referring initially to fig1 , it will 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 that are less than one picosecond in duration ( i . e . they are femtosecond pulses ). in fig1 , the laser beam 12 is shown being directed along the visual axis 14 and onto the cornea 16 of the eye . also shown in fig1 is the anterior chamber 18 of the eye that is located immediately posterior to the cornea 16 . there is also a lens 20 that is located posterior to both the anterior chamber 18 and the sclera 22 . in fig2 , five ( 5 ) different anatomical tissues of the cornea 16 are shown . the first of these , the epithelium 24 defines the anterior surface of the cornea 16 . behind the epithelium 24 , and ordered in a posterior direction along the visual axis 14 , are bowman &# 39 ; s capsule ( membrane ) 26 , the stroma 28 , descemet &# 39 ; s membrane 30 and the endothelium 32 . of these tissues , bowman &# 39 ; s capsule 26 and the stroma 28 are the most important for the present invention . specifically , bowman &# 39 ; s capsule 26 is important because it is very elastic and has superior tensile strength . it therefore , contributes significantly to maintaining the general integrity of the cornea 16 . for the methods of the present invention , bowman &# 39 ; s capsule 26 must not be compromised ( i . e . weakened ). on the other hand , the stroma 28 is intentionally weakened . in this case , the stroma 28 is important because it transfers intraocular pressure from the aqueous in the anterior chamber 18 to bowman &# 39 ; s membrane 26 . any selective weakening of the stroma 28 will therefore alter the force distribution in the stroma 28 . thus , as envisioned by the present invention , liob in the stroma 28 can be effectively used to alter the force distribution that is transferred through the stroma 28 , with a consequent reshaping of the cornea 16 . bowman &# 39 ; s capsule 26 will then provide structure for maintaining a reshaped cornea 16 that will effectively correct refractive imperfections . while referring now to fig2 , it is to be appreciated that an important aspect of the present invention is the identification of operational volumes 34 which are defined in the stroma 28 . although the operational volumes 34 are shown in cross - section in fig2 , they are actually three - dimensional , and extends from an anterior surface 36 that is located at a distance 38 below bowman &# 39 ; s capsule 26 , to a posterior surface 40 that is located at a distance 41 from the endothelium 32 . both the anterior surface 36 and the posterior surface 40 essentially conform to the curvature of the stroma 28 . for a more exact location of the anterior surface 36 of the operational volumes , the distance 38 will be about ten microns . for the posterior surfaces 40 , the distance 41 will be about one - hundred - fifty microns . in fig3 , incisions 44 a - 44 f are made in a plurality of operational volumes 34 a - 34 f as envisioned for the present invention . although six different volumes 34 a - 34 f are shown in fig3 ( also fig6 d and 6e ) it will be appreciated by the skilled artisan , this is only exemplary and presented here for purposes of disclosure . more specifically , for third order aberrations only three volumes 34 need to be identified . in any event , the exact number of volumes 34 , and their respective radial distances from the visual axis 14 for any specific higher order aberration can be ascertained from the well known zernike polynomials . as shown , for each operational volume 34 a - 34 f , a plurality of incisions 44 ′, 44 ″ and 44 ′″ are made , though there may be more or fewer incisions 44 , depending on the needs of the particular procedure . with this in mind , and for purposes of this disclosure , the plurality in a selected volume 34 will sometimes be collectively referred to as incisions 44 . further , as shown in fig3 , six operational volumes have been identified . however , any number of operational volumes 34 may be used for the present invention . as shown in fig3 , the exemplary incisions 44 for each operational volume 34 are made on respective cylindrical surfaces . although the incisions 44 are shown as circular cylindrical surfaces , these surfaces may be oval . when the plurality of incisions 44 is made in the stroma 28 , it is absolutely essential that it be confined within the respective operational volume 34 . with this in mind , it is envisioned that incisions 44 will be made by a laser process using the laser unit 10 . and , that this process will result in laser induced optical breakdown ( liob ). further , in the illustrated embodiment , it is important these cylindrical surfaces be concentric , and that they are centered on a respective central axis 45 a - 45 f distanced from and parallel to the visual axis 14 . cross - referencing fig3 with fig4 and 5 , it can be seen that each incision 44 has an anterior end 46 and a posterior end 48 . further , the incisions 44 ( i . e . the circular or oval cylindrical surfaces ) have a spacing 50 between adjacent incisions 44 . preferably , this spacing 50 is equal to approximately two hundred microns . fig5 also shows that the anterior ends 46 of respective individual incisions 44 can be displaced axially from each other by a distance 52 . typically , this distance 52 will be around ten microns . further , the innermost incision 44 ( e . g . incision 44 ′″ shown in fig4 ) will be at a radial distance “ r c ” that will be about 1 millimeter from the central axis 45 . from another perspective , fig6 a shows the incisions 44 centered on the central axis 45 to form a plurality of rings . in this other perspective , the incisions 44 collectively establish an inner radius “ r ci ” and an outer radius “ r co ”. preferably , each incision 44 will have a thickness of about two microns , and the energy required to make the incision 44 will be approximately 1 . 2 microjoules . as an alternative to the incisions 44 disclosed above , fig4 indicates that only arc segments 54 may be used , if desired . specifically , in all essential respects , the arc segments 54 are identical with the incisions 44 . the exception , however , is that they are confined within diametrically opposed arcs identified in fig4 and 6b by the angle “ α ”. more specifically , the result is two sets of diametrically opposed arc segments 54 . preferably , “ α ” is in a range between five degrees and one hundred and sixty degrees . an alternate embodiment for the arc segments 54 are the arc segments 54 ′ shown in fig6 c . there it will be seen that the arc segments 54 ′ like the arc segments 54 are in diametrically opposed sets . the arc segments 54 ′, however , are centered on respective axes ( not shown ) that are parallel to each other , and equidistant from the central axis 45 . as an alternative to the incisions 44 disclosed above , fig6 d indicates that incisions 44 may be created to form rectangular cylinders centered on the respective central axes 45 . similarly , fig6 e indicates that the incisions 44 may be created to form crosses centered on the respective central axes 45 . as shown in fig6 d and 6e , the rectangular cylinders and crosses are also aligned with the visual axis 14 . fig7 provides an overview of the bio - mechanical reaction of the cornea 16 when incisions 44 have been made in the operational volume 34 of the stroma 28 . as stated above , the incisions 44 are intended to weaken the stroma 28 . consequently , once the incisions 44 have been made , the intraocular pressure ( represented by arrow 56 ) causes a change in the force distribution within the stroma 28 . this causes bulges 58 a and 58 b that result in a change in shape from the original cornea 16 into a new configuration for cornea 16 ′, represented by the dashed lines . as intended for the present invention , this results in refractive corrections for the cornea 16 that improves vision . while the particular system and method for correcting higher order aberrations with changes in intrastromal biomechanical stress distributions as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated , it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims .
a method for correcting higher order aberrations in an eye requires laser induced optical breakdown of stromal tissue . in detail , the method identifies at least one volume of stromal tissue in the eye , with each volume defining a central axis parallel to the visual axis of the eye . thereafter , a pulsed laser beam is focused to a focal spot in each volume of stromal tissue to cause liob of stromal tissue at the focal spot . further , the focal spot is moved through the volume of stromal tissue to create a plurality of incisions centered about the respective central axis of the volume . as a result , a predetermined selective weakening of the stroma is caused for correction of the higher order aberration .