Abstract:
An ophthalmic laser system generating a first beam at a wavelength suitable for performing selective laser trabeculoplasty and selectively generating a second beam at a wavelength suitable for performing secondary cataract surgery procedures. The laser system is able to select between directing the first beam or the second beam to the eye of a patient. The first beam is suitably generated at 1064 nm from a Nd:YAG laser and the second beam is frequency doubled to 532 nm in a KTP doubling crystal.

Description:
RELATED APPLICATION  
         [0001]    This application is a continuation-in-part of PCT Application Serial No. PCT/AU03/001224, filed Sep. 18, 2003.  
         FIELD OF THE INVENTION  
         [0002]    This invention relates to a treatment laser instrument designed for use by ophthalmologists for performing selective laser trabeculoplasty (for treating glaucoma) procedures and secondary cataract surgery procedures. In particular, the invention relates to an ophthalmic laser system that can operate effectively in both the infrared region (for secondary cataract treatment) and other regions, such as the green region (for glaucoma treatment).  
         BACKGROUND TO THE INVENTION  
         [0003]    Glaucoma (abnormal intra-ocular pressure) is a major eye problem that leads to blindness in a significant percentage of the world population. Glaucoma is the most common cause of blindness in the world today. The established technique for treating glaucoma is drug based. Alternative treatment modalities have been sought to avoid the side effects and non-specificity associated with drug based treatments. Over the past few years a technique known as selective laser trabeculoplasty (SLT) has been invented by Latina. The technique is described in U.S. Pat. No. 5,549,596, assigned to The General Hospital Corporation. Latina describes the use of a frequency doubled Nd:YAG laser for the SLT procedure.  
           [0004]    SLT is an improvement over a previously used technique referred to as argon laser trabeculoplasty (ALT). ALT uses a thermal effect to coagulate loose trabecular meshwork cells believed to be present in patients with glaucoma. Because an Argon laser is essentially CW (if pulsed, the pulse duration is long compared to thermal transfer mechanisms) there is significant heat transfer into surrounding tissue. This results in damage to otherwise healthy cells. It has been found that the ALT process can only be used once or twice before collateral damage prevents any further benefit from ALT treatment.  
           [0005]    In contrast, SLT utilizes a pulsed laser (the pulse duration is short compared to thermal effects) so there is minimal heat transfer to surrounding tissue. SLT has been found to be repeatable, unlike the ALT process.  
           [0006]    A detailed discussion of the SLT modality and a comparison with ALT is found in Ocular Surgery News published 1 Mar. 2000.  
           [0007]    Another very common ophthalmic treatment is secondary cataract surgery. The most effective laser for secondary cataract surgery is a Nd:YAG laser operating at 1064 nm. These lasers are typically referred to as photodisruptors as they act by non-thermal mechanisms to cut tissue. A typical ophthalmic laser system consists of the laser head and a beam delivery system coupled to a conventional slit lamp assembly. A typical laser system for secondary cataract surgery is described in U.S. Pat. No. 6,325,792.  
           [0008]    At present, two separate laser systems are necessary to perform the procedures for treating the two most common eye problems.  
           [0009]    An attempt to address the problem of requiring multiple lasers for different treatment modalities has been described in U.S. Pat. No. 6,066,127. This patent describes a system for changing the laser cavity between a pulsed configuration and a continuous wave configuration by introducing a movable intracavity element. This approach is problematic because it is extremely difficult to maintain optimum alignment of the laser cavity with a movable intracavity element.  
           [0010]    A better solution is required.  
         SUMMARY OF THE INVENTION  
         [0011]    In one form, although it need not be the only or indeed the broadest form, the invention resides in an ophthalmic laser system comprising a laser module producing a beam of short pulses of radiation with high energy density at a first wavelength; a first beam path incorporating an attenuator, beam shaping optics, and means for directing the beam at said first wavelength to an eye of a patient; a second beam path incorporating a frequency conversion module that converts the beam at the first wavelength to a beam at a second wavelength, an attenuator, and means for directing the beam at said second wavelength to the eye of the patient; and extracavity deflecting means for selectively deflecting the beam at said first wavelength into the second beam path, said means being operable between a first position in which the beam at said first wavelength follows the first beam path and a second position in which the beam at said first wavelength is deflected to said second beam path.  
           [0012]    Preferably the beam at said first wavelength is a 1064 nm beam produced by a Nd:YAG laser, and said beam at said second wavelength is frequency-doubled to 532 nm. The beam is suitably doubled by a KTP doubling crystal or similar frequency doubling device.  
           [0013]    Preferably the extracavity deflecting means comprises a half wave plate and polarizer. The half wave plate is suitably remotely operable, such as by a servo motor or solenoid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    To assist in understanding the invention, preferred embodiments will be described with reference to the following figures in which:  
         [0015]    [0015]FIG. 1 shows a general schematic view of an ophthalmic laser system;  
         [0016]    [0016]FIG. 2 shows a schematic side view of the photodisruptor optical system of the ophthalmic laser system in FIG. 1; and  
         [0017]    [0017]FIG. 3 shows a schematic view of the SLT optical system of the ophthalmic laser system in FIG. 1;  
         [0018]    [0018]FIG. 4 shows a schematic view of the energy monitor system;  
         [0019]    [0019]FIG. 5 shows a schematic of the beam-shaping module of the photodisruptor optical system;  
         [0020]    [0020]FIG. 6 shows a schematic of the beam-shaping module of the SLT optical system; and  
         [0021]    [0021]FIG. 7 shows an external view of an ophthalmic treatment device incorporating the ophthalmic laser system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Referring to FIG. 1, there is shown an embodiment of an ophthalmic laser system  1  useful for treating glaucoma and secondary cataracts. The system is comprised of a laser module  2 , a photodisruptor optical system  3  and SLT optical system  4 , as shown separately in FIGS. 2 and 3.  
         [0023]    The ophthalmic laser system  1  of the present invention combines the photodisruptor optical system  3  and SLT optical system  4  into one integral unit, which uses a single laser module  2 . The laser module  2  is a Q switched Nd:YAG laser operating in the infrared spectrum. The laser emits a beam at 1064 nm wavelength, having a pulse width of less than 5 nsec. Other laser modules (such as Nd:YLF, Yb:YAG, etc) will also be suitable as will be readily apparent to persons skilled in the art.  
         [0024]    Referring now to FIG. 1 and FIG. 2, a pulsed beam from the laser module  2  is attenuated at attenuator/beam steering module  5 . An energy monitor system  6  measures the energy in each pulse. For the photodisruptor optical system the desired energy density is 0.3-10 mj in an 8-10 μm spot. A half wave plate  7  within the attenuator/beam steering module  5  is adjusted to regulate the intensity of the pulsed beam in the photodisruptor optical system  3 . A polarizing plate  8  may deflect the pulsed beam to the SLT optical system  4  depending on the orientation of the half wave plate  7 . The function of the attenuator/beam steering module  5  will be described in more detail later.  
         [0025]    Beam shaping optical module  9  expands the pulsed beam before it travels up to the folding mirror module  10 . The expanded beam is then focused by objective lens  13  to produce the 8-10 μm beam waist at the treatment site which is required to produce photodisruption. An aiming laser module  11  provides a continuous, visible laser beam that is split into two beams and deflected by folding mirror module  10  to give a targeting reference for the treatment beam. These two aiming laser beams converge with the pulsed treatment beam at the target site in a patient&#39;s eye  12  via objective lens  13 . An operator  14  views the patient&#39;s eye  12  through the folding mirror module  10 . A safety filter  15  protects the eye of the operator. The folding mirrors  10   a,    10   b  are positioned so that the viewing axis of the operator is not impeded. It will be appreciated by those skilled in the art that the mirrors may be replaced by prisms or other suitable beam steering optics.  
         [0026]    Referring to FIG. 3, the SLT optical system  4  comprises a mirror  16  that directs a deflected pulsed beam from the polarizing plate  8  in the attenuator/beam steering module  5  of FIG. 1 to the frequency conversion module, which is a frequency doubling module  17  in the preferred embodiment. To maximize frequency doubling efficiency the entire pulsed beam is deflected by attenuator/beamsteering module  5 . The frequency doubling module  17  converts the output of the laser module to half the wavelength so that the output of the SLT optical system is in the visible spectrum. For the particular embodiment the Nd:YAG laser module operates in the near infrared at 1064 nm which is frequency doubled to 532 nm, which is in the green region of the visible spectrum. The green pulsed beam is effective in treating glaucoma in patients.  
         [0027]    The pulsed green beam may be attenuated at the SLT attenuator  18  to regulate the energy in the pulsed green beam. An energy monitor system  19  measures the energy in each pulse. For the SLT process the desired energy density is 0.01-5 J/cm 2 , as described by Latina.  
         [0028]    Other wavelengths may be suitable for other ophthalmic applications in which case the frequency conversion module may triple or quadruple the fundamental frequency. In some applications it may even be desirable to use a tunable frequency conversion module, such as an optical parametric oscillator.  
         [0029]    A beam shaping module  20  adjusts the beam profile to provide an even energy distribution at the treatment plane. The green beam then travels to a second folding mirror module  21 . A second aiming laser module  22  provides a single aiming laser beam which is deflected by the second folding mirror  21  and transmitted through folding mirror module  10  and objective lens  13 , as shown in FIG. 1. The continuous visible laser aiming beam generated by the second aiming laser module  22  coincides with the green pulsed beam at the target site in a patient&#39;s eye  12  via objective lens  13  and contact lens  23 . As mentioned earlier, the mirror could be replaced by prisms or other suitable optical elements.  
         [0030]    Although two separate aiming laser modules  11 ,  22  are described, it will be appreciated that a single aiming laser module could be used with appropriate beam deflecting optics, such as a mirror, to direct the aiming laser beam through folding mirror module  10  for off-axis illumination or folding mirror module  21  for on-axis illumination.  
         [0031]    The present invention provides an ophthalmic laser system for treating glaucoma and secondary cataract conditions, using a single laser source. The present invention integrates two known laser treatment techniques, SLT and photodisruptor, into one integrated system.  
         [0032]    The method used to direct the laser beam from the laser module  2  to the photodisruptor optical system  3  or the SLT optical system  4  will now be described in detail. Referring to FIG. 1, the attenuator/beam steering module  5  first receives a pulsed and linearly polarized beam from laser module  2  at half wave plate  7 . The pulsed beam passes through the half wave plate to the polarizing plate  8 .  
         [0033]    The orientation of the half wave plate  7  determines the amount of the pulsed beam that is passed through the polarizing plate  8  into the photodisruptor optical system  3 . The orientation of the half wave plate  7  can be adjusted by motorized means so that the polarization angle of the component of the resulting beam which coincides with the transmission characteristic of the polarizing plate  8  will be passed through to the beam shaping module  9 . However, as the half wave plate  7  is rotated, the polarization of the beam is changed. Accordingly, only some portion of the beam will be transmitted.  
         [0034]    In the photodisruptor mode for treating secondary cataracts, the half wave plate  7  is rotated to permit transmission of the required pulsed laser beam emitted from the laser module  2 . If the SLT mode is required, the half wave plate  7  is oriented so that all the beam is reflected from the polarising plate  8  to the mirror  16  of the SLT optical system  4 .  
         [0035]    The ophthalmic laser system described above allows an operator to select the mode of treatment to be administered to a patient, simply by choosing one of two optical paths. A simple adjustment of the half wave plate  7  determines whether a SLT or a photodisruptor mode is chosen for treating glaucoma or secondary cataracts respectively. The adjustment of the half wave plate can be motorized so the selection of treatment modality may be by simple button selection.  
         [0036]    It will be appreciated that the directing of the Nd:YAG laser beam into the photodisruptor module path or the SLT module path can be achieved by any suitable means (such as a mirror) but the use of a polarizing plate is preferred.  
         [0037]    As mentioned above, each optical system includes an energy monitor system in the preferred embodiment. A schematic of the components of an energy monitor system is shown in FIG. 4. A small percentage of the beam is split by optic plate  24  towards a photodiode  25 . A number of filters and diffusers  26  are positioned in front of the photodiode  25 .  
         [0038]    As seen in FIG. 2, once the pulse beam is attenuated to the desired power, the beam is further conditioned by beam shaping optical module  9 . The beam shaping optical module  9  is shown in more detail in FIG. 5. Lenses  27  and  28  form a beam expander which expands the 3 mm diameter beam from the laser module  2  by ten times. The expanded beam is reflected into the optical viewing path by the folding mirror  10  which uses a wavelength selective coating to avoid blocking of the viewing path. The beam from folding mirror  10  is then focused by objective lens  13  to produce the 8-10 μm beam waist at the treatment site which is required to produce photodisruption.  
         [0039]    Referring to FIG. 6, the SLT beam is conditioned by beam shaping module  20  before the folding mirror module  21 . The beam shaping module  20  consists of two lenses  28 ,  29  that form a beam expander that is designed to produce a well defined treatment spot with an even energy distribution.  
         [0040]    The invention is conveniently embodied in an ophthalmic treatment device of the type shown in FIG. 7. The treatment device  30  is of the conventional form having a slit lamp assembly  31  mounted on a table  32  which is in turn mounted on a height adjusting pedestal  33 . The slit lamp assembly  31  is movable with respect to the table  32  using joystick  34 , in conventional manner. The ophthalmic laser system is mounted in the body  35  of the slit lamp assembly  31 . This is achieved by using a compact laser cavity and careful placement of optical components.  
         [0041]    The ophthalmic laser system is controlled by a control panel  36 . The joy stick  34  may incorporate a fire button  37  to fire the laser, or alternatively a foot pedal (not shown) may be used.  
         [0042]    The invention has been described with reference to one particular embodiment however, it should be noted that other embodiments are envisaged within the spirit and scope of the invention. For instance, one or two aiming lasers could be used, the photodisruptor or SLT beam path could be selected by a movable mirror, or the beam shaping optics could have a different configuration.