way that the change profile of the refractive index in the processing zone 17 is implementable as a result of processing the transparent organic or inorganic material, that is to say by processing the tissue or the structure, andif the control data are used in the laser processing apparatus 1is also implemented by an appropriate modification of the affected region in the processing zone 17 in accordance with the control data generated using the change profile of the refractive index.

[0095] FIG. 3 shows a second laser processing apparatus 1 according to the invention with a second planning device P according to the invention, again schematically, in which a laser device L and an examination apparatus M are fully integrated. This facilitates repeated, and in this case precisely repeatable, access to characterization data of the patient's eye 3. The planning device P, which satisfies the functions already described above, is integrated, at least temporarily, into the laser processing apparatus 1 and is in direct communication with the examination apparatus M and the control unit 12 of the laser device L.

[0096] In this example, the elements of the laser processing apparatus 1 and, in particular, of the laser device L comprised thereby are specified, but, in this case, too, only plotted to the extent that they are required for understanding the focal adjustment. The pulsed processing laser radiation 2, a femtosecond laser beam in this specific example, is focused on a focus 14 in a processing zone 17 of the patient's eye 3, for example in the cornea 4 thereof or in the vitreous humor 6 thereof, and the relative position of the focus 14 in the patient's eye 3 is adjusted along a scanning pattern 15 such that a modification of the affected region in the processing zone 17 is facilitated according to the control data in the control unit 12 (coordinates, pulse energies, processing time/number of scans in a region, etc., . . . ) which were generated using the change profile of the refractive index.

[0097] In this case, the patient's eye 3 is for example fixated by application of a patient interface 13 to the laser processing apparatus 1.

[0098] An xy-scanner 9, which is realized by two substantially orthogonally deflecting galvanometer mirrors in one variant, in this case deflects the pulsed processing laser radiation 2 emanating from the laser source 8 in two dimensions. Consequently, the xy-scanner 9 brings about an adjustment of the relative position of the focus 14 substantially perpendicular to the chief direction of incidence of the pulsed processing laser radiation 2 in the processing zone 17, that is to say in the cornea 4 or the vitreous humor 6 (in this example). In addition to the xy-scanner 9, a z-scanner 11 is provided for adjusting the depth position, said z-scanner being embodied as an adjustable telescope, for example. The z-scanner 11 ensures that the z-position of the relative position of the focus 14, i.e., the position thereof along the optical axis of incidence, is modified. The z-scanner 11 can be disposed upstream or downstream of the xy-scanner 9. The coordinates denoted below by x, y, z therefore relate to the deflection of the relative position of the focus 14.

[0099] Naturally, a person skilled in the art knows that the relative position of the focus 14 in a processing zone 17 can also be described in three dimensions by other coordinate systems; in particular, this need not necessarily be a rectangular coordinate system. Thus, it is not mandatory for the xy-scanner 9 to deflect about axes that are perpendicular to one another; rather, it is possible to use any scanner that is able to adjust the focus 14 in a plane not containing the axis of incidence of the processing laser radiation 2. Consequently, it is also possible to use oblique-angled coordinate systems, or else non-Cartesian coordinate systems.

[0100] For the purposes of controlling the relative position of the focus 14, the xy-scanner 9 and the z-scanner 11, which together realize a specific example of a three-dimensional scanning device 9, 11, are driven by a controller 12 via lines not denoted in any more detail. The same applies to the laser source 8 and the focusing apparatus 10. The same controller 12 (or a partial unit of the controller 12) controls the examination apparatus M. Thus, there is access to the different devices of the laser processing apparatus. The planning device P, which corresponds closely to the controller and can also physically be a part of the controller 12 in one variant, can therefore receive from the examination apparatus M the characterization data relating to the actual behavior of an indicator structure 18 in an examination zone 16, can compare these to a likewise supplied or defined target behavior of the indicator structure 18 in the examination zone 16 and can create a change profile of the refractive index in a processing zone 17 therefrom, and can ultimately ascertain from said change profile a scanning pattern 15 of focal points (focal spots) of pulsed processing laser radiation 2 of the laser processing apparatus 1 for the purposes of processing the material or the tissue and hence for the purposes of implementing the change profile of the refractive index in the processing zone 17, and can determine therefrom the control data for the control unit 12 of the laser processing apparatus 1 to carry out the scanning pattern 15, in principle at any time, and transfer said control data to the control unit 12.

[0101] This renders it possible to determine a change profile of the refractive index in the processing zone 17, to implement the change profile determined thus and to check and refine the implementation by repeating the planning method during the implementation in order to facilitate a precise correction of the refractive index. In particular, such a laser processing apparatus can be operated with a closed-loop method CL.

[0102] In this case, the examination radiation 27 from the examination apparatus M is supplied to the xy-scanner 9, for example in combination with the laser radiation 2 (for example via a beam splitter, a dichroic beam splitter, by application of polarization splitting or superposed at an angle) and is for example deflected together with the laser radiation 2 and focused together therewith by way of the focusing apparatus 10, wherein focused examination radiation 27 is generated, which may be superposed on the focused processing laser radiation 2. However, in this case the focusing of the examination radiation 27 can slightly deviate from that of the laser radiation 2, for example in order to optimally measure indicator structures 18 in the examination zones 16-1 and 16-2 (see FIG. 4).

[0103] FIG. 4 shows a schematic planning set up for LIRIC processing of a region of the cornea for the purposes of obtaining a desired change in the optical path of a patient's eyefor the purposes of setting the relative path length 26 by way of a change in the refractive index in the relevant region of the processing zone 17 of the cornea 4. The change in the refractive index in the processing zone 17 is caused by pulsed processing laser radiation 2 from a laser device L. By way of example, this can be implemented by heat-induced thermomechanical changes, in particular in collagen at different structure levels in natural eye tissue, by thermal expansion, stress generation and material contraction in the case of plastics such as PMMA or very generally by way of material changes by the use of fs lasers below the optical breakdown threshold (and hence without photodisruption) or above the optical breakdown threshold (i.e., with photodisruption). Examination radiation 27 is transmitted from a light source of an examination apparatus M to indicator structures 18, 18-V in various regions of one or more examination zones 16-1, 16-2 for the purposes of characterizing the actual behavior, wherein these examination zones 16-1, 16-2 are arranged along the optical path upstream and downstream of the processing zone 17, and a behavior of an indicator structure 18-V in an examination zone 16-1 upstream of the processed region 17-B of the processing zone 17 is compared to the behavior of the indicator structure 18 in an examination zone 16-1 downstream of the processed region 17-B of the processing zone 17, and/or a behavior of an indicator structure 18 in an examination zone 16-2, which is arranged in the optical path downstream of the processing zone 17 but not downstream of a region 17-B of the processing zone 17 processed by use of the scanning pattern 15 of focal spots, is compared to the behavior of an indicator structure 18 downstream of the region 17-B of the processing zone 17 processed by use of the scanning pattern 15. This actual behavior or the change in the actual behavior in the examination zone 16-1 of the cornea 4-V and 4-R upstream and downstream of the processed region 17-B of a processing zone 17 vis--vis the actual behavior in the examination zone 16-2 next to the processed region 17-B of the processing zone 17 is then compared to a defined target behavior.

[0104] In this case, the influence of a distorting transmitting medium 19, such as a tear film 24 in this case, is also taken into account.

[0105] The characterization data regarding the actual behavior, ascertained by operation of the examination apparatus M, are then used in the manner described above in order to generate in a planning device P the control data for a scanning pattern 15 of focal spots for the laser device L, the control data intending to implement the change profile of the refractive index for the purposes of adjusting the actual behavior to the target behavior. This can be repeated at any time, and so work can be carried out here in a closed loop CL method.

[0106] By way of example, if the required change of refractive index in the cornea is 0.005, the optical path between two indicator structures 18 will change by more than 50 nm in the case of a treatment zone length of at least 10 m. Using an examination apparatus M which uses phase-sensitive optical coherence tomography (OCT), this effect is easily measurable in comparison with the known limits of phase-sensitive optical coherence tomography with phase sensitivities of down to less than 1 pm.

[0107] In this case, suitable indicator structures can be natural tissue structures or boundaries, but also artificially created structures.

[0108] A very specific example embodiment of this planning set up of LIRIC processing of the cornea would lie in the use of a pulsed femtosecond laser L with an 80 MHz oscillator at a central wavelength of approximately 1064 nm, a phase-sensitive OCT at approximately 1060 nm as a measurement system M, by use of which it is possible to use an OCT measurement range 4-V with for example 5 . . . 500 m scanning depth around the corneal front side and an OCT measurement range 4-R with for example likewise 5 . . . 500 m around the corneal back side. The corneal front side indicator structure 18-V is compared to the corneal back side indicator structure 18 in the examination zone 16-1 (upstream and downstream of the processed region, that is to say the refractive index-modified zone) and additionally compared to the corneal front side 4-V indicator structure 18-V and the corneal backside 4-R indicator structure 18 in the examination zone 16-2 (next to the processed region)using corneal pachymetry in the specific case. This is elucidated in FIG. 4a, which in turn shows an excerpt of FIG. 4 in the form of a real image representation with marking of corresponding structures in a very specific measurement set up, wherein the effect of the processing in the processed region 17-B on the relative position of the indicator structure 18 was represented here in exaggerated fashion for illustrative purposes: the OCT measurement regions extend over the respective corneal interfaces. However, the indicator structures 18, 18-V are the interfaces themselves, the signals of which are ascertained in the OCT measurement region.

[0109] FIG. 5 illustrates a schematic planning set up for an LIRIC treatment of a transparent floater 21 in the vitreous humor 6: once again, the change in the refractive index in the processing zone 4 is caused by pulsed processing laser radiation 2 from a laser device L. Examination radiation 27 is projected from an observation light source M-L through the floater 21 in the processing zone 17 into an examination zone 16 on the retina 22 (and forms a virtual indicator structure (18) there) and the returning examination radiation 27 is detected by the detector of the examination apparatus M-D. Optionally, it is also possible to use the image representation 23 of the floater 21 by the processing laser radiation 2 as a virtual indicator structure (18) on the retina. In this case, too, the influence of distorting transmitting media in the light path 25 in the patient's eye, including the lens and the vitreous humor 6 itself, is taken into account. An adaptive optical unit 20 can likewise be part of the optical path in this case and can be taken into account.

[0110] In this case, the transparent floater 21 is processed until its effect on the retina 22 as examination zone 16 is minimized. This also includes adjusting the refractive index around the floater 21.

[0111] The aforementioned features of the invention, which are explained in various example embodiments, can be used not only in the combinations specified in an exemplary manner but also in other combinations or on their own, without departing from the scope of the present invention.

[0112] A description of an apparatus relating to method features is analogously applicable to the corresponding method with respect to these features, while method features correspondingly represent functional features of the apparatus described.