Method and device for determining an optimal position for making an incision in a cornea of a patient

Abstract

The invention relates to a device and a method for determining an optimal position for forming, using a cutting apparatus including a femtosecond L.A.S.E.R. source (10), an incision by generating a plurality of gas bubbles along a cutting line extending within a cornea of an eye of a patient, each gas bubble being generated by application, by the L.A.S.E.R. source, of L.A.S.E.R. energy into the cornea.

Description

[0001] METHOD AND DEVICE FOR DETERMINING AN OPTIMAL POSITION FOR PERFORMING AN INCISION IN A PATIENT'S CORNEA

[0002] TECHNICAL FIELD

[0003] The present invention relates to the technical field of surgical operations performed with femtosecond lasers, and more particularly to ophthalmic surgery, especially for applications involving cutting corneas or lenses.

[0004] By femtosecond laser, we mean a light source, capable of emitting a LASER beam in the form of ultra-short pulses, the duration of which is between 1 femtosecond and 100 picoseconds, preferably between 1 and 1000 femtoseconds, in particular on the order of a hundred femtoseconds.

[0005] EARLIER ART

[0006] An effective method for removing cataracts is known, consisting of:

[0007] cutting the opaque lens directly within the eye cavity to form cut portions of the lens, and

[0008] aspiration of the cut portions of the lens to extract it from the capsular bag, introduction of an implant to replace the lens.

[0009] This effective procedure is much less traumatic than traditional cataract removal methods, such as cryophakia. Indeed, this efficient procedure requires only one (or more) small incision(s) – known as "service" incision(s) – for the insertion of a suction needle and / or a working tip into the eye.

[0010] This (these) service incision(s) is / are made at the beginning of each procedure, to allow the practitioner access to the anterior chamber of the eye.

[0011] Since such incisions can cause corneal astigmatism, the practitioner's goal is to make each operative incision near a transition zone—called the limbus—between the cornea and the sclera of the patient's eye. Positioning an incision near the limbus helps reduce the astigmatism induced by the incision. As the limbus corresponds to the boundary between:

[0012] the cornea, which is transparent to laser radiation, and

[0013] the sclera, which is opaque to laser radiation,

[0014] The incision - made with a laser - must be made in the transparent cornea, as close as possible to the limbus to avoid making incomplete incisions.

[0015] The incision (or incisions) can be made by the practitioner, for example using a laser source.

[0016] The choice of position for each incision is made by the practitioner based on:

[0017] of a cross-sectional OCT image of the patient's eye, acquired by an OCT imaging system, the limbus not being visible on the OCT image, and

[0018] of a two-dimensional front view image of the patient's eye, acquired by a camera, on which the position of the limbus is sometimes difficult to determine, whether by a trained operator or by an automatic image processing method.

[0019] Furthermore, certain factors can interfere with making incisions near the limbus, such as the presence of a "gerontoxon"—an opaque lipid deposit located at the periphery of the cornea—in the patient's eye. This gerontoxon renders the laser ineffective for making an incision. Detecting such a gerontoxon on the two-dimensional image can also be difficult for the practitioner.

[0020] One aim of the present invention is to provide a device and a method enabling the practitioner to determine an optimal position (in particular an optimal angular position and an optimal radial position) for making one (or more) service incision(s) in a patient's eye.

[0021] DESCRIPTION OF THE INVENTION

[0022] To this end, the invention proposes a device for determining an optimal position for forming, using a cutting device including a femtosecond LASER source, an incision by generating a plurality of gas bubbles along a cutting line extending into the cornea of ​​a patient's eye, each gas bubble being generated by the application of LASER energy to the cornea by the LASER source. The determination device includes an imaging system for image acquisition and is notable in that the determination device further comprises a data processing unit including means for: receiving a reference image of the cornea, said reference image having been acquired by the imaging system prior to the emission of a plurality of calibration LASER beams into the cornea.

[0023] Receive at least one current image of the cornea, each current image having been acquired by the imaging system after the emission of the plurality of calibration LASER beams into the cornea, each calibration LASER beam being capable of focusing on a respective sampling point in the cornea, said sampling points defining a radial segment in the cornea extending between an axis of symmetry of the patient's eye and the periphery of the cornea, the length of said radial segment being less than a distance between the axis of symmetry and a supposed radial position of a limbus of the patient's eye; Detect, by comparing the reference image to each current image, at least one test bubble formed along the radial segment, each test bubble being associated with a respective calibration LASER beam.

[0024] Determine, based on at least one detected test bubble, a maximum distance, relative to the axis of symmetry of the patient's eye, to form the incision in the cornea of ​​the patient's eye.

[0025] Preferred but not limiting aspects of the device according to the invention are as follows:

[0026] The reference and current image(s) can be OCT images, with the detection methods being, for each current image, capable of:

[0027] ■ calculate, at each sampling point, a variation in the intensity of backscattered light received by the imaging system between the pixels of the current image and the pixels of the reference image,

[0028] ■ compare this calculated intensity variation to a threshold value to identify the formation of a gas bubble if the calculated intensity variation is greater than the threshold value;

[0029] The means for determining this may be suitable for:

[0030] ■ if a single test bubble is detected:

[0031] • assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the sampling point at which the test bubble is detected, k being a number between / z and 1,

[0032] If several test bubbles are detected: • select, from among the sampling points at each of which a test bubble is detected, the sampling point furthest from the axis of symmetry of the patient's eye, and

[0033] • assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the selected sampling point, k being a number between / i and 1;

[0034] the processing unit further includes means for recording the maximum distance determined in a memory;

[0035] the processing unit may also include means for estimating, from the maximum determined distance, an optimal position of the cutting line along which the gas bubbles forming the incision are likely to be generated, said cutting line extending between an external surface of the cornea and an internal surface of the cornea, the distance between each point of said cutting line and the axis of symmetry being less than the maximum determined distance;

[0036] The device may also include a display unit to show a final image illustrating the patient's cornea and the cutting line to allow the user to visualize the optimal position determined for the incision, said final image corresponding to:

[0037] ■ the reference image or the current image on which

[0038] ■ A representative shape of the cutting line is superimposed at the determined optimal position.

[0039] The invention also relates to a method for determining an optimal position for forming, using a cutting device including a femtosecond LASER source (10), an incision by generating a plurality of gas bubbles along a cutting line extending into a cornea of ​​a patient's eye, each gas bubble being generated by the application of LASER energy to the cornea by the LASER source, notable in that the method comprises the following steps:

[0040] • Receipt by a data processing unit of a reference image of the cornea, said reference image having been acquired by the imaging system prior to the emission of a plurality of calibration LASER beams into the cornea,

[0041] • Receipt by the data processing unit of at least one current image of the cornea, each current image having been acquired by the imaging system subsequent to the emission of the plurality of calibration LASER beams into the cornea, each calibration LASER beam being capable of focusing on a respective sampling point in the cornea, said sampling points defining a radial segment in the cornea extending between an axis of symmetry of the patient's eye and the periphery of the cornea, the length of said radial segment being less than a distance between the axis of symmetry and a supposed radial position of a limbus of the patient's eye,

[0042] • Detection by the data processing unit, by comparing the reference image to the current image, of at least one test bubble formed along the radial segment, each test bubble being associated with a respective calibration LASER beam,

[0043] • Determination, based on at least one detected test bubble, of a maximum distance, relative to the axis of symmetry of the patient's eye, to form the incision in the cornea of ​​the patient's eye.

[0044] Preferred but not limiting aspects of the process according to the invention are as follows:

[0045] The reference and current image(s) can be OCT images, the detection step (230, 330) comprising, for each current image, the substeps consisting of:

[0046] ■ calculate, at each sampling point, a variation in the intensity of backscattered light received by the imaging system (80) between the pixels of the current image and the pixels of the reference image,

[0047] ■ compare this calculated intensity variation to a threshold value to identify the formation of a gas bubble if the calculated intensity variation is greater than the threshold value;

[0048] The determination step may include the following sub-steps for each elementary zone:

[0049] ■ if a single test bubble is detected:

[0050] • assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the sampling point at which the test bubble is detected, k being a number between / z and 1,

[0051] ■ If several test bubbles are detected:

[0052] • select, from among the sampling points at each of which a test bubble is detected, the sampling point furthest from the axis of symmetry of the patient's eye, and

[0053] • assign to the maximum distance, a multiple k between the axis of symmetry of the patient's eye and the position of the selected sampling point, k being a number between and 1;

[0054] the method may also include the next step of recording by the data processing unit, the maximum distance determined in a memory; the method may also include the next step of estimating by the data processing unit, from the maximum distance determined, an optimal position of the cutting line along which the gas bubbles forming the incision are likely to be generated, said cutting line extending between an external surface of the cornea and an internal surface of the cornea, the distance between each point of said cutting line and the axis of symmetry being less than the maximum distance determined;

[0055] The process may also include the subsequent step of displaying, by a display unit, a final image illustrating the patient's cornea and the cutting line to enable the user to visualize the optimal position determined for the incision, said final image corresponding to:

[0056] ■ the reference image or the current image on which

[0057] ■ A representative shape of the cutting line is superimposed at the determined optimal position.

[0058] BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Other features and advantages of the invention will become clear from the description given below, which is by way of example and not limitation, with reference to the attached figures, in which:

[0060] Figure 1 is a schematic representation of an example of an ocular tissue cutting device using a femtosecond laser;

[0061] Figure 2 is a schematic representation of a device for determining an optimal position for making an incision;

[0062] Figure 3 is a schematic representation of a method for determining an optimal position for making an incision;

[0063] Figure 4 is a schematic cross-sectional representation of an eyeball of a patient to be treated.

[0064] DETAILED DESCRIPTION OF THE INVENTION

[0065] The invention relates to a method and device for determining an optimal position for making an incision in a patient's eye using a cutting device including a femtosecond laser necessary to generate a plurality of gas bubbles forming the incision. In the following description, the invention will be described, by way of example, for cutting a cornea, it being understood that the present invention can be applied to determining an optimal position for making an incision in other ocular tissues.

[0066] 1. Cutting device

[0067] With reference to Figure 1, one embodiment of the cutting device is illustrated. The cutting device comprises:

[0068] a femtosecond laser 10,

[0069] an optical scanning scanner 30 downstream of the laser 10,

[0070] an optical focusing system 40 downstream of the scanning optical scanner 30, and

[0071] a control system 50 allowing the optical scanning scanner 30 and the optical focusing system 40 to be controlled.

[0072] 1.1. Femtosecond laser

[0073] The femtosecond laser 10 is capable of emitting a laser beam in the form of pulses. For example, the 10 laser emits light with a wavelength of 1030 nm, in the form of 400 femtosecond pulses. The 10 laser has a power of 20 W and a frequency of 500 kHz.

[0074] 1.2. Optical scanning

[0075] The optical scanning scanner 30 allows the beam from the laser 10 to be directed to move along a path predefined by the user in a focal plane 61.

[0076] 1.3. Optical focusing system

[0077] The optical focusing system 40 allows the beam to be focused in the focusing plane 61 - corresponding to the cutting plane.

[0078] 1.4. Formatting System

[0079] The cutting device may also include a shaping system 20 - such as a liquid crystal spatial light modulator (or "SLM") - between the femtosecond laser 10 and the scanning optical scanner 30. This shaping system 20 is positioned on the path of the beam from the femtosecond laser 10.

[0080] The shaping system 20 can be configured to modulate the phase of the beam from the femtosecond laser 10 (obtaining a modulated laser beam) by distributing the energy of the beam from the femtosecond laser 10 into a plurality of impact points in its focal plane, the application of the laser beam thus modulated at each impact point inducing the generation of a spherical gas bubble at each impact point.

[0081] More specifically, the shaping system allows, from a Gaussian LASER beam generating a single point of impact, and by means of the phase mask, to distribute its energy by phase modulation so as to simultaneously generate several points of impact in its focal plane from a single LASER beam shaped by phase modulation (a single beam upstream and downstream of the SLM).

[0082] Generating multiple impact points from a single modulated laser beam allows for improved cut quality, in addition to reducing ocular tissue cutting time. Specifically, the shaping system creates a homogeneous cutting plane in which residual tissue bridges are all approximately the same size (even if part of the modulated laser beam is obscured, the number of impact points in the cutting plane remains the same). This improved cut quality facilitates subsequent dissection by the practitioner.

[0083] 1.5. Control System

[0084] The control system 50 allows the optical scanning scanner 30 to be controlled, the optional shaping system 20 and the optical focusing system 40.

[0085] The control system 50 may consist of one (or more) workstation(s), and / or one (or more) computer(s), or may be of any other type known to those skilled in the art. The control system 50 may, for example, include a mobile phone, an electronic tablet (such as an iPad®), a personal digital assistant (PDA), etc. In all cases, the control system 50 includes a processor programmed to control the femtosecond laser 10, the optical scanning scanner 30, the optical focusing system 40, the shaping system 20, etc.

[0086] 2. Determination device

[0087] With reference to Figure 2, the determination device 70 comprises:

[0088] an 80 imaging system for acquiring OCT (Optical Coherence Tomography) type images, or Scheimpflug type images (visible light mapping), or UBM type images (Ultrasonic Bio Microscopy),

[0089] a processing unit 90 - including for example a processor and a memory - to process the images acquired by the acquisition system 80 and to determine a map (two or three-dimensional) representative of one (or more) optimal position(s) for making one (or more) incision(s) in a plurality of elementary zones 62 of the ocular tissue 60.

[0090] The 70 determination device can be integrated into the cutting device.

[0091] Specifically, in a preferred embodiment:

[0092] The processing unit 90 is part of the control system 50, and

[0093] The acquisition system 80, the shaping system 20, the scanning optical scanner 30 and the focusing optical system 40 are mounted in a compartment fixed to the end of a robotic arm, while the femtosecond laser 10 can be integrated into a housing on which the robotic arm is fixed.

[0094] Alternatively, the determining device 70 may be remote from the cutting device and include wired or wireless communication means (not shown) for the exchange of information between the determining device 70 and the cutting device.

[0095] In all cases, the determination device 70 is programmed to implement the determination process described below.

[0096] 3. Determination Method

[0097] 3.1. General Information The process includes the following steps:

[0098] Acquisition of a reference image of the ocular tissue to be treated,

[0099] Emission into an elementary zone 62 of the ocular tissue of at least two LASER beams at different positions,

[0100] Acquisition of at least one current image of the ocular tissue,

[0101] Comparison of the current image to the reference image to detect at least one gas bubble associated with one of the LASER beams,

[0102] Determination of an extreme position for the formation of a gas bubble in the elementary zone 62.

[0103] Each elementary zone 62 can consist of:

[0104] a line (for example, 50 or 100 pm), in particular a radial line extending between an axis of symmetry A Sym and a limbus of the ocular tissue,

[0105] a surface (of 50x50 pm or of 100x100 pm or of 100x100 pm), in particular a surface extending longitudinally along the radial line, or

[0106] an elementary volume (of 50x50x50pm or of lOOXXLOOXXLOOpm or of lOOXXLOOXXLOOPm), in particular a volume extending longitudinally along the radial line.

[0107] In all cases, the determined extreme position corresponds to a maximum distance (particularly a maximum radius) from the axis of symmetry As ym of the patient's eye, to form the incision in the elementary zone 62 of the cornea of ​​the patient's eye (generating a plurality of adjacent gas bubbles).

[0108] Combining elementary zones allows you to define a total line, a total surface area, or a total volume to be cut.

[0109] 3.2. Acquisition

[0110] The reference image and the current image(s) acquired by the imaging system can be of type OCT, or of type Scheimpflug, or of type UBM.

[0111] One of the advantages of OCT image acquisition is that an OCT imaging system has high sensitivity (100 dB), enabling the acquisition of high-quality images. Furthermore, the cutting device incorporates an OCT imaging system, eliminating the need for a separate imaging system. Finally, the OCT reference image can also be used to verify the alignment of the cutting device with the ocular tissue to be treated.

[0112] For OCT image acquisition, an optical beam 81 is directed towards the ocular tissue 60, and a small portion of the light 82 that is backscattered (by the different layers) of the ocular tissue 60 is recombined on one (or more) sensor(s) of the imaging system 80 with a reference signal. The signal recorded by the sensor(s) is modulated according to the optical path difference between the signal backscattered by the ocular tissue 60 and the reference signal. This recorded signal is used to construct the OCT image, which can be a one-dimensional or two-dimensional image.

[0113] More specifically, the OCT 80 imaging system can be used:

[0114] - in "A-scan mode", or

[0115] - in "B mode" (also called "B-scan").

[0116] The "A mode" allows the acquisition of a one-dimensional OCT image. It is based on the emission of light information 81 (by an emitter of the imaging system) and the reception of the interference between a backscattered light 82 (by the sensor of the imaging system) along a propagation line and the reference light: the one-dimensional OCT image obtained (from the signal recorded by the sensor) is representative of the axial backscattering profile (i.e. in depth Z) of the ocular tissue 60 at the point considered (with coordinates X, Y in the focal plane 61).

[0117] The "B-mode" allows the acquisition of a two-dimensional OCT image, by implementing a transverse scan of the ocular tissue 60, for example along a direction X perpendicular to the optical axis Z of the ocular tissue 60. This yields a plurality of backscatter profiles in "A-mode" established for different points of the ocular tissue 60 along the X direction. The stacking of these backscatter profiles in "A-mode" allows the construction of a two-dimensional OCT image (XZ).

[0118] 3.3. Comparison

[0119] The comparison step detects the potential formation of a gas bubble. Indeed, the backscattering properties of light by the ocular tissue 60 are the source of contrast in OCT images, revealing morphological information. When a gas bubble forms in the ocular tissue 60, it causes a variation in the backscattering properties of the ocular tissue 60. The comparison step relies on detecting the variation in intensity of the backscattered light received by the imaging system 80 between the pixels of the current image and the pixels of the reference image. If this variation in intensity exceeds a predefined threshold value, then it indicates the formation of a gas bubble at the point of impact of the laser beam in question.

[0120] For a gas bubble to form, the laser pulse point must be located within the patient's cornea. The sclera—which extends to the periphery of the cornea—is opaque to laser radiation, so applying the laser beam to a pulse point within the sclera will not result in gas bubble formation. To minimize corneal astigmatism caused by the incision, the pulse point should be located near the limbus, the transition zone between the cornea and the sclera of the patient's eye.

[0121] The objective of the comparison step is therefore to identify a maximum distance, relative to the axis of symmetry As ym of the patient's eye, to form the incision in the cornea of ​​the patient's eye.

[0122] This comparison step ensures that the maximum distance relative to the axis of symmetry As ymis sufficient to achieve the expected cutting effect and that a distance greater than the maximum distance would result in a lack of effectiveness, the point of impact then potentially being located in the sclera of the ocular tissue.

[0123] As will be described in more detail later, the maximum distance can be determined by emitting a plurality of LASER beams at distinct impact points within the elementary area, thus forming a series of successive impact points, for example along the radial line extending between the axis of symmetry A Sym and the limbus of the ocular tissue.

[0124] 3.4. Determination

[0125] As previously stated, LASER beams are emitted at a plurality of sampling points for each elementary area 62 of the ocular tissue 60, for example at eight points regularly spaced 250pm apart on a line of 1750pm.

[0126] More specifically, for each elementary zone 62, each LASER beam is emitted (simultaneously or successively) at a respective sampling point. A current image is acquired for each elementary zone 62 once all LASER beams have been emitted in said elementary zone 62. The current image is compared to the reference image to detect if one (or more) gas bubble(s) has / have formed.

[0127] If several gas bubbles are formed at several successive sampling points, then the distance (relative to the axis of symmetry As) ym ) of the point of impact furthest from the axis of symmetry As ym is selected as the maximum distance for the formation of a gas bubble.

[0128] More precisely, first, second, third (...etc.) LASER beams are emitted to focus the elementary zone 62 under consideration onto first, second, third (...etc.) respective sampling points, positioned at increasing distances relative to the axis of symmetry A Sym of the patient's eye (radial distance between axis of symmetry A) Sym and first point of impact < radial distance between axis of symmetry A Sym and second point of impact < radial distance between axis of symmetry A Sym and third point of impact, etc).

[0129] A current image is acquired and compared to the reference image to detect the possible formation of gas bubbles:

[0130] If only one gas bubble has formed at the sampling point associated with the first laser beam, then only the position of the first sampling point is located in the cornea (and allows the generation of a gas bubble): the distance between the axis of symmetry As ym and the position of the first sampling point corresponds to the maximum distance allowing the formation of a gas bubble in the elementary zone 62 under consideration; a new elementary zone 62 is then studied,

[0131] If several gas bubbles are formed, for example for the first and second beams, then the position of the impact point of the second beam (which is at a greater distance from the axis of symmetry A) Sym ) corresponds to the maximum distance allowing the formation of a gas bubble in the elementary zone 62 considered; a new elementary zone 62 is then studied.

[0132] 3.5. Summary

[0133] Thus, and as illustrated in Figure 3, the process comprises, for each elementary zone:

[0134] a) Acquisition of a reference image (200 units),

[0135] b) emission 210 of a plurality of LASER beams at a plurality of respective sampling points Pmin-Pmax positioned at increasing distances relative to the axis of symmetry As ym of the patient's eye, c) acquisition 220 of a current image of the ocular tissue, said current image containing the plurality of sampling points,

[0136] d) detection 230 of one (or more) gas bubble(s) by comparing the current image to the reference image,

[0137] e) selection 240 from the set of gas bubbles, of the gas bubble generated at the sampling point furthest from the axis of symmetry As ym from the patient's eye,

[0138] f) recording 250 of the distance between the axis of symmetry As ymfrom the patient's eye and the sampling point associated with the gas bubble selected in memory,

[0139] g) if not all elementary zones have been treated, repeat steps b) to g) for a new elementary zone 62.

[0140] Of course, it is also possible to acquire a single current image for several elementary zones simultaneously (if these elementary zones are located in the same Bscan plane). In this case, the processing steps (bubble detection and determination of the minimum energy value for each elementary zone) can be implemented for these several elementary zones from a single current image in order to save time.

[0141] Once all 62 elementary zones have been processed, a map (including a three-dimensional one) of the maximum distances is obtained – relative to the axis of symmetry As ymof the patient's eye - for the formation of gas bubbles in each of the elementary zones of the ocular tissue.

[0142] For each maximum distance determined, it is possible to estimate an optimal position of a cutting line extending into the cornea, and along which gas bubbles forming the incision can be generated, said cutting line extending between an external surface of the cornea and an internal surface of the cornea, the distance between each point of said cutting line and the axis of symmetry being less than the maximum distance determined.

[0143] 4. Presentation of results to the practitioner

[0144] Advantageously, the device and method according to the invention can be configured to present to the practitioner the optimal position(s) for forming an incision(s) using the cutting device. In particular, the device and method according to the invention can be adapted to illustrate, on an image of the patient's eye (reference image or current image, etc.) a representative shape of the cutting line superimposed at the level of the determined optimal position(s).

[0145] In particular, the determination device may include a display unit to display a final image illustrating the patient's cornea and the cutting line(s) to enable the practitioner to visualize the optimal position(s) determined for the incision(s).

[0146] The display unit can be of any type known to a person skilled in the art, such as a screen.

[0147] 5. Example

[0148] With reference to Figure 4, the device and procedure were tested by a practitioner to determine the optimal incision position to be made in a patient's eye according to the following principle:

[0149] The practitioner selects the incision parameters (Width, Angle, Length, Energy), and performs calibration shots (spots or small lines) in the cornea around a presumed radial position of the limbus (every 500 pm, for example), with an energy equal to the energy parameterized for the incision.

[0150] Acquisition of an OCT image passing through the laser cuts, and

[0151] Automatic analysis of the OCT image to determine the maximum radius at which a cavitation bubble is visible, which corresponds to the maximum radius for making incisions; automatic positioning of the incision at the maximum effective radius (with a potential margin defined by the surgeon) and display to the practitioner.

[0152] Validation or modification of the displayed position of the incisions.

[0153] 6. Conclusions

[0154] Thus, the invention allows the determination of an optimal position to form an incision in the cornea of ​​a patient by generating a plurality of gas bubbles along a cutting line extending between an external surface and an internal surface of the cornea.

[0155] This allows:

[0156] to reduce the astigmatism induced by the incision, and

[0157] to limit the risks of making incomplete incisions. The reader will have understood that many modifications can be made to the invention described above without materially departing from the new lessons and advantages described here.

[0158] Therefore, all such modifications are intended to be incorporated within the scope of the attached claims.

Claims

DEMANDS 1. Device (70) for determining an optimal position for forming, using a cutting device including a femtosecond LASER source (10), an incision by generating a plurality of gas bubbles along a cutting line extending into a cornea of ​​a patient's eye, each gas bubble being generated by the application of LASER energy to the cornea by the LASER source, the determination device (70) including an imaging system (80) for image acquisition, characterized in that the determination device (70) further comprises a data processing unit (90) including means for: • Receive a reference image of the cornea, said reference image having been acquired (200, 300) by the imaging system (80) prior to the emission (210, 310) of a plurality of calibration LASER beams into the cornea, • Receive at least one current image of the cornea (60), each current image having been acquired (220, 320) by the imaging system (80) subsequent to the emission of the plurality of calibration LASER beams into the cornea, each calibration LASER beam being capable of focusing at a respective sampling point in the cornea, said sampling points defining a radial segment in the cornea extending between an axis of symmetry of the patient's eye and the periphery of the cornea, the length of said radial segment being less than a distance between the axis of symmetry and a supposed radial position of a limbus of the patient's eye, • Detect, by comparing the reference image to each current image, at least one test bubble formed along the radial segment, each test bubble being associated with a respective calibration LASER beam, • Determine, based on at least one detected test bubble, a maximum distance, relative to the axis of symmetry of the patient's eye, to form the incision in the cornea of ​​the patient's eye.

2. A determination device according to claim 1, wherein the reference and current image(s) are OCT images, the means for detection being, for each current image, capable of: calculate at each sampling point, a variation in intensity of backscattered light received by the imaging system (80) between the pixels of the current image and the pixels of the reference image, compare this calculated intensity variation to a threshold value to identify the formation of a gas bubble if the calculated intensity variation is greater than the threshold value.

3. A determination device according to any one of claims 1 or 2, wherein the means for determining are adapted to: if a single test bubble is detected: assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the sampling point at which the test bubble is detected, k being a number between and 1, If several test bubbles are detected: select, from among the sampling points at each of which a test bubble is detected, the sampling point furthest from the axis of symmetry of the patient's eye, and assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the selected sampling point, k being a number between and 1.

4. A determination device according to any one of claims 1 to 3, wherein the processing unit further comprises means for: • record the maximum distance determined in a memory.

5. A determination device according to any one of claims 1 to 4, wherein the processing unit further comprises means for: • estimate, from the maximum distance determined, an optimal position of the cutting line along which the gas bubbles forming the incision are likely to be generated, said cutting line extending between an external surface of the cornea and an internal surface of the cornea, the distance between each point of said cutting line and the axis of symmetry being less than the maximum distance determined.

6. A determination device according to claim 5, further comprising a display unit for displaying a final image illustrating the patient's cornea and the cutting line to enable the user to visualize the optimal position determined for the incision, said final image corresponding to: the reference image or the current image on which19 A representative shape of the cutting line is superimposed at the determined optimal position.

7. Method for determining an optimal position for forming, using a cutting device including a femtosecond LASER source (10), an incision by generating a plurality of gas bubbles along a cutting line extending into a cornea of ​​a patient's eye, each gas bubble being generated by application, by the LASER source, of LASER energy into the cornea, characterized in that the process comprises the following steps: • Reception by a data processing unit (90) of a reference image of the cornea (60), said reference image having been acquired (200, 300) by the imaging system (80) prior to the emission (210, 310) of a plurality of calibration LASER beams into the cornea, • Receipt by the data processing unit (90) of at least one current image of the cornea (60), each current image having been acquired (220, 320) by the imaging system (80) subsequent to the emission of the plurality of calibration LASER beams into the cornea, each calibration LASER beam being capable of focusing on a respective sampling point in the cornea, said sampling points defining a radial segment in the cornea extending between an axis of symmetry of the patient's eye and the periphery of the cornea, the length of said radial segment being less than a distance between the axis of symmetry and a supposed radial position of a limbus of the patient's eye, • Detection (230, 330) by the data processing unit (90), by comparing the reference image to the current image, of at least one test bubble formed along the radial segment, each test bubble being associated with a respective calibration LASER beam, • Determination (240, 250; 340, 350) based on at least one test bubble detected, of a maximum distance, relative to the axis of symmetry of the patient's eye, to form the incision in the cornea of ​​the patient's eye.

8. A determination method according to claim 7, wherein the reference and current image(s) are OCT images, the detection step (230, 330) comprising, for each current image, the substeps of: calculate, at each sampling point, a variation in the intensity of backscattered light received by the imaging system (80) between the pixels of the current image and the pixels of the reference image,20 compare this calculated intensity variation to a threshold value to identify the formation of a gas bubble if the calculated intensity variation is greater than the threshold value.

9. A determination method according to any one of claims 7 or 8, wherein the determination step includes the following substeps for each elementary zone: if a single test bubble is detected: ■ Assign to the maximum distance, a multiple k of the distance between the axis of symmetry of the patient's eye and the position of the sampling point at which the test bubble is detected, k being a number between 0 and 1, if several test bubbles are detected: ■ Select, from among the sampling points at each of which a test bubble is detected, the sampling point furthest from the axis of symmetry of the patient's eye, and ■ assign to the maximum distance, a multiple k between the axis of symmetry of the patient's eye and the position of the selected sampling point, k being a number between and 1.

10. A method for determining according to any one of claims 7 to 9, which further comprises the following step: • recording by the data processing unit (90), of the maximum distance determined in a memory.

11. A method for determining according to any one of claims 7 to 10, which further comprises the following step: • estimation by the data processing unit (90), from the maximum distance determined, of an optimal position of the cutting line along which the gas bubbles forming the incision are likely to be generated, said cutting line extending between an external surface of the cornea and an internal surface of the cornea, the distance between each point of said cutting line and the axis of symmetry being less than the maximum distance determined.

12. A method for determining according to claim 11, which further comprises the following step: • display by a display unit of a final image illustrating the patient's cornea and the cutting line to allow the user to visualize the optimal position determined for the incision, said final image corresponding to: the reference image or the current image on which21 A representative shape of the cutting line is superimposed at the determined optimal position.

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