Abstract:
The invention involves the apparatus and the technique for non-invasive surgery to remove cataracted-lens tissue from an afflicted lens. The beam output of a laser is focused to a spot of maximum power density at the anterior surface of a cataracted lens and scanned over a predetermined area or areas of the cataracted lens. The beam is selective and safe since it&#39;s diffuse as it enters the eye through the cornea and is also diffuse (being divergent) in the unlikely event that the beam passes through an opening it has created in the cataracted lens. This diffusion assures against damage to either or both of the cornea and the retina. Focal power levels are used sufficient to achieve cataract material destruction thru ablative photodecomposition, thermal decomposition, photofragmentation, photoemulsification or any combination thereof. Various features are disclosed for assuring safety and uniformity in the removal of involved tissue.

Description:
BACKGROUND OF THE INVENTION 
     This application is a continuation-in-part of my application Ser. No. 592,710 and Ser. No. 592,709, both filed Mar. 23, 1984, and said application Ser. No. 592,710 is a continuation-in-part of my application Ser. No. 571,827, filed Jan. 19, 1984. 
    
    
     The invention relates to laser surgery and in particular to a method and apparatus for non-invasively removing cataractous lens tissue from an afflicted eye. 
     Present-day methods for removing cataractous tissues or cataracts are surgically invasive and relatively complicated, requiring the use of a hospital operating room, sterile conditions, sutures, and other instrumentation. Furthermore, recovery from such an operation involves a relatively long rehabilitation period and other complications attendant with invasive surgery. 
     Accordingly, it is desirable to carry out such operations using surgically non-invasive or relatively non-invasive techniques. Such non-invasive techniques would allow a doctor to conduct cataract-removal procedures on an out-patient basis, eliminating the expense and complications attendant with invasive surgery. 
     The search has continued for new methods of removing cataracts via a simple procedure which may be conducted on an out-patient basis. The present invention has been made as a result of that search. 
     BRIEF STATEMENT OF THE INVENTION 
     It is a general object of the invention to avoid or substantially eliminate above-identified problems of the prior art. 
     Another object is to provide a method and apparatus for non-invasive removal of cataractous natural-lens tissue from an afflicted eye. 
     A specific object is to meet the above objects without damage to the retina or to the cornea. 
     A further specific object is to provide the ophthalmological surgeon with a tool for performing a cataract-removal operation of the character indicated, with minimum dependence upon the manipulative skill of the surgeon. 
     The invention meets these objectives and provides certain further features in apparatus (a) which enables the beam output of a laser to be focused from a convergent-ray bundle to a focal spot of maximum power density at the anterior surface of a cataracted lens and (b) which scans the focal spot over a predetermined area or areas of the cataracted lens. The beam is afocal and therefore diffuse as it enters the eye through the cornea, and it is also diffuse (being divergent) in the controllably unlikely event that the laser energy passes through an opening it has created in the cataracted lens; the diffusion assures against damage to either or both of the cornea and the retina, for power levels sufficient to achieve ablative photodecomposition and/or thermal decomposition and/or photofragmentation and/or photoemulsification of the cataracted-lens tissue. Various features are disclosed for assuring safety and uniformity in the removal of involved tissue. 
    
    
     DETAILED DESCRIPTION 
     The invention will be illustratively described in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a simplified optical diagram of components of apparatus of the invention, shown in application to an eye in which cataracted-lens tissue is being removed; 
     FIG. 2 is a simplified block diagram of computer and scanner control elements used in connection with the apparatus of FIG. 1; and 
     FIG. 3 is a diagram on an enlarged scale to illustrate a program of scan action, involved in use of the apparatus of FIGS. 1 and 2. 
    
    
     In FIG. 1, a patient&#39;s eye 10 is shown with a cataracted natural lens 11 which will be understood to be confined by a posterior capsule or sac (not shown). The vitreous membrane 12 separates the vitreous body 13 from aqueous contents, primarily in the anterior chamber 14, the confined by the cornea 15 and including a dilated iris 16, dilation being to establish an opening of 7 to 8 mm diameter about the central axis 17 of the eye. The patient&#39;s head will be understood to have been immobilized by suitably fixed restraint (not shown), and anesthesia and akinesia of the lids and extraocular muscles will be understood to have been created by a lid-anesthetic block and retrobulbar injection of local anesthetic solution (e.g., Xylocaine 2%). 
     The objective lens 19 of a viewing microscope is shown to have been aligned with the axis 17. The microscope may be of the binocular-viewing stereo variety, including a local light source 20 and suitable optical means for projecting visible light through objective 19 for illumination of the field of view of non-invasive surgery on lens 11. The term &#34;Viewing Microscope&#34; will be understood to be a generic designation of purely optical means (such as the binocular device mentioned above) as well as electronically scanned means (such as a video camera, equipped with objective 19). 
     Field viewing via objective 19 is through a partially reflecting mirror 22 which also serves to fold the bundle of rays 23 shown issuing from a fixed objective 24 and convergent at an included angle α to the surface of the cornea 15, beyond which the rays are further convergent to a focal spot at the cataracted lens 11. The ray bundle 23 is largely comprised of laser energy from a suitable source (not shown) but having an output beam 25 which is subjected to expansion via a first pair of optical elements 26-27, and then via a second pair which includes the objective 24 and another element 28. Element 27 establishes a collimated-light region between elements 27-28, and element 28 is mounted for axial displacement, to permit Z-axis manipulation (or modulation) of the depth position of the focal spot of greatest laser-power density within the cataracted lens 11. Means such as a helium-neon laser is suggested by legend as providing a steady source of visible light via a rod or fiber element 29 having a truncated end for projecting visible light through the focusing system of lenses 28-24, so that the spot of instantaneous laser-energy focus can also be a visible spot in the field of view of the microscope. Finally, a shutter comprising a transversely actuable body 30 with a sloped reflecting end face 31 is actuable into and out of laser beam 25 for transient effective discard of laser output, when necessary or desired, all as suggested by a double-headed arrow 32. 
     The laser which produces the beam 25 may be a commercially available near-infrared pulsed laser of the neodymium-YAG variety wherein the energy of individual pulses is from about 1 to about 30 millijoules, in which case the preferred convergent-ray angle α is in the range of about 16 to about 20 degrees. In this event, the focal spot of laser energy induces photofragmentation and/or photoemulsification of cataractous tissue of lens 11. Alternatively and preferably, the laser beam 25 may be the output of an ultraviolet laser, such as an excimer laser or a frequency-quadrupled neodymium-YAG laser, producing a focal spot which decomposes the cataractous tissue of lens 11 through ablative photodecomposition and/or thermal decomposition, depending upon the wavelength of involved laser radiation; in the excimer-laser situation, the convergence angle α is preferably in the range from about 25 to about 30 degrees, the power density at the focal spot is about 1 to about 5 joules per square centimeter, and the diameter of the focal spot is in the range from about 30 to about 100 microns. The depth of ablation for each excimer-laser pulse is about 1 to 2  microns, and the frequency of pulse repetition is in the range from about 20 to about 500 pulses per second. 
     Whatever the laser selected for use of the invention, it will be understood that power levels are selected to achieve the indicated decomposition at the focal spot but to be sufficiently diffuse at entry to the cornea and, in the event of passage to the retina, to be of no harm to either the cornea or the retina. Also, the indicated decomposition of cataractous-lens tissue is not without generation of bubbles and/or fragmented debris within the aqueous of anterior chamber 14, and an irrigation/aspiration procedure is recommended to remove the same. Such procedure may involve a single canula device as described in said application Ser. No. 592,710, or, as shown, a first needle probe 33 through the cornea at one margin location may discharge a flow of isotonic purging solution into the anterior chamber 14 while another such probe 34 draws off a corresponding flow. 
     The mirror 22 is a component part of a two-dimensional scanning system for causing the focal spot (at lens 11) to sweep a regular pattern of coverage of the field (i.e., of lens 11) which is to be surgically non-invasively decomposed by laser action. The swept field is thus generally transverse or normal to the axis 17 and is also therefore generally normal to the Z-axis displacement capability of the focal spot by reason of axial displacement of optical element 28. The swept field may be covered by any of a variety of known mirror-displacement techniques, utilizing polar-coordinates (where radius R and angular displacement θ are the variables), or utilizing rectilinear coordinates (where horizontal displacement X and vertical displacement Y are the variables). For diagrammatic and descriptive purposes, it is more simple to consider mirror 22 as being mounted via a two-axis gimbal system, wherein a first pivot axis 35 (perpendicular to the plane of FIG. 1) is the reference about which mirror 22 is reciprocably tilted to produce a Y-axis component of focal-spot displacement, and wherein a second pivot axis 36 (in the plane of FIG. 1) is the reference about which mirror 22 is reciprocably tilted to produce an X-axis component of focal-spot displacement. 
     Referring now to FIG. 2, separate drive systems or actuators 37-38-39 are shown for imparting displacement motion to each of the respective X, Y and Z-axis components of scanning and depth motion of the focal spot. The X-axis and Y-axis drivers 37-38 impart rotary reciprocation about axes 36-35 in a coordinated pattern to develop a raster-like scan of the field, and the Z-axis driver 39 imparts linear reciprocation along the involved part of the axis of laser projection (including visible light projection from means 29). Drivers 37-38-39 may be servo motors responding to analog inputs. In a first mode (shown by legend to be selected at a computer 41), each of the drivers is manually operated, as suggested by associated knobs 37&#39;-38&#39;-39&#39;; and for purposes of coordinated positioning of the focal spot in the scanable X-Y field, a single joystick control 40 is shown with connections to the first-mode inputs 37&#39;-38&#39; of the X-Y field. In a second mode, computer 41 is programmed for a predetermined coordination of X-Y-Z component displacement to accomplish X-Y scanning as a function of depth (Z-axis) scanning, all within a predetermined volume of stored digital data at means 42, for outer limits of scan action. Digital/analog devices 42-43-44 couple the three limited-coordinate outputs of means 42, to the respective drivers 37-38-39, for second-mode operation. Separate outputs 46-47 are also shown for the shutter-open and shutter-close action suggested by the double-headed arrow 32 of FIG. 1. 
     An illustrative technique of use of the described apparatus will now be given, commencing after the fixation, blocking and anesthetizing procedures have been accomplished: 
     1. The surgeon maintains continuous monitoring vigil of the field (lens 11), as viewed and illuminated via objective 19. 
     2. He then initiates visible-light projection of the focal spot (of system 28-24) via injection means 29. 
     3. He positions the focal spot on lens 11 at a point on the outer perimeter which he elects to define as an outer limit of surgery, adjustment being manual at 40 and at 39&#39;. 
     4. Once satisfied as to focus on the elected outer perimeter, the operator activates means 42 to enter into storage the two-dimensional focal-spot coordinates (X-Y). 
     5. Joystick 40 is then manipulated to move the visible spot in a continuous circular path which is to become the limiting perimeter of lens-tissue decomposition; in the event of video observation via objective 19, it will be understood that an associated field-monitoring display (not shown) may include means for continuous display of the perimeter thus described by joystick manipulation and entered into storage at 42. 
     6. All is now in readiness for commencement of non-invasive laser surgery, subject to: 
     (a) centering the joystick position (focal spot on axis 17) and making a Z-axis adjustment at 39&#39; to assure focus at the anterior surface of lens 11 for this centered position; 
     (b) entering into storage a first circular perimeter of relatively small diameter D 1  to limit X-Y scan at the central focus setting Z 1  (see FIG. 3); and 
     (c) entering into storage a succession of increased diameters D 2 , D 3  . . . D n  determining progressively expanding limits of X-Y scan at each of a succession of X-Y scans, it being understood that diameter D n  corresponds to the stored outer limiting perimeter described in connection with step 5 above, and it being further understood that for each of these successive diameters, a corrective Z-axis increment of indexed drive is entered into storage, consistent with the known Z-axis or depth dimension of laser-pulse ablation or other decomposition of lens tissue, whereby each X-Y scan of its particularly limited field can be at a correct Z-axis focal-spot position of depth in lens 11. 
     7. Visible-light display of the circle of the limiting perimeter described in connection with step 5 above is no longer necessary, so that the source for light injected at 29 may be switched off, with reliance only upon stored memory of its coordinate data. At the same time, the isotonic injection/aspiration flow via 33-34 is initiated. 
     8. The laser beam 25 is activated and shutter 30 activated to expose laser radiation to lens 11 in accordance with computer control of X, Y, Z action (start/stop button at computer 41), as limited by stored perimeter coordinates for each of the succession of scans, thus effectively shaving by layer decomposition, up to the nth layer, at which point the stored outer limiting perimeter will have been reached. 
     9. The surgeon continues the X-Y scans at full or substantially full perimeter (diameter D n  for a sequence of successive Z-axis increments), until his observation of the field reveals a perceptible reddening color change of the outer perimeter (due to light reflected from posterior-eye structure). This color change signals that the surgery has progressed to a depth at which all or substantially all cataracted tissue has been removed at the perimeter (designated P in FIG. 3). 
     10. Once the disclosed perimeter P is observed, a &#34;Reverse&#34; button is pressed at computer 41 to initiate a reversed succession of limiting-perimeter X-Y scans (at diameters, D n-1 , D n-2  . . . D 1 ) for successive Z-axis or depth increments. Observation of the field should show progressively inward spreading of an annulus of color change which is indicative of accomplished decomposition of cataractous tissue, until the last X-Y scan, within the minimum limiting perimeter of diameter D 1 , whereupon shutter 30 will have been actuated to closed position and/or laser beam 25 shutdown, all under computer control. 
     11. The described sequence of operations will be understood to enable and involve a fully automatic &#34;rough cut&#34; in which all or substantially all cataractous-lens tissue will have been removed, with possible partial removal of posterior-capsule tissue (at layer 48 in FIG. 3). At the same time, careful inspection under microscope may reveal isolated local regions of remnant cataractous tissue. The &#34;fine cut&#34; removal of such remnant tissue may be accomplished by manual (e.g., joystick 40) maneuvering of a small-perimeter region within the field, at a reduced level of laser-beam energy, all while observing uniformly reddened color change of the field. Alternatively, areas to be fine-cut vs. areas not to be fine-cut may be defined by closed-perimeter development through joystick manipulation of the spot of focused light, with concurrent coordinate-data entry into storage, and one or more single X-Y scans at the adjusted appropriate depth of Z-axis depth may be automatically run via computer control, as limited by the stored coordinate-data of the involved closed perimeter or perimeters, circular or otherwise shaped. The described invention will be seen to have achieved all stated objects, with a basic simplicity of operation, in that the customary finely tuned manual skill and dexterity of the ophthalmological surgeon is no longer required. Partial removal of posterior-capsule tissue is of no significance since it is not characterized by the light-attenuating or light-diffusing or scattering properties of cataractous tissue, and no substantial harm flows from an inadvertent failure to remove all the cataractous tissue. The main point is that the invention permits removal of all the cataractous tissue, as long as the surgeon or operator is careful to recognize that it remains to be removed, however local the remnant. 
     While the invention has been described in detail for preferred apparatus and technique, it will be understood that modifications may be made without departing from the scope of the invention. For example, a simple provision for manual adjustment (suggested at 50 in FIG. 2) of the computer program can enable the operator/surgeon to change the rate of limiting perimeter increment and/or decrement as may be judged more appropriate for accommodating X-Y scan limitations, from one to the next scan, to the particular lens (11) curvatures which the skilled surgeon can perceive in his viewing of each patient&#39;s particular lens (11) contour configuration.