WO2014018104A1 - Method and apparatus for performing a posterior capsulotomy - Google Patents

Abstract

Laser posterior capsulotomy is a safe, painless, and effective way to treat posterior capsule opacification (PCO), which is the haze that sometimes develops in the posterior portion of the lens capsule after cataract surgery and IOL implantation. To perform a laser posterior capsulotomy, an ophthalmologist focuses a pulsed laser beam to a spot on the posterior capsule's surface, then scans the beam across the affected tissue. The affected tissue ruptures upon absorbing enough laser light, and the cellular remnants are absorbed by the vitreous humor. Unfortunately, the relatively long pulses used in conventional laser posterior capsulotomy can cause undesired damage to the eye and to the IOL. These risks can be mitigated by using a pulsed laser beam with a pulse duration of about 50-100 femtoseconds, a pulse repetition rate of about 10-50 Hz, and an energy per pulse of about 5-150 μj.

Description

METHOD AND APPARATUS FOR PERFORMING A POSTERIOR

CAPSULOTOMY

CROSS-REFERENCE TO RELATED PATENT APPLICATION

[0001] This applications claims the benefit, under 35 U.S.C. § 119(e), of U.S. Application No. 61/675,391, filed on July 25, 2012, and entitled "Posterior Capsulotomy Performed using Picosecond and Femtosecond Laser Pulses," which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Under normal circumstances, a healthy eye can produce an image on the retina of an object in an object plane. Objects in or near the object plane yield crisp, or focused images, whereas objects that are too far from the object plane appear blurry or out of focus. The distance in front of and behind the object plane over which an object appears to be in focus on the image plane is called the "depth of field" and depends on both the eye's focal length (optical power) and aperture size. A healthy eye can change its optical power (and its depth of field) to image objects at near distances (e.g., less than 1 m), intermediate distances (e.g., about 1 m to about 5 m), and far distances (e.g., more than about 5 m) to the front surface of the retina 190 in a process known as accommodation.

[0003] There are two major conditions that affect an individual's ability to focus on near and intermediate distance objects: presbyopia and pseudophakia. Presbyopia is the loss of accommodation of the crystalline lens of the human eye that often accompanies aging. In a presbyopic individual, this loss of accommodation first results in an inability to focus on near distance objects and later results in an inability to focus on intermediate distance objects. It is estimated that there are approximately 90 million to 100 million presbyopes in the United States. Worldwide, it is estimated that there are approximately 1.6 billion presbyopes. Presbyopia can be treated with reading glasses or accommodative intraocular lenses (IOLs), such as the electro- active IOLs disclosed in U.S. Patent Nos. 7,926,940 and 8,215,770, which are incorporated herein by reference in their entireties.

[0004] Pseudophakia is the replacement of the crystalline lens of the eye with an IOL, usually following surgical removal of the crystalline lens during cataract surgery. For all practical purposes, an individual will get cataracts if he or she lives long enough. Furthermore, many individuals with cataracts have a cataract operation at some point in their lives. In fact, up to one- third of adults in the developed world have cataract surgery, and many of these surgeries involve removal and replacement of the crystalline lens with an artificial intra-ocular lens (IOL).

Aphakia, which is the absence of the crystalline lens, can also be corrected using artificial IOLs.

[0005] An IOL can be implanted in the capsular sac following removal of the natural

(crystalline) lens, e.g., during cataract surgery. The IOL is typically positioned so that its optical center is aligned with the foveaola. Spring-like fixtures called haptics hold the IOL in place by pushing against the capsule's inner surface to produce radial compressive forces that keep the IOL in a central location. By keeping the IOL centered laterally, these haptics improve the implanted IOL's performance.

[0006] The IOL's performance depends on the IOL's location along the eye's anterior- posterior axis— the eye's optical axis. Put differently, the IOL's performance depends on the distance between the IOL's principal plane and the center of the foveaola. The IOL's location along the eye's anterior-posterior axis is fixed by making the IOL vault in the posterior direction when the haptics are engaged, contacting the posterior surface of the lens capsule (see FIGS. 1, 2A, and 2B, described below), also known as the capsular sac. The capsular sac's posterior surface is also known as the posterior lens capsule or simply the posterior capsule. The IOL is typically stable in such a location, since the anterior capsule adheres to the edges of the IOL's anterior surface after surgery and forms a shrink-wrap type effect, similar to a seal.

[0007] Frequently, remnants of cellular debris, including lens epithelial cells and cortical cells, are left behind after cataract surgery, even when the surgeon takes great care to wash the empty capsule with saline solution before implanting the IOL. Insufficient dilation of the pupil during cataract surgery may also contribute to an increased risk of secondary cataract formation. Post- operative ly, these cellular remnants proliferate over periods of 3-12 months and beyond, and attach themselves to the wall of the posterior capsule. The proliferating cellular remnants can become several layers thick. Initially, they create a haze that impairs the patient's vision before eventually rendering the posterior capsule opaque in a process called posterior capsule opacification (PCO). The haze developed in the initial phases of the capsular opacification increases light scatter and reduces retinal image contrast. Eventually, the worsening

opacification causes the patient to lose visual acuity and to complain of glare and light sensitivity. In general, the greater the amount of remaining lens material after extraction, especially in the area of Soemmering' s ring, the greater the probability of PCO formation and laser capsulotomy.

[0008] Other forms of PCO include a fibrosis inside the lens capsule. This fibrosis can appear within days of cataract surgery and develops as lens epithelial (covering) cells migrate from the anterior capsule to the posterior capsule when the anterior lens capsule is opened to remove the primary cataract and insert the IOL. The epithelial cells can transform into myofibroblasts, which are precursors to muscle cells and capable of contraction. Collagen deposits on these

myofibroblasts leaves the posterior lens capsule with a white, fibrous appearance. In addition, another cataract may also form from wrinkling of the lens capsule, either due to contraction of the myofibroblasts on the capsule or because of stretching of the capsule by the haptics that hold the IOL in place.

[0009] Demographics influence the likelihood of developing PCO. For instance, younger cataract patients are more likely to develop PCO than geriatric patients, especially pediatric patients who are experiencing ocular growth. The incidence of PCO is higher in women than in men. And fifty percent of patients who experience papillary capture, or iris capture, of the IOL develop some form of PCO. (Iris capture occurs if the IOL moves through the pupil from the posterior chamber to the anterior chamber.)

[0010] The degree and incidence of capsule opacification also varies with the type of implant used in the initial cataract operation. Larger implants are associated with decreased opacification, and round-edged silicone implants are associated with a greater incidence of opacification than acrylic implants, which have a square-edged design. The incidence of PCO is lower with silicone IOLs than with rigid IOLs.

SUMMARY

[0011] Embodiments of the present invention include systems and methods for performing a posterior capsulotomy. An exemplary system includes a laser and at least one optical element in optical communication with the laser. The generates a pulsed laser beam with a pulse duration of about 1 femtosecond to about 10 picoseconds, a pulse repetition rate of about 10 Hz to about 150 kHz, and an energy per pulse of about 5 μΐ to about 150 μΐ. The optical element guide the pulsed laser beam to a spot on or about a posterior capsule of a human eye so as to cause ablation of at least a portion of the posterior capsule in the human eye, e.g., via photo-ionization.

[0012] The laser may be a solid-state laser, such as an Nd:YAG laser, Yb:YAG laser, or Er:YAG laser, that emits the pulsed laser beam at a wavelength of about 800 nm to about 1500 nm (e.g., about 1000 nm to about 1300 nm). The pulse duration may be about 50 femtoseconds to about 500 femtoseconds, the pulse repetition rate may be about 10 Hz to about 25 Hz, and the energy per pulse may be about 8 μΐ to about 100 μΐ.

[0013] In some examples, the optical element comprises a lens to focus the pulsed laser beam to the spot on the posterior capsule, e.g., with a focused spot size (diameter) may be about 1 μιη to about 50 μιη. The lens may have a depth of focus of about 1 μιη to about 250 μιη and may be configured to focus the spot such that about 0% to about 50% of the depth of focus is anterior to (in front of) the posterior capsule of the human eye. For instance, the lens may focus the spot on a posterior surface of an intraocular optic implanted in the human eye.

[0014] Some embodiments of the lens include either a rigid contact lens or a soft contact lens. In such an embodiment, the pulsed laser beam may be collimated, and this contact lens may be configured to focus the collimated pulsed laser beam to the spot on the posterior capsule. This contact lens may also be configured to compensate for an aberration, caused by the human eye, in the pulsed laser beam. [0015] Embodiments of the system may also include a beam scanner that is operably coupled to the optical element. In operation, this beam scanner scans the spot across at least a portion of the posterior capsule, e.g., at a rate of about 0.75 mm/s. For instance, the beam scanner may scan the pulsed laser beam so as to deliver about 100 μ] to about 1 mJ to a given location on the posterior capsule. The system may also include a diagnostic system, in optical communication with the human eye, that monitors the posterior capsule during the posterior capsulotomy.

[0016] Other embodiments include a system for performing a posterior capsulotomy that comprises a laser, at least one optical element, and a beam scanner. In operation, the laser generates a pulsed laser beam having a pulse duration of about 50 femtoseconds to about 500 femtoseconds, a pulse repetition rate of about 10 Hz to about 50 Hz, an energy per pulse of about 5 μ] to about 500 μΐ, and a wavelength of about 800 nm to about 1500 nm. The optical element, which is in optical communication with the laser, guides the pulsed laser beam to a spot having a diameter of about 1 μιη to about 50 μιη and a depth of focus of about 1 μιη to about 25 μιη at a location on a posterior capsule of a human eye. The beam scanner, which is in optical communication with the laser and the optical element, scans the spot with respect to the posterior capsule so as to deliver about 100 μΐ to about 1 mJ to a given location on the posterior capsule. The focused pulses cause ablation of at least a portion of the given location of the posterior capsule via photo-ionization of tissue in the human eye.

[0017] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the following drawings and the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosed technology and together with the description serve to explain principles of the disclosed technology.

[0019] FIG. 1 is a cross section of a healthy human eye. [0020] FIGS. 2A-2C illustrate the lens capsule, the anterior lens capsule, and the posterior lens capsule in a healthy human eye.

[0021] FIG. 3A is a diagram of a pulsed laser system that emits a picosecond or femtosecond pulsed laser beam suitable for performing a posterior capsulotomy.

[0022] FIG. 3B is close-up of a a picosecond/femtosecond pulsed laser beam focused to a spot on the posterior capsule.

[0023] FIG. 4 is a plot of the temperature rise in corneal tissue as a function of exposure time to nanosecond and femtosecond YAG laser pulses.

[0024] FIG. 5 is a plot of ablation threshold as a function of pulse width (duration) for pulses at different center wavelengths and pulse repetition frequencies.

[0025] FIG. 6 is a plot of ablation depth as a function of laser pulse energy and duration.

[0026] FIG. 7 is a plot of the depth of field as a function of numerical aperture for immersed and dry lenses.

DETAILED DESCRIPTION

[0027] Presently preferred embodiments of the invention are illustrated in the drawings. An effort has been made to use the same or like reference numbers to refer to the same or like parts.

[0028] The Eye and the Posterior Capsule

[0029] FIG. 1 shows a cross section of a healthy human eye 100. The white portion of the eye is known as the sclera 110 and is covered with a clear membrane known as the conjunctiva 120. The central, transparent portion of the eye that provides most of the eye's optical power is the cornea 130. The iris 140, which is the pigmented portion of the eye and forms the pupil 150. The sphincter muscles constrict the pupil 150 and the dilator muscles dilate the pupil 150. The pupil 150 is the natural aperture of the eye 100. The anterior chamber 160 is the fluid- filled space between the iris and the innermost surface of the cornea 130. The crystalline lens 170 is held in the lens capsule 175 and provides the remainder of the eye's optical power. (The lens capsule's posterior surface is known as the posterior capsule.) The retina 190, which is separated from the back surface of the iris 140 by the posterior chamber 180, acts as the "image plane" of the eye 100 and is connected to the optic nerve 195, which conveys visual information to the brain.

[0030] FIGS. 2A-2C illustrate the lens 170 and lens capsule 175 (FIG. 1) in greater detail. The lens 170 comprises epithelial cells 230 that regulate the lens's homeostatic functions and generate fiber cells, including cortical fiber cells 232 and nuclear fiber cells 234. These fiber cells are long, thin, transparent cells that form the bulk of the lens 170. They range in diameter from about 4-7 microns, have lengths of up to 12 mm, and stretch lengthwise from the anterior pole to the posterior pole.

[0031] The lens capsule 175 is a smooth, transparent basement membrane that completely surrounds the lens 170. It is very elastic and causes the lens 170 to assume a more globular shape when not under tension from zonules 238 that connect the lens capsule 175 to the ciliary apparatus 236. The curvature of the lens capsule's anterior surface, or anterior capsule 210, may greater than that of the lens capsule's posterior surface, or posterior capsule 220. The lens capsule's thickness varies from about 2-3 microns at its posterior pole to about 25-30 microns at its anterior pole.

[0032] Conventional Posterior Capsulotomies

[0033] A posterior capsulotomy is a procedure performed on the eye to remove the posterior capsule opacification (PCO; cloudiness) that develops on the posterior capsule of the lens 170 (FIG. 1) after cataract removal. A posterior capsulotomy is generally performed after positive diagnostic evidence of capsular opacification becomes established because the tendency and rate of PCO varies widely from patient to patient and from eye to eye. When performed correctly, a posterior capsulotomy improves visual acuity and contrast sensitivity and decreases glare. For example, after a posterior capsulotomy, the patient may see as well as after his original cataract surgery, e.g., at an acuity of about 20/30.

[0034] Unlike an anterior capsulotomy, which is a procedure performed during cataract extraction to remove a cataract and implant an intraocular lens (IOL), a posterior capsulotomy occurs after implantation of the IOL and can be performed using either invasive and non- invasive techniques. For instance, in an invasive capsulotomy, a surgeon cuts a hole in the posterior capsule with a knife to remove the blockage from the light path. This hole is typically 2-3 mm in diameter and is sized to prevent incursion of the vitreous into the anterior chamber through this opening. The hole may be created during cataract surgery, although this increases the risk of IOL decentration and subluxation and increases the risk of incursion of the vitreous into the capsule, which contributes to the postoperative inflammation commonly observed during healing. The hole can also be created after cataract surgery by making a small incision in the eye and performing a posterior capsulotomy using a surgical blade. Unfortunately, this involves an additional incision and opening of the capsular bag, adding to the risk of IOL displacement and ophthalmitis.

[0035] Alternatively, a posterior capsulotomy can be performed by focusing the beam from a pulsed Nd: YAG laser on the posterior capsule. This focused beam of laser light disrupts the opacification on the posterior capsule by causing the opacified area to rupture and fragment. A laser posterior capsulotomy may be performed in an ophthalmologist's office as an outpatient procedure. An hour before the procedure, the ophthalmologist or her assistant administers a drop of a pressure-lowering drug, such as timoptic or apraclonidine, to patient's eye along with a weak dilating drop to enlarge the pupil. The ophthalmologist may also anesthetize the eye, e.g., if using a contact lens to focus the beam on the posterior capsule.

[0036] In a conventional laser posterior capsulotomy procedure, the patient puts his head in the chinrest of a slit lamp microscope attached to a Nd:YAG laser. A head strap keeps the patient's head still. The ophthalmologist then places a special lens on the front of the patient's eye. The ophthalmologist applies repeated bursts from the Nd: YAG laser to the posterior capsule in a spiral or circular pattern, disrupting the PCO. An opening forms on the posterior part of the lens capsule as part of the PCO falls off of the posterior capsule and into the vitreous. The entire procedure lasts only a few minutes and generally does not cause any pain.

[0037] Although conventional laser posterior capsulotomy is generally a safe and effective procedure, it poses several risks, including undesired damage to the eye. For instance, conventional laser capsulotomy procedures may cause the posterior capsule to burst open in an uncontrolled manner, causing an incursion of the vitreous humor into the lens capsule, where it has a considerable antigenic effect. For instance, incursion of the vitreous humor into the lens capsule may lead to chronic inflammation and the formation of synecchia, which is the adhesion of the iris to the cornea or lens. It may also cause blockage of the Schlemm's canal and the trabecular meshwork, disrupting the outflow of the aqueous humor. This disruption in the outflow of the aqueous humor may cause an increase in intraocular pressure, which can lead to glaucoma or exacerbate existing glaucoma.

[0038] A conventional laser posterior capsulotomy may also cause damage to the implanted IOL, e.g., because the pulsed laser beam is focused to a spot on the IOL's surface instead of the posterior capsule's surface. Focuing the pulsed laser beam onto the IOL's surface may lead to ablation of the IOL, creating a pit and a localized point of fracture on the IOL's surface that releases products of photo-disruption of the IOL material into the eye. In addition, the pit on the IOL's surface may scatter light, thereby reducing image quality. The scattering may be worse if multiple pits are created before the posterior capsule is successfully opened. Even if the laser beam is focused properly, the photo-disruption caused by each pulse can extend over a diameter of up to 100 μιη, which may encompass the IOL's posterior surface.

[0039] Damage to the IOL may be greater when the IOL comprises a sensitive or fragile optical element, such as a liquid-crystal spatial light modulator or other electro-active element, instead of just a passive polymeric optical disc. Examples of IOLs with sensitive or fragile elements include an accommodating IOL with dual optics that are connected by pre-tensioned springs for adjusting the distance between the individual optical components. Another IOL susceptible to laser damage includes a liquid encased in flexible and compressible shells. A single nanosecond laser pulse focused into such a liquid cell or a dual optic may cause extensive and irreversible damage.

[0040] Posterior Capsulotomies with Picosecond and Femtosecond Laser Pulses

[0041] FIG. 3A illustrates a pulsed laser system 300 for posterior capsulotomies that enables a more precise disruption of PCO with a lower likelihood of incidental damage to the intraocular lens or the vitreous. This pulsed laser system 300 includes a pulsed laser 310, such as a Nd:YAG laser, that emits a pulsed laser beam 311 at a wavelength of about 800 nm or 1064 nm with a pulse width (duration) of about 1 femtosecond to about 10 picoseconds, a pulse repetition rate of about 10 Hz to about 150 kHz, and an energy per pulse of about 5 μΐ to about 150 μΐ. Other suitable pulsed lasers include, but are not limited to Yb:YAG lasers emitting at 1030 nm and doubled Er:YAG lasers emitting at 1479 m.

[0042] In some cases, the pulse width may be about 10-250 fs, about 50-100 fs, or any other suitable value or range between 1 fs and 10 ps. Similarly, the pulse repetition rate may be about 10 Hz to about 10 kHz, about 10 Hz to about 1 kHz, about 10-100 Hz, about 10-25 Hz, about 30-50 Hz, or any other suitable value or range between 10 Hz and 150 kHz. And the energy per pulse may be about 8-100 μΐ, about 10-75 μΐ, about 15-50 μΐ, or any other suitable value or range between 5-150 μΐ. The pulsed laser beam's wavelength may be about 800 nm to about 1500 nm. The pulse parameters may be chosen based on the desired ablation as described in greater detail below.

[0043] The pulsed laser system 300 also includes one or more optical elements that direct and focus the pulsed laser beam 311 to a focused spot 313 on the posterior capsule 220. In the example shown in FIG. 3 A, a mirror 320 reflects the pulsed laser beam 311 towards a collimating lens 322, which collimates the pulsed laser beam 311. The collimated pulsed laser beam 311 propagates next through a beamsplitter 324, where it is combined with a bidirectional optical coherence tomography (OCT) beam 351 from an OCT diagnostic system 350. As understood by those of ordinary skill in the art, the OCT system 351 uses broadband

interferometry to generate a three-dimensional representation of structures within the eye 100. The pulsed laser beam 311 and the OCT beam 351 reflect off a scanning mirror 326 towards the eye 100.

[0044] A therapeutic contact lens 330 disposed on the eye 100 focuses the collimated pulsed laser beam 311 to a focused spot 313 on the posterior capsule 220 as shown in FIGS. 3A and 3B. This focused spot 313 has a depth of focus of about 1 μιη to about 50 μιη (e.g., about 10 μιη, 15 μιη, 20 μιη, 30 μιη, 40 μιη, or 50 μιη) and a diameter of about 1 μιη to about 50 μιη (e.g., about 10 μιη, 20 μιη, 25 μιη, 30 μιη, or 40 μιη). In some examples, up to 50% of the depth of focus, which is the conjugate of the depth of field, may be in front of the posterior capsule 220. As understood by those of skill in the art, the depth of focus and the focused spot size depend on the pulsed laser beam's wavelength and the contact lens's focal length as well as the beam diameter, among other things.

[0045] The size of the focused spot 313 also depends on aberrations in the optical elements and the eye 100 itself. In some cases, the therapeutic contact lens 330, which may be rigid or soft, is designed to compensate for some or all of these aberrations, which may be measured before the laser posterior capsulotomy procedure. For instance, the therapeutic contact lens 330 may compensate for spherical aberration in the collimating lens 322 used to collimate the pulsed laser beam 311. Similarly, if the eye 100 is astigmatic, the contact lens 330 may include compensatory astigmatism to offset the eye's astigmatism as described in greater detail below. The therapeutic contact lens's posterior surface may be designed to contact the cornea. And the therapeutic contact lens's anterior surface may be designed to contact an optical fiber or other optical element or waveguide that delivers the pulsed laser beam 311. If desired, index-matching fluid may be applied to therapeutic contact lens's anterior surface to reduce optical coupling losses.

[0046] An ophthalmologist may perform a posterior capsulotomy on a patient's eye 100 using the pulsed laser system 300 as follows. First, the ophthalmologist may administer a pressure- lowering drug, a dilating drug, and, if desired, a local anesthetic to the eye 100. The

ophthalmologist secures the patient's eye in a fixed position, e.g., using a chin strap to hold the patient's head in place or a vacuum to keep the patient's eye 100 from moving. The

ophthalmologist views a magnified image of the eye 100 with a slit lamp microscope 360, video camera, or other suitable imaging system. Using the slit lamp microscope 360, the

ophthalmologist adjusts the pulsed laser system 300 so as to align the focused spot 313 to a desired position on the posterior capsule. (If desired, the pulsed laser 310 may emit the pulsed laser beam 311 at reduced energy levels or repetition rates to avoid ablating tissue in the eye 100 during alignment.) For instance, the ophthalmologist may move one or more lenses or other optical elements in the pulsed laser system 300 so as to move the focused spot 313 back and along the eye's optical axis (i.e., roughly perpendicular to the plane of the retina). The ophthalmologist may confirm the focused spot's position on the posterior capsule's surface using the OCT system's sensor array or a separate video camera or sensor array that can detect pulsed laser light scattered or reflected off structures in the eye 100.

[0047] Once the pulsed laser beam 311 is focused on the posterior capsule's surface, the ophthalmologist actuates the pulse laser 310 to provide one or more laser pulses at the desired pulse duration(s), energy level(s), repetition rate(s), and wavelength(s). The ophthalmologist steers the focused spot 313 across the posterior capsule's surface by tilting the scanning mirror 326 left and right, and up and down, to ablate different areas of tissue in the eye 100. For instance, the ophthalmologist may scan the focused spot 313 along a circular or spiral track on the surface of the posterior capsule 220. The size of the resulting capsulotomy may be about 1.5 mm to about 3.0 mm (e.g., about 1.75 mm, 2.00 mm, 2.25 mm, 2.50 mm, or 2.75 mm).

Because the laser beam 311 pulses on and off, the ophthalmologist can create a continuous ablation path by scanning the focused spot 313 slowly or a dotted or dashed ablation path by scanning the focused spot 313 quickly.

[0048] In some instances, the ophthalmologist may use a controller 370 coupled to the beam scanner (rotating mirror 326), pulsed laser 310, and diagnostic system (OCT system 350) to control the focused spot's trajectory across the posterior capsule 220. The controller 370 may include a processor and a user interface, such as a display and joystick or keyboard, that allows the user to choose the scanning speed, the scan pattern (e.g., raster, circle, spiral), and one or more of the pulsed laser beam's parameters so as to deliver a predetermined amount of energy to a given region of the eye 100. Once the program is selected, the controller 370 automatically actuates the pulsed laser 310 and the rotating mirror 326 scan the focused spot 313 appropriately. The controller 370 may use data from the OCT system 350 to adjust the scan trajectory, e.g., to compensate for undesired movement.

[0049] For instance, the user may select the amount of delivered energy to cause photo- ionization of eye tissue as described in greater detail below and/or to limit the temperature increase in the surrounding tissue to about 0-5° C (e.g., about 1° C, 2° C, 3° C, or 4° C) during ablation. In some cases, this translates to scanning the focused spot 313 across at least a portion of the posterior capsule 220 so as to deliver about 10 μ] to about 1 mJ to a given location on the posterior capsule 220. This may result in an ablation that is about 0.2 μιη to about 5.0 μιη deep (e.g., a depth of about 0.5 μιη, 1.0 μιη, 1.5 μιη, 2.0 μιη, 3.0 μιη, 4.0 μιη, or any other value between 0.2 μιη and 5.0 μιη). Depending on the pulse duration(s) and energy level(s), this equates to a scan rate of anywhere from about 2.5 μιη/s to about 7.5 mm/s (e.g., 25 μηι/s to 100 mm/s, 100 μηι/s to 10 mm/s, 0.25-1.0 mm/s, 0.5 mm/s, or 0.75 mm/s) for a spot size (diameter) of 50 μιη. (The scan rate or scan speed is the speed with which the beam scanner causes the focused spot 313 to move from location to location.) The ophthalmologist may confirm the focused spot's position on the posterior capsule's surface and the efficacy of the treatment using the OCT system 350 to monitor the tissue ablation, e.g., by detecting changes in the tissue's appearance or shock waves caused by rupturing cells.

[0050] Consider a posterior capsulotomy with a desired diameter of about 3 mm and a circumference of about 10 mm. At a spot size of 50 μιη, 200 adjacent spots are sufficient to traverse the posterior capsulotomy's circumference. Each spot takes 200 shots, assuming a total delivery of 1 mJ per spot, delivered in 20 msec. This means that the whole operation can be performed in about 4 seconds with these energy delivery parameters.

[0051] As understood by those of ordinary skill in the art, embodiments of the pulsed laser system 300 may include different types and arrangements of optical elements. For instance, the optical train may include prisms or additional lenses to shape the pulsed laser beam 311. It may also include one or more lengths of optical fiber to guide the pulsed laser beam 311 (and the OCT beam 351) from the pulsed laser 310 to a beam-steering or -deflecting device, such as the scanning mirror 326 shown in FIG. 3A.

[0052] Similarly, the scanning mirror 326 shown in FIG. 3A may be replaced or combined with any other suitable beam-scanning device, including but not limited to an acousto-optic deflector, a translating or rotating prism, and a translating mirror. In fiber-optic systems, the beam-steering device may include one or more translating or rotating prisms or mirrors optically coupled to the end of an optical fiber that guides the pulsed laser beam 311. [0053] In addition, the OCT diagnostic system 350 may be replaced or augmented by other diagnostic monitoring systems, including Scheimflug imaging, ultrasound biomicroscopy, microscopes, video cameras, etc. Like the OCT diagnostic system 350, these additional monitoring systems may share some or all of the pulsed laser beam's optical path. They may also use separate optical paths, such as oblique imaging, or even non-imaging diagnostic techniques, such as temperature monitoring.

[0054] Laser Ablation Mechanisms

[0055] Using a pulsed laser beam in a posterior capsulotomy with a pulse width on the order of picoseconds or femtoseconds and a peak power in the range of gigawatts and above provides all the benefits of the conventional posterior capsulotomy procedures with lower risk and fewer drawbacks. This reduction in risks stems at least in part from the mechanism by which ablation occurs. As understood by those of skill in the art, laser induced cutting or disruption of tissue may occur through one or more of three mechanisms: (1) vaporization, (2) mechanical breakdown involving the formation of sonic acoustic pulses and cavitations, and (3) electronic interaction resulting in photo-ionization and formation of ballistic electrons that interact with the lattice to cause its disruption. While all three mechanisms lead to cavities (holes) in tissue, vaporization causes extensive melting over an extended damage zone. Mechanical breakdown causes less melting but still allows the damage zone to spread, leading to roughened walls bordering the incision. Electronic interaction further reduces temperature increases and leads to the most precise cuts in the tissue.

[0056] The tissue disruption mechanism depends upon the peak power of the laser pulse. Vaporization tends to be observed only at low peak powers or when using continuous wave lasers. As the peak power increases, more energy is converted into electronic processes, such as photoionization, rather than direct conversion to molecular vibrations leading to cavitations, and mechanical breakdown, or formation of a sonic acoustic pulse. Without being bound by any particular theory, evidence suggests that laser pulses with peak powers at terawatts and higher levels, and of typical duration of picoseconds or less interact with tissue through photo-ionization alone. Photo-ionization leads to a cascade of adiabatic energy dissipation processes, including the launch of a stress wave to be launched, which in turn leads to tissue ablation.

[0057] As understood by those of skill in the art, the temperature of tissue surrounding an irradiation site, such as the focused spot 313 in FIGS. 3 A and 3B, is often used as a proxy measurement for tissue's absorption of dissipated energy. In general, higher temperatures correspond to higher energy absorption. Because energy absorption leads to damage, including ablation, it is often beneficial to confine energy absorption to the tissue being treated.

[0058] FIG. 4 is a plot of the temperature rise versus exposure time for tissue irradiated with nanosecond laser pulses (upper curve) and femtosecond laser pulses (lower curve). If a The nanosecond laser pulses and femtosecond laser pulses may have the same pulse energies, but the peak power of the femtosecond laser pulses is higher in proportion to their shorter pulse width. Nevertheless, FIG. 4 shows that the irradiated tissue's temperature remains fairly constant during irradiation with femtosecond laser pulses, whereas its temperature rises by nearly 8° C for tissue irradiated with nanosecond laser pulses. (The exponential decay at t = 80 s represents tissue rupture.) Thus, the data plotted in FIG. 4 suggest that surrounding tissue tends to absorb less energy when irradiated with femtosecond laser pulses than with nanosecond laser pulses, all other things being equal. Without being bound by any particular theory, this reduction in energy absorption may be due to the shift in the tissue disruption mechanism associated with

transitioning from nanosecond to femtosecond pulse durations.

[0059] In addition, the threshold energy requirement for ablation decreases substantially as the disruption mechanism shifts from vaporization to mechanical breakdown. The threshold ablation energy falls still further when the mechanism involves photo-ionization as suggested by FIG. 5, which shows the ablation threshold versus pulse duration for different wavelengths and pulse repetition frequencies. FIG. 5 shows that the ablation threshold varies sublinearly with pulse duration. For a pulse width of under 100 fs at a wavelength of 625 nm and a repetition rate of 8 kHz, the ablation threshold may be under 1 μ]. The ablation threshold climbs to about 10 μ] at a pulse duration of 1 ps. Evidence also suggests that using a laser pulse at a wavelength that is strongly absorbed by human tissue (e.g., wavelengths of about 800 nm to about 1500 nm, about 900 nm to about 1300 nm, or about 1000 nm to about 1100 nm) also decreases the threshold energy at which optical breakdown occurs or tissue disruption. This reduction in threshold disruption energy makes pulsed lasers well-suited for use as surgical incision tools in

ophthalmology, e.g., for cutting corneal tissue and performing posterior capsulotomies.

[0060] Pulse Width, Energy, Repetition Rate, Depth of Focus, and Spot Size

[0061] Suitable pulse peak powers, energy deposition rates, pulse repetition rates, and the scan rate to be used for posterior capsulotomy can be determined based at least in part on the desired ablation depth. As shown in FIGS. 2A-2C, the posterior capsule 220 is much thinner than the anterior capsule 210, and may therefore be cut with less energy than is used for anterior capsulorhexis (the procedure performed during IOL implantation to open the anterior capsule 210). The posterior capsule's thickness and its proximity to other structures in the eye 100 may restrict the range of possible energies per pulse and repetition rates. Put differently, the posterior capsule's size and location limit the desired ablation depth, which depends in part on the pulse duration, pulse energy, and repetition rate.

[0062] FIG. 6 is a plot of ablation depth versus pulse energy for pulses of different durations at wavelength of 1006 nm. It shows that the ablation depth tends to be greater for shorter pulses at a given pulse energy. For example, a 100 fs pulse with a pulse energy of 10 μΐ creates a pit with a depth of about 0.5 μιη, whereas a 1 ps pulse with the same pulse energy creates a pit that is only about 0.02 μιη deep. FIG. 6 also shows that ablation depth (about 0.3 μιη) is about the same for 100 fs pulse with a pulse energy of about 25 μΐ as it is for a 1 ps pulse with an energy of about 50 μΧ Without being bound by any particular theory, these data suggest that ablation depth scales with pulse peak power; that is, shorter pulses tend to yield larger ablation depths for a given pulse energy.

[0063] The data shown in FIG. 6 can be used to select an appropriate combination of pulse energy and pulse duration for ablating the posterior capsule 220 (FIG. 2). As noted above, the posterior capsule 220 is only a few microns thick (e.g., about 2-3 μιη thick), which is close to the ablation depth at threshold pulse energy for low energy nanosecond pulses (1 μιη at 500 μΧ). At conventional ranges of nanosecond YAG laser pulse energies (e.g., about 1-5 mJ), the ablation depth of a single pulse is in the range of about 5-50 μηι, which is up to 25 times the thickness of the posterior capsule 220.

[0064] TABLE 1 (below) lists different combinations of pulse width, pulse energy, and number of pulses to achieve an ablation depth of about 3.5 μιη, which is about the thickness of the posterior capsule. A laser pulse with a duration 1-30 ps may have an ablation threshold of about 10-50 μΐ per pulse and a pulse energy of about 250-600 μΐ to achieve an ablation depth of 3.5 μιη. Such a pulsed laser beam may have a repetition rate of 10-25 Hz. For a pulse width of about 100 fs, the ablation threshold drops to about 3-5 μΐ per pulse. This corresponds to an energy of about 150 μΐ to ablate 3.5 μιη of tissue, or about 30-50 pulses to ablate through the entire thickness. At a repetition rate of about 30-50 Hz, the incision of the capsule can be completed relatively quickly, e.g., about 3 seconds to about 30 seconds (5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds). Reducing the pulse width (duration) to under 100 fs (e.g., to 50 fs or 65 fs) and increasing either the repetition rate, the dwell period (the time that focused spot 313 remains focused on a given location), or both to maintain the magnitude of total energy delivered to a single spot may limit the capsule's rise in temperature as explained above.

TABLE 1 : Total laser pulse energy to ablate about 3.5 μιη for posterior capsulotomy

Pulse Width Energy for Ablation Depth Threshold Ablation No. of Pulses to Ablate of3.5 μm Energy through the Capsule

65 fs 90 μ} 0.5 μΐ 180

100 fs 150 μ] 4 μ] 38

l ps 250 μ] 10 μ] 25

30 ps 600 μ] 60 μ] 10

8 ns 0.95 mJ 500 μ] 2

[0065] Beam Steering and Energy Deposition

[0066] As described above with respect to FIG. 3A, the ophthalmologist may raster or steer the focused spot 313 along at least a portion of the posterior capsule's surface. In some cases, the pulsed laser system 300 may provide computer-controlled beam steering to deliver a preset number of pulses at each of several locations on the posterior capsule 220. The focused spot 313 dwells at each location for a dwell period determined by the pulse repetition period, pulse energy, and desired amount of energy to be delivered to the posterior capsule location. For instance, the focused spot 313 may dwell on a particular location for about 0.2 seconds to deliver 1 mJ with a pulse energy of 100 μ] at a repetition rate of 50 Hz before moving to the next location.

[0067] As indicated above, the scan rate may range from about 2.5 μιη/s to about 7.5 mm/s (e.g., 25 μητ/s to 100 mm/s, 100 μηι/s to 10 mm/s, 0.25-1.0 mm s, 0.5 mm/s, or 0.75 mm/s) for a spot size (diameter) of 50 μιη. By selecting the scan speed appropriately, the ophthalmologist can make a smooth, continuous incision in the posterior capsule 220 by the end of the entire exposure period. For example, a laser beam pulsed at a repetition rate of 1 KHz can be rastered (scanned) at a rate of 0.75 mm/s to generate a smooth incision along the raster direction. If the posterior capsulotomy is about 3.0 mm in diameter, the total time required to complete the scan at this repetition rate and scan speed is approximately 1.3 seconds. The total time could be reduced by increasing the repetition rate of the laser pulses.

[0068] Like the dwell time, the scan speed depends on the pulse energy, pulse width, repetition rate, and desired ablation depth for a given ablation threshold. However, limiting the pulse width may result in a proportional increase in the pulse energy, number of pulses, or both to achieve a desired ablation depth. Thus, there is a trade-off among peak power, pulse width, and repetition rate in to order to maintain a constant total amount of energy delivered per second. Fortunately, the total energy required to ablate through a specified depth (e.g., thickness of the posterior capsule) in one spot is known, since data on the energy required to ablate to a particular depth as a function of laser pulse width and energy per pulse are available in literature. As a result, it is possible to determine suitable combinations of peak power, pulse width, repetition rate, and scan speed for a desired ablation depth.

[0069] As explained above, limiting the laser pulse width (duration) to 100 fs or less (e.g., 50- 100 fs) may beneficially reduce the rise in temperature of the posterior capsule during the procedure. It may also be beneficial to operate at a pulse rate of 150 kHz or less, or one pulse every 6.5 μβ, which is the dissipation period of the stress wave that disrupts the lattice. For instance, consider a laser pulse width of 100 fs with a threshold energy of ablation of 8 μΐ/ρώβε and a total energy required to ablate 3.5 μηι of 150 μΧ Applying about 20-30 pulses of this laser beam produces the desired ablation, with the diameter of the ablated area being about 30-50 μιη in corneal tissue. When the diameter of the illuminated spot is about 20-25 μιη or less, the diameter of the ablated area is relatively independent of the energy per pulse as long as peak power is in the Terawatt range.

[0070] Therapeutic Contact Lens

[0071] Referring again to FIG. 3A, a therapeutic contact lens 330 focuses the pulsed laser beam 311 to a desired location on the posterior capsule. In some cases, the therapeutic contact lens 330 may focus the pulsed laser beam to a spot 313 whose diameter is about 10λ, where λ is the wavelength of the laser beam. For a Nd:YAG laser (pulsed laser 310) operating at the fundamental mode (1064 nm), this equates to a focused spot diameter of about 10 microns. In practice, however, the diameter of the focused spot 313 may be higher because the pulsed laser beam 311 passes though several layers of optical media and several optical surfaces, each of which may aberrate the pulsed laser beam 311. These surfaces include the anterior and posterior surfaces of the cornea 130 (FIG. 1) and the surfaces of the intraocular lens 340.

[0072] As explained above, one way to compensate for these aberrations is to fabricate and fit a custom therapeutic contact lens 330 to correct for ocular aberrations. This therapeutic contact lens 330 is designed by mapping the emerging wave front from the eye 100 with an optical aberrometer or other suitable wavefront measurement device. These wavefront measurements may be made at the wavelength of the laser beam that will be used to perform the surgery (the pulsed laser beam 311 in FIGS. 3A and 3B). The distance between the posterior capsule 220 and the posterior pole of the cornea 130 (FIG. 1) is measured during surgery using OCT,

Schiemphluf photography, or any other suitable biometric technique. This allows proper focusing of the femtosecond laser system, so that the posterior capsule is placed behind the focal point of the laser system, by a distance equal to half the depth of field. [0073] The acquired wavefront data is used to compute the geometry for a contact lens (e.g., therapeutic contact lens 330) whose posterior surface contacts the cornea 130 (FIG. 1). The contact lens may be designed using conventional, commercially available optical software, such as ZEMAX or Code V, using the wavefront data and the specifications of the laser beam as inputs. Once the design is completed, the therapeutic contact lens may be machined as a hard lens from an optical-grade polymethyl methacrylate (PMMA) or a silicone copolymer. The contact lens may also be a soft lens that is molded or cryomachined out of an acrylic polymer, a silicone polymer, a silicone hydrogel copolymer, or any other suitable material. In both rigid and soft embodiments, the contact lens may have a minimum diameter of about 11 mm in order to cover the "white to white" dimension on the cornea 130.

[0074] The contact lens may be designed to compensate for aberrations in a number of different ways. For example, the contact lens may be designed to effectively planarize the wavefront emerging from the eye 100 so as to allow the laser's focusing mechanism to provide an undistorted focused beam. Put differently, the contact lens may be designed be designed to compensate for aberrations introduced by the eye 100. Another possibility is to illuminate the eye 100 with a collimated laser pulse. In these cases, the therapeutic contact lens 330, the IOL 340, and the eye 100 itself may provide the desired focusing power. The therapeutic contact lens 330 also provides optical compensation of the aberrations measured on the eye 100.

[0075] In both cases, the numerical aperture of the focusing system may be controlled so as to maintain a shallow depth of field (e.g., about 25λ (about 25 μιη for a Nd:YAG laser operating at λ = 1064 nm), about 10λ or less, etc.) so as to prevent ablation of tissue surrounding the posterior capsule 220. As shown in FIG. 7, the depth of field decreases with increasing numerical aperture. The depth of field also tends to be lower for dry lenses than for immersed (wet) lenses at a given numerical aperture. FIG. 7 shows that the depth of field is about 25 μιη for a numerical aperture of about 0.25 and about 30 μιη for a numerical aperture of about 0.3.

[0076] Conclusion

[0077] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "operably couplable", to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[0078] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0079] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations.

[0080] However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations).

[0081] Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.).

[0082] It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0083] The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1. A system for performing a posterior capsulotomy, the system comprising:

a laser configured to generate a pulsed laser beam having a pulse duration of about 1 femtosecond to about 10 picoseconds, a pulse repetition rate of about 10 Hz to about 150 kHz, and an energy per pulse of about 5 μΐ to about 150 μ J; and

at least one optical element, in optical communication with the laser, configured to guide the pulsed laser beam to a spot on or about a posterior capsule of a human eye so as to cause ablation of at least a portion of the posterior capsule in the human eye.

2. The system of claim 1, wherein the laser is further configured to generate the pulsed laser beam at a wavelength of about 800 nm to about 1500 nm.

3. The system of claim 1, wherein the laser is further configured to generate the pulsed laser beam at a wavelength of about 1000 nm to about 1300 nm.

4. The system of claim 1, wherein the laser is a solid-state laser.

5. The system of claim 1, wherein the pulse duration is about 50 femtoseconds to about 500 femtoseconds.

6. The system of claim 1, wherein the pulse repetition rate is about 10 Hz to about 25 Hz.

7. The system of claim 1, wherein the energy per pulse is about 8 μΐ to about 100 μΐ.

8. The system of claim 1, wherein the at least one optical element comprises a lens to focus the pulsed laser beam to the spot on the posterior capsule.

9. The system of claim 8, wherein the lens has a depth of focus of about 1 μιη to about 250 μιη.

10. The system of claim 9, wherein the lens is configured to focus the spot such that about 0% to about 50% of the depth of focus is anterior to the posterior capsule of the human eye.

11. The system of claim 8, wherein the lens is configured to focus the spot to a diameter of about 1 μιη to about 50 μιη.

12. The system of claim 8, wherein the lens is configured to focus the spot on a posterior surface of an intraocular optic implanted in the human eye.

13. The system of claim 8, wherein the lens comprises at least one of a rigid contact lens and a soft contact lens.

14. The system of claim 13, wherein the pulsed laser beam is a collimated pulsed laser beam and the at least one the rigid contact lens and the soft contact lens is configured to focus the collimated pulsed laser beam to the spot on the posterior capsule.

15. The system of claim 13, wherein the at least one the rigid contact lens and the soft contact lens is configured to compensate for an aberration, caused by the human eye, in the pulsed laser beam.

16. The system of claim 1, further comprising:

a beam scanner, operably coupled to the at least one optical element, configured to scan the spot across at least a portion of the posterior capsule.

17. The system of claim 16, wherein the beam scanner is further configured to scan the pulsed laser beam so as to deliver about 100 μΐ to about 1 mJ to a given location on the posterior capsule.

18. The system of claim 16, wherein the beam scanner is further configured to scan the pulsed laser beam at a rate of about 0.75 mm/s.

19. The system of claim 1, further comprising:

a diagnostic system, in optical communication with the human eye, configured to monitor the posterior capsule during the posterior capsulotomy.

20. A method of performing a posterior capsulotomy, the method comprising: focusing a pulsed laser beam having a pulse duration of about 1 femtosecond to about 10 picoseconds, a pulse repetition rate of about 10 Hz to about 150 kHz, and an energy per pulse of about 5 μ] to about 150 μ J to a spot at a location on a posterior capsule of a human eye so as to cause ablation of at least a portion of the posterior capsule via photo-ionization of tissue in the human eye.

21. The method of claim 20, further comprising:

generating the pulsed laser beam.

22. The method of claim 20, wherein the pulsed laser beam is at a wavelength of about 800 nm to about 1500 nm.

23. The method of claim 20, wherein the pulse duration is about 50 femtoseconds to about 100 femtoseconds.

24. The method of claim 20, wherein the pulse repetition rate is about 10 Hz to about 25 Hz.

25. The method of claim 20, wherein the energy per pulse is about 8 μΐ to about 100 μΐ.

26. The method of claim 20, wherein focusing the pulsed laser beam comprises transmitting the pulsed laser beam through at least one of a rigid contact lens and a soft contact lens in contact with the human eye.

27. The method of claim 26, wherein the at least one of the rigid contact lens and the soft contact lens is configured to compensate for an aberration, caused by the human eye, in the pulsed laser beam.

28. The method of claim 20, wherein focusing the pulsed laser beam comprises focusing the pulsed laser beam with a depth of focus of about 1 μιη to about 25 μιη.

29. The method of claim 28, wherein focusing the pulsed laser beam comprising focusing about 0% to about 50% of the depth of focus anterior to the posterior capsule of the human eye.

30. The method of claim 20, wherein focusing the pulsed laser beam comprises focusing the spot to a diameter of about 1 μιη to about 50 μιη.

31. The method of claim 20, wherein focusing the pulsed laser beam comprises focuses the pulsed laser beam on a posterior surface of an intraocular optic implanted in the human eye.

32. The method of claim 20, further comprising:

scanning the spot across at least a portion of the posterior capsule so as to deliver about 100 μΐ to about 1 mJ to a given location on the posterior capsule.

33. The method of claim 20, further comprising:

scanning the spot across at least a portion of the posterior capsule at a rate of about 0.75 mm/s.

34. The method of claim 20, further comprising:

monitoring the posterior capsule during the ablation of the tissue with a diagnostic system.

35. A system for performing a posterior capsulotomy, the system comprising:

a laser to generate a pulsed laser beam having a pulse duration of about 50 femtoseconds to about 500 femtoseconds, a pulse repetition rate of about 10 Hz to about 50 Hz, an energy per pulse of about 5 μΐ to about 500 μΐ, and a wavelength of about 800 nm to about 1500 nm;

at least one optical element, in optical communication with the laser, to guide the pulsed laser beam to a spot having a diameter of about 1 μιη to about 50 μιη and a depth of focus of about 1 μιη to about 25 μιη at a location on a posterior capsule of a human eye so as to cause ablation of at least a portion of the posterior capsule via photo-ionization of tissue in the human eye; and

a beam scanner, in optical communication with the laser and the at least optical element, to scan the spot with respect to the posterior capsule so as to deliver about 100 μΐ to about 1 mJ to a given location on the posterior capsule.