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Claims  |
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We claim:
1. A system for use in ophthalmic diagnosis and analysis and for support of
ophthalmic surgery, comprising,
three dimensional mapping means for sensing locations, shapes and features
on and in a patient's eye in three dimensions, and for generating data and
signals representing such locations, shapes and features,
display means receiving signals from the three dimensional mapping means,
for presenting to a user images representative of said locations, shapes
and features of the eye, at targeted locations including display control
means for enabling a user to select the target location and to display a
cross section of portions of the eye,
position analysis means associated with and receiving signals from the
three dimensional mapping means, for recognizing the occurrence of changes
of position of features of the eye,
target tracking means associated with the position analysis means, for
searching for a feature of target tissue and finding said features new
position after such a change of position, and for generating a signal
indicative of the new position, and
tracking positioning means for receiving said signal from the target
tracking means and for executing a change in the aim of the three
dimensional mapping means to the new position of said feature of the
target tissue, to thereby follow the feature and stabilize the images on
the display means.
2. The system of claim 1, wherein the display means is a video display, and
further including surgical microscope means directed at the patient's eye,
for taking video microscopic images of target areas of the ocular tissue
and for feeding video image information to the video display means to
cause such video microscopic images to be displayed, assisting the user in
diagnosis and analysis.
3. The system of claim 1, further including display control means for
enabling the user to cause to be displayed on the display means different
cross sections of the patient's tissue, as selected by the user.
4. The system of claim 1, wherein the tracking positioning means includes a
turning mirror under automatic control, and the system including an
objective lens assembly associated with the mapping means and having a
final focussing lens, with the turning mirror positioned within the
objective lens assembly and movable with respect to the final focussing
lens.
5. An instrument and system for high precision ophthalmic laser surgery at
a surgical site, comprising,
a laser pulsed source for producing a visible light laser beam having a
power capable of effecting a desired type of surgery in an eye,
laser firing control means for enabling a surgeon/user to control the aim,
depth, and timing of the firing of the laser to effect the desired
surgery,
three dimensional mapping means directed at a patient's eye, for obtaining
data representing the location and shapes of features on and inside the
eye,
microprocessor means for receiving data from the three dimensional mapping
means and for converting the data to a format presentable on a screen and
useful to the surgeon/user in precisely locating features of the eye and
the aim and depth of the laser beam within those features, and
display means for displaying microprocessor-generated images representing
the topography of the eye and the aim and depth of the laser beam before
the next pulse of the laser is fired to the surgeon/user in preparation
for and during surgery, with display control means for enabling the
surgeon/user to select areas of the eye for display, including images of
cross sections of portions of the eye.
6. The instrument and system of claim 5, wherein the display means
comprises a single video screen divided into multiple displays.
7. The instrument and system of claim 5, wherein the three dimensional
mapping means, the microprocessor means, and the display means include
means for presenting images to the surgeon/user indicating precise current
location of laser aim and depth in computer generated views which comprise
generally a plan view and selected cross sectional views of the eye
representing features of the eye at different depths.
8. The instrument and system of claim 5, including an optical path with a
focusing lens capable of controlling the focus of the laser beam on the
eye tissue, and thus the depth at which the laser beam is effective,
within about 5 microns, with depth control means for the surgeon to vary
the focus of said lens to control the depth at which the laser beam is
effective.
9. The instrument and system of claim 8, including system program means
enabling the surgeon/user to pre-program a pattern of lesions in the
ocular tissue along three axes in three dimensions and to activate the
laser to follow the preselected pre-programmed path of surgery
automatically.
10. The instrument and system of claim 5, further including tracking means
for following movements of the eye during surgery and for following the
movement of features at the surgical site of the eye with the three
dimensional mapping means and with the laser, including means associated
with the microprocessor for recognizing features at the surgical site
after said features have moved and redirecting the three dimensional
mapping system and the laser to the new location of said features.
11. The instrument and system of claim 10, wherein the display means
includes a video monitor which has a frame rate and wherein the tracking
means has the capability of following the features, identifying a new
location of those features and re-presenting images of those features to
the surgeon/user in a time period less than the frame rate of the video
display means.
12. The instrument and system of claim 10, wherein the tracking means
includes electromagnetically driven turning mirror means along an optical
path of both the three dimensional mapping means and the laser beam, for
shifting the aim of the three dimensional mapping means and a laser beam
in response to the recognized to the recognized shift in position of the
features of the eye.
13. The instrument and system of claim 10, wherein the display means
comprises a video monitor which as a frame rate and the tracking means
includes fast tracking means and backup slow tracking means with the
backup slow tracking means including means for following the features at
the surgical site, identifying a new location of said features and
re-presenting images of said features to the surgeon/user in a time period
at least as fast as the video frame rate, and the fast tracking means
being capable of tracking movement of the tissue at much faster closed
loop response times; and the backup slow tracking means having means for
analyzing tissue position based on the three-dimensional topography of the
tissue as determined, and for searching and finding, using the
microprocessor means, a feature of the tissue when that feature is not
found by the fast tracking means and for moving to the new position of the
subject tissue feature and enabling the fast tracking means tore-commence
fast tracking.
14. The instrument and system of claim 5, wherein the display means
comprises a video display monitor, and further including surgical
microscope means on a common optical path with the laser beam, for
obtaining a greatly enlarged image of a small region of the eye at which
the laser beam is directed and for generating a video image of that small
region for presentation on the display means.
15. The instrument and system of claim 14, wherein the surgical microscope
means includes intensified video camera means for imaging at low light
levels at high magnification while remaining within safe illumination
levels for human clinical procedures.
16. The instrument and system of claim 14, wherein the display means
comprises a video screen divided to show the image from the surgical
microscope means as well as topography information obtained from the three
dimensional mapping means and generated by said microprocessor means.
17. The instrument and system of claim 14, further including eye
illumination means also along the common optical path with the laser beam,
the surgical microscope and the three dimensional mapping means.
18. The instrument and system of claim 14, further including optical
zooming mean associated with the surgical microscope means, for forming an
image of adjustable magnification range of not less than tenfold increased
magnification, of said small region of the eye with optical elements
located a considerable and comfortable distance from the patient.
19. The instrument and system of claim 18, wherein the optical path
includes a final focusing lens at the exterior of the instrument, with the
final focusing lens positioned at least 100 mm from the patient's eye.
20. A system for facilitating precisely controlled surgery using a focused
laser beam, comprising,
user interface means for presenting information to a surgeon/user and for
enabling control of the surgical procedure by the surgeon/user, including
video display means for presenting precise information to the surgeon/user
relating to the location in a patient's tissue at which the system is
targeted, and the three-dimensional topography and contours of features of
the subject tissue and including means for displaying images of cross
sections of portions of the patient's tissue, and including means in the
control of the surgeon/user for scanning across the tissue to change the
information on the video display means as desired by the surgeon/user and
for enabling control of the firing of a surgical laser beam by the
surgeon/user,
an imaging system connected to the video display means, including
three-dimensional mapping means for generating, reading, and interpreting
data to obtain information regarding the location in three dimensions of
significant features of the tissue to be operated upon, and including
microprocessor means for interpreting the data and presenting the data to
the video display means in a format useful to the surgeon/user,
a short pulse visible light laser power source for generating a laser beam
capable of effecting the desired laser surgery in the patient's tissue,
including within transparent tissue of the patient,
optical path means for receiving the laser beam and redirecting the laser
beam and focusing it as appropriate toward a desired target in the tissue
to be operated upon,
surgical microscope means positioned to intercept and to be coaxial with
the optical path means, for taking surgical microscopic images of said
target along the optical path means and for feeding video image
information to the video display means, and
tracking means in the optical path means and associated with the
microprocessor means, for tracking movements of the subject tissue at
which the system is targeted without damaging the subject tissue before
the next pulse of the laser is fired and shifting the optical path means
accordingly before the next pulse of the laser is fired, such that
information and images generated by the three dimensional mapping mans and
by the surgical microscope means, as well as the aiming and position of
the laser beam, follow changes in position of the tissue.
21. The laser surgical system of claim 1, further including first control
interlock means for preventing firing of the surgical laser beam except
when the tracking means is properly tracking movements of the subject
tissue at which the system is targeted, by preventing the laser from
firing a next pulse of energy unless the tracking means has tracked the
subject tissue.
22. The laser surgical system of claim 1, further including means for
superimposing program templates over images created by the imaging system,
for automatically effecting a pre-selected pattern of laser surgery.
23. The laser surgical system of claim 1, wherein the imaging system
includes scattered light detection means for detecting scattered light
from the features of the tissue, with means for filtering out
substantially all specularly-reflected light for the scattered light
detection means.
24. The laser surgical system of claim 1, wherein the surgical microscope
means includes an intensified video camera means for imaging at low light
levels at high magnification while remaining within safe illumination
levels for human clinical procedures.
25. The laser surgical system of claim 1, wherein the optical path means
includes a final focussing lens with means for focussing the laser beam,
the three dimensional mapping means and the surgical microscope means an
appreciable and comfortable distance from the final focussing lens with
respect to the patient, a distance of not less than about 50 mm.
26. The laser surgical system of claim 25, including an objective lens
assembly of which the final focussing lens comprises a front element, and
wherein the tracking means includes a turning mirror under automatic
control of the microprocessor means, with the turning mirror positioned
within the objective lens assembly and movable with respect to the final
focussing lens.
27. The laser surgery system of claim 1, including tracking and
profilometer camera means associated with the three dimensional mapping
means and with the tracking means, also intercepting and directed along
said optical path means and having an angle of view, for obtaining data
from the patient's tissue along said optical path means and for sending
data to the microprocessor means of the imaging system, for generation of
topographical information to the presented on the video display means.
28. The laser surgery system of claim 27, wherein the tracking means
includes a electromagnetically driven turning mirror which affects the
angle of view of the tracking and profilometer camera means and also the
aim of the surgical microscope means and the laser beam, the
electromagnetically driven mirror being under the control of signals
generated by the microprocessor means of the imaging system to follow
recognized features of the patient's tissues after movement of that
tissue.
29. The laser surgery of claim 1, wherein the tracking means includes fast
tracking means for tracking movements of the tissue at tracking closed
loop response times of one millisecond or less.
30. The laser surgery system of claim 29, wherein the tracking means
further includes backup slow tracking means for analyzing tissue position
based on the three-dimensional topography of the tissue as determined, and
for searching and finding, using the microprocessor means, a feature of
the tissue when that feature is not found by the fast tracking means
within a predetermined time and for shifting the optical path means to
reposition the optical path means on the tissue feature.
31. The laser surgery system of claim 30, wherein the backup slow tracking
means includes a video camera having a frame rate, and wherein the slow
tracking means operates at tracking closed loop response times equal to
the video camera frame rate.
32. A system for use in ophthalmic laser surgery, comprising,
a laser source for producing a pulsed visible light laser beam having a
power capable of effecting a desired type of surgery at targeted tissue at
a selected surgical site in the ocular tissues,
optical path means for delivering the laser beam, including beam directing
means for controlling aim and depth of focus of the laser beam,
three dimensional mapping means for sensing locations, shapes and features
on and in a patient's eye in three dimensions, and for generating data and
signals representing such locations, shapes and features,
display means receiving signals from the three dimensional mapping means,
for presenting to a surgeon user images representative of said locations,
shapes and features of the eye including at depths in the eye selectable
by the surgeon,
position analysis means associated with and receiving signals from the
three dimensional mapping means, for recognizing the occurrence of changes
of position of features of targeted tissue of the eye,
target tracking means associated with the position analysis means, for
searching for a feature of targeted tissue and finding the feature's new
position after such a change of position, and for generating a signal
indicative of the new position of the targeted feature tissue, and
tracking positioning means for receiving said signal from the target
tracking mean and for executing a change in the aim of the three
dimensional mapping means to the new position of a targeted tissue feature
to thereby follow the feature and stabilize the images on the display
means, and for simultaneously and accordingly adjusting the aim of the
laser beam to be directed at a new position of the targeted feature.
33. The system of claim 32, further including pre-programmed surgery
execution means for automatically controlling timing of laser firing in
conjunction with automatically controlling the beam directing means as to
laser aim and depth of focal point in accordance with a preselected
surgical path in three dimensions, to fully automatically execute a
selected surgical procedure on the eye, and including tracking feedback
means associated with the target tracking means and the surgery execution
means, for sending signals to the pre-programmed surgery execution means
to confirm that a feature's new position has been found, and to
discontinue laser firing if such a confirming signal is not received by
the surgery execution means within a preselected period of time.
34. The system of claim 32, wherein the display means is a video display
monitor, and further including surgical microscope means positioned to
intercept and to be coaxial with the optical path means, for taking video
microscopic images of target areas of the ocular tissue and for feeding
video image information to the video display monitor to cause such video
microscopic images to be displayed, assisting the surgeon in the laser
surgery.
35. The system of claim 32, further including surgeon control means
connected to the beam directing means for enabling a surgeon user to
control the aim and depth of focus of the laser beam.
36. A method for conducting laser surgery, comprising,
providing a system for imaging a patient's tissue in three dimensions,
displaying images is selected formats on a display screen in front of a
surgeon, delivering a visible light laser beam at the patient's tissue and
firing the laser in accordance with a surgical path in three dimensions as
selected by the surgeon directing the laser and for tracking the patient's
tissue so as to stabilize images presented on the display screen and to
essentially immobilize the subject target tissue on the display screen in
spite of actual movements of the tissue,
placing a patient adjacent to the system,
under control of the surgeon, reviewing the patient's tissue at different
locations and along different cross-sections by selection of desired
images on the display screen,
under control of the surgeon, selecting a surgical path in three dimensions
for surgery on the subject tissue and comprising a series of locations for
targeting the focal point of and firing the laser beam to effect the
surgery, and entering the precise surgical path as selected by the surgeon
into a computer and memory of the system,
under control of the surgeon, initiating the firing of the laser along the
programmed surgical path selected by the surgeon, and
automatically interrupting the surgery along the programmed surgical path
whenever the tracking device of the system has failed to relocate a moved
tissue feature within a pre-selected period of time.
37. The method of claim 36, further including the surgeon's surveying video
microscopic images of the subject ocular tissue along with the other
images displayed on the screen, as a guide to the surgeon in controlling
the laser surgery, using a surgical microscope which views the patient's
eye tissue at substantially the same region viewed by the three
dimensional imaging system, with the system having means for presenting a
video microscopic image of the subject targeted tissue on the display
screen.
38. A method for conducting ophthalmic laser surgery using an imaging
system which displays for the surgeon precise information as the location
and configuration of features of the patient's eye and as to the aim and
depth of focal point of a surgical laser beam, comprising,
generating with a laser source a visible light laser beam having a power
capable of effecting a desired type of surgery in the eye,
delivering the laser beam along an optical path,
controlling aim and depth of focus of the laser beam with a beam directing
means associated with the laser optical path,
sensing locations, shapes and features on and in a patient's eye in three
dimensions with a three dimensional mapping means, and generating data and
signals representing such locations, shapes and features,
presenting to a surgeon user images representative of said locations,
shapes and features of the eye at the target site, on a display mans which
receives signals from the three dimensional mapping means including images
of cross sections of portions of the eye,
recognizing the occurrence of changes of position of features of the at the
targeted site, with a position analysis means associated with and
receiving signals from the three dimensional mapping means,
searching for a target site feature and finding the target site feature's
new position after such a change of position ,and generating a signal
indicative of the new position, with a target tracking means associated
with the position analysis means, and
automatically executing a change in the aim of the three dimensional
mapping means to the new position of the feature with a tracking
positioning means receiving said signal from the target tracking means, to
thereby follow the target site feature and stabilize the images on the
display means, and simultaneously and accordingly adjusting automatically
the aim and depth of the focus of the laser beam to be directed at the new
position of a feature targeted.
39. The method of claim 38, further including the step of reviewing by the
surgeon different cross-sections of the ocular tissues by manually
selecting different formats to be presented on the display means.
40. The method of claim 38, further including monitoring the patient's
tissue with a surgical microscope, and sending signals from the surgical
microscope to the display means to present video display of greatly
magnified images of the eye tissue, with the surgical microscope sharing a
common optical path with the laser beam, including a final focussing lens,
such that the video microscopic images displayed comprise a microscopic
region at the same location and focal depth that the laser beam is
directed.
41. The method of claim 40, including illuminating the patient's eye tissue
at a low light level within a safe illumination level for human clinical
procedures for said monitoring of the patient's tissue on the video
display, the surgical microscope including an intensified video camera for
imaging at low light levels at high magnification.
42. The method of claim 38, further including performing laser ophthalmic
surgery automatically, in accordance with pre-programmed surgical paths in
three dimensions, by selecting a software-based surgical path and
initiating the program to automatically aim, focus and fire the laser
sequentially at the preselected points establishing the surgical path.
43. The method of claim 42, further including automatically interrupting
the aiming and firing of the laser along the pre-programmed path whenever
the target tracking means fails to relocate a moved feature within a
preselected period of time, thereby interrupting the execution of the
pre-programmed surgery immediately when the ocular features subjected to
the surgery become transposed an unsafe distance from the intended focal
point of the laser beam.
44. The method of claim 42, wherein the system includes surgeon-controlled
means for writing and editing pre-programmed surgical path templates, and
the method including the surgeon's writing a pre-programmed surgical
template before initiating the automatic execution of the surgery along
the pre-programmed path. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates to surgical methods and apparatus, and in particular
the invention is directed to improved methods and apparatus for precision
laser surgery. In one preferred embodiment, the system of the invention is
used for effecting precise laser eye surgery. In other embodiments the
invention is applicable to non-surgical diagnostic procedures or
non-medical procedures involving precision laser operations, such as
industrial processes.
Beginning in approximately 1960, largely due to the work of Dr. Littman at
Carl Zeiss, the first surgical microscopes were introduced. Prior to that
time, surgeons who required a more magnified image of the region in which
they sought to operate used a special set of loupes that have magnifying
lenses attached to the lower portion of the spectacles, especially in
ophthalmology but also in otoringology and other specialties. In other
disciplines such as urology and internal surgery, barrel type endoscopes
were used.
Due in part to the pioneering work of Dr. Joaquin Barraquer, the surgical
microscope came into wide use in ophthalmology; at first for corneal
transplant surgery and later for cataract surgery among other procedures.
The levels of magnification, zooming capabilities, and definition of the
work region provided the surgeon the means to better direct his surgical
invasions. The end result was increasingly more accurate surgical
procedures with less trauma to the patients and a lowered level of
complications arising from surgery.
The early successes with now conventional surgical microscopes based on
direct optics for observing a target image, gave rise to the creation of
several ophthalmic study groups, most notably the International Ophthalmic
Microsurgical Study Group ("IOMSG"), to promote new concepts and
techniques in microsurgery. Since their inception in 1966, the invited
reports presented at the IOMSG meetings have been published by Karger,
Basel as their Developments in Ophthalmology series.
The advent of microsurgery brought on by the use of surgical microscopes
rekindled interest in the ophthalmic community for the pioneering of
increasingly more accurate surgical procedures. In their continued quest
for accuracy and control, ophthalmologists eventually turned to another of
the discoveries which occurred around 1960, the laser.
During the 60s, 70s, and 80s, lasers were used extensively in ophthalmology
and have now become a commonplace tool in most surgical specialties'
instrumentalia. There are several distinct advantages to the laser as a
scalpel replacement which have come into evidence.
Since a laser's energy is composed of light photons, by selecting the
wavelength of the laser emission to correspond to the preferential
absorption band of an imbedded tissue, a laser can be deemed to perform
"non-invasive" surgery, in that the surgeon need not perforate the
overlying tissue layers in order to generate an effect at a prescribed
depth.
Biological tissues are, however, broad band absorbers of energy, albeit not
uniformly so. In practice therefore, "non-invasive" laser surgery
corresponds to the effort to minimize the laser energy deposition onto the
living tissues on the way to and directly behind the targeted tissues
along the optical path of the laser beam when compared to the energy
deposition at the intended target.
During the early 1980s, Dr. Aron-Rosa (U.S. Pat. No. 4,309,998) introduced
a mode locked Nd:YAG laser for use in Ophthalmology which claimed to
evidence plasma decay induced generation of outwardly expanding shock
waves. Dr. Frankhauser (U.S. Pat. No. 4,391,275) claimed a somewhat
similar result using a Q-switched Nd:YAG laser. Ultrashort pulsed lasers
have now established themselves as the modality of choice for many
surgical procedures where propagating thermal effects are to be
suppressed.
In 1986, this approach was taken one step further by development of an
excimer pumped dye laser (not to be confused with an excimer laser which,
due to the highly energetic photons characteristic of ultraviolet lasers,
are characteristically penetrative photoablative lasers--See Trockel, U.S.
Patent Pending, Schneider and Keates, U.S. Pat. No. 4,648,400,
Srinivasian, U.S. Pat. No. 4,784,135, and L'Esperance, U.S. Pat. No.
4,665,913) which could predictably cause plasma effects with significantly
less pulse energy than previously demonstrated. (See Ferrer and Sklar,
Vol. XIV, Developments in Ophthalmology, Karger 1987, and Troutman et al.
in the same Volume and in Trans. of Am. Ophth. Soc. 1986).
Laboratory experiments conducted by the applicants herein (unpublished)
showed that imbedded cavities of diameters smaller than 0.5 micrometers
are possible provided that tightly contained plasmas could be generated
with a less than 0.5 millijoule pulse. The importance of the smallness of
the induced lesions is related to the accuracy and error tolerances which
can be achieved by the guidance and delivery systems of surgical
instruments using such lasers. Lasers today are varied. It is well
appreciated that the limitations on the achievable accuracy and control of
laser surgical instruments today is no longer paced by the development of
laser technology, but by the imaging and tracking technologies needed to
effectively use the laser.
An understanding of current practices and the range of instruments in use
for target acquisition, target recognition, and target tracking is helpful
in order to appreciate the limitations of the current technologies. The
principal instruments used today, for example in ophthalmology, for
targeting diagnostics and inspection are (1) the surgical microscope, (2)
the slit lamp microscope, (3) the keratometer, (4) the pachymeter, (5) the
corneoscope, (6) the specular microscope, (7) the A&B ultrasonic scanners,
and (8) the fundus camera. (There is a host of additional equipment used
to determine intra ocular pressure, tonometers, tensiometers, perimeters
for visual field testing, and the various devices used to approximate the
eye's refraction.) Items 1, 2, and 8 provide the surgeon with an image of
his target. Items 3, 4, 5, 6, and 7 provide the surgeon with measurements
of specific dimensions of a patient's eye and condition.
These instruments have proven efficacious to within previously acceptable
tolerances.
It is an object of the present invention to accommodate much more demanding
tolerances in laser surgery, particularly eye surgery but also for other
medical specialties, through a method, apparatus and system for
high-precision laser surgery which provides the surgeon "live" images
essentially in real time, containing the full supporting diagnostic
information about depth and position at which a surgical laser will be
fired. In a computer, the full information content of a given signal is
interpreted so as to provide this supporting diagnostic information, and
the resulting accuracy achievable is within a few human cells or better.
It is further within the scope of this invention to provide non-surgical
tools for measurement of the entire refraction of the eye rather than
relying solely on the approximate curvature (keratometric "k" readings) of
the anterior surface of the cornea. This calls for curvature readings of
all of the reflective surfaces of the eye and allows for measurement of
astigmatism and accommodation between the various optical components of
the eye.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method, apparatus and system
for carefully controlled and precision laser microsurgery includes a user
interface which gives the physician ample and precise three dimensional
visual information as to the topography of the area to be operated upon
and as to the aiming location and depth penetration of the surgical laser
beam.
The system is also useful for non-medical operations, such as industrial
operations, wherein a focused laser beam is used to perform operations on
an object subject to movement, with a high degree of precision.
In the user interface, a video screen is provided in front of the surgeon,
and the screen may even be divided into four quadrants: one quadrant
showing an image of cell walls in real time taken from a video camera
based, zooming surgical microscope which may be capable of enlargement
from 25 times to 500 times, for example. The surgical microscope image
might show a region having a dimension of as small as the order of 100
microns, for example. This real-time video image is of tissue at the
precise location and depth at which the surgical laser is currently
directed, or, in the alternative, of critical cells directly posterior to
the target which should be monitored to help assure no damage to these
sensitive tissues (e.g., corneal endothelial cells posterior to, but along
the optical axis of, a laser pulse). The surgical microscope may be used
to scan different regions at different depths under the control of the
surgeon/user, even though the laser is not yet being fired.
Two of the other quadrants of the video screen may be dedicated to
computer-generated images showing cross sections through the tissues to be
operated upon. The cross sections may be taken through two separate and
orthogonal planes, or other cross sectional planes may be selected by the
surgeon. Each computer-generated image may have a crossbar or other
indicator showing precisely where the surgical laser is currently
directed.
A fourth quadrant of the video screen may be dedicated to a
computer-generated plan view, greatly enlarged but not to the extent of
the surgical microscope view. In this last quadrant, and/or on any of the
other cross sectional representations, there may be superimposed a
"template" selected by the physician, for automatically controlling the
path of the firing of the laser, to precisely control the size and
location of the laser generated lesions to be formed in the course of the
microsurgery. Thus, the surgeon may draw on a bank of prior experience and
knowledge relating to a particular form of microsurgery, such as
ophthalmic surgery directed to a particular type of correction. By laying
the template in effect on the computer-generated image of the region, he
can then execute a pre-stored program to automatically execute the surgery
in a precisely controlled preselected manner. It should be noted, however,
that without the accompanying three-dimensional targeting capability and
the image stabilization means, the utility of template generated surgery
would be severely limited either to non-sensitive tissues (where high
three dimensional precision is not usually a consideration) or to
relatively stationary or immobilized targets (not usually available at
high magnification in a biological system which is "alive").
The accuracy of the apparatus and system of the invention preferably is
within 5 microns, as determined by a closed loop system which incorporates
actual measurement of the target position within the loop. (For example, a
microstepper motor based assembly may have a single step resolution of 0.1
micron verified against a motor encoder, but thermal gradients in the
slides may yield greater variations. Moreover, position of the slide can
be verified via an independent optical encoder, but the random vibrations
of the target can invalidate the relative accuracy of the motor.) Thus,
the surgeon has knowledge of the shape of tissues within the field of view
and the precise location of where he is aiming the instrument within those
structures, within an accuracy of 5 microns. Such precision was not
attainable in a | | |
