RU2510259C2 - Apparatus for laser surgical ophthalmology - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to medical equipment. An apparatus for ophthalmic laser surgery comprises a source generating a fs-laser beam, a laser beam blooming telescope, a scanner following the telescope and used to deflect the laser beam in a plane perpendicular to a beam trace, and a focusing f-theta objective following the scanner and used to focus the laser beam. According to the invention, an input lens of the telescope is presented in the form of a control lens of a varied refractive power, preferentially formed by an electrically controlled fluid or liquid-crystal lens.

EFFECT: invention provides an increase of input lens speed.

7 cl, 2 dwg

Description

Technical field

The invention relates to a device for ophthalmic laser surgery. More specifically, the invention relates to a device for laser surgery, providing rapid changes in the position of the focus of the laser beam generated by this device, along the z coordinate. The term "coordinate z" according to conventional notation corresponds to the direction of propagation of the beam. Accordingly, any direction perpendicular to the z coordinate is considered as a direction in the x-y plane. In this plane, the laser beam is traditionally deflected by a scanner in order to scan over the area of the eye on which the laser beam should act.

State of the art

Laser systems emitting short pulses of radiation within the femtosecond (FS) range are used in ophthalmic surgery, among other tasks, to perform incisions in the corneal tissue, as well as in the lens. The effect used in this case is an optical breakdown, leading to the so-called photodestruction of irradiated tissue. To ensure photodestruction, a rather strong focusing of the laser beam is required, which is achieved by using optics with a correspondingly high aperture during the focusing process. In well-known ophthalmic PS laser systems, focusing optics are usually an f-theta lens, which guarantees a flat image field and avoids undesired beam focus movements along the z coordinate during scanning with a laser beam.

FS laser systems have a strong position in ophthalmology, for example, for LASIK operations (laser in-situ keratomileusis - laser intrastromal keratomileusis). LASIK is a method of influencing the cornea in order to eliminate visual defects, in which first a small surface disk (the so-called flap) is cut from the surface of the cornea, remaining attached to the corneal tissue with its edge. Then the flap is bent off and the stroma of the cornea, which was opened as a result of the flap bending, is ablated with short-wave laser radiation, for example, from an excimer laser emitting at 193 nm, in accordance with the ablation profile developed for an individual patient. In this embodiment, the FS laser system is used to perform an incision during the formation of the flap.

In order to cut the flap, the surface of the cornea to be treated is usually flattened by means of the applanation plate pressed against it and the beam focus is controlled in two coordinates in the plane inside the cornea. Due to the flat image field provided by the f-theta lens, in this case it is not necessary to move the beam focus along the z coordinate. Such movement may be required only in the marginal region of the flap, if it seems desirable to direct the trajectory of the incision in the marginal region of the flap upwards to bring it out of the corneal stroma.

Various solutions to the problem of moving the focus along the z coordinate have been proposed. WO 03/032803 A2 describes the movement for this purpose along the z axis (i.e., along the beam propagation direction) of the entire focusing lens. An alternative solution would be to design a zoom lens with a zoom feature. However, both of these options have the disadvantage that mechanical movement or setting the degree of zooming of the focusing lens should be carried out with high accuracy, since it is transferred to a change in focus position on a 1: 1 scale. If the desired focus movement between successive pulses of laser radiation is several micrometers, a correspondingly fast mechanical movement to the same distance of the focusing lens or the objective lens, which provides for zooming, is necessary. Known mechanical drives are unsuitable for this.

An alternative solution is described in DE 102005013949 A1. The laser system contains a two-lens beam expander installed behind the scanner and made according to the scheme of the telescope, as well as a focusing lens mounted directly behind the scanner. The input lens of the beam expander (which is a positive lens) can be moved along the axis of the beam (i.e., along the z coordinate) through a linear drive. This movement of the input lens changes the divergence of the laser beam emerging from the beam expander. With a fixed position of the focusing lens, this leads to a change in the position of the focus along the z coordinate. One of the advantages of this solution compared to adjusting the z coordinate of the focusing optics is to improve reproducibility and accuracy of the movement, since the optical system converts the movement of the input lens of the beam expander into focus movement with a decrease, for example, by 10 times. However, the achievable rate of change in position of the input lens imposes restrictions on the speed of movement of the focus of the beam that has been converted to the focal plane. With respect to the three-dimensional sections that are required for the extraction of the corneal lenticle, the method for changing the focus position according to DE 102005013949 A1 is much faster than the method described in WO 03/032803 A2, simply because if the position of the input lens is rearranged, the masses of the expander’s moving components the beam is essentially smaller than in the case of changing the position of the entire focusing optics or even a single focusing lens. Modern focusing optics can weigh several kilograms, and it must be moved without creating vibrations. The input lens of the beam expander, on the contrary, can have a relatively small aperture and have a correspondingly small size and weight. Despite this, conventional linear drives do not meet the requirements if the formation of a lenticular in the cornea or other three-dimensional sections must be carried out in an acceptable short time using a laser with a sufficiently high pulse repetition rate. The speeds of reliable movement of the input lens of the beam expander without any angular displacements when using conventional linear drives can be, for example, 1-3 mm / s and even (in the case of appropriate mechanical guiding of the lens) 5 mm / s. However, to cut out a lenticular using an FS laser with a pulse frequency in the range of tens or hundreds of kilohertz or more, the same principle of refocusing along the z coordinate requires the input lens moving speed of 10 mm / s or more. These speeds cannot be provided by available linear actuators, at least systems that satisfy the requirements for precision tuning.

Disclosure of invention

The problem solved by the invention is to create a laser device that more closely meets the requirements of guiding when performing a three-dimensional incision in ophthalmic surgery. To solve this problem, the invention provides a device for ophthalmic laser surgery, comprising: a source generating a femtosecond laser beam; a telescope for expanding a laser beam, containing an input lens made as a controlled lens with a variable refractive power; a scanner mounted behind the telescope to deflect the laser beam in a plane perpendicular to the beam path (in the x-y plane); at least a single-lens focusing lens mounted behind the scanner, preferably an f-theta lens, and a program-controlled electronic control means configured to provide a section profile, the execution of which requires beam focus movements along the beam path (along the z coordinate), with the ability to carry out these movements only by control lens with variable refractive power without changing the settings of the focusing lens.

The variable refractive power lens is preferably electrically adjustable and is, for example, a liquid lens operating in accordance with the principle of electro-wetting (also called electrocapillarity), or, alternatively, a liquid crystal lens. Known liquid lenses are based on the Lippmann effect (see, for example, W.Monch, WFKrogmann, H. Zappe: Variable Brennweite durch flussige Mikrolinsen [Changing the focal length by liquid microlenses], Photonik 4/2005, pp. 44-46) . As a result of applying electric voltage to the electrodes of the liquid lens, the surface tension and, as a result, the curvature of the boundary surface of the liquid change. This change in turn leads to a change in the focal length of the liquid lens. In this case, liquid lenses, upon supplying electric voltage to them, are able to change their refractive power within 10 diopters (diopters) or more within a few milliseconds.

Also known are liquid crystal lenses based on reorientation and / or local shear of liquid crystals forming the liquid crystal layer, and, for example, monomers in the presence of an electric field. The reorientation or shift of liquid crystals causes a change in the refractive index of the liquid crystal layer and, as a result, a change in the refractive power of the lens.

Electric adjustment of the lens with variable refractive power provides a significantly faster z-axis adjustment than linear movement of the lens itself, without requiring the use of mechanical drive devices. As a result, it becomes possible to obtain higher tuning rates. Moreover, as a result of the absence of mechanical drive means and moving parts, no friction occurs (with the exception of internal friction in a liquid or in liquid crystals). Thereby, high reliability, long service life and stability are achieved (no mechanical wear).

The fast movement of the focus (focal zone) along the z coordinate, provided by the invention, makes its use particularly attractive in ophthalmic applications that use focused PS laser radiation and which require rapid guiding when making three-dimensional sections in order to reduce exposure time. One possible application that can benefit from quick guiding is the extraction of the corneal lenticle. In this operation, carried out for the purpose of refractive correction, a volume in the form of a lens element is cut out from the stroma of the cornea. For this, it is necessary to ensure accurate and fast three-dimensional positioning of the focus of the FS laser pulses. This task does not cause difficulties for the x, y directions due to the correspondingly high scanner speed. For example, well-known mirror scanners constructed using the galvanometric principle are able to provide the required deviations even with a pulse repetition rate in the megahertz range. The use of an input lens with a variable refractive power in a telescope allows moving the focus along the z coordinate in the range from 50 μm to hundreds of micrometers in a few milliseconds or at least several tens of milliseconds. In particular, during the extraction of the corneal lenticle, this allows you to complete the required incision within a few minutes (for example, in 2-4 minutes), reducing the inconvenience that the patient experiences during such an operation to an acceptable short time. In addition, the invention opens the way to refractive correction of the eye without the use of an excimer laser, since the high accuracy and reproducibility of the beam focus position along the z coordinate allows the incision to be made during the extraction of the lenticle, which exactly corresponds to the visual defect to be removed.

EP 1837696 A1 has already described an optical system comprising at least one focusing lens, at least two lenses in a telescope and a scanning unit mounted on the beam path behind the telescope and in front of the focusing lens to deflect the beam in the x-y plane, at least one of the telescope lenses is an electrically adjustable liquid lens and serves to compensate for the field curvature of the focusing lens. In contrast to this solution, a lens with variable refractive power according to the invention serves to move the focus of the beam along the z coordinate, which are defined by the profile of the intraocular incision.

According to the invention, the variable refractive power lens may be a positive or, alternatively, a negative lens.

The variable refractive power lens and its associated activating agent (which includes a driver voltage source) are preferably configured to allow the beam focus to move along the beam path by 100 μm in less than 30 ms, preferably less than 24 ms, particularly preferably less than in 18 ms.

According to an additional aspect of the invention, a method for ophthalmic laser surgery, comprising the following operations:

- the formation of a pulsed femtosecond laser beam aimed at the patient’s eye,

- scanning the laser beam using a scanner in accordance with the profile of the section, which must be made inside the eye and which requires the focus of the beam along the path of the beam, and

- controlling a lens with a variable refractive power for performing beam focus movements without changing the setting of the laser beam focusing means.

The section profile may correspond, for example, to excision of the corneal lenticle.

Brief Description of the Drawings

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

Figure 1 schematically in section shows a portion of the human eye, including the cornea, which is superimposed on the corneal lenticular profile.

Figure 2 schematically shows an example of a device according to the invention for the implementation of ophthalmic laser surgery.

The implementation of the invention

Figure 1 shows, in cross section, the cornea 10 of the human eye. The optical (visual) axis 12 of the eye is drawn by a dash-dot line. The cornea 10 has anterior and posterior surfaces 14, 16. The thickness d of the cornea of a typical human eye is 500 μm, of course, with possible deviations to a greater or lesser extent, from person to person. The sclera and limb of the eye are indicated in figure 1 as 18; the edge of the limb is designated as 20.

The dashed line in Fig. 1 shows the intra-corneal - more precisely, the intrastromal - lenticular 22, which must be excised by exposure to focused FS laser radiation, followed by surgical removal, through an opening that will be made in the cornea 10. This opening can also be formed by laser cut. Femtosecond extraction of the lenticle allows correcting visual defects, such as myopia and myopic astigmatism. Typically, the lenticular 22 is formed by making a substantially planar posterior incision 24 and a curved front (frontal) incision 26. It should be understood that the planar posterior (lower) surface of the lenticular should not be considered necessary. In principle, the trajectory of the section can be freely selected for both the upper and lower sides of the lenticular. The diameter of the lenticule — indicated in FIG. 1 as a — is selected, for example, in the range of 4-10 mm, and its maximum thickness b is, for example, 50-150 μm. Moreover, the choice of a = 6-8 mm and b = 80-100 microns allows you to correct visual defects in the range from -5 to -6 diopters. It should be understood that the diameter and thickness of the lenticle can vary depending on the severity of the corrected visual impairment. Often, the thickness of the lenticle can be as little as a few tens of micrometers, which in combination with its essentially flat bottom side (formed by a flat back section 24) means that when scanning with a laser beam outside the top of the lenticle (i.e., the zone in which the lenticular 22 has a maximum thickness), the focus of the laser beam should move along the direction of propagation (trajectory) of the beam by a distance corresponding to the thickness of the lenticle.

Next, a laser device shown in FIG. 2 will be described, which comprises a femtosecond laser source 28 (formed, for example, by a fiber laser) generating pulsed laser radiation 30 with pulse durations within the femtosecond range and with a pulse repetition rate preferably lying in the range of more than 50 kHz to thousands of kilohertz or even more than 1 MHz. The generated laser beam 30 is expanded by a multi-lens beam expander 32. The expanded laser beam 34 enters the scanner 36, designed to deflect the laser beam 34 in the x-y plane, orthogonal to the beam propagation direction (coordinate z of the coordinate system, also shown in figure 2), and, thereby, scanning the area of the eye with a laser beam, exposed. In the presented embodiment, the scanner 36, operating in accordance with the galvanometric principle, is formed by two tiltable flat mirrors 40, 42, which are under the control of the control unit 38. It should be understood that scanners based on other principles (for example, scanning using an appropriately controlled crystal) are equally applicable.

Behind the scanner 36, a f-theta focal lens 44 with lenses 46, 48 is mounted, which focuses the laser beam into focus 50. Using a f-theta focal lens 44 provides a flat image surface, so that regardless of the angle of the laser beam, its focus 50 always in the plane orthogonal to the z coordinate. It should be understood that the two-lens design of the focusing lens 44 is shown in FIG. 2 only as an example: the lens 44 can be built with any other number of lenses.

In the presented example, the beam expander 32 is a telescope according to the Galileo scheme, i.e. with a negative (eg, biconcave) input lens 52 and with a positive (eg biconvex) output lens 54. Alternatively, a Kepler telescope with two positive lenses can be used. The input lens 52 is constructed as a lens with a variable refractive power, i.e. its refractive power can vary under the influence of an applied electric driver voltage ± U. The achievable tuning range of the refractive power of the lens 52 is preferably noticeably greater than 10 diopters. Changing the refractive power of the input lens 52 leads to a change in the divergence of the laser beam incident on the output lens 54, and, consequently, to the focus focus 50 of the beam along the z coordinate. The input lens 52 is configured as a liquid lens or a liquid crystal lens provided with electrodes 56 (very schematically shown in FIG. 2) to which a driver voltage is applied. The dashed lines show the control lines connecting the control unit 38 to the deflecting mirrors 40, 42 and to the driver voltage source 58 ± U.

The control unit 38 controls the source 58 of the driver voltage and, therefore, the voltage at the electrodes of the input lens 52 in accordance with the profile of the intraocular section. The corresponding control program for the control unit 38 is recorded in its memory (not shown). In the case of liquid lenses based on the principle of electric wetting, the refractive power of the lens depends on the square of the applied voltage. Therefore, if the input lens 52 is configured as a liquid lens, its focal distance can be controlled by relatively small voltage changes. For example, when the voltage changes by about 10 V, it can be easily achieved, provided that the parameters of the input lens 52 (including its aperture and electrostrictive properties) are correctly selected, a change in its refractive power by about 10 dpt. In this case, subject to proper design, the reaction time of a liquid lens can be from tens to several milliseconds.

Thus, changes in the f-theta focus position of the lens 44 can be made quite quickly, i.e. meet the requirements of fast efficient cutting of the FS lenticular with a laser system. For example, a full linear scan with the beam focus moving along the z coordinate by about 100 μm can take about 10-40 ms. When used according to the invention in the expander 32 of the beam of the lens with electric control of its refractive power, movements of the focus (focal zone) are provided with the frequencies required for the effective use of femtosecond extraction of the lenticular.

Commercially available liquid lenses operating on the basis of the principle of electro-wetting, contain liquids with high transparency within the range of 300-1300 nm. Accordingly, for the extraction of the lenticular (as well as for other corneal incisions), it is possible to use both the main radiation frequency of typical PS laser sources corresponding to the wavelength in the near infrared (NIR) range, and the harmonic corresponding to the ultraviolet (UV) range, for example, the third harmonic.

The wavelength in the UV range is particularly convenient for correcting refraction by femtosecond extraction of the lenticular, since the required precision for controlling the focus of the beam is more easily achieved for a wavelength close, for example, to 340 nm. In particular, it is desirable to obtain a focal zone diameter of not more than 1 μm. For wavelengths in the NIR range, obtaining the named diameter value causes certain difficulties.

The design of the input lens 52 of the beam expander 32 in the form of a lens with variable refractive power also has the advantage of allowing the use of lenses with a relatively small aperture, for example lenses with a diameter of 2-6 mm. This makes it possible to use a small driver voltage and provide higher refocus frequencies.

In addition, the effects of wavefront errors introduced by the input lens 52 on the focusing quality are quite small. In particular, liquid lenses on the market have a wavefront error of λ / 4. The use of lenses of this quality in a focusing lens 44 with a variable focal length would not allow to obtain the quality of focusing, limited by diffraction.

The variable refractive power lens used in the context of the invention should be transmittance at least for PS laser pulses within the NIR range, preferably in the range of 1000-1100 nm. In this case, it is desirable to ensure that the focus of the beam along the z coordinate is at least 300 μm, preferably at least 350 μm and most preferably at least 400 μm, only by adjusting the lens with variable refractive power, without further moving the focusing lens for this purpose optics. It is desirable to provide the indicated maximum focus movement by restructuring a lens with a variable refractive power of at least 7.5 diopters, preferably between 8 diopters and even 8.5 diopters. An optical system that projects a laser beam into its focal zone (i.e., a telescope-beam expander, a focusing lens and any optical elements mounted between them) must have the corresponding transmittance. The error in adjusting the lens with variable refractive power within the working range of the adjustment (which may be about 9 or 10 diopters) should preferably not exceed 3%, preferably 2% and, as a specific example, about 1%. Using commercially available components, a design can be obtained in which a change in the control voltage applied to the lens with a variable refractive power by about 1 V causes a change in its refractive power by about 1 diopters, with a change in its refractive power by about 0.1 diopter causes the focal zone to move along the z coordinate by about 3-4 microns.

Claims (7)

1. Device for ophthalmic laser surgery, containing:
source (28) generating a femtosecond laser beam;
a telescope (32) for expanding a laser beam, comprising an input lens (52) made as a controlled lens with a variable refractive power;
a scanner (36) installed behind the telescope to deflect the laser beam in a plane perpendicular to the beam path;
a focusing lens (44) mounted behind the scanner for focusing the laser beam and
program-controlled electronic control tool (38), configured to provide a section profile, the execution of which requires beam focus movements (50) along the beam path, with the ability to carry out these movements only by changing the surface curvature of a liquid lens with a variable refractive power by changing its surface tension or by changing the refractive the ability of the specified lens by reorienting and / or local shear of liquid crystals forming its liquid crystal sky layer. 2. The device according to claim 1, characterized in that the lens (52) with variable refractive power is a positive lens. 3. The device according to claim 1, characterized in that the lens (52) with variable refractive power is a negative lens. 4. The device according to any one of the preceding paragraphs, characterized in that the lens (52) with variable refractive power is made with the possibility of electrical adjustment. 5. The device according to claim 1, characterized in that the lens (52) with variable refractive power and the associated activating means (58) are configured to allow the focus (50) of the beam to move along the beam path by 100 μm in less than 30 ms preferably less than 24 ms, particularly preferably less than 18 ms. 6. The device according to claim 1, characterized in that the section profile corresponds to a corneal lenticular. 7. The device according to claim 1, characterized in that the focusing lens is an f-theta lens.

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