Patent ID: 12239578

DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENTS

In general, the present invention relates to a method of generating a complete through surface incision of a portion of the eye, such as a complete incision of a full thickness or partial thickness of the cornea of the eye. An example of a possible partial thickness corneal incision (PTI) of the anterior corneal surface of an eye is shown inFIGS.4A-B. Examples of full thickness corneal incisions (FTI) are shown inFIGS.5-6.

InFIG.4A, an anterior surface200and a posterior surface202of a cornea204of an eye are shown. A first pass of a first femtosecond laser beam is performed in its entirety at a low energy above the photo-disruption threshold. The first laser beam has an energy in a range of 3 μJ-5 μJ and is a low numerical aperture laser beam that passes through a liquid patient interface201, wherein a low numerical aperture laser beam is used so that the laser focal point will be far enough to reach the lens posterior region and effectively fragment cataractous materials within the eye. In particular, the first pass of the first laser beam begins at a position A within the cornea204and moves linearly toward a position B located past the anterior surface200and in a chamber filled with a balanced salt solution (BSS). As shown inFIGS.4A-B, the first pass is along a linear path, wherein a first full cut206is formed. Along the path of the first full cut206, just below the anterior surface of the cornea, an uncut region210can remain. As shown inFIG.4B, subsequent to the first pass, a second pass208of a second femtosecond laser beam that is a low numerical aperture laser beam is performed at an energy, such as 6 μJ-14 μJ, which is greater in value than the energy of the first femtosecond laser beam. The second pass208is performed along a portion of the same linear path as the first pass that is near the anterior surface200of the cornea204. In particular, the second pass208begins at the point C prior to the uncut layer210and ends at position B. Point C is at a pre-programed distance209below the corneal surface S (200), typically 100-300 μm. In other words, the second pass208includes the uncut layer210and extends to the end of the overcut at point B.

Note that prior to executing any incisions, the laser system ofFIG.7uses built in biometry scanning to automatically map the anterior and/or posterior cornea surfaces at the incision site and automatically determines beam path for both the first and second passes. In the present case, such automatic mapping and determining would identify the first pass path A→B. With the corneal anterior surface S also being identified, the system traces back along the path, starting at the surface S (200), for a predetermined distance, typically 100-300 μm to position the second pass start point C. After completion of the first pass, a one-plane partial thickness incision is formed, wherein the term “one-plane” regards the fact that the resultant path from the first pass is contained within a single plane. The term “partial thickness” regards the fact that the start point A is intentionally within the body of the cornea.

InFIG.5A, a first pass of a first femtosecond laser beam is performed in its entirety at a low energy above the photo-disruption threshold. The first laser beam is a low numerical aperture laser beam that passes through a liquid patient interface201. In particular, the first pass begins at a position A in the aqueous humor of the eye, moves linearly toward a position B located in the interior of the cornea204, and then changes direction and moves linearly to position C past the anterior surface200and in a chamber filled with a balanced salt solution. The first pass is along an angled path, wherein two linear cuts300and304are formed. When attempting to cut across the junction between dissimilar media (e.g. cornea to BSS or stoma to Bowman's membrane), the difference in optical breakdown threshold will result in small uncut regions being formed. Just above the posterior corneal surface, in segment300, an uncut layer306remains. Just below the anterior corneal surface, in the last full cut segment304, a second uncut layer308remains.

As shown inFIG.5B, subsequent to the first pass, a second pass of a second femtosecond laser beam that is a low numerical aperture laser beam is performed. Note that the energies of the first and second passes of the first and second laser beams are similar to the energies of the first and second laser beams ofFIGS.4A-B. The second pass is performed along a portion of the same linear path as the first pass that is near the anterior surface200of the cornea204. In particular, the second pass begins at the point D prior to the region of uncut cornea308and ends at position C so as to define portion301. In other words, the second pass includes the uncut layer308.

Note that prior to executing any incisions, the laser system ofFIG.7uses built in biometry scanning to automatically map the anterior and/or posterior cornea surfaces at the incision site and automatically determines beam path for both the first and second passes. In the present case, such automatic mapping and determining would identify the first pass path A→B→C. With the corneal anterior surface S (200) also being identified, the system traces back along the path S→B→A, starting at the surface S, for a predetermined distance, typically 100-300 μm, to position the second pass start point D. The second pass path is also defined as D→B→C. Should the programmed length of the second pass be such that D lies on the segment S→B, then the second pass will be simply defined by the linear path D→S.

Note that there is no need for a second pass at the uncut layer306, since the Descement membrane's stiffness is such that the thin uncut layer of the uncut layer306will be broken naturally from structural weakness and the residual heat emanating from the laser beam's upward displacement in the aqueous humor of the eye.

After completion of both passes, a two-plane full thickness incision is formed, wherein the term “two-plane” regards the fact that the resultant incision forms two planes. The term “full thickness” regards the fact that the resultant incision intentionally cuts from the posterior to anterior surface of the cornea.

InFIG.6A, a first pass of a first femtosecond laser beam is performed in its entirety at a low energy above the photo-disruption threshold. The laser beam is a low numerical aperture laser beam that passes through a liquid patient interface201. In particular, the first pass begins at a position A in the aqueous humor of the eye, moves linearly toward a position B located in the interior of the cornea204, and then changes direction and moves linearly to position C. Next, the laser beam changes direction and moves linearly past the anterior surface200to a position D in a chamber filled with a balanced salt solution. The first pass is along a zigzag angled path, wherein linear full cuts400,402and406are formed. Just above the posterior corneal surface, in segment400, an uncut layer404remains. Just below the anterior corneal surface, in the last full cut segment406, a second uncut layer408remains.

As shown inFIG.6B, subsequent to the first pass, a second pass of a second femtosecond laser beam that is a low numerical aperture laser beam is performed. Note that the energies of the first and second passes of the first and second laser beams are similar to the energies of the first and second laser beams ofFIGS.4A-B. The second pass is performed along a portion of the same linear path as the first pass that is near the anterior surface200of the cornea204. In particular, the second pass begins at the point E prior to the region of uncut cornea408and ends at position D. In other words, the second pass includes the uncut layer408. Note that prior to executing any incisions the laser system ofFIG.7uses built in biometry scanning to automatically map the anterior and/or posterior cornea surfaces at the incision site and automatically determines the second pass path. In the present case, such automatic mapping and determining would identify the first pass path A→B→C→D. With the corneal anterior surface S being identified, the system traces back along the first pass path, starting at the surface S, for a predetermined distance, typically 100-300 μm to position the second pass start point E. The system then performs a second pass along the path E→C→D. Note that if the length S→C is greater than the second pass length then the second pass will be performed along a single linear path E→D.

Note that there is no need for a second pass at the uncut layer404, since the Descement membrane's stiffness is such that the thin uncut layer of the uncut layer404will be broken naturally from structural weakness and the residual heat emanating from the upstream laser beam in the aqueous humor of the eye.

After completion of both passes, a three-plane full thickness incision is formed, wherein the term “three-plane” regards the fact that the resultant incision forms three planes. The term “full thickness” regards the fact that the resultant incision intentionally cuts from the posterior to anterior surface of the cornea.

Note that there are several principles involved regarding the use of a second pass on the incomplete cuts at the anterior surface of the cornea for the incisions shown inFIGS.4A-B,5A-B and6A-B. First, the second pass results in increased visibility of the incision entrance for the surgeon. Second, the stiffness of the Bowman's membrane is much greater than that of the Descement's membrane and so structural weakness of the Bowman's membrane and residual heat from the air bubbles produced by photodisruption in the balanced salt solution will not be sufficient in themselves to break the uncut layer at the anterior surface of the cornea. Thus, a second pass of the laser beam is necessary break the uncut layer. On a related point, the present two-pass technique avoids the use of just a single pass of a laser beam to form a full cut at the anterior surface of the cornea. Most nerves reside between the endothelial cells and the Bowman's membrane and so a single pass laser technique could induce unwarranted pain to the patient due to the aggravation of the nerves by the laser. In contrast, the presently described two pass technique results in the further softening of the residual uncut layers and so helps to ease the opening of the wound.

In order to form the first and second pass patterns ofFIGS.4-6, a laser system is provided as shown inFIG.7and as described in U.S. patent application Ser. No. 12/831,783, the entire contents of which are incorporated herein by reference. In particular, the laser system includes a treatment laser501which should provide a beam504. The beam should be of a short pulse width, together with the energy and beam size, to produce photodisruption. Thus, as used herein, the term laser shot or shot refers to a laser beam pulse delivered to a location that results in photodisruption. As used herein, the term photodisruption essentially refers to the conversion of matter to a gas by the laser, with accompanying shock wave and cavitation bubble. The term photodisruption has also been generally referred to as Laser Induced Optical Breakdown (LIOB). In particular, wavelengths of about 300 nm to 2500 nm may be employed. Pulse widths from about 1 femtosecond to 100 picoseconds may be employed. Energies from about a 1 nanojoule to 1 millijoule may be employed. The pulse rate (also referred to as pulse repetition frequency (PRF) and pulses per second measured in Hertz) may be from about 1 KHz to several GHz. Generally, lower pulse rates correspond to higher pulse energy in commercial laser devices. A wide variety of laser types may be used to cause photodisruption of ocular tissues, dependent upon pulse width and energy density. Thus, examples of such lasers are disclosed in U.S. Patent Application Publication No. 2007/084694 A2 and WO 2007/084627A2, the entire contents of each of which are incorporated herein by reference. These and other similar lasers may be used as therapeutic lasers. For procedures on the cornea the same type of therapeutic laser as described herein may be used, with the energy and focal point being selected to perform the desired procedure.

In general, the optics502for delivering the laser beam504to the structures of the eye should be capable of providing a series of shots to the natural lens in a precise and predetermined pattern in the x, y and z dimension. The z dimension as used herein refers to that dimension which has an axis that corresponds to, or is essentially parallel with the anterior to posterior (AP) axis of the eye. The optics should also provide a predetermined beam spot size to cause photodisruption with the laser energy reaching the structure of the eye intended to be cut.

In general, the control system503for delivering the laser beam504may be any computer, controller, and/or software hardware combination that is capable of selecting and controlling x-y-z scanning parameters and laser firing. These components may typically be associated at least in part with circuit boards that interface to the x-y scanner, the z focusing device and/or the laser. The control system may also, but does not necessarily, have the further capabilities of controlling the other components of the system, as well as, maintaining data, obtaining data and performing calculations. Thus, the control system may contain the programs that direct the laser through one or more laser shot patterns. Similarly, the control system may be capable of processing data from the slit scanned laser and/or from a separate controller for the slit scanned laser system.

The laser optics502for delivering the laser beam504includes a beam expander telescope505, a z focus mechanism506, a beam combiner507, an x-y scanner508, and focusing optics509. There is further provided relay optics510, camera optics511, which include a zoom, and a first ccd camera512.

Optical images of the eye514and in particular optical images of the natural lens of the eye520are conveyed along a path513. This path513follows the same path as the laser beam504from the natural lens through the laser patient interface516, the focusing optics509, the x-y scanner508and the beam combiner507. There is further provided a laser patient interface516, a structured light source517and a structured light camera518, including a lens. Examples of patient interface and related apparatus that are useful with the present system are provided in regular and provisional U.S. patent application Ser. No. 12/509,021 and Ser. No. 61/228,457, wherein each was filed on the same day as the present application and wherein the entire disclosures of each of which are incorporated herein by reference.

The structured light source517may be a slit illumination having focusing and structured light projection optics, such as a Schafter+Kirchhoff Laser Macro Line Generator Model 13LTM+90CM, (Type 13LTM-250S-41+90CM-M60-780-5-Y03-C-6) or a StockerYale Model SNF-501L-660-20-5, which is also referred to as a slit scanned laser. In this embodiment the structured illumination source517also includes slit scanning means519. The operation of using a scanned slit illumination is described in described in U.S. patent application Ser. No. 12/831,783.

The images from the camera518may be conveyed to the controller503for processing and further use in the operation of the system. They may also be sent to a separate processor and/or controller, which in turn communicates with the controller503. The structured light source517, the camera518and the slit scanning means519include a means for determining the position and apex of the lens in relation to the laser system. Based at least on part from the determined position and apex of the lens, the scanning of the laser beam504upon the eye520can be controlled by controller503. For example, to make a corneal incision, a point of focus of a laser, such as a femtosecond laser, generates a low numerical aperture beam that passes through a liquid patient interface201that adjoins the eye and is scanned during a first pass across a planar or curved surface within the volume of the target tissue to form the incision. The beam is a low numerical aperture beam and has an intensity at focus is chosen to be at a low energy that just exceeds the laser induced optical breakdown threshold of the tissue. As each pulse is delivered, a plasma-mediated photo-disruption occurs, vaporizing a miniscule volume of tissue at or near the point of focus. A cavitation bubble subsequently forms near the point of focus which helps cleave the damaged region to form the incision. Using a scanning laser guidance system as shown inFIG.6, laser pulses are placed contiguously in three dimensions across the desired planar or curved surfaces to form the overall incision. During the first pass of the laser beam, a partial cut will result in the manner discussed with respect toFIGS.2A-B. In this situation, a second pass of a laser beam is automatically performed shortly after completion of the first pass wherein scanning of a second low numerical aperture laser beam that passes through the liquid patient interface is performed at a higher energy and scanning speed when compared with the first pass. The second pass involves having the laser beam follow a portion of the same path as followed by the laser beam of the first pass near the anterior surface of the cornea. At least in the case of making an incision into an anterior portion of the cornea, the laser parameters, including energy and scanning speed, are optimized to cut through the denser cells without compromising effectiveness within the stroma. For example, during the first pass, the XY spacing between shots ranges from 4 to 8 μm, the Z spacing of the shots ranges from 4 to 5 μm, the energy ranges from 3 to 5 μJ and the pulse repetition frequency is approximately 80 kHz. During the second pass, the XY spacing between shots ranges from 6 to 10 μm, the Z spacing of the shots ranges from 4 to 8 μm, the energy ranges from 6 to 14 μJ and the pulse repetition frequency is approximately 80 kHz. After scanning of the second pass, the partial cut near the anterior surface of the cornea has evolved into a full cut. Note that in the case of making an incision at the anterior surface portion of the cornea, the incision extends only minimally into the stroma. Note that the above mentioned two pass process can be applied to form the incisions shown inFIGS.4-6.

From the foregoing description, one skilled in the art can readily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and/or modifications of the invention to adapt it to various usages and conditions.