JP5551771B2 - Ophthalmic laser surgery device - Google Patents

Description

  The present invention relates to an apparatus for ophthalmic laser surgery. In particular, the present invention relates to an apparatus for laser surgery that can rapidly move the focal point of the laser beam formed by the apparatus in the z-direction, and the expression “z-direction” is expressed by a conventional notation. Means the direction of the beam path (the propagation direction of the beam). Thus, any direction in the plane perpendicular to the z direction should be understood as the xy direction. Therefore, in order to scan the region of the eye to be treated by the laser beam, the conventional method deflects the laser beam by the scanner in this plane.

  Laser systems that emit short-pulse radiation in the femtosecond range are used for ophthalmic surgery, especially for incisions in the cornea and even the lens. The action utilized in this regard is optical transmission destruction, which results in so-called light cutting of the irradiated tissue. In order to generate such a light cut, a relatively strong focus of the laser beam is required, which is achieved by a relatively high aperture of the focusing optics used to perform the focus. Is done. In known ophthalmic fs laser systems, the focusing optics is usually constituted by a so-called fθ objective that guarantees planar field imaging and prevents harmful z-direction displacement of the beam focus during the scanning process with the laser beam. Is done.

  The fs laser system has a firm position in ophthalmology, for example LASIK applications, where LASIK stands for “laser in-situ keratomileesis” and reduces vision defects Means a corneal treatment technique for removal, in which a small covering disc (so-called flap) is first cut from the corneal surface, which remains partly connected to the corneal tissue, and then this flap is moved aside The stromal tissue that has been folded and subsequently exposed after the flap has been folded is removed by short wavelength laser light, eg, 193 nm excimer laser radiation, according to the ablation profile established for the individual patient. In this case, the fs laser system is used to make a flap incision.

  To perform a flap incision, it is well known to flatten the cornea of the eye to be treated by pressing the platen and guide the beam focus two-dimensionally in a plane in the cornea. Due to the planar field imaging achieved by the fθ objective, in this case there is no need to z-shift the beam focus. Only in the peripheral region of the flap, movement of the focal position in the z direction may be necessary if it is desired to guide the peripheral incision of the flap upwards out of the corneal stroma.

  Various solutions have been proposed in the state of the art due to the focal displacement in the z direction. International Publication No. 03/032803 A2 proposes to displace the focusing objective lens as a whole along the z-axis, that is, along the beam path. This modification is to configure the focusing objective as a zoom objective. However, both methods have the disadvantage that the mechanical displacement or zoom setting of the focusing objective lens has to be performed very precisely since it is converted into a 1: 1 position change of the focal position. For the desired displacement of the focal spot by several μm between successive pulses of the laser beam, a corresponding mechanical displacement of the same distance of the rapid focusing objective lens or objective zoom lens is correspondingly necessary. Become. Conventional mechanical drive mechanisms are not suitable for this.

  An alternative solution is shown in German Offenlegungsschrift 10 2005 013 949 A1. The laser system has a two-lens beam expander in the form of a telescope, a downstream scanner, and a focusing lens just downstream of the scanner. The incident lens configured as a converging lens of the magnifying device can be moved in the beam direction, that is, in the z direction by a linear drive mechanism. Such displacement of the incident lens changes the divergence of the laser beam emitted from the beam expander. If the position of the focusing lens is constant, the focal position changes in the z direction in this way. One advantage of this solution lies in the better reproducibility and higher accuracy of the displacement compared to z-displacement of the focusing optics, because the optical imaging system is a beam expander. This is because the displacement path of the incident lens is reduced and converted into a displacement path of the in-focus position that is smaller by a factor of 10, for example. However, the achievable speed of changing the position of the incident lens sets a limit on the displacement speed of the beam focus that is being converted to the focal plane. For a three-dimensional incision as required for corneal lenticule extraction, the focal position changing method according to German Patent Application Publication No. 10 2005 013 949 Al is the method shown in International Publication No. 03/032803 A2. Clearly faster, simply because the repositioning of the entrance lens of the beam expander is more than the refocusing of the entire focusing optic or even a single focusing lens alone. This is because the mass to be moved is extremely small. Current focusing optics can quickly weigh several kilograms, in which case it must be moved without vibration. On the other hand, the entrance lens of the beam expander may have a relatively small aperture and correspondingly be small and light. Nevertheless, if it is desired to perform an intracorneal lenticule incision or another three-dimensional incision in a reasonably short time with a sufficiently high repetition rate laser, conventional linear drive mechanisms do not meet the requirements. In the case of the conventional linear drive mechanism, the position change speed that can be guided with high reliability and no vibration of the incident lens of the beam expanding device is, for example, 1 mm / s to 3 mm / s. Up to 5 mm / s may be feasible with a reasonable effort to However, for lenticule incisions, when using a 2-digit to 3-digit kHz range, or even higher fs laser repetition rates, with the same principle of repositioning the z focus, at least 10 mm / s and it Increasing the repositioning speed of the incident lens is required, and that repositioning cannot be achieved with currently commercially available linear drive systems, at least systems that meet the requirements for adjustment accuracy.

  It is an object of the present invention to create a laser device that is better suited for 3D incision guidance in ophthalmic surgery. To achieve this object, according to the present invention, a telescope for expanding said laser beam, comprising a light source of a pulsed femtosecond laser beam and an incident lens in the form of a lens having a variable refractive power controllable. A scanner downstream of the telescope that deflects the laser beam in a plane perpendicular to the beam path (xy plane), and at least a unit downstream of the scanner that focuses the laser beam. In order to achieve a predetermined incision profile that requires displacement of the focal point (50) of the beam in the direction of the beam path (z direction) with a focusing objective lens of one lens, in particular an fθ objective lens. It is configured to bring about these displacements by simply controlling the lens with variable refractive power without changing the focusing setting of the focusing objective lens. And a program-controlled electronic control unit, ophthalmic laser surgical apparatus is provided.

  The variable power lens is preferably electrically adjustable, and may be, for example, a liquid lens that operates on the principle of electrowetting (sometimes referred to as electrocapillarity), or alternatively a liquid crystal lens. Liquid lenses are well known per se and are based on the Lippmann effect, in this regard, see, for example, W. Phonik 4/2005, pages 44-46. Moench, W.M. F. Krogmann, H.M. See the article by Zappe, “Variable Brennweight durches flussige Mikrolinen (variable focal length with liquid microlenses)”. As a result of applying a voltage to the electrode mechanism of the liquid lens, the surface tension changes, and as a result, the curvature of the liquid interface changes. Then, the change in curvature causes a change in the focal length of the liquid lens. In particular, the liquid lens enables a change in refractive power of 10 dpt or more within a few milliseconds by changing the applied voltage.

  Liquid crystal lenses are likewise well known per se and are based on the reorientation or / and displacement of liquid crystals and, for example, liquid crystals in liquid crystal layers formed from monomers, for example, in the presence of an electric field. The reorientation or deviation of the liquid crystal changes the refractive index of the liquid crystal layer, thereby changing the refractive power of the lens.

  The ability to electrically control a lens with variable refractive power makes it possible to reliably move the focal point in the z direction faster than repositioning the entire lens linearly, and achieve this without a mechanical repositioning device. To do. As a result, it is possible to change the position at high speed, in which no mechanical driving means and mechanical movement parts are present, so that no frictional force is generated (apart from internal friction of liquid or liquid crystal). This ensures high reliability, long durability life, and high robustness (no mechanical wear).

  The rapid focal displacement in the z direction made possible by the present invention is an ophthalmic application that performs surgery by highly repeating focused fs laser radiation, and an ophthalmology that pursues rapid 3D incision guidance for short treatment times. It is particularly attractive for use in applications. One possible application that can benefit from this rapid 3D incision guidance is corneal lenticule extraction, in which the nearly lenticular three-dimensional element is removed from the corneal stroma for corneal refractive index correction. Cut out. A precise and rapid three-dimensional placement of the fs laser pulse focus is important for this. In the xy direction, this is not a problem due to the corresponding rapid operation of the scanner. For example, a conventional mirror scanner operating on the galvanometer principle can easily ensure the necessary deflection even at pulse repetition frequencies in the MHz range. In the z-direction, the use of a telescopic variable power entrance lens allows easy movement of the beam focus in the high 2 digit to 3 digit range within a few milliseconds or at least a few tens of milliseconds. . For example, in corneal lenticulectomy, this allows the entire lenticule incision to be performed in a few minutes (eg, 2-4 minutes), and the discomfort experienced by the patient during that type of surgery, which is a preferred short length of time. Is suppressed. In addition, the present invention enables excimer lasers because the high accuracy and reproducibility of the z-positioning of the beam focus allows for incision guidance during the lenticule extraction process that is exactly matched to eliminate vision defects. Open the way to correcting the refractive index of the eye without using it as usual.

  European Patent Application No. 1 837 696 A1 discloses at least one focusing lens, at least two lenses in the telescope, and a focusing lens downstream of the telescope for beam deflection into the xy plane. And a scanning unit disposed in the beam path upstream of the optical system, and at least one of the telescope lenses is an electrically adjustable liquid lens, and the liquid lens corrects the field curvature of the focusing lens. An imaging system has already been described. On the other hand, in the case of the present invention, the variable power lens has the role of realizing a z displacement of the beam focus that is predetermined by a given incision profile to be made on the eye.

  The variable refractive power lens in the present invention may be a converging lens or a diverging lens.

  The variable power lens and the actuating means assigned to it (including the voltage driver) preferably direct the beam focus to the beam path by less than 30 ms, more preferably less than 24 ms, more preferably less than 18 ms by 100 μm. It is set to be displaced in the direction of.

  According to another aspect of the invention, it is necessary to provide a pulsed femtosecond laser beam directed to the patient's eye and to displace the focal point (50) of the beam in the direction of the beam path. According to the incision profile to be achieved in the eye, to scan the laser beam with a scanner and to achieve beam focus displacement without changing the focus setting of the focusing means for focusing the laser beam. And controlling an electrically controllable variable power lens. A method for laser surgical ophthalmic treatment is provided. The incision profile may represent a corneal lenticule incision, for example.

  The invention will be further described below with reference to the accompanying drawings.

1 is a cross-sectional schematic view of a portion of a human eye including a cornea, showing a corneal lenticule incision. FIG. 1 is a schematic diagram of an example of an apparatus according to the invention for ophthalmic laser surgery.

  First, referring to FIG. There, the cornea represented by 10 of the human eye is shown in cross-section. The optical axis of the eye (line of sight) is drawn using a dash-dot line and is indicated by 12. The cornea 10 has a front surface 14 and a rear surface 16. The thickness d is in the range of about 500 μm in a normal human eye, and can naturally vary upward or downward depending on the person. The sclera and limbus of the eye are indicated in FIG. 1 by 18 and the limbus is indicated by 20.

  Also depicted in dashed lines in FIG. 1 is a lenticule 22 in the cornea, more precisely in a stroma that is cut out by a therapeutic procedure with focused fs laser radiation, which in turn continues to the cornea 10. It is removed surgically through the opening provided. This opening can likewise be created using a laser incision. Femtosecond lenticule extraction can correct vision defects such as myopia and myopic astigmatism. Typically, the lenticule 22 is created by a substantially flat rear incision 24 and a curved front incision 26. It will be appreciated that the flat rear of the lenticule is by no means essential. In principle, the incision guide can be freely selected for the upper and lower sides of the lenticule. The diameter of the lenticule indicated by a in FIG. 1 is, for example, in the range of 4 mm to 10 mm, and the maximum lenticule thickness indicated by b is, for example, 50-150 μm. For example, if the value a = 6-8 mm and the value b = 80-100 μm, a vision defect of about −5 dpt to −6 dpt can be corrected. It will be appreciated that both the lenticule diameter and lenticule thickness can vary depending on the severity of the vision defect to be corrected. Often, the thickness of the lenticule will be several tens of microns, which, in combination with the generally flat lenticule bottom surface (formed by the rear lenticule incision 24), is the lenticule apex (ie, where the lenticule 22 has the maximum thickness). In the process of linear scanning of the laser beam exceeding), it means that the beam focus of the laser beam needs to move in the direction of beam propagation corresponding to the lenticule thickness.

  Reference is now further made to FIG. The laser device shown there comprises a femtosecond laser source 28 constituted, for example, by a fiber laser, which has a pulse duration in the femtosecond region, preferably 3 from the high 2 digit kHz region. Generate pulsed laser radiation 30 with a pulse repetition frequency that is in the order of the order of kHz or even in the MHz region. The generated laser beam 30 is expanded by a multiple lens beam expanding device 32. The expanded laser beam 34 then reaches the scanner 36, which lasers in the xy plane perpendicular to the beam propagation direction (z direction, see also the coordinate system depicted in FIG. 2). It serves to deflect the beam 34 and thereby sweep the area of the eye to be treated with a laser beam. In the exemplary case shown, the scanner 36 is constituted by two tiltable deflection mirrors 40, 42 that operate according to the galvanometer principle and can be controlled by the control unit 38. It will be appreciated that scanners operating by other principles (eg, scanning with appropriately controllable crystals) are possible as well.

  Disposed downstream of the scanner 36 is an fθ focusing objective lens 44 having lenses 46, 48 that focus the laser beam to a focal position 50. The configuration of the focusing objective 44 as an fθ objective results in a planar field imaging where the focal position 50 is always in a flat plane perpendicular to the z direction, regardless of the deflection angle of the laser beam. It will be appreciated that the two lens configuration of the focusing objective 44 shown in FIG. 2 is merely exemplary. The objective lens 44 may be configured using any other number of lenses.

  In the illustrated exemplary case, the beam expander 32 is constituted by a Galilean telescope having an entrance lens 52 (concave lens) with negative refractive power and an exit lens 54 (convergence lens) with positive refractive power. Alternatively, a Kepler-type telescope having two convex lenses is also possible. The incident lens 52 is configured as a lens having a variable refractive power, and the refractive power of the lens can be changed by an applied electric driver voltage ± U. The achievable refractive power deviation of the lens 52 is preferably more than 10 dpt. The change in the refractive power of the entrance lens 52 results in a change in the divergence of the laser beam incident on the exit lens 54, and thus the z deviation of the beam focus 50. The incident lens 52 is configured as a liquid lens or a liquid crystal lens, and has an electrode mechanism 56 schematically shown only in FIG. 2, and a driver voltage is applied to the electrode mechanism 56. The broken line shows the control connection between the control unit 38 and the deflection mirrors 40, 42 and the voltage driver 58 for the driver voltage ± U.

  The control unit 38 controls the voltage driver 58 and thus the electrode voltage of the incident lens 52 according to the incision profile to be realized in the eye. The corresponding control program for the control unit 38 is stored in a memory not shown in detail. In the case of a liquid lens based on the electrowetting principle, the refractive power of the lens depends on the square of the applied voltage. Control of the focal length of the incident lens 52 is therefore performed by a relatively small voltage deviation when this lens is configured as a liquid lens. For example, with a voltage deviation of about 10V, a refractive index deviation of about 10 dpt can be easily achieved (depending on the aperture and shape of the electrostrictive lens 52) if the incident lens 52 is of an appropriate size. In this regard, with proper design, the response time of the liquid lens can be in the range of tens of ms to several ms down.

  Thus, the focus of the fθ objective 44 can be repositioned within the time required for effective and rapid lenticule incision by the fs laser system. For example, one complete linear scan can be easily performed in a time of about 10 ms to 40 ms with a z-movement of the beam focus of about 100 μm. According to the present invention, by using an electrically controllable variable power lens for the beam expanding device 32, the number of focal movements required to be effectively applied in the process of femtosecond lenticule extraction is reduced. As a result.

  Liquid lenses operating on the electrowetting principle that are currently on the market contain highly transparent liquids in the range of about 300 nm to 1300 nm. Thus, for lenticule extraction (and also for other corneal incisions), the fundamental wavelength located in the low infrared region of a normal fs laser source and the harmonics located in the UV region, eg this fundamental wavelength Both third order harmonics can be used.

  The required beam focusing accuracy is most easily achieved, for example, with wavelengths around 340 nm, so UV wavelengths are particularly suitable for refractive index correction by femtosecond lenticule extraction. For example, a focus diameter of 1 μm or less is sought. At NIR wavelengths, such a small focal diameter cannot be achieved without difficulty.

  The design of the input lens 52 of the beam expander 32 in the form of a variable power lens further has the advantage that a lens having a relatively small aperture, for example a lens diameter of about 2 mm to 6 mm, can be used. As a result, the driver voltage can be kept small, and a faster switching frequency can be obtained.

  Third, the effect of any wavefront error of the incident lens 52 on the achievable focus quality is sufficiently small. Currently commercially available liquid lenses, for example, only have a wavefront quality of λ / 4, which when used as a zoom lens for a focusing objective lens 44, allows diffraction limited focusing. It is insufficient.

  The variable power lens used within the scope of the present invention should propagate for fs laser pulses at least in the NIR wavelength region, preferably at least about 1000 nm to 1100 nm. Overall, the z of the beam focus is at least 300 μm, preferably at least 350 μm, and even more preferably at least 400 μm, simply by controlling the variable power lens without the need for additional adjustment of the focusing optics. It is desirable to allow displacement. Such maximum focal shift should preferably be achievable by a photorefractive bias of the variable power lens of at least 7.5 dpt, more preferably at least 8 dpt, and even more preferably at least 8.5 dpt. An optical imaging system that images the generated laser beam at the beam focus (ie, telescope or beam expander, focusing objective, and any optical elements placed in the middle) ensures a corresponding transmission ratio Should. Adjustment accuracy within the working bias range of the variable power lens (which can be, for example, about 9 dpt or about 10 dpt) is preferably at least 3%, more preferably at least 2%, for example about 1%. Should be reached. A design with a voltage deviation of about 1V of the control voltage applied to the variable power lens results in a photorefractive deviation of about 1 dpt, while a photorefractive deviation of about 0.1 dpt results in a z displacement of about 3-4 μm. Can always be achieved using currently commercially available components.

Claims (9)

A telescope (32) for expanding the laser beam, comprising a light source (28) for a pulsed femtosecond laser beam and an incident lens (52) in the form of a variable power controllable lens; A scanner (36) downstream of the telescope for deflecting the laser beam in a plane perpendicular to a path; a focusing objective lens (44) downstream of the scanner for focusing the laser beam; To achieve a predetermined incision profile that requires the beam focus (50) to be displaced in the direction of the beam path, without changing the focusing setting of the focusing objective, simply variable power only by controlling the lens, and a these displacements program-controlled electronic control unit is configured to provide (38), said variable power of the lens By varying by at least 7.5 diopters its refractive power, at least 300μm only it has been configured to effect the displacement of the focal point of the beam, ophthalmic laser surgical device in the direction of the path of the beam.   The apparatus for ophthalmic laser surgery according to claim 1, wherein the lens (52) of variable refractive power is a converging lens.   The apparatus for ophthalmic laser surgery according to claim 1, wherein the lens (52) of variable refractive power is a diverging lens.   The apparatus for ophthalmic laser surgery according to any one of the preceding claims, wherein the lens (52) of variable refractive power is electrically adjustable.   The apparatus for ophthalmic laser surgery according to claim 4, wherein the lens (52) of variable refractive power is a liquid lens operating on the principle of electrocapillarity.   The apparatus for ophthalmic laser surgery according to claim 4, wherein the lens (52) of variable refractive power is a liquid crystal lens.   The lens (52) of variable refractive power and so as to move the beam focus (50) in the direction of the beam path by less than 30 ms, more preferably less than 24 ms, more preferably less than 18 ms by 100 μm. The apparatus for ophthalmic laser surgery according to any one of the preceding claims, wherein actuating means (58) associated therewith are configured.   The apparatus for ophthalmic laser surgery according to any one of the preceding claims, wherein the incision profile represents a corneal lenticule incision.   The apparatus for ophthalmic laser surgery according to any one of the preceding claims, wherein the focusing objective lens is an fθ objective lens.

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