Laser unit for intrastromal refractive surgery

The present invention generally relates to a laser unit for performing an intraocular laser ophthalmic surgery. More specifically, the present invention relates to a laser surgery in which the stromal tissue is scored on concentric cylindrical surfaces, the surfaces oriented parallel to and aligned with the visual axis of the eye. The present invention is particularly, but not exclusively, useful for performing an intraocular laser ophthalmic surgery in which corneal re-formation takes place by inducing redistribution of biomechanical forces in the cornea.

BACKGROUND OF THE INVENTION [0002] The cornea of ​​the eye has five (5) distinguishable different layers of tissues. Proceeding in the posterior direction from the anterior surface of the cornea, these layers are: the anterior epithelium; Bowman layer (membrane); framework; Descemeta membrane; and corneal endothelium. There is a space behind the cornea that contains the aqueous humor of the eye called the anterior chamber. Importantly, the aqueous humor pressure in the anterior chamber exerts pressure on the cornea with biomechanical consequences. In particular, the aqueous humor in the anterior chamber of the eye exerts intraocular pressure on the cornea. This causes stresses and tensions that cause corneal tension.

[0003] Structurally, the cornea of ​​the eye has a thickness (T) that extends between the anterior epithelium and the corneal endothelium. Typically, "T" is approximately five hundred micrometres (T = 500 μίΓ). From the biomechanical perspective, the Bowman layer and the stroma are the most important layers of the cornea. In the cornea, the Bowman layer is a relatively thin layer (e.g., 20 to 30 μιτι), which is located below the anterior epithelium in the anterior hundred micrometers of the cornea. The root thus covers almost all of the remaining four hundred micrometers of the cornea. In addition, the tissue of the Bowman layer creates a relatively strong, elastic membrane that effectively counteracts stress. On the other hand, the root contains relatively weak connective tissue.

[0004] Biomechanically, the Bowman layer and the framework are subject to significant intraocular pressure which is exerted on the cornea by the aqueous humor of the eye in the anterior chamber. In particular, this pressure is transferred from the anterior chamber, and through the framework, to the Bowman membrane. It is known that the way in which forces are transmitted through the stroma will affect the shape of the cornea. Thus, by disrupting the forces between the connective tissue in the stroma, the total distribution of forces in the cornea can be changed. Consequently, this changed force distribution will then act on the Bowman layer. In response, the shape of the Bowman layer changes, and thanks to the elasticity and strength of the Bowman layer, this change will have a direct impact on the shape of the cornea. With this in mind and in accordance with the present invention,

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[0005] As is well known, all different corneal tissues are susceptible to the phenomenon of Laser Induced Optical Breakdown (LIOB). In addition, it is known that different tissues will react differently to the laser beam, and that the orientation of tissue subjected to LIOB can also affect how the tissue reacts to LIOB. With this in mind, the framework requires specific consideration.

[0006] The framework essentially comprises a plurality of plaques that extend substantially parallel to the surface of the anterior eye. In the stroma, plaques are bound together through tissue resembling glue, which is inherently weaker than the plaques themselves. Consequently, LIOB can be performed on layers parallel to plaques with less energy (e.g., 0.8 μJ) than the energy required by LIOB for making incisions that are oriented perpendicular to the plaques (e.g., 1.2 μJ). However, one skilled in the art will recognize that these energy levels are only exemplary. If it is possible to use a closer focusing optics, the required energy levels will be correspondingly lower. In any case, depending on the desired result, it may be advisable to only make incisions in the framework. On the other hand,

[0007] In view of the above, it is an object of the present invention to provide a laser unit for performing a laser ophthalmic surgery that changes the shape of the cornea in order to obtain refractive correction to improve the patient's eyesight. Another object of the present invention is to provide a laser unit for performing a laser ophthalmic surgery that requires minimal LIOB of the stroma. It is yet another object of the present invention to provide a laser unit for performing a laser ophthalmic surgery that avoids exposure of the Bowman layer and, instead, leaves it intact for use to provide structural support to the cornea with an altered shape.

[0008] Examples of laser units and methods for performing intra-teeth incisions and modeling have been disclosed in WO2006 / 051364 and US2004 / 0044355.

SUMMARY OF THE INVENTION [0009] According to the present invention there is provided a laser unit, which is defined by the present patent claim, for conducting methods of intraocular laser ophthalmic surgery that change the shape of the cornea under the influence of biomechanical forces. Importantly, for these methods, the volume of tissue undergoing surgery, which is located only in the corneal stroma, is determined. In particular, this operative volume extends backwardly from slightly below the Bowman layer (s) to a significant depth in the stroma that is approximately nine-tenth the thickness of the cornea. Thus, with a cornea having a thickness T "(e.g., approximately 500 μιτ), the operating volume extends from below the Bowman layer (e.g. 100 μιτ) to the depth of the cornea,

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Approx. 450 μιτι). In addition, the operating volume extends radially from the visual axis of the eye to a distance of about 5.0 mm (i.e., the operating volume has a diameter of about 10.0 mm).

[0010] In general, a laser unit according to the present invention is capable of generating a so-called femtosecond laser beam. In other words, the duration of each pulse in the beam will be approximately less than one picosecond. After generation, the beam is directed and focused on a number of foci in the stroma. A well-known effect is the laser induced Optical Breakdown (LIOB) of the stromal tissue at each focus. In particular, and in accordance with the present invention, the displacement of the focus in the framework forms a series of incisions, each cut being made on parts of a corresponding cylindrical surface.

[0011] Geometrically, the corresponding cylindrical surfaces on which the incisions were made are concentric, and they are centered on the visual axis of the eye. And they can be round cylinders or oval (elliptical) cylinders. In addition, each cylindrical surface has a front end and a rear end. In order to maintain the position of the cylindrical surface in the operating volume, the posterior end of the incision is located not deeper in the stroma than approximately 0.9T from the anterior surface of the eye. On the other hand, the front end of the cylindrical cut is located in the notch more than at least eight micrometers backwards from the Bowman layer. Each of these "notches" will have a thickness of about two micrometers.

In a preferred procedure, each incision is approximately two hundred micrometers from an adjacent incision, and the incision located inwardly (i.e., the central incision) can be located about 1.0 millimeter from the visual axis. Of course, there may be many such cylindrical cuts (preferably five), and each of them may define a substantially cylindrically shaped wall. Such a system may be particularly useful for the treatment of senile dullness of vision. In a variant of this procedure, which would be more suitable for the treatment of astigmatism, the LIOB-treated portions of the cylindrical surfaces may define polar opposing segments of the arch. In this case, each arc segment preferably extends along an arc that ranges from five degrees to one hundred and sixty degrees.

[0013] For additional variations of the methods carried out by the laser unit of the present invention, in addition to or instead of the above mentioned incisions, differently configured LIOB layers may be formed in the framework tissue of the operative volume. To form these layers, LIOB is carried out in all or in part of the ring-shaped area. In addition, each layer will lie in a plane substantially perpendicular to the visual axis of the eye. For the purposes of the present invention, the layers are spaced approximately ten micrometers from each adjacent layer, and each layer will have an internal diameter "di" and an outer diameter "to". These "layers" will have a thickness of about one micrometer. As indicated above, the present invention provides for the production of a number of such layers adjacent to each other,

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[0014] In yet another variation of the present invention, "radial incisions" can be made in the framework. In particular, the radial cuts will be located at a predetermined azimuthal angle θ and will be substantially coplanar with the visual axis of the eye. Each radial incision will be in the operating volume described above and will extend outward from the visual axis from the internal diameter "ri" to the outer diameter "ro". In addition, if necessary, there may be many "radial incisions", each "radial incision" having its own specific azimuthal angle θ.

According to the present invention, all "cuts" and "layers" (i.e., cylindrical incisions, annular layers and radial incisions) will weaken the framework tissue and hence will redistribute the biomechanical forces in the framework. In particular, the weaknesses in the stroma resulting from LIOB "incisions" and "layers" will accordingly cause "bulging" or "flattening" in response to intraocular pressure from the anterior chamber. As mentioned above, however, these changes will be slightly limited by the Bowman layer. The benefit of this limitation is the preservation of corneal integrity. Note: in areas where layers have been formed, a cornea may appear, which may eventually cause a slight bulge. Regardless, with appropriate prior planning,

[0016] In view of the above, it is clear that the physical consequences of making "cuts" or "layers" in the framework are slightly different. Although both attenuate the stroma and thereby allow the intraocular pressure of the aqueous humor in the anterior chamber to change the shape of the cornea, "incisions" (i.e., LIOB parallel and radial with respect to the visual axis) will cause bulging of the cornea. On the other hand, "layers" (ie LIOB perpendicular to the visual axis) will tend to flatten the cornea. In either case, the "incisions" themselves, or the combination of "incisions" and "layers" will be used to change the shape of the cornea with only a negligible amount of tissue removed.

[0017] According to the present invention, various treatments can be adapted to treat identifiable refractive imperfections. In particular, in addition to the cuts themselves, the present invention provides for the use of different combinations of cuts and layers. In any case, the selection of incisions or incisions and layers will depend on how the shape of the cornea should be changed. Also in any case, it is extremely important that the cuts and layers are centered on the visual axis (i.e. they must be centered). Some examples are:

Farsightedness: Only cylindrical incisions are necessary for this procedure. Short-sightedness: A combination of cylindrical cuts (round or oval) and annular layers can be used. In this case, a series of notches are spaced from the visual axis starting from the radial distance "rc", and a series of layers are located inside the cuts. In particular, the "di" of a series of layers may be zero (or very little), and "up to" a number of layers may be smaller than 2rc (up to <2rc). In an alternative treatment, only radial incisions may be used, or in combination with cylindrical incisions and annular layers. If used, each of the radial incisions is made with their respective azimuth angle θ,

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The inner radius "r1" and the outer radius "ro" are all defined in advance.

Hyperopia: A combination of cylindrical incisions and annular layers can be used. In this case, a series of notches are spaced from the visual axis by the distance between the internal radius "rci" and the external radius "rco", with the radius and in which the "di" of the series is greater than 2 degrees (to> di > 2rco). Astigmatism: Cylindrical cuts may be used alone or in combination with annular layers. In particular, the arc segments of the cylindrical cuts are oriented on a predetermined line that is perpendicular to the axis of view. Then layers can be created between the segments of the arch.

[0018] Whenever a combination of cuts and layers is required, the energy for each pulse used to create the cylindrical cuts will be approximately 1.2 micrometers. On the other hand, as mentioned above, the energy for each pulse used to form the annular layers will be approximately 0.8 micro-ray.

BRIEF DESCRIPTION OF THE DRAWINGS The new features of the invention, as well as the invention itself, both as to its structure and its operation, will best be understood from the attached drawing, in combination with the accompanying description, in which like references refer to similar parts, and on which:

Fig. 1 is a cross-sectional view of the cornea of ​​the eye, shown relative to the schematically illustrated laser unit;

Fig. 2 is a cross-sectional view of the cornea showing a defined operating volume in accordance with the present invention;

Fig. 3 is a perspective view of a series of cylindrical surfaces in which laser incisions can be made by LIOB;

Fig. 4 shows a cross-sectional view of the cuts on a series of cylindrical surfaces, in view along the line 4-4 of Fig. 3, with the notches depicted for the typical treatment of hyperopia;

Fig. 5A is a cross-sectional view of a series of cylindrical surfaces in a view taken along line 5-5 of Fig. 3 when full incisions have been made on the cylindrical surfaces;

Fig. 5B is a cross-sectional view of a series of cylindrical surfaces in a view along line 5-5 of Fig. 3 when partial incisions were made along the arc segments on cylindrical surfaces to treat astigmatism;

Fig. 5C shows a cross-sectional view of an alternative embodiment for cuts made similar to those shown in Fig. 5B and for the same purpose;

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Fig. 6 is a cross-sectional view of the cornea showing the biomechanical consequence of making incisions in the cornea according to the present invention;

Fig. 7 is a perspective view of a series of layers formed via LIOB, in accordance with the present invention;

Fig. 8 is a perspective view of the layers taken along line 8-8 of Fig. 7;

Fig. 9A is a cross-sectional view of a combination of cuts and layers, in a plane view including the axis of the eye, with a combination adapted to treat hyperopia;

Fig. 9B is a cross-sectional view of a combination of cuts and layers in a plane view including the axis of the eye, with a combination adapted to treat myopia;

Fig. 9C shows a cross-sectional view of a combination of cuts and layers, in a plane view including the axis of the eye, with a combination adapted to treat astigmatism; and

Fig. 9D is a top view of radial cuts that are coplanar with the axis of view.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [0020] Referring initially to Figure 1, it can be seen that the present invention includes a laser unit 10 for generating a laser beam 12. More specifically, the laser beam 12 is preferably a pulsed laser beam and the laser unit 10 generates pulses for the beam 12 , which have a duration of less than one picosecond (i.e. they constitute femtosensis pulses). In Fig. 1, the laser beam 12 is shown as directed along the visual axis 13 and towards the ocular cornea 16. Fig. 1 also shows the anterior chamber 18 of the eye, which is located just behind the cornea 16. There is also a lens 20 which is positioned at the back of both the anterior chamber 18 and the sclera 22.

[0021] Fig. 2 shows five (5) different anatomical tissues of the cornea 16. The first of them, the front epithelium 24 defines the front surface of the cornea 16. Behind the front epithelium 24, and arranged in the backward direction along the visual axis 14, there is a layer (membrane Bowman 26, 28th root, Descemet 30 membrane and corneal endothelium 32. Of these tissues, the Bowman layer 26 and framework 28 are the most important for the present invention. In particular, the Bowman layer 26 is important because it is very resilient and has a high tensile strength. For this reason, it contributes significantly to maintaining the overall integrity of the cornea 16.

[0022] In the case of methods carried out by the laser unit according to the present invention, the Bowman layer 26 can not be exposed (i.e., weakened). On the other hand, the stem 28 is deliberately weakened. In this case, the root 28 is important because it transfers the intraocular pressure from the aqueous humor in the anterior chamber 18 to the Bowman 26 membrane. Each selective weakening of the stroma 28 will therefore result in a change in the distribution of force in the framework 28. Thus, as provided in the present invention , LIOB in stroma 28 can be effective

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The Bowman layer 26 will then provide a structure holding the transformed cornea 16 that will effectively improve the refractive imperfections.

[0023] Referring now to Fig. 2, it should be noted that an important aspect of the present invention is the operating volume 34, which is defined in the framework 28. Although the operating volume 34 is shown in FIG. 2 in cross-section, this operating volume 34 is in fact three-dimensional, and extends from the front surface 36, located at a distance 38 from the Bowman layer 26, to the posterior surface 40, located at a depth of 0.9T in the cornea 16. Both the front surface 26 and the posterior surface 40 correspond in general to the curvature of the frame 28. In addition, the operating volume 34 extends between the surfaces 36 and 40 through the radial distance 42. In order to more accurately locate the front surface 36 of the operating volume, the distance 38 will be more than about eight micrometers. Thus, the operative volume 34 will extend from a depth of about one hundred micrometers in the cornea 16 (i.e., the distance 38 below the Bowman layer 26) to a depth of about four hundred fifty micrometers (i.e., 0.9T). In addition, the radial distance 42 will be approximately 5.0 millimeters.

[0024] Fig. 3 shows a series of cuts 44 provided in the present invention. As can be seen, the cuts 44a, 44b and 44c are only exemplary, and depending on the needs of the procedure, there may be more or less cuts 44. With this in mind and for the purposes of disclosure, this series will sometimes collectively referred to as incisions 44.

[0025] As shown in Fig. 3, the cuts 44 are made on the respective cylindrical surfaces. Although the incisions 44 are shown as circular cylindrical surfaces, these surfaces may be oval. When the incisions 44 are made in the root 28, it is absolutely important to limit them to the operating volume 34. With this in mind, it is provided that the cuts 44 will be made in the laser process using the laser unit 10. And that this process will cause an induced phenomenon optical disintegration laser (LIOB). In addition, it is important that these cylindrical surfaces are concentric and that they are centered on the axis (e.g., the visual axis 14). In addition, each incision 44 has a forward end 46 and a rear end 48. As can best appreciated by referring to FIG. 3 of FIG. 4, incisions 44 (i.e. round or oval cylindrical surfaces) have a gap 50 between adjacent notches 44. Preferably, this distance 50 is equal to approximately two hundred micrometers. Figure 4 also shows that the front ends 46 of individual single cuts 44 may be axially spaced apart at a distance of 52. Typically, this distance 52 will be about 10 micrometers. Furthermore, the innermost notch 44 (e.g., incision 44a shown in Fig. 4) will be at a radial distance "rc" of about 1 millimeter from the axis of view 14. From another perspective, Fig. 5A shows cuts 44 centered on the axis of view 14, to form a series of rings. In this other perspective, the incisions 44 define together the internal radius "rci" and the external radius "rco". preferably,

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[0026] Alternatively to the notches 44 disclosed above, it is indicated in Figure 3 that only arc segments 54 may be used if desired. In particular, in all material respects, the segments of the arch 54 are identical to the notches 44. The exception, however, is that they are polar limited opposing arcs identified in FIGS. 3 and 5B by the angle α. More specifically, the result is two sets of polar opposing arc segments 54. Preferably, "α" ranges between five degrees and one hundred and sixty degrees.

[0027] An alternative embodiment of the arc segments 54 are the arc segments 54 'shown in Figure 5C. It can be seen that the segments of the arch 54 ', similar to the segments of the arch 54, are polar opposite sets. The arc segments 54 ', however, are centered on respective axes (not shown) that are parallel to each other and equidistant from the visual axis 14.

Fig. 6 shows an illustrative biochemical reaction of the cornea 16 after incisions 44 in the operation volume 34 of the root 28. As stated above, the incisions 44 have the function of weakening the root 28. Consequently, when incisions are made 44 intraocular pressure (indicated by an arrow 56) will result in a change in the force distribution in the cornea 28. This results in bulges 58a and 58b that change the shape from the original cornea 16 to the new configuration of the cornea 16 'represented by dashed lines. In accordance with the aims of the present invention, this correlates the refraction of the cornea 16, which improves vision.

[0029] In addition to the notches 44 disclosed above, the present invention also provides for the formation of a plurality of layers 60, such that in conjunction with the notches 44, correct vision correction is provided. More specifically, as far as the layers 60 are concerned, they are shown in Fig. 7 as formed on substantially flat ring-shaped surfaces that together have the same inner diameter "di" and the same outer diameter "to". It should be noted, however, that deviations from the configurations shown in Fig. 7 are possible. For example, the inner diameter "di" may be zero. In this case, the layers have the shape of a disk. On the other hand, the outside diameter "to" can be as much as 8.0 millimeters. In addition, the outer diameter "to" may vary from the layer 60a, the layer 60b, the layer 60c, etc.

[0030] From another perspective, Figure 8 shows that the layers 60 may be stacked with a separation distance 62 between adjacent layers 60, equal to approximately ten micrometers. As in the incisions 44 disclosed above, each layer 60 has a thickness of approximately one micrometer. As mentioned above, the LIOB energy for the layers 60 will typically be less than the laser energy required to form the incisions 44. In the case of the layers 60, the laser energy for LIOB cuts 44 will be approximately 0.8 micro-ray.

For the purposes of the present invention, different combinations of cuts 44 and layers 60 or only cuts 44 are provided. In particular, examples of the use of cuts 44 and layers 60 can be given to treat specific situations such as myopia, myopia, hyperopia and astigmatism. In detail, in the case of myopia, a series of notches 44 should be used in this treatment. Preferably, the incisions 44 are generally arranged as shown in Figs. 4 and 5A. Furthermore, in the case of hyperopia, there are usually five single incisions 44 that extend from the inner radius of about 1 mm to the external radius.

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At approximately 1.8 mm, with a 200 micrometer gap between adjacent notches 44. If the hyperopia / hyperopia are required for correction, the incisions 44 will then preferably extend further to an outside diameter of about 2.3 mm. In the case of hyperopia, a combination of cylindrical cuts 44 and ring layers 60, as shown in Fig. 9A, can be used. In this case, a series of cuts 44 are spaced apart from the visual axis 14 in the range between the internal radius "rci" (e.g., rci = 1 mm) and the outer radius."rco" (eg rco = 3 mm), with rco> rci, and additionally, the "di" of a series of layers 60 is greater than 2 rco (up to> di> 2rco). In the case of myopia, a combination of cylindrical cuts 44 and ring layers 60, as generally shown in Fig. 9B, can be used. In this case, a series of notches 44 are spaced from the visual axis 14 starting from the radial distance & quot; rc & quot; and a series of layers 60, with a decreasing outer diameter & quot; up to the back, are disposed within the notches 44. More specifically, in this case & quot; di "series of layers 60 may be zero (or very low value), and" to "of each layer 60 in a series of layers 60 may be smaller than 2rc (to <2rc). Finally, in the case of astigmatism, only parts of cylindrical cuts 44 may be used, which form arch segments 54 (see FIGS. 5B and 5C), or in combination with annular layers 60 (see FIG. 9C). In particular, the arc segments 54 of the cylindrical cuts 44 are oriented on a predetermined line 64 that is perpendicular to the axis of view 14. Then, if desired, layers 60 may be formed between the segments of the arch 54 (see FIG. 9C).

In the variations of the methodology described above, the present invention also provides for the formation of radial cuts 66. Radial notches 66a and 66b shown in Fig. 9D are merely exemplary, and are sometimes referred to individually or collectively as radial incisions (incisions) 66. What is important the radial incisions 66 are coplanar with the axis of vision 14, and they are always located in the operating volume 34.

[0033] As shown in Figure 9D, each radial incision 66 is actually determined by the following parameters: the deepest distance in the framework 28, Z (distal), the distance below the Bowman layer 26, Z (proximal), the inner radius, "ri", outer radius "ro" and azimuthal angle "θ" which is measured from baseline 68. By selecting the values ​​of these parameters, each radial incision 66 can be precisely defined. For example, as shown in FIG. 9D, the radial incision 66a is set by the azimuthal angle θ wherein the radial incision 66b has an azimuth angle θ2. Both radial cuts 66a and 66b have the same inner radius "ri" and the same external radius "ro". Z (distal) and Z (proximal) will be determined for radial cuts 66a and 66b in a similar manner,

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