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 an operational volume 34 which is defined in the stroma 28 . although the operational volume 34 is shown in cross - section in fig2 , this operational volume 34 is 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 depth 0 . 9 t in the cornea 16 . both the anterior surface 36 and the posterior surface 40 essentially conform to the curvature of the stroma 28 . further , the operational volume 34 extends between the surfaces 36 and 40 through a radial distance 42 . for a more exact location of the anterior surface 36 of the operational volume , the distance 38 will be greater than about eight microns . thus , the operational volume 34 will extend from a depth of about one hundred microns in the cornea 16 ( i . e . a distance 38 below bowman &# 39 ; s capsule 26 ) to a depth of about four hundred and fifty microns ( i . e . 0 . 9 t ). further , the radial distance 42 will be approximately 5 . 0 millimeters . fig3 illustrates a plurality of cuts 44 envisioned for the present invention . as shown , the cuts 44 a , 44 b and 44 c are only exemplary , as there may be more or fewer cuts 44 , depending on the needs of the particular procedure . with this in mind , and for purposes of this disclosure , the plurality will sometimes be collectively referred to as cuts 44 . as shown in fig3 , the cuts 44 are made on respective cylindrical surfaces . although the cuts 44 are shown as circular cylindrical surfaces , these surfaces may be oval . when the cuts 44 are made in the stroma 28 , it is absolutely essential they be confined within the operational volume 34 . with this in mind , it is envisioned that cuts 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 , it is important these cylindrical surfaces be concentric , and that they are centered on an axis ( e . g . the visual axis 14 ). further , each cut 44 has an anterior end 46 and a posterior end 48 . as will be best appreciated by cross - referencing fig3 with fig4 , the cuts 44 ( i . e . the circular or oval cylindrical surfaces ) have a spacing 50 between adjacent cuts 44 . preferably , this spacing 50 is equal to approximately two hundred microns . fig4 also shows that the anterior ends 46 of respective individual cuts 44 can be displaced axially from each other by a distance 52 . typically , this distance 52 will be around ten microns . further , the innermost cut 44 ( e . g . cut 44 a shown in fig4 ) will be at a radial distance “ r c ” that will be about 1 millimeter from the visual axis 14 . from another perspective , fig5 a shows the cuts 44 centered on the visual axis 14 to form a plurality of rings . in this other perspective , the cuts 44 collectively establish an inner radius “ r ci ” and an outer radius “ r co ”. preferably , each cut 44 will have a thickness of about two microns , and the energy required to make the cut 44 will be approximately 1 . 2 microjoules . as an alternative to the cuts 44 disclosed above , fig3 indicates that only arc segments 54 may be used , if desired . specifically , in all essential respects , the arc segments 54 are identical with the cuts 44 . the exception , however , is that they are confined within diametrically opposed arcs identified in fig3 and 5b 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 fig5 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 visual axis 14 . fig6 provides an overview of the bio - mechanical reaction of the cornea 16 when cuts 44 have been made in the operational volume 34 of the stroma 28 . as stated above , the cuts 44 are intended to weaken the stroma 28 . consequently , once the cuts 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 . in addition to the cuts 44 disclosed above , the present invention also envisions the creation of a plurality of layers 60 that , in conjunction with the cuts 44 , will provide proper vision corrections . more specifically , insofar as the layers 60 are concerned , fig7 shows they are created on substantially flat annular shaped surfaces that collectively have a same inner diameter “ d i ” and a same outer diameter “ d o ”. it will be appreciated , however , that variations from the configurations shown in fig7 are possible . for example , the inner diameter “ d i ” may be zero . in that case the layers are disk - shaped . on the other hand , the outer diameter “ d o ” may be as much as 8 . 0 millimeters . further , the outer diameter “ d o ” may be varied from layer 60 a , to layer 60 b , to layer 60 c etc . from a different perspective , fig8 shows that the layers 60 can be stacked with a separation distance 62 between adjacent layers 60 equal to about ten microns . like the cuts 44 disclosed above , each layer 60 is approximately one micron thick . as mentioned above , the energy for liob of the layers 60 will typically be less than the laser energy required to create the cuts 44 . in the case of the layers 60 the laser energy for liob of the cuts 44 will be approximately 0 . 8 microjoules . for purposes of the present invention , various combinations of cuts 44 and layers 60 , or cuts 44 only , are envisioned . specifically , examples can be given for the use of cuts 44 and layers 60 to treat specific situations such as presbyopia , myopia , hyperopia and astigmatism . in detail , for presbyopia , a plurality of only cuts 44 needs to be used for this procedure . preferably , the cuts 44 are generally arranged as shown in fig4 and 5a . further , for presbyopia it is typical for there to be five individual cuts 44 that extend from an inner radius of about 1 mm to an outer radius of about 1 . 8 mm , with a 200 micron separation between adjacent cuts 44 . when hyperopia / presbyopia need to be corrected together , the cuts 44 will then preferably extend further to an outer radius of about 2 . 3 mm . for hyperopia , a combination of cylindrical cuts 44 and annular layers 60 can be used as shown in fig9 a . in this case , the plurality of cuts 44 is distanced from the visual axis 14 in a range between and inner radius “ r ci ” ( e . g . r ci = 1 mm ) and an outer radius “ r co ” ( e . g . r co = 3 mm ), wherein r co & gt ; r ci , and further wherein “ d i ” of the plurality of layers 60 is greater than 2r co ( d o & gt ; d i & gt ; 2r co ). for myopia , a combination of cylindrical cuts 44 and annular layers 60 can be used as generally shown in fig9 b . in this case a plurality of cuts 44 is distanced from the visual axis 14 beginning at a radial distance “ r c ”, and a plurality of layers 60 , with decreasing outer diameter “ d o ” in a posterior direction , is located inside the cuts 44 . more specifically , for this case “ d i ” of the plurality of layers 60 can be zero ( or exceedingly small ), and “ d o ” of each layer 60 in the plurality of layers 60 can be less than 2r c ( d o & lt ; 2r c ). and finally , for astigmatism , the portions of cylindrical cuts 44 that form arc segments 54 can be used alone ( see fig5 b and 5c ), or in combination with annular layers 60 ( see fig9 c ). specifically arc segments 54 of cylindrical cuts 44 are oriented on a predetermined line 64 that is perpendicular to the visual axis 14 . layers 60 can then be created between the arc segments 54 , if desired ( see fig9 c ). in a variation of the methodologies noted above , the present invention also envisions the creation of radial cuts 66 . the radial cuts 66 a and 66 b shown in fig9 d are only exemplary , and are herein sometimes referred to individually or collectively as radial cut ( s ) 66 . importantly , the radial cuts 66 are coplanar with the visual axis 14 , and they are always located within the operational volume 34 . as shown in fig9 d , each radial cut 66 is effectively defined by the following parameters : a deepest distance into the stroma 28 , z ( distal ) , a distance below bowman &# 39 ; s capsule 26 , z ( proximal ) , an inner radius , “ r i ”, an outer radius “ r o ”, and an azimuthal angle “ θ ” that is measured from a base line 68 . by setting values for these parameters , each radial cut 66 can be accurately defined . for example , as shown in fig9 d , the radial cut 66 a is established by the azimuthal angle θ 1 , while the radial cut 66 b has an azimuthal angle θ 2 . both of the radial cuts 66 a and 66 b have the same inner radius “ r i ” and the same outer radius “ r o ”. the z ( distal ) and z ( proximal ) will be established for the radial cuts 66 a and 66 b in a similar manner as described above for the cylindrical cuts 44 . while the particular method for intrastromal refractive surgery 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 performing intrastromal ophthalmic laser surgery requires laser induced optical breakdown of stromal tissue without compromising bowman &# 39 ; s capsule . in detail , the method creates cuts in the stroma over all , or portions of , a plurality of concentric cylindrical surfaces . importantly , these cuts are all centered on the visual axis of the patient &# 39 ; s eye . in accordance with the present invention , cuts can be made either alone or in conjunction with the removal of predetermined volumes of stromal tissue . the actual location of cuts in the surgery will depend on whether the treatment is for presbyopia , myopia , hyperopia or astigmatism .