Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F9/00825—Methods or devices for eye surgery using laser for photodisruption
  • A61F9/00834—Inlays; Onlays; Intraocular lenses [IOL]
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F2009/00885—Methods or devices for eye surgery using laser for treating a particular disease
  • A61F2009/00887—Cataract
  • A61F2009/00889—Capsulotomy

Definitions

• 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.
• near distances e.g., less than 1 m
• intermediate distances e.g., about 1 m to about 5 m
• far distances e.g., more than about 5 m
• 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.
• 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.
• an individual will get cataracts if he or she lives long enough.
• many individuals with cataracts have a cataract operation at some point in their lives.
• IOL intra-ocular lens
• Aphakia which is the absence of the crystalline lens, can also be corrected using artificial IOLs.
• An IOL can be implanted in the capsular sac following removal of the natural
• 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.
• 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.
• opacification causes the patient to lose visual acuity and to complain of glare and light sensitivity.
• PCO 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 fibrosis.
• myofibroblasts leaves the posterior lens capsule with a white, fibrous appearance.
• 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.
• 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.)
• 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.
• 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 ⁇ to about 150 ⁇ .
• 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.
• 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 ⁇ to about 100 ⁇ .
• 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 ⁇ to about 50 ⁇ .
• the lens may have a depth of focus of about 1 ⁇ to about 250 ⁇ 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.
• the lens may focus the spot on a posterior surface of an intraocular optic implanted in the human eye.
• the lens include either a rigid contact lens or a soft contact lens.
• 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.
• 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.
• the beam scanner may scan the pulsed laser beam so as to deliver about 100 ⁇ ] 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.
• Other embodiments include a system for performing a posterior capsulotomy that comprises a laser, at least one optical element, and a beam scanner.
• 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 ⁇ ] to about 500 ⁇ , 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 ⁇ to about 50 ⁇ and a depth of focus of about 1 ⁇ to about 25 ⁇ 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 ⁇ 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.
• FIG. 1 is a cross section of a healthy human eye.
• FIGS. 2A-2C illustrate the lens capsule, the anterior lens capsule, and the posterior lens capsule in a healthy human eye.
• 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.
• FIG. 3B is close-up of a a picosecond/femtosecond pulsed laser beam focused to a spot on the posterior capsule.
• 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.
• 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.
• FIG. 6 is a plot of ablation depth as a function of laser pulse energy and duration.
• FIG. 7 is a plot of the depth of field as a function of numerical aperture for immersed and dry lenses.
• 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.
• 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.
• 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.
• 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.
• PCO posterior capsule opacification
• 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.
• 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.
• 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.
• IOL intraocular lens
• 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.
• 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.
• a pressure-lowering drug such as timoptic or apraclonidine
• conventional laser posterior capsulotomy is generally a safe and effective procedure, it poses several risks, including undesired damage to the eye.
• 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.
• 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.
• 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 ⁇ , which may encompass the IOL's posterior surface.
• 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.
• 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.
• 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 ⁇ to about 150 ⁇ .
• 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.
• 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.
• 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.
• the energy per pulse may be about 8-100 ⁇ , about 10-75 ⁇ , about 15-50 ⁇ , or any other suitable value or range between 5-150 ⁇ .
• 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.
• 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.
• 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.
• OCT optical coherence tomography
• the OCT system 351 uses broadband
• the pulsed laser beam 311 and the OCT beam 351 reflect off a scanning mirror 326 towards the eye 100.
• 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 ⁇ to about 50 ⁇ (e.g., about 10 ⁇ , 15 ⁇ , 20 ⁇ , 30 ⁇ , 40 ⁇ , or 50 ⁇ ) and a diameter of about 1 ⁇ to about 50 ⁇ (e.g., about 10 ⁇ , 20 ⁇ , 25 ⁇ , 30 ⁇ , or 40 ⁇ ).
• 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.
• 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.
• the size of the focused spot 313 also depends on aberrations in the optical elements and the eye 100 itself.
• 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.
• the therapeutic contact lens 330 may compensate for spherical aberration in the collimating lens 322 used to collimate the pulsed laser beam 311.
• 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.
• 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.
• 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 may administer a pressure- lowering drug, a dilating drug, and, if desired, a local anesthetic to the eye 100.
• 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.
• ophthalmologist views a magnified image of the eye 100 with a slit lamp microscope 360, video camera, or other suitable imaging system.
• a slit lamp microscope 360 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.
• 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.
• 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.
• 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.
• 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).
• 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.
• 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.
• 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.
• 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 ⁇ ] to about 1 mJ to a given location on the posterior capsule 220.
• 0-5° C e.g., about 1° C, 2° C, 3° C, or 4° C
• this equates to a scan rate of anywhere from about 2.5 ⁇ /s to about 7.5 mm/s (e.g., 25 ⁇ /s to 100 mm/s, 100 ⁇ /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 ⁇ .
• 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.
• embodiments of the pulsed laser system 300 may include different types and arrangements of optical elements.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the temperature of tissue surrounding an irradiation site is often used as a proxy measurement for tissue's absorption of dissipated energy.
• 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.
• 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 ⁇ ].
• the ablation threshold climbs to about 10 ⁇ ] at a pulse duration of 1 ps.
• ophthalmology e.g., for cutting corneal tissue and performing posterior capsulotomies.
• 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.
• 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.
• 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.
• 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 ⁇ creates a pit with a depth of about 0.5 ⁇ , whereas a 1 ps pulse with the same pulse energy creates a pit that is only about 0.02 ⁇ deep.
• FIG. 1 fs pulse with a pulse energy of 10 ⁇ creates a pit with a depth of about 0.5 ⁇
• a 1 ps pulse with the same pulse energy creates a pit that is only about 0.02 ⁇ deep.
• ablation depth (about 0.3 ⁇ ) is about the same for 100 fs pulse with a pulse energy of about 25 ⁇ as it is for a 1 ps pulse with an energy of about 50 ⁇
• ablation depth scales with pulse peak power; that is, shorter pulses tend to yield larger ablation depths for a given pulse energy.
• 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).
• the posterior capsule 220 is only a few microns thick (e.g., about 2-3 ⁇ thick), which is close to the ablation depth at threshold pulse energy for low energy nanosecond pulses (1 ⁇ at 500 ⁇ ).
• the ablation depth of a single pulse is in the range of about 5-50 ⁇ , which is up to 25 times the thickness of the posterior capsule 220.
• a laser pulse with a duration 1-30 ps may have an ablation threshold of about 10-50 ⁇ per pulse and a pulse energy of about 250-600 ⁇ to achieve an ablation depth of 3.5 ⁇ .
• Such a pulsed laser beam may have a repetition rate of 10-25 Hz.
• the ablation threshold drops to about 3-5 ⁇ per pulse. This corresponds to an energy of about 150 ⁇ to ablate 3.5 ⁇ of tissue, or about 30-50 pulses to ablate through the entire thickness.
• 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.
• the ophthalmologist may raster or steer the focused spot 313 along at least a portion of the posterior capsule's surface.
• 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 ⁇ ] at a repetition rate of 50 Hz before moving to the next location.
• the scan rate may range from about 2.5 ⁇ /s to about 7.5 mm/s (e.g., 25 ⁇ /s to 100 mm/s, 100 ⁇ /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 ⁇ .
• 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.
• the scan speed depends on the pulse energy, pulse width, repetition rate, and desired ablation depth for a given ablation threshold.
• 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.
• peak power, pulse width, and repetition rate 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.
• the total energy required to ablate through a specified depth e.g., thickness of the posterior capsule
• 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.
• it is possible to determine suitable combinations of peak power, pulse width, repetition rate, and scan speed for a desired ablation depth it is possible to determine suitable combinations of peak power, pulse width, repetition rate, and scan speed for a desired ablation depth.
• limiting the laser pulse width (duration) to 100 fs or less 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 ⁇ , 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 ⁇ / ⁇ and a total energy required to ablate 3.5 ⁇ of 150 ⁇ Applying about 20-30 pulses of this laser beam produces the desired ablation, with the diameter of the ablated area being about 30-50 ⁇ in corneal tissue. When the diameter of the illuminated spot is about 20-25 ⁇ 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.
• a therapeutic contact lens 330 focuses the pulsed laser beam 311 to a desired location on the posterior capsule.
• the therapeutic contact lens 330 may focus the pulsed laser beam to a spot 313 whose diameter is about 10 ⁇ , where ⁇ is the wavelength of the laser beam.
• ⁇ is the wavelength of the laser beam.
• 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.
• 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,
• 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.
• 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.
• 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.
• the contact lens may be designed to compensate for aberrations in a number of different ways.
• 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.
• 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.
• 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.
• 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 ⁇ for a numerical aperture of about 0.25 and about 30 ⁇ for a numerical aperture of about 0.3.
• 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.
• 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.

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• 2013
  • 2013-03-13 WO PCT/US2013/030821 patent/WO2014018104A1/fr not_active Ceased

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