Abstract:
An ocular implant adapted to be disposed within Schlemm&#39;s canal of a human eye with a body extending along a curved longitudinal central axis in a curvature plane, a first strut on one side of the implant and a second strut on an opposite side of the implant, the circumferential extent of the first strut with respect to the plane of curvature being greater than the circumferential extent of the second strut with respect to the plane of curvature. The invention also includes methods of using the implant.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119 of U.S. Patent Appl. No. 61/730,895, filed Nov. 28, 2012, the entirety of which is incorporated by reference. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
       FIELD 
       [0003]    The present disclosure relates generally to devices that are implanted within the eye. More particularly, the present disclosure relates to systems, devices and methods for delivering ocular implants into the eye. 
       BACKGROUND 
       [0004]    According to a draft report by The National Eye Institute (NEI) at The United States National Institutes of Health (NIH), glaucoma is now the leading cause of irreversible blindness worldwide and the second leading cause of blindness, behind cataract, in the world. Thus, the NEI draft report concludes, “it is critical that significant emphasis and resources continue to be devoted to determining the pathophysiology and management of this disease.” Glaucoma researchers have found a strong correlation between high intraocular pressure and glaucoma. For this reason, eye care professionals routinely screen patients for glaucoma by measuring intraocular pressure using a device known as a tonometer. Many modern tonometers make this measurement by blowing a sudden puff of air against the outer surface of the eye. 
         [0005]    The eye can be conceptualized as a ball filled with fluid. There are two types of fluid inside the eye. The cavity behind the lens is filled with a viscous fluid known as vitreous humor. The cavities in front of the lens are filled with a fluid know as aqueous humor. Whenever a person views an object, he or she is viewing that object through both the vitreous humor and the aqueous humor. 
         [0006]    Whenever a person views an object, he or she is also viewing that object through the cornea and the lens of the eye. In order to be transparent, the cornea and the lens can include no blood vessels. Accordingly, no blood flows through the cornea and the lens to provide nutrition to these tissues and to remove wastes from these tissues. Instead, these functions are performed by the aqueous humor. A continuous flow of aqueous humor through the eye provides nutrition to portions of the eye (e.g., the cornea and the lens) that have no blood vessels. This flow of aqueous humor also removes waste from these tissues. 
         [0007]    Aqueous humor is produced by an organ known as the ciliary body. The ciliary body includes epithelial cells that continuously secrete aqueous humor. In a healthy eye, a stream of aqueous humor flows out of the anterior chamber of the eye through the trabecular meshwork and into Schlemm&#39;s canal as new aqueous humor is secreted by the epithelial cells of the ciliary body. This excess aqueous humor enters the venous blood stream from Schlemm&#39;s canal and is carried along with the venous blood leaving the eye. 
         [0008]    When the natural drainage mechanisms of the eye stop functioning properly, the pressure inside the eye begins to rise. Researchers have theorized prolonged exposure to high intraocular pressure causes damage to the optic nerve that transmits sensory information from the eye to the brain. This damage to the optic nerve results in loss of peripheral vision. As glaucoma progresses, more and more of the visual field is lost until the patient is completely blind. 
         [0009]    In addition to drug treatments, a variety of surgical treatments for glaucoma have been performed. For example, shunts were implanted to direct aqueous humor from the anterior chamber to the extraocular vein (Lee and Scheppens, “Aqueous-venous shunt and intraocular pressure,”  Investigative Ophthalmology  (February 1966)). Other early glaucoma treatment implants led from the anterior chamber to a sub-conjunctival bleb (e.g., U.S. Pat. No. 4,968,296 and U.S. Pat. No. 5,180,362). Still others were shunts leading from the anterior chamber to a point just inside Schlemm&#39;s canal (Spiegel et al., “Schlemm&#39;s canal implant: a new method to lower intraocular pressure in patients with POAG?”  Ophthalmic Surgery and Lasers  (June 1999); U.S. Pat. No. 6,450,984; U.S. Pat. No. 6,450,984). 
       SUMMARY OF THE DISCLOSURE 
       [0010]    A cannula for delivering an ocular implant into Schlemm&#39;s canal of an eye is provided, comprising a rigid curved tube adapted to extend through an anterior chamber of the eye to achieve tangential entry into Schlemm&#39;s canal, a trough portion formed by an opening extending along a distal portion of the rigid curved tube, and an asymmetric tip disposed at a distal end of the trough portion, the asymmetric tip being located at an intersection between an upper camming surface and a lower camming surface, the upper camming surface being configured to contact scleral tissue of the eye to guide the trough portion into Schlemm&#39;s canal, the lower camming surface being configured to contact a scleral spur of the eye to guide the trough portion into Schlemm&#39;s canal. 
         [0011]    In some embodiments, the asymmetric tip is configured to not pierce the scleral tissue. In other embodiments, the asymmetric tip is configured to pierce the trabecular meshwork. In some embodiments, the asymmetric tip is formed by the upper camming surface being shorter than the lower camming surface. 
         [0012]    In one embodiment, the rigid curved tube and the trough portion define a path for directing the ocular implant from a location outside of the eye to a location within Schlemm&#39;s canal of the eye. 
         [0013]    In some embodiments, the asymmetric tip is sufficiently blunt to slide along an outer wall of Schlemm&#39;s canal without cutting the scleral tissue underlying the outer wall of Schlemm&#39;s canal. 
         [0014]    In one embodiment, the asymmetric tip has an asymmetric V-shape. 
         [0015]    In some embodiments, the cannula is shaped and dimensioned so that at least part some of the trough portion can be advanced into Schlemm&#39;s canal while a first portion of the rigid curved tube is disposed inside the anterior chamber and a second portion of the rigid curved tube is extended through an incision in the eye to a location outside of the eye. 
         [0016]    An ocular implant and delivery system is also provided, comprising a rigid curved cannula adapted to extend through an anterior chamber of an eye to achieve tangential entry into Schlemm&#39;s canal of the eye, a trough portion formed by an opening extending along a distal portion of the rigid curved cannula, an ocular implant configured to be carried inside the rigid curved cannula and advanced distally through the rigid curved cannula and along the trough portion into Schlemm&#39;s canal, and an asymmetric tip disposed at a distal end of the trough portion, the asymmetric tip being located at an intersection between an upper camming surface and a lower camming surface, the upper camming surface being configured to contact scleral tissue of the eye to guide the trough portion into Schlemm&#39;s canal, the lower camming surface being configured to contact a scleral spur of the eye to guide the trough portion into Schlemm&#39;s canal. 
         [0017]    In some embodiments, the asymmetric tip is configured to not pierce the scleral tissue. In other embodiments, the asymmetric tip is configured to pierce the trabecular meshwork. In some embodiments, the asymmetric tip is formed by the upper camming surface being shorter than the lower camming surface. 
         [0018]    In one embodiment, the rigid curved tube and the trough portion define a path for directing the ocular implant from a location outside of the eye to a location within Schlemm&#39;s canal of the eye. 
         [0019]    In some embodiments, the asymmetric tip is sufficiently blunt to slide along an outer wall of Schlemm&#39;s canal without cutting the scleral tissue underlying the outer wall of Schlemm&#39;s canal. 
         [0020]    In one embodiment, the asymmetric tip has an asymmetric V-shape. 
         [0021]    In some embodiments, the cannula is shaped and dimensioned so that at least part some of the trough portion can be advanced into Schlemm&#39;s canal while a first portion of the rigid curved tube is disposed inside the anterior chamber and a second portion of the rigid curved tube is extended through an incision in the eye to a location outside of the eye. 
         [0022]    In some embodiments, the rigid curved cannula and the trough portion define a path for directing the ocular implant from a location outside of the eye to a location within Schlemm&#39;s canal of the eye. 
         [0023]    In another embodiment, the asymmetric tip is sufficiently blunt to slide along an outer wall of Schlemm&#39;s canal without cutting the scleral tissue underlying the outer wall of Schlemm&#39;s canal. 
         [0024]    In some embodiments, the asymmetric tip has an asymmetric V-shape. 
         [0025]    In another embodiment, the rigid curved cannula is shaped and dimensioned so that at least part some of the trough portion can be advanced into Schlemm&#39;s canal while a first portion of the rigid curved cannula is disposed inside the anterior chamber and a second portion of the rigid curved cannula is extended through an incision in the eye to a location outside of the eye. 
         [0026]    A cannula for delivering an ocular implant into Schlemm&#39;s canal of an eye is also provided, comprising a rigid body having a distal curved portion adapted to gain tangential entry into Schlemm&#39;s canal, a lumen extending from a proximal end of the body through at least part of the distal curved portion, the lumen being adapted to contain the ocular implant, a trough formed in the distal curved portion, the trough being defined by an opening along the body that provides access to a concave inner surface, and a distal tip at a distal end of the trough, the distal tip being in a position offset from a central axis of the trough. 
         [0027]    In some embodiments, the distal tip is formed at an intersection between an upper camming surface and a lower camming surface. In one embodiment, the upper camming surface is smaller than the lower camming surface. 
         [0028]    In some embodiments, the distal tip is sufficiently blunt to slide along an outer wall of Schlemm&#39;s canal without cutting scleral tissue underlying the outer wall of Schlemm&#39;s canal. 
         [0029]    A method of inserting an ocular implant into Schlemm&#39;s canal of an eye is provided, the method comprising inserting a curved cannula having a distal trough portion through an anterior chamber of the eye to gain tangential entry of the trough portion into Schlemm&#39;s canal, allowing an upper camming surface of a distal tip of the distal trough portion to contact scleral tissue of the eye to guide the distal trough portion into Schlemm&#39;s canal, allowing a lower camming surface of the distal tip of the distal trough portion to contact a scleral spur of the eye to guide the distal trough portion into Schlemm&#39;s canal, and advancing an ocular implant through the curved cannula and along the distal trough portion into Schlemm&#39;s canal. 
         [0030]    In some embodiments of the cannulas described herein, a diameter of the rigid curved tube is larger than a width of Schlemm&#39;s canal. In one embodiment, the diameter of the rigid curved tube is approximately 400-500 microns. In another embodiment, the diameter of the rigid curved tube is approximately 350-550 microns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a stylized representation of a medical procedure in accordance with this detailed description. 
           [0032]      FIG. 2  is an enlarged perspective view further illustrating the delivery system and the eye shown in the previous figure. 
           [0033]      FIG. 3A  is a perspective view further illustrating the eye and cannula shown in the previous figure. 
           [0034]      FIG. 3B  is a section view further illustrating the eye shown in  FIG. 3A . 
           [0035]      FIG. 3C  is perspective view further illustrating the anatomy of the eye shown in  FIG. 3B . 
           [0036]      FIG. 3D  is a perspective view showing a portion of eye shown in  FIG. 3C . 
           [0037]      FIG. 3E  is an additional perspective view showing the ocular implant and the cannula shown in  FIG. 3D . 
           [0038]      FIG. 4  is a photographic image showing a histology slide HS. Histology slide HS of  FIG. 4  was created by sectioning and staining tissue from a cadaveric eye. An ocular implant was implanted in Schlemm&#39;s canal of the cadaveric eye prior to sectioning. 
           [0039]      FIG. 5A  is a stylized line drawing illustrating histology slide HS shown in the previous figure. 
           [0040]      FIG. 5B  is a simplified cross-sectional view illustrating the eye from which the histology sample was taken. 
           [0041]      FIG. 6  is a stylized perspective view illustrating the anatomy of an eye. 
           [0042]      FIG. 7  is a stylized perspective view depicting the surface that defines the anterior chamber of the eye shown in  FIG. 6 . 
           [0043]      FIG. 8  is a stylized perspective view further illustrating Schlemm&#39;s canal SC and iris  30  shown in  FIG. 6 . 
           [0044]      FIGS. 9A- 9C  are plan views of the surface that defines anterior chamber of the eye shown in  FIG. 6 . 
           [0045]      FIG. 10  is an enlarged side view showing a cannula extending into anterior chamber defined by an inner surface of a dome shaped wall. 
           [0046]      FIGS. 11A-11C  are plan views of a cannula created using multiview projection. 
           [0047]      FIG. 11D  is an axial view further illustrating the cannula shown in  FIG. 11A . 
           [0048]      FIGS. 12A-12D  are lateral cross-sectional views of the tip portion of a cannula. 
           [0049]      FIG. 12E  is a lateral cross-sectional view of a trough portion of the cannula. 
           [0050]      FIG. 12F  is a plan view of the cannula including a plurality of section lines. 
           [0051]      FIGS. 13A-13D  form a sequence of stylized section views illustrating the insertion of the tip portion of a cannula into Schlemm&#39;s canal located in the anterior chamber of an eye. 
           [0052]      FIGS. 13E-13H  form a sequence stylized side plan views further illustrating the insertion of the tip portion into Schlemm&#39;s canal. 
           [0053]      FIG. 14  is an abstract graphical representation further illustrating the insertion of the tip portion of a cannula into Schlemm&#39;s canal. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
         [0055]      FIG. 1  is a stylized representation of a medical procedure in accordance with this detailed description. In the procedure of  FIG. 1 , a physician is treating an eye  20  of a patient P. The physician is holding a hand piece of a delivery system  70  in his or her right hand RH. The physician&#39;s left hand LH is holding the handle H of a gonio lens  23  in the procedure of  FIG. 1 . Some physicians may prefer holding the delivery system hand piece in the right hand and the gonio lens handle in the left hand. 
         [0056]    During the procedure illustrated in  FIG. 1 , the physician may view the interior of the anterior chamber using gonio lens  23  and a microscope  25 . Detail A of  FIG. 1  is a stylized simulation of the image viewed by the physician. A distal portion of a cannula  72  is visible in Detail A. A shadow-like line indicates the location of Schlemm&#39;s canal SC, which is a tube-like structure that encircling the iris and lying under various tissue (e.g., the trabecular meshwork) that surround the anterior chamber. A distal opening  74  of cannula  72  is positioned near Schlemm&#39;s canal SC of eye  20 . 
         [0057]    Methods in accordance with this detailed description may include the step of advancing the distal end of cannula  72  through the cornea of eye  20  so that a distal portion of cannula  72  is disposed in the anterior chamber of the eye. Cannula  72  may then be used to access Schlemm&#39;s canal of the eye, for example, by piercing the wall of Schlemm&#39;s canal with the distal end of cannula  72 . Distal opening  74  of cannula  72  may be placed in fluid communication with a lumen defined by Schlemm&#39;s canal. An ocular implant carried by the cannula may be advanced out of distal opening  74  and into Schlemm&#39;s canal. Insertion of the ocular implant into Schlemm&#39;s canal may facilitate the flow of aqueous humor out of the anterior chamber of the eye. Examples of ocular implants that may be delivered through the cannula of this invention may be found, e.g., in U.S. Pat. No. 7,740,604; U.S. Pat. No. 8,267,882; U.S. Pat. No. 8,425,449; US Patent Publ. No. 2009/0082860; and US Patent Publ. No. 2009/0082862. 
         [0058]      FIG. 2  is an enlarged perspective view further illustrating delivery system  70  and eye  20  shown in the previous figure. In  FIG. 2 , cannula  72  of delivery system  70  is shown being advanced and extending through a dome-shaped wall  90  of eye  20 . Dome shaped wall  90  includes the cornea  36  of eye  20  and scleral tissue that meets the cornea at a limbus of the eye. A distal portion of cannula  72  is disposed inside the anterior chamber AC defined by dome-shaped wall  90 . In the embodiment of  FIG. 2 , cannula  72  is sized and configured so that a distal opening of cannula  72  can be placed in fluid communication with Schlemm&#39;s canal while a proximal portion of cannula  72  is extending through an incision in cornea  36 . 
         [0059]    In the embodiment of  FIG. 2 , an ocular implant (not shown) is disposed in a lumen or passageway within cannula  72 . Delivery system  70  includes a mechanism that is capable of advancing and retracting the ocular implant along the length of cannula  72 . Suitable delivery systems are described in more detail in, e.g., U.S. Pat. No. 8,512,404; U.S. Pat. No. 8,337,509; US Patent Publ. No. 2011/0009874; and US Patent Publ. No. 2013/0158462. The ocular implant may be placed in Schlemm&#39;s canal of eye  20  by advancing the ocular implant through the distal opening of cannula  72  while the distal opening is in fluid communication with Schlemm&#39;s canal. 
         [0060]      FIG. 3A  is a perspective view further illustrating eye  20  shown in the previous figure. In  FIG. 3A , cannula  72  is shown extending through a cornea  36  of eye  20 . In  FIG. 3B , a distal opening  74  of cannula  72  is shown disposed inside an anterior chamber AC of eye  20 . In  FIG. 3A , a cutting plane PP is shown extending across eye  20 .  FIG. 3B  is a stylized cross-sectional view taken along cutting plane PP shown in  FIG. 3A . The cutting plane of  FIG. 3A  extends laterally across Schlemm&#39;s canal SC and the trabecular meshwork TM of the eye. 
         [0061]    Eye  20  includes an iris  30  that defines a pupil  32  of the eye. Schlemm&#39;s canal SC forms a ring around iris  30  with pupil  32  disposed in the center of that ring. Schlemm&#39;s canal SC has a first major side  50 , a second major side  52 , a first minor side  54 , and a second minor side  56 . First major side  50  is on the outside of the ring formed by Schlemm&#39;s canal SC and second major side  52  is on the inside of the ring formed by Schlemm&#39;s canal SC. Accordingly, first major side  50  may be referred to as an outer major side of Schlemm&#39;s canal SC and second major side  52  may be referred to as an inner major side of Schlemm&#39;s canal SC. With particular reference to  FIG. 3B , it will be appreciated that first major side  50  is further from pupil  32  than second major side  52 . In the schematic view shown in  FIG. 3A , first major side  50  is an outer major side of Schlemm&#39;s canal SC and second major side  52  is an inner major side of Schlemm&#39;s canal SC. A scleral spur  80  extends around minor side  56  toward the trabecular meshwork TM. 
         [0062]      FIG. 3C  is perspective view further illustrating the anatomy of eye  20  shown in  FIG. 3B . Eye  20  includes a dome-shaped wall  90  that defines and encloses the anterior chamber AC. Dome-shaped wall  90  comprises a cornea  36  and scleral tissue  34 . The scleral tissue  34  meets the cornea  36  at a limbus of eye  20 . Dome-shaped wall  90  includes a scleral spur  80  that encircles anterior chamber AC. Schlemm&#39;s canal SC resides in a shallow depression in the scleral tissue located near scleral spur  80 . The trabecular meshwork TM is fixed to scleral spur  80  and extends over Schlemm&#39;s canal. Together, Schlemm&#39;s canal SC, trabecular meshwork TM, and scleral spur  80  encircle anterior chamber AC along dome-shaped wall  90 . Iris  30  of eye  20  is disposed inside the anterior chamber AC. Iris  30  defines a pupil  32 . Schwalbe&#39;s line  82  is disposed at the end of Descemet&#39;s membrane  84 . Descemet&#39;s membrane  84  is one of the inner-most layers of cornea  36 . Descemet&#39;s membrane extends across cornea  36  toward Schlemm&#39;s canal SC and terminates near the upper edge of Schlemm&#39;s canal SC. 
         [0063]      FIG. 3D  is a perspective view showing a portion of eye shown in the previous figure. In  FIG. 3D , the tip portion of a cannula  72  can be seen extending into trabecular meshwork TM. In some useful embodiments, cannula  72  can be curved to achieve substantially tangential entry into Schlemm&#39;s canal SC. Also in the embodiment of  FIG. 3D , a curved distal portion of cannula  72  is dimensioned to be disposed within the anterior chamber of the eye. In  FIG. 3D , an ocular implant  86  can be seen extending from a lumen in cannula  72  into a trough  140  defined by cannula  72 . Ocular implant  86  can be advanced through a distal opening of cannula  72  along the trough  140  and into Schlemm&#39;s canal SC. Scleral spur  80  and Schwalbe&#39;s line  82  are also visible in  FIG. 3D . 
         [0064]      FIG. 3E  is an additional perspective view showing ocular implant  86  and cannula  72  shown in the previous figure. By comparing  FIG. 3E  with the previous figure, it will be appreciated that ocular implant  86  has been advanced in a distal direction D while cannula  72  has remained stationary so the distal end of ocular implant  86  is disposed inside Schlemm&#39;s canal SC and the remainder of the implant is disposed in trough  140  and inside the lumen of the cannula. Trough  140  opens into an elongate opening extending through the side wall of cannula  72 . In the embodiment of  FIG. 3E , the elongate opening defined by the cannula provides direct visualization of the ocular implant as it is advanced into Schlemm&#39;s canal. A configuration allowing direct visualization of the ocular implant has a number of clinical advantages. During a medical procedure, it is often difficult to monitor the progress of the implant by viewing the implant through the trabecular meshwork. For example, blood reflux may push blood into Schlemm&#39;s canal obstructing a physician&#39;s view the portion of the implant that has entered Schlemm&#39;s canal. With reference to  FIG. 3E , ocular implant  86  tracks along trough  140  as it is advanced distally along cannula  72  into Schlemm&#39;s canal. The trough opening allows the physician to monitor the progress of the implant by viewing the implant structures as they advance through the trough prior to entering Schlemm&#39;s canal. The trough opening also allows the physician to identify the position of the proximal end of the ocular implant with respect to the incision made by the cannula to access Schlemm&#39;s canal. 
         [0065]    The ocular implants referenced above are intended to reside partially or wholly within Schlemm&#39;s canal. One function of the cannula is to deliver a leading edge of the ocular implant into Schlemm&#39;s canal so that the ocular implant can be advanced circumferentially into Schlemm&#39;s canal. The cannula of this invention provides features to help the user guide the distal end of the cannula into Schlemm&#39;s canal. These cannula features take advantage of the shapes and properties of the various tissue structures of and around Schlemm&#39;s canal to achieve this goal. 
         [0066]    When inserting a cannula through the anterior chamber and the trabecular meshwork into Schlemm&#39;s canal under gonio lens visualization, the physician may use anatomical landmarks to guide the cannula placement and advancement. One convenient landmark is scleral spur  80  which has the appearance of a white line encircling the anterior chamber AC. Another convenient landmark is a pigment line centered on Schlemm&#39;s canal SC. An additional convenient landmark is Schwalbe&#39;s line  82 . 
         [0067]    An ocular implant residing in Schlemm&#39;s canal of a cadaveric eye can be seen in  FIG. 4 .  FIG. 4  is a photographic image showing a histology slide HS. Histology slide HS of  FIG. 4  was created by implanting the ocular implant into Schlemm&#39;s canal of the eye, then sectioning and staining a portion of the eye. The photograph of  FIG. 4  was created while examining the section of tissue using a light microscope. 
         [0068]      FIG. 5A  is a stylized line drawing illustrating histology slide HS shown in the previous figure.  FIG. 5B  is a simplified cross-sectional view illustrating the eye from which the histology sample was taken.  FIG. 5A  and  FIG. 5B  are presented on a single page to illustrate the location of the histology sample relative to other portions of the eye  20 . Eye  20  includes a dome-shaped wall  90  having a surface  92  defining an anterior chamber AC. Dome-shaped wall  90  of eye  20  comprises a cornea  36  and scleral tissue  34 . The scleral tissue  34  meets the cornea  36  at a limbus of the eye. In  FIG. 5B , surface  92  is shown having a generally hemispherical shape. 
         [0069]      FIG. 6  is a stylized perspective view illustrating a portion of eye  20  discussed above. Eye  20  includes an iris  30  defining a pupil  32 . In  FIG. 6 , eye  20  is illustrated in a cross-sectional view created by a cutting plane passing through the center of pupil  32 . Eye  20  includes a dome-shaped wall  90  having a surface  92  defining an anterior chamber AC. In  FIG. 6 , surface  92  is shown having a generally hemispherical shape. Dome-shaped wall  90  of eye  20  comprises a cornea  36  and scleral tissue  34 . The scleral tissue  34  meets the cornea  36  at a limbus  38  of eye  20 . Additional scleral tissue  34  of eye  20  surrounds a posterior chamber PC filled with a viscous fluid known as vitreous humor. A lens  40  of eye  20  is located between anterior chamber AC and posterior chamber PC. Lens  40  is held in place by a number of ciliary zonules  42 . 
         [0070]    Whenever a person views an object, he or she is viewing that object through the cornea, the aqueous humor, and the lens of the eye. In order to be transparent, the cornea and the lens can include no blood vessels. Accordingly, no blood flows through the cornea and the lens to provide nutrition to these tissues and to remove wastes from these tissues. Instead, these functions are performed by the aqueous humor. A continuous flow of aqueous humor through the eye provides nutrition to portions of the eye (e.g., the cornea and the lens) that have no blood vessels. This flow of aqueous humor also removes waste from these tissues. 
         [0071]    Aqueous humor is produced by an organ known as the ciliary body. The ciliary body includes epithelial cells that continuously secrete aqueous humor. In a healthy eye, a stream of aqueous humor flows out of the eye as new aqueous humor is secreted by the epithelial cells of the ciliary body. This excess aqueous humor enters the blood stream and is carried away by venous blood leaving the eye. 
         [0072]    In the illustration of  FIG. 6 , the cutting plane passing through the center of pupil  32  has also passed through Schlemm&#39;s canal. Accordingly, two laterally cut ends of Schlemm&#39;s canal SC are visible in the cross-sectional view of  FIG. 6 . In a healthy eye, aqueous humor flows out of anterior chamber AC and into Schlemm&#39;s canal SC. Aqueous humor exits Schlemm&#39;s canal SC and flows into a number of collector channels. After leaving Schlemm&#39;s canal SC, aqueous humor is absorbed into the venous blood stream and carried out of the eye. 
         [0073]      FIG. 7  is a stylized perspective view depicting the surface  92  that defines anterior chamber AC of the eye shown in  FIG. 6 . In  FIG. 7 , surface  92  is shown having a generally hemispherical shape.  FIG. 7  may be used to illustrate some fundamental geometric concepts that will be used below to describe the various ocular implant delivery cannula structures. Geometry is a branch of mathematics concerned with the properties of space and the shape, size, and relative position of objects within that space. In geometry, a sphere is a round object in three-dimensional space. All points on the surface of a sphere are located the same distance r from a center point so that the sphere is completely symmetrical about the center point. In geometry, a point represents an exact location. A point is a zero-dimensional entity (i.e., it has no length, area, or volume). Geometrically speaking, at any point on a spherical surface, one can find a normal direction which is at right angles to the surface. For a spherical surface all normal directions intersect the center point of the sphere. Each normal direction will also be perpendicular to a line that is tangent to the spherical surface. In  FIG. 7 , a normal line N is illustrated using dashed lines. Normal line N is at right angles to spherical surface  92 . Normal line N is also perpendicular to a reference line TAN. Reference line TAN is tangent to spherical surface  92  in  FIG. 7 . 
         [0074]    A method in accordance with this detailed description may include the step of advancing a distal portion of a cannula into the anterior chamber of the eye. The cannula may then be used to access Schlemm&#39;s canal, for example, by piercing the wall of Schlemm&#39;s canal with the distal end of the cannula. An ocular implant may be advanced out of the distal opening of the cannula and into Schlemm&#39;s canal. A path  94  taken by an ocular implant as it follows Schlemm&#39;s canal along surface  92  is illustrated using a row of dots in  FIG. 7 . 
         [0075]    Scleral tissue above the trabecular meshwork, and the scleral spur below the trabecular meshwork, are harder than the meshwork tissue. If the physician advances the cannula&#39;s distal tip against the scleral tissue above the canal, the angle of the scleral tissue with respect to the approach angle of the cannula, as well as the hardness of that tissue, will tend to guide the cannula tip downward toward and into the meshwork. This effect can be enhanced if the cannula&#39;s distal tip is sharp enough to easily penetrate the meshwork but not sharp enough to easily pierce scleral tissue. If, on the other hand, the physician advances the cannula&#39;s distal tip onto the scleral spur below the meshwork, the cannula is likely to miss the meshwork and Schlemm&#39;s canal altogether. 
         [0076]    Likewise, as the ocular implant advances into Schlemm&#39;s canal, the ocular implant may press against the scleral tissue supporting the outer major wall of Schlemm&#39;s canal and the scleral tissue of the dome-shaped wall that defines the anterior chamber of the eye. As the body of the ocular implant presses against the dome-shaped wall of the eye, the dome-shaped wall provides support for Schlemm&#39;s canal and the ocular implant. The support provided by the dome-shaped wall may be represented by force vectors. The direction of these force vectors may be at right angles to points on the spherical surface that defines the anterior chamber. Accordingly, the outer major wall of Schlemm&#39;s canal may be supported by the dome shaped wall as the ocular implant advances circumferentially into Schlemm&#39;s canal. 
         [0077]    During delivery, it is desirable that the ocular implant follow the lumen of Schlemm&#39;s canal as it is advanced out the distal opening of the cannula. The ability of the ocular implant to be advanced into and follow the lumen of Schlemm&#39;s canal may be referred to as trackability. Characteristics of an ocular implant that effect trackability include axial pushability and lateral flexibility. Axial pushability generally concerns the ability of an ocular implant to transmit to the distal end of the ocular implant an axial force applied to the proximal end of the ocular implant. Lateral flexibility concerns the ease with which the ocular implant body can bend to conform to the shape of the lumen. Trackability may be adversely affected when twisting forces are applied to a curved body. For example, twisting the body of a curved ocular implant about its longitudinal axis may cause the curved body to steer away from a desired path. 
         [0078]      FIG. 8  is a stylized perspective view further illustrating Schlemm&#39;s canal SC and iris  30  shown in  FIG. 6 . The surface  92  that defines the anterior chamber AC of eye  20  is depicted using dashed lines in  FIG. 8 . In the embodiment of  FIG. 8 , Schlemm&#39;s canal SC and iris  30  are shown in cross-section, with a cutting plane passing through the center of a pupil  32  defined by iris  30 . Schlemm&#39;s canal SC comprises a first major side  50 , a second major side  52 , a first minor side  54 , and a second minor side  56 . Schlemm&#39;s canal SC forms a ring around iris  30  with pupil  32  disposed in the center of that ring. With reference to  FIG. 8 , it will be appreciated that first major side  50  is on the outside of the ring formed by Schlemm&#39;s canal SC and second major side  52  is on the inside of the ring formed by Schlemm&#39;s canal SC. Accordingly, first major side  50  may be referred to as an outer major side of Schlemm&#39;s canal SC and second major side  52  may be referred to as an inner major side of Schlemm&#39;s canal SC. With reference to  FIG. 8 , it will be appreciated that first major side  50  is further from pupil  32  than second major side  52 . 
         [0079]    A path  94  taken by an ocular implant as it follows Schlemm&#39;s canal along surface  92  is illustrated using a row of dots in  FIG. 8 . As the ocular implant advances into Schlemm&#39;s canal, the ocular implant may press against the outer major wall of Schlemm&#39;s canal and the dome-shaped wall that defines the anterior chamber. 
         [0080]    Some embodiments include an ocular implant delivery cannula with a distal tip that is offset from the longitudinal center line of the cannula. This arrangement facilitates the intuitive use of anatomical landmarks that can be easy observed using gonioscopic visualization. When the body of the cannula is generally centered on Schlemm&#39;s canal, the tip portion of the cannula will pierce the trabecular meshwork and the wall of Schlemm&#39;s canal at a point slightly above the center of Schlemm&#39;s canal. The offset distal tip also provides the distal end of the cannula with a lower camming surface for guiding the cannula distal end over the scleral spur and an optional upper camming surface for guiding the cannula distal end into Schlemm&#39;s canal when the cannula has a diameter larger than a width of Schlemm&#39;s canal. The camming surfaces are configured to direct the cannula into Schlemm&#39;s canal when the cannula is wider or oversized with respect to a width of the canal. 
         [0081]      FIGS. 9A-9C  are plan views of the surface  92  that defines anterior chamber AC of the eye shown in  FIG. 6 .  FIG. 9A  may be referred to as a front view of surface  92 ,  FIG. 9B  may be referred to as a top view of surface  92 , and  FIG. 9C  may be referred to as a side view of surface  92 . 
         [0082]    In  FIGS. 9A-9C , a cannula  72  is shown extending into anterior chamber AC. Cannula  72  may be used to deliver an ocular implant to a target location within anterior chamber AC. Examples of target locations that may be suitable in some applications include areas in and around Schlemm&#39;s canal, the trabecular meshwork, and the suprachoroidal space of an eye. A path  94  that may be taken by an ocular implant as it follows Schlemm&#39;s canal along surface  92  is illustrated using a row of dots in  FIGS. 9A-9C . 
         [0083]      FIG. 10  is an enlarged side view showing cannula  72  extending into anterior chamber AC defined by surface  92 . Cannula  72  may be used, for example, to deliver an ocular implant to a target location within Schlemm canal SC. In the stylized plan view of  FIG. 10 , a scleral spur  80  is disposed in anterior chamber AC. Scleral spur  80  is fixed to surface  92  and encircles anterior chamber AC. Scleral spur  80  defines a spur plane  104 . 
         [0084]    Referring still to  FIG. 10 , cannula  72  can include a body member  120  extending along a longitudinal axis. Body member  120  can include a proximal end  126  and a tubular portion  130  extending distally from the proximal end. Body member  120  can also include a tip portion  132  disposed at a distal end thereof. A trough portion  140  of body member extends between tip portion  132  and tubular portion  130 . In the embodiment of  FIG. 10 , tip portion  132  has a semi-circular transverse cross-section including a tip chord line segment. A secant  136  extending beyond the tip chord is shown in  FIG. 10 . Trough portion  140  of body member  120  has a semi-circular transverse cross-section including a trough chord line segment.  FIG. 10  includes a secant  138  extending beyond the trough cord. 
         [0085]    As shown in  FIG. 10 , tip portion  132  and trough portion  140  are adapted and configured such that, when tubular portion  130  is extending through an incision in the dome shaped wall defining anterior chamber AC and tip portion  132  is extending into Schlemm&#39;s canal of the eye, secant  136  intersects spur plane  104  at an acute angle A and secant  138  intersects spur plane  104  at an obtuse angle O. 
         [0086]      FIGS. 11A-11C  are plan views of cannula  72  created using multiview projection.  FIG. 11D  is an axial view further illustrating cannula  72 . Cannula  72  of  FIGS. 11A-11D  may be used to deliver an ocular implant into Schlemm&#39;s canal of an eye.  FIG. 11A  may be referred to as a top view of cannula  72 ,  FIG. 11B  may be referred to as a side view of cannula  72 , and  FIG. 11C  may be referred to as a bottom view of cannula  72 . 
         [0087]    In  FIGS. 11A-11D , cannula  72  comprises a body member  120  extending along a medial plane  122 . Body member  120  can include a proximal end  126  and a tubular portion  130  extending distally from the proximal end. Body member  120  can also include a tip portion  132  disposed at a distal tip  128  thereof. The distal tip  128  can be offset from the medial plane  122  of body member  120 . The distal tip  128  can form a point at the intersection of lower camming surface  129  and upper camming surface  131 . In one alternative embodiment, the distal tip may be at one side of the cannula, in which case there will be no upper camming surface. In some embodiments, distal tip  128  can be sharpened enough to pierce trabecular meshwork tissue but not sharp enough to easily pierce scleral tissue. 
         [0088]    Body member  120  also includes a trough portion  140  extending between distal tip  128  and tubular portion  130 . Trough portion  140  is configured to fluidly communicates with a lumen  144  defined by tubular portion  130  and a distal opening  142  defined by tip portion  132 . Because of the offset position of distal tip  128 , tip portion  132  is asymmetric about medial plane  122  and trough portion  140  is symmetric about medial plane  124 . 
         [0089]      FIG. 12A  through  FIG. 12D  are lateral cross-sectional views of tip portion  132  of cannula  72 .  FIG. 12E  is a lateral cross-sectional view of trough portion  140  of cannula  72 .  FIG. 12F  is an enlarged plan view showing a portion of cannula  72  shown in the previous figure. In this embodiment, the cannula is formed from a tube (such as a hypotube) with material removed from the distal end to form the trough portion and the distal tip  129 . In other embodiments, the cannula may have a non-tubular shape.  FIG. 12F  shows the cannula  72  including the tip portion  132 , distal tip  128 , camming surfaces  129  and  131 , and trough portion  140 . In  FIG. 12F , a number of section lines can be seen traversing crossing cannula  72 . These section lines have been used to create a number of lateral cross-sections illustrating the shape of cannula  72 . 
         [0090]    Section  146 A of  FIG. 12A  was created by cutting tip portion  132  along section line A-A shown in  FIG. 12F . Section  146 B, section  146 C, and section  146 D, of  FIGS. 12B ,  12 C, and  12 D, respectively, were made by cutting tip portion  132  along section line B-B, section line C-C, and section line D-D, respectively. By examining section  146 A, section  146 B, section  146 C and section  146 D it will be appreciated that tip portion  132  can have a semi-circular transverse cross-section. 
         [0091]    As shown in  FIGS. 12A-12D , section  146 A has a chord  136 A. Section  146 B, section  146 C, and section  146 D have a chord  136 B, a chord  136 C and a chord  136 D, respectively. By examining chord  136 A, chord  136 B, chord  136 C and chord  136 D it will be appreciated that the chord length of tip portion  132  increases as tip portion  132  extends proximally away from its distal point. Section  146 E was created by cutting through portion  140  along section line E-E shown in  FIG. 12F . In the embodiment of  FIG. 12E , section  146 E has a chord  136 E. 
         [0092]    Referring to  FIGS. 11A-11D  and  12 A- 12 E, as the physician advances the cannula through the anterior chamber toward the trabecular meshwork under visual guidance (using, e.g., the scleral spur, pigmented area and Schwalbe&#39;s line as anatomical landmarks), the camming surfaces  129  and  131  and the cannula&#39;s tip portion  132  are configured to guide an oversized cannula relative to the width of Schlemm&#39;s canal into Schlemm&#39;s canal. In some embodiments, a diameter of the cannula can be between approximately 350-550 microns, or alternatively, between 400-500 microns. Schlemm&#39;s canal typically has a width of approximately 300 microns, so it can be a challenge to guide a conventional cannula that is wider than Schlemm&#39;s canal into the canal. In the present embodiment, the upper camming surface  131  of the cannula will engage scleral tissue above the meshwork. Since the distal tip  128  is not sharp enough to easily pierce scleral tissue, upper camming surface  131  is configured to contact the scleral tissue and guide the distal tip  128  into Schlemm&#39;s canal. The lower camming surface  129  is configured to contact the scleral spur below the meshwork to guide the tip  128  into the Schlemm&#39;s canal. The distal tip&#39;s offset, placing it above the cannula&#39;s longitudinal center axis, along with the physician&#39;s use of the anatomical landmarks, helps ensure that the cannula is not positioned so low with respect to the meshwork that the upper camming surface engages the scleral spur to push the cannula tip downward away from the meshwork. 
         [0093]      FIGS. 13A-13D  form a sequence of stylized section views illustrating the insertion of tip portion  132  of cannula  72  into Schlemm&#39;s canal SC located in the anterior chamber AC of an eye.  FIGS. 13E-13H  form a sequence stylized side plan views further illustrating the insertion of the tip portion into Schlemm&#39;s canal. 
         [0094]    In  FIG. 13A  and  FIG. 13E , tip portion  132  of cannula  72  has been advanced into Schlemm&#39;s canal so that section  146 A (shown in  FIG. 12A ) of tip portion  132  is aligned with the incision in Schlemm&#39;s canal created by the cannula&#39;s distal tip  128 . Section  146 A includes a chord  136 A. Referring to  FIG. 13A , chord  136 A defines a line that intersects a spur plane  104  of the eye at a chord angle  148 A. Spur plane  104  is defined by a scleral spur  102  that encircles the anterior chamber AC of the eye. 
         [0095]    In  FIG. 13B  and  FIG. 13F , tip portion  132  of cannula  72  has been advanced into Schlemm&#39;s canal so that section  146 B of tip portion  132  is aligned with the incision in Schlemm&#39;s canal. Section  146 B includes a chord  136 B. In  FIG. 13B , chord  136 B defines a line that intersects spur plane  104  at a chord angle  148 B. 
         [0096]    In  FIG. 13C  and  FIG. 13G , tip portion  132  of cannula  72  has been advanced into Schlemm&#39;s canal so that section  146 C of tip portion  132  is aligned with the incision in Schlemm&#39;s canal. Section  146 C includes a chord  136 C. In  FIG. 13C , chord  136 C defines a line that intersects spur plane  104  at a chord angle  148 C. 
         [0097]    In  FIG. 13D  and  FIG. 13H , tip portion  132  of cannula  72  has been advanced into Schlemm&#39;s canal so that section  146 D of tip portion  132  is aligned with the incision in Schlemm&#39;s canal. Section  146 D includes a chord  136 D. In the embodiment of  FIG. 13D , chord  136 D defines a line that intersects spur plane  104  at a chord angle  148 D. 
         [0098]      FIG. 14  is an abstract graphical representation further illustrating the insertion of tip portion  132  of a cannula into Schlemm&#39;s canal SC. The profile of each section view illustrated in  FIGS. 12A-12D  is included in  FIG. 14 . These profiles form contour lines illustrating the tapered shape of tip portion  132  and trough portion  140 . The profiles associated with section  146 A, section  146 B, section  146 C, section  146 D, and section  146 E are labeled in  FIG. 14 . 
         [0099]    As tip portion  132  is inserted into Schlemm&#39;s canal, inner major wall  52  of Schlemm&#39;s canal rides along a first leading edge of tip portion  132 . The insertion of tip portion  132  into Schlemm&#39;s canal SC causes inner major wall  52  to separate from outer major wall  50 . The changing shape of Schlemm&#39;s canal is illustrated with a plurality of Schlemm&#39;s canal profiles shown using dashed lines in  FIG. 14 . 
         [0100]    In the embodiment of  FIG. 14 , tip portion  132  and trough portion  140  are adapted and configured such that, when tubular portion  130  is extending through an incision in the dome shaped wall defining anterior chamber AC and tip portion  132  is extending into Schlemm&#39;s canal of the eye, secant  136  intersects spur plane  104  at an acute angle A and secant  138  intersects spur plane  104  at an obtuse angle O. 
         [0101]    While embodiments of the present invention have been shown and described, modifications may be made, and it is therefore intended in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.