JP6117864B2 - Equipment, method and control program for ophthalmic surgery, especially laser refractive surgery - Google Patents

Description

  The present invention relates to an apparatus for ophthalmic surgery, particularly laser refractive surgery. The invention further relates to a control program for such a device and to a method for creating such a control program.

  In this case, laser refractive surgery should be understood as modifying the imaging characteristics of the optical system “eyeball” using laser irradiation. The interaction of the incident laser with the eyeball changes the refractive properties of one or more components of the eyeball. Since the imaging properties of the eyeball are primarily determined by the cornea, refractive laser ophthalmic surgery often involves treatment of the cornea. In such treatment, a specific application of an incision and / or a specific excision of tissue changes the shape of the cornea and therefore the term reshaping is also used.

  A prominent example of reshaping the cornea to change the refractive properties of the cornea is the reshaping of the cornea by LASIK (Laser In Situ Corneal Curvature). In LASIK, small superficial slices, usually called flaps in the specialist field, are first cut from the cornea. The flap is left part of its edge connected to the adjacent corneal tissue, so that the flap is easily folded aside and subsequently folded again. In the past, in practice, two methods in particular have been used for the generation of flaps, one is a mechanical method using a microkeratome and the other is a laser-based method, in which a femtosecond method is used. Laser irradiation (ie, pulsed laser irradiation with a pulse width of fs region) is used to make a flat subsurface incision in the cornea that is directed outward except in the hinged joint region. To the surface of the cornea. After the generated flap has been folded, tissue excision (removal) is performed from the substrate exposed thereby according to a predetermined removal profile. The ablation profile specifies how much tissue is removed from which location of the cornea. The removal profile is calculated so that after removal, the cornea has an optimal shape for the treated eye and the previously existing optical imaging defects of the eye are corrected as much as possible. Appropriate methods for calculating removal profiles have long been obtained in the specialist field.

  For example, an excimer laser with an irradiation wavelength in the UV region of approximately 193 nm is used for removal.

  Once the removal profile is determined for the eye to be treated, it is then calculated how the required ablation can be optimally achieved using available laser radiation. The laser irradiation used is usually pulsed irradiation. It is therefore a matter of calculating the sequence of laser pulses in interaction with the cornea, in particular the substrate, to perform the required cornea reshaping in space and time.

  Beam guiding means for directing a laser beam on the eye to be treated are known per se in the prior art so that the required sequence of laser pulses in space and time is achieved. In particular, the beam guiding means is a deflection unit, also known as a scanning mechanism, which acts to deflect the laser beam in the lateral direction (xy direction), and the laser at the required height position (z direction). A focusing optical device for focusing the beam may be provided. The deflection unit may comprise, for example, one or more galvanometer controlled deflection mirrors.

  The present invention is not limited to the LASIK technique. The invention also applies to other laser surgical operations on the eye, for example in the case of PRK (corneal excision refractive surgery), LASEK, EPI-LASIK, or in the case of an incision procedure in which the incision is made only in the cornea be able to. Furthermore, the present invention is also not limited to the treatment of the cornea by laser surgery, for example the application of the present invention to the treatment of the lens is also conceivable.

  The beam guidance means described is controlled using a program-controlled computer according to a removal profile or, more generally, according to a treatment profile. If the treatment is a non-removable surgical treatment, the treatment profile can also be an incision profile that specifies, for example, where and at what depth the incision is made.

  The treatment profile requires a reference point, to which the order of the laser points is spatially related. For LASIK removal in particular, it has been proposed to use the pupil center point as a reference point for the removal profile. The pupil is the opening left open by the iris diaphragm, through which the illumination light enters the eyeball and passes over the retina, but the pupil has a relatively sharp outline and therefore uses a camera It is suitable for shooting and evaluating using an image processing program. Appropriate camera technology and processing programs are available in the prior art.

  On the other hand, the human eyeball is not a stationary object but an object that constantly moves. There are various types of eye movements, some of which are performed on different time scales. The only important thing is to decide that the eyeball never stops. This is especially true even when trying to fix the line of sight to a designated object, and even then, unavoidable fixed shake occurs. Since the pupil will share more or less the above eye movement, the eye can be tracked for movement by observing or monitoring the pupil with a camera. A corresponding eye tracking device (eye tracker) takes a series of images of the pupil, including the surrounding irises, and then tracks the eye movement by evaluating the series of images using software. In image evaluation, in particular, what is determined is the instantaneous position of the pupil center. The removal center (the center of the removal profile) is always realigned to the pupil center thus determined, ensuring that the required spatial sequence of laser pulses is directed to the exact location of the eye part to be treated Can do.

  However, using the pupil center as a reference point for the removal profile does not take into account the depth of the anterior chamber of the eye located in front of the pupil, nor does it take into account the thickness of the cornea. Leads to various shortcomings. The eye movement is generally a rotational movement, and the rotation point is located in the vitreous. When the eyeball moves at a certain angle, the center of the pupil moves in the pupil plane by a first value, and the point located on the surface of the cornea moves in the corneal plane by a second value. Since the distance from the rotation point is far compared with the distance between the pupil center and the rotation point, the second value is larger than the first value. Thus, in the presence of eye movement, the registration of the removal profile to the center of the pupil will produce inaccurate results.

Therefore, it is conceivable to use a patient-specific point on the cornea that has a fixed spatial relationship to the pupil center instead of the pupil center as the reference point for the removal profile.
In particular, in this case, it can be considered that the pupil axis penetrates the surface of the cornea. The pupil axis extends through the center of the pupil and through the surface of the cornea. In the case of treatment of the cornea, by using a point located on the cornea as a reference point of the treatment profile, it occurs when a point located away from the cornea, for example, the center of the pupil, is used as a reference point. The above systematic error can be avoided.

  In order to geometrically calculate the treatment center located on the cornea from the pupil center, information about the radius of rotation of the eyeball and the radial distance between the two centers is required. The latter is mainly determined from the depth of the anterior chamber of the eyeball, and a small portion of this radial distance is further determined from the thickness of the cornea.

  The present invention allows the depth of the anterior chamber, including the thickness of the cornea, to vary from person to person, and to improve the surgical outcome, the depth of the anterior chamber of the patient is individually measured for each patient. It is derived from the finding that it is advantageous to determine exactly (including corneal thickness if necessary) by measurement and to take this measurement into account when calculating the corneal treatment center from the position of the pupil center. For example, in a study group with patients, it can be seen that the anterior chamber thickness, including the cornea thickness, varies between about 2.8 mm and 4.5 mm within the study group. It was. In view of this confirmed range of change, assuming a standard value of, for example, 3.5 mm with respect to the depth of the anterior chamber including the thickness of the cornea is relative to the actual condition in the case of the current patient. It may not be very appropriate, so if the treatment center is calculated from the pupil center using such standard values, it may be necessary to assume a relatively large error constantly, 1 is one aspect of the teachings of the present invention.

  An object of the present invention relates to ophthalmic surgery, in particular laser refractive surgery, to disclose a method by which a reference point can be determined on the eye during treatment for a specified treatment profile, by which method It will be possible to achieve improved surgical results.

According to the invention, for this purpose, an apparatus for ophthalmic surgery, in particular laser refractive surgery,
A laser beam source;
Beam guiding means for providing position and time controlled guidance of the laser beam emitted by the laser beam source on the eye to be treated;
A camera that takes images of the iris and pupil of the eyeball;
A computer controlled computer connected to the camera and controlling the beam guiding means according to the treatment profile, and based on the image data supplied by the camera, the position of a specific point on the cornea of the eyeball during treatment of the eyeball A program controlled computer configured to determine and align the treatment profile to the position of the point on the cornea so determined;
A device is provided.

  According to the invention, in this case, the device comprises a measuring device for measuring the depth dimension of the eyeball to be treated, the depth dimension being the depth of the anterior chamber and, if necessary, the thickness of the cornea The computer is supplied with the measurement data of the measuring device and is set to determine the position of a specific point on the cornea in consideration of the measured depth dimension.

  That is, the present invention measures the depth of the anterior chamber and, if necessary, the thickness of the cornea individually for each patient, and the laser treatment is made to a point on the cornea that is determined taking these measurements into account. Teaches to align. Preferably, the reference point is located in front of the cornea. Measurements can be taken immediately before the start of surgery.

  For example, coherent optical interferometry suitable for non-contact measurement of living tissue such as optical coherence tomography (OCT) or coherence region reflectometry (OLCR: optical low coherence reflectometry) has been available for the past. It has become. These measurement methods are performed using broadband irradiation light (for example, SLED, ASE, supercontinuum laser), and can measure the anatomy with high resolution down to a region of 1 μm or less.

  In a preferred development, the present invention teaches that such a coherent optical interferometric measuring device is integrated into a laser surgical instrument, which is in particular an OLCR measuring device. The high measurement accuracy of such a measuring device makes it possible to accurately discriminate and record variations in anterior chamber depth and corneal thickness between various patients. The integration of the measuring device into the laser surgical instrument is performed in particular so that the measuring beam emitted from the measuring device is guided to the eyeball coaxially with the laser beam used for treatment, so that the patient is positioned only once. If necessary, measurements can be repeated during surgery.

  Not only the depth of the anterior chamber but also the diameter of the entire eyeball can vary from person to person. Due to the different diameters of the eyeballs, the rotational radius in the case of a rotational movement of the eyeball results correspondingly different. Thus, in the preferred embodiment, provisions are made to set up the computer to determine the position of a particular point on the cornea, taking into account the patient-specific eye turning radius as confirmed prior to surgery. By taking into account the individually measured turning radii, further improvements can be made compared to using the turning radii designated as standard values.

  As described above, the point where the pupil axis penetrates the surface of the cornea can be used as a specific point on the cornea. Alternatively, it is possible to use a point on the cornea that is in a fixed position relative to the penetration point.

Especially in the case of LASIK therapeutic procedures, the flap is first folded to perform the removal, and during the removal it is not possible to directly scan the surface of the cornea for a given point. Thus, the reference point for the removal center can be calculated only by indirect means.
This possibility may consist in continuously determining the current movement dimension of the pupil center, indicating the current position of the pupil center relative to a given reference position, from the image data of the camera during the laser treatment.
The movement dimension of the pupil center can be determined in particular in the form of a displacement vector, which represents the direction and amount of displacement of the pupil center relative to the reference position. Thereby, the eye movements that occur during the laser treatment procedure can each be represented by a displacement vector relative to this reference position of the pupil center.

Using the measured depth dimension, a movement dimension corresponding to the movement dimension of the pupil center can then be calculated for a particular point on the cornea, for example also in the form of a displacement vector.
The current position of a particular point on the cornea can be calculated from the movement dimension of the particular point on the cornea thus calculated and the known reference position of this point. Suitably in this case, the reference position of a particular point on the cornea is the position occupied by the particular point on the cornea when the pupil center is at that reference position. For example, the position where the pupil axis penetrates the surface of the cornea and the position of the associated pupil center can be determined once at the start of surgery and stored as a specific point on the cornea and the reference position of the pupil center. .

  The present invention is a control program for an instrument for ophthalmic surgery, particularly laser refractive surgery, where the instrument is a laser beam source and a laser beam emitted by the laser beam source onto the eye to be treated. Beam guidance means for performing beam position and time control guidance, a camera for taking images of the iris and pupil of the eyeball, and a computer connected to the camera, executing a control program and controlling the beam guidance means according to the treatment profile A control program is further provided. The control program allows the computer to determine the position of a specific point on the cornea of the eyeball based on the image data supplied by the camera during the treatment of the eyeball, and to determine the position of the point on the cornea so determined. Designed to align the treatment profile with respect to. In this case, the control program determines the position of a particular point on the cornea taking into account the measured depth dimension of the eye to be treated, which depth dimension is determined by the depth of the anterior chamber, and if necessary. Represents the thickness of the cornea.

  The control program can be stored, for example, on a machine-readable portable data medium or a memory chip that can be accessed by a computer.

  Furthermore, the present invention provides a method for creating a control program for a computer controlled computer of an ophthalmic surgery, in particular a laser refractive surgery instrument, wherein the instrument is spatially and temporally determined by the required treatment profile. It relates to a method in which the laser irradiation is set to be guided on or in the eye according to a general order and the treatment profile is aligned with a specific position of the eye to be treated. According to the present invention, in this method, the depth dimension of the eyeball to be treated is measured at least once prior to surgery, and the depth dimension is determined by the depth of the anterior chamber and, if necessary, the thickness of the cornea. And a control program is created to determine the specific value of the eyeball during the surgery taking into account the measured depth dimension.

  With respect to the laser surgical instrument according to the present invention, the previously disclosed and described preferred exemplary embodiments apply equally to the control program and method.

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

1 is a schematic block diagram of an exemplary embodiment of an apparatus for laser refractive surgery of an eyeball. FIG. It is sectional drawing of the front site | part of an eyeball. FIG. 3 is a cross-sectional view of a front portion of an eyeball at a position where the eyeball is rotated with respect to FIG. 2.

  In FIG. 1, an eyeball to be treated by laser refractive surgery is schematically indicated by reference numeral 10. The cornea of the eyeball 10 and the edge of the pupil are indicated at 12 and 14, respectively.

  The laser surgical instrument according to FIG. 1 shows, as is known per se, a fixed light source (eg LED or laser) 18, which emits a (weak) fixed beam 18 'to fix the position of the eyeball. Therefore, the patient's line of sight is directed to the fixed beam 18 '.

The laser surgical instrument further includes a treatment laser 20 that emits treatment irradiation light 20 ′. The treatment irradiation light 20 ′ is guided to the scanning mirrors 24, 24 ′ via the lens 22, and the eyeball 10 via the deflection mirror 26. Directed to. For LASIK therapy, the laser 20 can be, for example, an excimer laser whose irradiation wavelength is 193 nm. It will be appreciated that other therapeutic wavelengths may be used for other therapeutic purposes if desired. A program-controlled computer C controls the laser 20 and the scanning mirrors 24, 24 'according to a pre-calculated treatment profile. In the following, it is assumed that LASIK treatment is performed using the indicated surgical instrument, and therefore a removal profile is assumed as the treatment profile.

  The laser surgical instrument further includes a device (eye tracker) that tracks eye movement. The eye tracker includes a camera 30, and an image of an eyeball, specifically a pupil and an iris, is taken in the direction of an arrow 32 through the deflecting mirror 28 using the camera 30. The captured image is then either computer C or, although not shown, to track eye movements that are generally unavoidable for the patient despite attempting to fix the line of sight to the fixed ray 18 '. It is evaluated in the preceding image processing unit. Computer C takes into account the detected eye movement when controlling the scanning mirrors 24, 24 'in order to thereby keep the removal profile as constant as possible with respect to a specific reference point on the corneal surface. .

  Further, the laser surgical instrument incorporates a measuring device 34 for OLCR (optical low coherence reflectometry), which is guided to the eyeball 10 via the deflecting mirror 42 in a manner known per se. A measuring beam source is provided. The measuring device 34 receives the irradiation light reflected from the eyeball 10 through the deflecting mirror 42 through the same path as the measurement irradiation light of the measuring device 34 is emitted. This is indicated by the double arrow 36.

  At the start of LASIK, before the flap is cut off and folded back, the measuring device 34 measures the depth of the anterior chamber of the eyeball, including the thickness of the cornea. In that regard, reference is now made to FIG. In FIG. 2, the anterior chamber of the eyeball is indicated by 44, 46 indicates the iris, and 48 indicates the lens of the eyeball 10. The total dimension of the depth of the anterior chamber and the thickness of the cornea is indicated by d.

  Further shown in FIG. 2 is the pupil axis 50, which connects the pupil center point P with the penetration point D through which the pupil axis 50 penetrates the anterior surface of the cornea 12.

The rotation of the eyeball causes the pupil axis 50 to move and the pupil center P and the penetration point D to move accordingly. This situation is represented in FIG. In FIG. 3, the new pupil axis is indicated by 50 '. For comparison, the pupil axis 50 in the state of FIG. 2 is shown. a and b indicate the distances to which the pupil center P and the penetration point D have moved relative to the state according to FIG.
When the eyeball moves, the penetration point D moves considerably larger than the pupil center P, and the difference between the movement distances a and b is the depth of the anterior chamber 44 and the thickness of the cornea 12, that is, the total depth dimension d. You will see that it depends.

  The computer C of the laser surgical instrument aligns the removal profile with the penetration point D instead of the pupil center P as the removal center. For this purpose, for example, the computer C determines the position of the pupil center P and the position of the penetrating point D once before the start of the operation, and writes (stores) the determined value as a reference position. During the laser treatment, the computer C continuously determines each current position of the pupil center P based on the image data of the camera 30, and the displacement of the pupil center P between the stored reference position and the current state. Calculate a displacement vector indicating the amount and direction of. From the displacement vector with respect to the pupil center P thus determined, the computer C can obtain the rotation radius in the same manner based on the measured depth dimension d and the rotation radius of the eyeball 10, or obtain a standard value. , But the displacement vector for penetrating point D can be calculated. This calculation is possible using simple mathematics, for example with the help of the intercept theorem well known in geometry. From the displacement vector of the penetration point D thus obtained and the stored reference position of this point, the computer C can then calculate the current position of the penetration point D. It is quite obvious that the amount of computation for these calculations is relatively small.

Claims (5)

A device for ophthalmic laser surgery having a corneal flap,
A laser beam source (20);
Beam guiding means (24, 24 ', 26) for providing position and time controlled guidance of the laser beam emitted by the laser beam source on the eye to be treated;
A camera (30) for taking images of the iris and pupil of the eyeball;
Is connected to the camera, said a beam influencing means for controlling the program-controlled computer (C) according to the treatment profile with a removal profile, based on data of the iris and pupil of the image of the eye to be supplied by the camera During the treatment of the eyeball (10), the position of the specific point (D) on the cornea (12) of the eyeball is determined, and the position of the point (D) on the cornea thus determined is determined. A program-controlled computer (C), set to align the treatment profile with respect to the cornea point (D) located in front of the cornea (12);
A measuring device (34) for measuring a depth measurement (d) of the eyeball to be treated, supplying depth measurement data to the computer, wherein the depth measurement determines the depth of the anterior chamber Representing a measuring device (34);
In a device comprising
The measurement device (34) is a coherent optical interference measurement device configured for optical low coherence reflectometry (OLCR);
The computer measures the depth surveying (d), to confirm the displacement surveying (a) with respect to the pupil center (P) from the data of the eye of the iris and pupil of the image of the camera (30), determined in this way The position of the specific point (D) of the cornea is determined based on the measured displacement measurement (a), the measured depth measurement (d), and the radius of rotation of the eyeball (10). The displacement surveying (a) represents the direction and degree of displacement of the pupil center (P) relative to the reference position of the pupil center (P);
The computer adjusts the position of the removal profile as a removal center to the penetration point (D) instead of the pupil center (P).   The apparatus according to claim 1, wherein the ophthalmic laser surgery is a laser refractive surgery. The depth surveying (d) are characterized by that table the thickness of the cornea (12), according to claim 1 or 2 device.   The specific point on the cornea is a point where the pupil axis (50) penetrates the surface of the cornea (D) or a point fixed relative to the penetration point. The device according to any one of claims 1 to 3. A method for creating a control program for a program controlled computer of an ophthalmic laser surgical instrument having a corneal flap, wherein the instrument is determined by a desired treatment profile with a removal profile Wherein the treatment profile is aligned with respect to a specific position of the eye to be treated, wherein the treatment profile is set to direct laser irradiation onto or into the eye,
Before the surgery, and, a depth surveying and (d) before the depth surveying representing the depth of the anterior chamber of the eye (10) for applying a therapy to (d), the light low coherence reflectometry Measuring at least once by (OLCR);
During the ophthalmic laser surgery and according to the designed control program, the computer determines a displacement survey (a) for the pupil center (P) from the camera image data, and the displacement survey thus determined and the Based on the measured depth survey (d) and the radius of rotation of the eyeball (10), the position of a specific point (D) of the cornea located in front of the cornea is determined, and the displacement survey (a) Creating the control program such that represents the direction and degree of displacement of the pupil center (P) relative to a reference position of the pupil center (P),
The computer adjusts the position of the removal profile as a removal center to the penetration point (D) instead of the pupil center (P).

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