Abstract:
A system and method are provided for treating VitreoRetinal-Interface Syndromes (VRS) by using a femtosecond laser system to relieve vitreoretinal adhesions in an eye. Operationally, fibers in the vitreous body are severed by the laser system to create Posterior Vitreous Detachments (PVD) that relieve the adhesions. In a first embodiment for the present invention, tissue material on selected planes within the vitreous body is photoaltered to sever the fibers. Sequentially, or alternatively, to the first embodiment, in another embodiment, fibers at or near the vitreoretinal interface of the eye are photoaltered for this same purpose.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to systems and methods for performing ophthalmic surgical procedures using laser devices. More particularly, the present invention pertains to systems and methods for treating vitreous/retinal adhesions in the vitreous cavity of an eye. The present invention is particularly, but not exclusively, useful as a system and method for severing fibers in the vitreous cavity to relieve tension (traction) forces on the retina, to thereby prevent retinal detachments. 
       BACKGROUND OF THE INVENTION 
       [0002]    The retina is a sensory membrane that lines the inner eye at the back of the eye. The retina includes several layers. One such layer includes millions of rods and cones. In their combination, the rods and cones function to convert light that is focused on the retina into signals which are then transmitted to the brain by way of the optic nerve. In terms of size, the retina covers about 65 percent of the interior surface of the eye and includes the macula near its center. A dimple called the fovea is formed in the macula which includes cones, but not rods. Functionally, the macula and fovea provide the ability for a person to see fine details. This is an important portion of a person&#39;s vision, and is often referred to as central vision. 
         [0003]    Inside the eye, the vitreous humor is a clear, viscous, gel-like material that fills the void in the eye between the retina and the crystalline lens. Embryologically, the vitreous serves as a scaffold for ocular development. After the first few decades of life, however, the vitreous gel starts to degenerate. With this degeneration, changes to the gelatinous nature of the vitreous body occur. In particular, as a person ages, the vitreous body can decompose or liquefy, and fibers can develop in the vitreous body. In turn, this aging process can cause the vitreous humor to undergo anomalous or partial separation from the retinal surface. When this happens, fibers in the vitreous body which have become attached to the retina are able to pull on various retinal structures in tangential, as well as anterior-posterior, directions. Vitreous pockets (enclosures) can then develop and fiber elements in these pockets will consequently exert traction forces on areas of the retinal surface. Anomalous posterior vitreous separation with residual traction on the optic disc or macula, as well as resultant fluid currents from ocular saciacic movements, can lead to a group of disorders which are collectively termed VitreoRetinal-Interface Syndromes (VRS). These include but are not limited to: epiretinal membrane, lamellar macular hole, full thickness macular hole, vitreopapillary and vitreomacular traction syndromes, symptomatic vitreomacular adhesion, peripheral retinal tears, vitreous hemorrhage from shearing or avulsing of retinal blood vessels and retinal detachment. 
         [0004]    In the context of the present invention, the membranes at the interface between the vitreous humor and the retina are of particular concern. Respectively, these membranes are the cortex of the vitreous (i.e. cortical vitreous) and the Internal Limiting Membrane (ILM). As an anatomical structure, the cortex of the vitreous surrounds the vitreous humor, and it has a thickness that is in the range of 20-50 microns. It functions as a so-called “sac” which borders and defines the body of the vitreous humor. The ILM, on the other hand, overlies the retina in juxtaposition with the cortex of the vitreous. 
         [0005]    Anatomically, the ILM is a relatively thin layer of tissue with a thickness of slightly more than 10-20 microns and, importantly, it does not contribute to the optical functionality of the retina. Normally, at their interface, the cortex of the vitreous and the ILM do not exert friction or traction forces on each other. With this in mind, however, the concern for the present invention arises when the cortex of the vitreous and the ILM adhere (i.e. attach or stick) to each other. 
         [0006]    From an optical perspective, image perception by an eye relies on light that enters through the pupil and crystalline lens. This light is focused by the crystalline lens, and passes through the vitreous humor to be incident on the retina of the eye. An important portion of this focused light is directed onto the macula and the retinal tissue immediately surrounding the macula. As a practical matter, this light contributes most to the imaging capability of the eye. It will pass through the vitreous humor and be confined within what is hereinafter defined as an optical channel. 
         [0007]    For purposes of the present invention, the optical channel will be generally cylindrical-shaped. It will have a cross-section diameter of greater than about 5 mm, and it will extend from the posterior surface of the crystalline lens to the ILM of the retina. Safety margins can be included with the optical channel and appropriately established around the optical channel. 
         [0008]    In light of the above, it is an object of the present invention to provide a system and method for severing vitreous fibers that are attached to the retinal surface, to thereby prevent or alleviate the traction forces that cause VitreoRetinal-Interface Syndromes (VRS). Another object of the present invention is to provide a system and method for using a pulsed femtosecond laser to sever fibers in the vitreous humor. Still another object of the present invention is to provide interventional treatments for VRS that are easy to use, are simple to implement and are comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0009]    In general, the purpose of the present invention is to provide a method, a system, and a set of executable instructions stored on a computer medium which will effectively eliminate traction forces that may develop between the vitreous humor and the retina. These forces can result for any of several reasons and can cause a variety of conditions, collectively referred to as VitreoRetinal-Interface Syndromes (VRS). For example, a detached retina is a VRS. As implied above, VRS conditions typically result from traction forces that are generated at the interface between the vitreous humor and the retina. 
         [0010]    As envisioned for the present invention, traction forces resulting from vitreoretinal adhesions can be eliminated in either of several ways. For one, local areas of adhesion at the interface between the cortical vitreous and the Internal Limiting Membrane (ILM) of the retina can be directly photoablated by Laser Induced Optical Breakdown (LIOB) to remove the adhesive tissues. For another, fibers that form in the vitreous humor, and that pull on the retina to cause or aggravate VRS, can be severed by creating LIOB cutting planes in the vitreous humor. Further, bubbles which are formed in the vitreous humor during LIOB in the above-mentioned methodologies will coalesce into larger bubbles with high surface tension. These larger bubbles can then be further manipulated to facilitate release of residual vitreoretinal adhesion sites to thereby improve the efficacies of these methodologies. 
         [0011]    Structurally, a system for severing fibers in the vitreous humor by LIOB includes a laser unit and a control unit for moving the focal point of a laser beam within the gelatinous material. In this combination, an imaging unit is provided for creating an anatomical profile of the vitreous humor of the eye. In particular, this anatomical profile will show the relationship of the vitreous humor with both the crystalline lens and the retina of the eye. Also included here is a programming unit that uses parameters obtained from the anatomical profile to define a laser pathway through the vitreous humor for use during the LIOB that is to be performed. A computer, which is connected in combination with both the imaging unit and the programming unit, obtains information respectively from these units regarding the anatomical profile and the pathway. The computer then uses this information for collective use in creating a control input to the laser unit. The control input is then transmitted to the laser unit, which, in response, generates a laser beam and moves the focal point of the laser beam along the pathway to perform the intended LIOB. 
         [0012]    In detail, for one embodiment of the present invention, fibers that extend into the vitreous humor can be severed to relieve tension forces on the retina to prevent or reverse VRS. For this aspect of the present invention, a method for severing fibers can begin by first defining an optical channel that is characterized by an identified axis extending through the gelatinous material. For this purpose, the identified axis can be a visual axis, an optical axis, a central axis, or some other axis well known in the pertinent art which is anatomically oriented on the eye. Based on the selected axis, the optical channel is established to extend through the vitreous humor. Further, the optical channel is substantially cylindrical, or cone-shaped, and it extends radially outward to a distance r from the axis. Typically, r will be greater than about 5 mm. Preferably, the optical channels will overlie the macula for vitreomacular disorder but other channels will be defined to overlie (i.e. cover) the macula of the retina of the eye. Channels, along different axes, may be necessary to treat peripheral diseases. 
         [0013]    With the optical channel defined, the method for severing fibers can include the step of establishing a first plane (or a plurality of mutually parallel first planes) in the gelatinous material that is/are oriented substantially perpendicular to the axis. Also, the method includes the step of establishing a second plane (or a plurality of mutually parallel second planes) in the gelatinous material that is/are oriented substantially parallel to the axis. Typically, the first and second planes are formed in a sequence so gas bubbles which are induced by LIOB do not interfere with the laser pattern. Next, material in the first and second planes is selectively photoablated to sever fibers in the gelatinous material. 
         [0014]    For another embodiment of the present invention, a localized area of vitreoretinal adhesion is identified in the back of the eye. Specifically, the area of adhesion will typically be at the interface between the vitreous humor and the ILM of the retina (i.e. the vitreoretinal interface). Based on the location of the adhesion, a Target Tissue Volume (TTV) is identified that includes both a portion of the cortex of the vitreous and a portion of the ILM that are juxtaposed with each other in the area of vitreoretinal adhesion. In detail, the TTV will have a posterior surface that is located in the tissue of the adhesion and is oriented substantially parallel to the vitreoretinal interface. Further, the posterior surface of the TTV is located within a predetermined distance from the vitreoretinal interface. 
         [0015]    Preferably, the posterior surface of the TTV can be located anterior to the vitreoretinal interface. It can happen, however, that the posterior surface will need to be located within the ILM of the retina, posterior to the vitreoretinal interface. In this latter case, the posterior surface of the TTV will still be oriented substantially parallel to the vitreoretinal interface. Further, in order to avoid delicate cellular elements of the retina, it will be important that the layer of ILM which is included in the TTV be less than approximately ten microns thick. As envisioned for the present invention, the location and orientation of the anterior surface of the TTV is discretionary. 
         [0016]    Once the Target Tissue Volume (TTV) has been defined, a laser pathway is appropriately defined through the TTV. Photoablation of target tissue along the pathway in this volume will then eliminate the vitreoretinal adhesion in the localized area. As implied above, any bubbles that result from this protocol can be subsequently manipulated to enhance the efficacy of the protocol. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0018]      FIG. 1  is a schematic presentation of the operative components of the present invention; 
           [0019]      FIG. 2  is a cross-section view of an eye showing fibers extending from the back of the eye into the vitreous humor; 
           [0020]      FIG. 3  is a perspective view of a photoablation pattern for use with the system and methodology of the present invention; 
           [0021]      FIG. 4  is a top plan view of the photoablation pattern of  FIG. 3 ; 
           [0022]      FIG. 5  is a perspective view of an alternate photoablation pattern for use with the system and methodology of the present invention; 
           [0023]      FIG. 6  is a top plan view of the photoablation pattern of  FIG. 5 ; 
           [0024]      FIG. 7  is a cross-section view of an eye showing a vitreoretinal adhesion; 
           [0025]      FIG. 8  is a plan view of a portion of the fundus of the eye enclosed within the line  8 - 8  in  FIG. 7 ; 
           [0026]      FIG. 9A  is a cross-section view of the fundus of the eye shown in  FIG. 7 , as seen along the line  9 - 9  in  FIG. 8 , showing a Target Tissue Volume (TTV) with its posterior surface anterior to the vitreoretinal interface; 
           [0027]      FIG. 9B  is a cross-section view of the fundus of the eye shown in  FIG. 7 , as seen along the line  9 - 9  in  FIG. 8 , showing a Target Tissue Volume (TTV) with its posterior surface established within the Internal Limiting Membrane (ILM) of the retina, posterior to the vitreoretinal interface; 
           [0028]      FIG. 9C  is a cross-section view of the fundus of the eye shown in  FIG. 9A  or  FIG. 9B  after a Posterior Vitreous Detachment (PVD) has developed; and 
           [0029]      FIG. 10  is an operational flow chart for use with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring initially to  FIG. 1 , a system in accordance with the present invention is shown and is generally designated  10 . As shown, the system  10  includes a laser unit  12 , and an imaging unit  14 , that are each respectively positioned for optical interaction with an eye  16 . More specifically, the laser unit  12  and the imaging unit  14  are positioned to direct their respective light beams along an axis  18 . 
         [0031]    For the present invention, the axis  18  is defined relative to selected anatomical features of the eye  16 , and it will normally be a reference base that is well known in the pertinent art, such as a visual axis, a central axis or an optical axis. The laser unit  12  may also be of a type that is well known in the pertinent art and is capable of generating a pulsed femtosecond laser beam  20  (i.e. a beam having a sequence of laser pulses with ultra-short pulse durations [e.g. less than approximately 500 fs]). In particular, a laser beam  20  capable of passing through tissue to a subsurface focal point to perform Laser Induced Optical Breakdown (LIOB) of subsurface tissues in the eye  16  is to be used. In addition, the laser unit  12  can include a beam steering component for moving the focal spot of the laser beam  20  along a selected path to photoablate target tissue via LIOB. For example, the beam steering component can include a pair of mirrors (not shown) mounted on respective tip-tilt actuators to steer the laser beam  20  in respective, orthogonal directions. Further, the imaging unit  14  is typically of a type that is capable of creating a three-dimensional image of anatomical features in the eye  16 , such as an Optical Coherence Tomography (OCT) imaging system, or any other suitable imaging device that is well known in the pertinent art such as a Scheimpflug device, a confocal imaging device, an optical range-finding device, an ultrasound device or a two-photon imaging device. 
         [0032]      FIG. 1  also shows that the system  10  includes a computer  22  which is electronically connected with the imaging unit  14  and with the laser unit  12 . A programming unit  24 , which is electronically connected between the imaging unit  14  and the computer  22 , is also included. In detail, the computer  22  receives input from both the imaging unit  14  and the programming unit  24 , and it uses this input to control the laser unit  12  in accordance with a predetermined protocol. The programming unit  24  can include non-transitory, computer-readable medium (e.g. persistent memory) having executable instructions stored thereon that direct the computer  22  to perform the processes described herein. 
         [0033]    Referring now to  FIG. 2 , several pertinent structures in the eye  16  are identified including the cornea  26 , the sclera  28 , the lens  30 , the vitreous humor  32 , the retina  34  and the macula  36 . Together, the sclera  28  and retina  34  establish a container that holds the vitreous humor  32 .  FIG. 2  also shows that a plurality of fine fibers  38  extend from the macula  36  and into the vitreous humor  32 . As explained above, these fibers  38  can create traction forces on the retina  34  that can cause the vitreous humor  32  to pull on the retina  34 . 
         [0034]    Continuing with reference to  FIG. 2 , an optical channel  40  is shown extending through the vitreous humor  32 . As indicated above, the optical channel  40  is defined in its relationship with the axis  18 . In detail, the optical channel  40  is substantially cylindrical shaped, and it is characterized by a variable radius r that extends radially outward from the axis  18 . Typically, r will be greater than about 5 mm, and the optical channel  40  will be formed with a slightly increasing or decreasing taper as it extends in a posterior direction. With these dimensional characteristics, the optical channel  40  is established to extend through the vitreous humor  32 . As shown, the optical channel  40  extends from the crystalline lens  30  of the eye  16  to the retina  34  of the eye  16  and covers (i.e. overlies), the macula  36  of the retina  34  with possible extension to the retinal periphery. 
         [0035]    For an operation of the system  10  of the present invention, the imaging unit  14  is first used to create an anatomical profile of the vitreous humor  32  of the eye  16 . Specifically, this anatomical profile identifies the dimensional relationship between the crystalline lens  30  and the retina  34  of the eye  16 . The programming unit  24 , which is electronically connected to the imaging unit  14 , is used to locate the optical channel  40  in the vitreous humor  32 . Once the optical channel  40  has been defined and located in the eye  16 , the programming unit  24  defines pathway(s) (not shown) through the portion of the vitreous humor  32  that may be inside or outside the optical channel  40 . Importantly, the pathway(s) is/are detailed according to parameters obtained from the anatomical profile that have been created by the imaging unit  14 . 
         [0036]    As noted above, the computer  22  is connected to the imaging unit  14 , and to the programming unit  24 . With these connections, the computer  22  obtains the necessary information regarding the anatomical profile and the pathway(s) that is/are required to create a control input for the laser unit  12 . Operationally, this control input is then used by the laser unit  12  to generate the laser beam  20 . The computer  22  also uses this control input for moving a focal point of the laser beam  20  along the pathway(s) in the vitreous humor  32 . Specifically, all of this is done in accordance with the control input to operate the laser unit  12  for severing fibers  38  in the vitreous humor  32  without substantially disturbing the retina  34 . 
         [0037]    In more detail, as best appreciated by cross-referencing  FIGS. 2 and 3 , the method for severing fibers  38  can include the step of establishing one or more first planes  42 ,  42 ′ in the vitreous humor  32  that is/are oriented substantially perpendicular to the axis  18 . Also, as shown, the method includes the step of establishing one or more second planes  44 ,  44 ′ (see  FIG. 4  and description below) in the vitreous humor  32 . As shown, the second planes  44 ,  44 ′ are either oriented substantially parallel to the axis  18 , or they will intersect with the axis  18 . In  FIG. 3  it is shown that for an optional arrangement, the first plane  42  can be formed with a hole  46  to avoid intersection with the optical channel  40  (shown in  FIGS. 1 and 2 ). For this arrangement the second plane  44  can include a pair of mutually coplanar sections  44   a ,  44   b  which are arranged to straddle the optical channel  40  (see  FIG. 2 ). In this case the sections  44   a  and  44   b  are coplanar with the axis  18 . 
         [0038]      FIG. 4  shows an arrangement having a first plane  42  formed with a hole  46  and a pair of second planes  44 ,  44 ′ with second plane  44  positioned at a selected angle, θ, relative to axis  18 , to second plane  44 ′. It will be appreciated that this arrangement of planes  44 ,  44 ′ will also pertain without the hole  46 . 
         [0039]      FIGS. 5 and 6  illustrate an arrangement in which fibers  38  ( FIG. 2 ) are severed on a first plane  42  and four second planes  44 ,  44 ′,  44 ″,  44 ′″. 
         [0040]    Once defined, material in the first plane(s)  42 ,  42 ′ ( FIG. 2 ) and material in the second plane(s)  44 ,  44 ′,  44 ″,  44 ′″ ( FIGS. 4 and 5 ) is selectively photoablated to sever fibers  38  in the vitreous humor  32 . Specifically, this can be done by moving the focal point of a laser beam  20  ( FIG. 1 ) along a pathway(s) within the first plane(s)  42 ,  42 ′ and second plane(s)  44 ,  44 ′,  44 ″,  44 ′″ to sever the fibers  38 . 
         [0041]    In another aspect of the present invention, it is understood that an adhesion  50  will sometimes form at the vitreoretinal interface  52  between the vitreous humor (vitreous body)  32  and the retina  34 . Such an adhesion  50  may form for any of several reasons, and they are collectively referred to in the medical art as VitreoRetinal-Interface Syndromes (VRS). In the event, their common characteristic is that the adhesion  50  will create traction forces on the retina  34  that may eventually lead to damage or detachment of the retina  34 . As indicated in  FIG. 7 , adhesions  50  occur in the back of the eye  16  and, as shown in  FIG. 8 , they can be extensive. In detail, the anatomical consequences of an adhesion  50  at the vitreoretinal interface  52  will perhaps be best appreciated with reference to  FIG. 9A . 
         [0042]      FIG. 9A  shows that the vitreoretinal interface  52  is established by the cortex  54  of the vitreous body  32  (a.k.a. the cortical vitreous) and the Internal Limiting Membrane (ILM)  56  of the retina  34 . Anatomically, the cortex  54  functions as a so-called “sac” for the vitreous body  32  and it varies in thickness through a range of about 20 μm to 50 μm. On the other hand, the thickness  58  of the ILM  56  is less than around 20 μm. 
         [0043]    It is an important object for the present invention that tissue in the adhesion  50  of a VRS be photoablated for the purpose of separating the cortex  54  from the ILM  56 . Specifically, this photoablation needs to be accomplished before traction forces in the adhesion  50  are able to somehow damage the retina  34 . The intended result here is the creation of a Posterior Vitreous Detachment (PVD)  60  such as the one shown in  FIG. 9C . In particular, the consequence of creating a PVD  60  is to sever fibers  38  that can form in the adhesion  50 , and to thereby relieve traction forces on the retina  34  that could otherwise damage the retina  34 . 
         [0044]    Operationally, in accordance with the present invention, a PVD  60  can be initiated or developed by first defining a Target Tissue Volume (TTV)  62 . Importantly, the TTV  62  will be defined with a posterior surface  64  that is located in the adhesion  50  and is oriented substantially parallel to the vitreoretinal interface  52 . As envisioned for the present invention, the posterior surface  64  can extend completely across the extent of the adhesion  50  (see  FIG. 8 ). On the other hand, the anterior surface  66  of the TTV  62  is somewhat indefinite and is essentially discretionary.  FIGS. 9A and 9B  indicate that, depending on the nature of the adhesion  50 , and the depth to which fibers  38  have penetrated into the ILM  56  of the retina  34 , the exact location of the posterior surface  64  of the TTV  62  may be varied. Specifically, in  FIG. 9A , a situation is shown wherein the posterior surface  64  of the TTV  62  is established at a distance d a  in the anterior direction from the vitreoretinal interface  52 . On the other hand, in  FIG. 9B , a situation is shown wherein the posterior surface  64  of the TTV  62  is established at a distance d p  in the posterior direction from the vitreoretinal interface  52 . In either case, the purpose is to photoablate tissue on the posterior surface  64  of the TTV  62  and thereby create a PVD  60  (see  FIG. 9C ), whereby the cortex  54  (vitreous body  32 ) is separated from the ILM  56  (retina  34 ) to prevent adverse traction forces from acting on the retina  34 . 
         [0045]    An operation of the present invention is perhaps best appreciated with reference to the operational flow chart which is shown in  FIG. 10  and generally designated  70 . In  FIG. 10  it will be seen that after the start of a medical protocol (procedure) for the treatment of a VRS, block  72  of the chart  70  indicates that the first task to be accomplished is the identification of an adhesion  50 . As envisioned for the present invention, the identification of an adhesion  50  will be accomplished essentially by the imaging unit  14 . Once an adhesion  50  has been identified, inquiry block  74  then queries whether Laser Induced Optical Breakdown (LIOB) of the vitreous body  32  is required. If so, inquiry block  76  allows for the continued LIOB of tissue in the adhesion  50  to the extent necessary for a proper performance of tissue photoablation in the vitreous body  32 . 
         [0046]    In the event that LIOB in the vitreous body  32  is either not necessary (inquiry block  74 ), or requires augmentation (inquiry block  76 ), block  78  indicates a Target Tissue Volume (TTV)  62  needs to be defined. As envisioned for the present invention, the definition of the TTV  62  is essentially accomplished by the programming unit  24 , using anatomical parameters pertinent to the vitreoretinal interface  52 , the cortex  54  of the vitreous body  32 , and the Internal Limiting Membrane (ILM)  56  of the retina  34 , as disclosed above. Once the TTV  62  has been defined, block  80  indicates that LIOB is to be performed within the TTV  62 . 
         [0047]    As set forth in chart  70 , and indicated by block  80 , LIOB in the TTV  62  is performed for the specific purpose of creating a Posterior Vitreous Detachment (PVD)  60 . Inquiry block  82  then indicates that the development of a PVD  60  is monitored. This monitoring may be done either visually, electronically (e.g. by using the imaging unit  14 ) or by a combination of both. If a PVD  60  has developed, the inquiry block  84  proceeds further to question whether continued LIOB in the TTV  62  is necessary. If not, the protocol is stopped. On the other hand, when no PVD  60  has yet developed, inquiry block  86  questions whether time has expired. This is a precautionary action that is taken to prevent, or limit, undue exposure of tissue to the photoablation effects of LIOB. When the procedure time has expired, inquiry block  88  indicates that the options are either to wait for at least an additional twenty-four hours before resuming the procedure, or to simply stop the procedure. 
         [0048]    While the particular Interventional Treatments for VitreoRetinal-Interface Syndromes as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended as to the details of construction or design herein shown other than as described in the appended claims.