U.S. patent application number 09/741407 was filed with the patent office on 2001-09-20 for optical tracking based on a change in optical reflection across a reference mark on an object to be tracked.
Invention is credited to Lai, Ming.
Application Number | 20010022648 09/741407 |
Document ID | / |
Family ID | 22177124 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022648 |
Kind Code |
A1 |
Lai, Ming |
September 20, 2001 |
Optical tracking based on a change in optical reflection across a
reference mark on an object to be tracked
Abstract
An optical tracking device and method are disclosed for tracking
lateral movement of an object. A scanning probe beam and a
time-resolved detection are implement in the disclosed technique. A
particular application is for tracking the eye movement during a
laser surgery.
Inventors: |
Lai, Ming; (Dublin,
CA) |
Correspondence
Address: |
FISH & RICHARDSON, PC
4350 LA JOLLA VILLAGE DRIVE
SUITE 500
SAN DIEGO
CA
92122
US
|
Family ID: |
22177124 |
Appl. No.: |
09/741407 |
Filed: |
December 19, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09741407 |
Dec 19, 2000 |
|
|
|
09300194 |
Apr 27, 1999 |
|
|
|
6179422 |
|
|
|
|
60083248 |
Apr 27, 1998 |
|
|
|
Current U.S.
Class: |
351/209 |
Current CPC
Class: |
A61F 9/008 20130101;
A61B 3/113 20130101; A61F 2009/00872 20130101; A61F 2009/00897
20130101; A61F 2009/00846 20130101; A61F 9/00804 20130101 |
Class at
Publication: |
351/209 |
International
Class: |
A61B 003/14 |
Claims
What is claimed is:
1. A method for optically tracking movement of an object,
comprising: selecting a reference mark on an object where first and
second surface areas on opposite sides of the reference mark on the
object are different in an optical property; repetitively scanning
an optical probe beam from the first surface area to the second
surface area across the reference mark at a selected scanning speed
along a selected direction so that a property of a scattered probe
beam that is scattered from the object changes due to the change in
the optical property in the first and second surface areas when the
probe beam passes through the reference mark; detecting a time at
which the change in the property of the scattered probe beam occurs
when the probe beam scans across the reference mark; determining a
time difference between the time and a reference time; and using
the time difference to determine an amount of movement of the
object along the selected direction.
2. The method as in claim 1, wherein the reference mark includes a
boundary between the first and second surface areas with different
optical reflectivities, and the property in the scattered probe
beam is an optical amplitude.
3. The method as in claim 2, wherein the object is an eye and the
reference mark includes the limbus of the eye with the sclera area
being the first surface area and the cornea area being the second
surface area.
4. The method as in claim 1, further comprising: using the measured
movement of the object along the selected direction to control a
direction of another optical beam incident to the object to follow
the movement of the object.
5. The method as in claim 4, further comprising: scanning the other
optical beam over the object according to a predetermined spatial
pattern in addition to directing the other optical beam to track
the object.
6. The method as in claim 1, further comprising: selecting a second
reference mark located between the first and second surface areas
and orientated in a direction different from the reference mark;
repetitively scanning a second optical probe beam from the first
surface area to the second surface area across the second reference
mark at a second selected scanning speed along a second selected
direction so that a property of a second scattered probe beam that
is scattered from the object changes due to the change in the
optical property in the first and second surface areas when the
second probe beam passes through the second reference mark, wherein
the second selected direction is different from the selected
direction; detecting a time at which the change in the property of
the second scattered probe beam occurs when the second probe beam
scans across the second reference mark; determining a time
difference between the time and a second reference time; using the
time difference to determine an amount of movement of the object
along the second selected direction; and determining movement of
the object in a surface defined by the selected direction and the
second selected direction.
7. The method as in claim 6, wherein the second selected direction
is substantially orthogonal to the selected direction.
8. The method as in claim 6, further comprising: using the measured
movement of the object along the selected direction and the second
selected direction to control a direction of another optical beam
incident to the object to follow the movement of the object.
9. The method as in claim 8, further comprising: scanning the other
optical beam over the object according to a predetermined spatial
pattern in addition to directing the other optical beam to track
the object.
10. The method as in claim 6, wherein the scanning of the probe
beam is independent of the movement of the object.
11. The method as in claim 6, wherein the scanning of the probe
beam is controlled to follow the movement of the object.
12. The method as in claim 1, wherein the scanning of the probe
beam is independent of the movement of the object.
13. The method as in claim 1, wherein the scanning of the probe
beam is controlled to follow the movement of the object.
14. An optical device, comprising: a probe scanner to scan an
optical probe beam across a reference mark on an object where first
and second surface areas on opposite sides of the reference mark on
the object are different in an optical property, said probe scanner
operable to repetitively scan the optical probe beam from the first
surface area to the second surface area across the reference mark
at a selected scanning speed along a selected direction; and a
probe detection unit positioned to receive a scattered probe beam
that is scattered from the object and to detect a change in a
property of the scattered probe beam due to the change in the
optical property in the first and second surface areas when the
probe beam passes through the reference mark, wherein said probe
detection unit is operable to detect a time at which the change in
the property of the scattered probe beam occurs and an amount of
movement of the object along the selected direction according to a
time difference between the time and a reference time.
15. The device as in claim 14, further comprising: an optical
scanner to receive and scan an optical beam over the object
according to a selected spatial scanning pattern; and a control
unit operable to control the optical scanner to track the movement
of the object according to the detected amount of movement of the
object, wherein scanning of said probe scanner is independent of
the movement of the object.
16. The device as in claim 15, wherein the optical beam is operable
to interact with the surface of the object so as to change a shape
of the object and the probe beam does not change the shape of the
object.
17. The device as in claim 14, further comprising: an optical
scanner to receive and scan an optical beam over the object
according to a selected spatial scanning pattern; a shared optical
scanner positioned to receive both said optical beam from said
optical scanner and said optical probe beam from said probe scanner
and to direct both said optical beam and said probe beam to the
object; and a control unit operable to control the shared optical
scanner to control said optical beam and said probe beam to track
the movement of the object according to the detected amount of
movement of the object.
18. The device as in claim 14, wherein said probe scanner includes
a probe light source to produce the probe beam, a projecting lens
to project the probe beam, and a rotating wheel having a plurality
of apertures located between the projecting lens and the probe
light source.
19. The device as in claim 14, wherein said probe scanner includes
a probe a probe light source to produce the probe beam, and a
rotating wheel having a plurality of projecting lenses to rotate
said projecting lenses into an optical path of the probe beam, one
at a time.
20. The device as in claim 14, further comprising: a second probe
scanner to scan a second optical probe beam across a second
reference mark located between the first and second surface areas
and orientated in a direction different from the reference mark,
said second probe scanner operable to repetitively scan the second
probe beam at a second selected scanning speed across the second
reference mark along a second selected direction, wherein a second
scattered probe beam produced from scattering of the second probe
beam from the object is detected to determine an amount of movement
of the object along the second selected direction.
Description
[0001] This application claims the benefit of U.S. provisional
application No. 60/083,248, filed on Apr. 27, 1998.
TECHNICAL FIELD
[0002] The present invention relates to tracking an object by
optical means, and more specifically, to automatic monitoring and
tracking a movable object such as an eye.
BACKGROUND
[0003] Monitoring and tracking a laterally movable object are
important in many applications. In certain applications, it is
desirable to have a tracking device not only to monitor the
displacement of the object but also to follow the movement of the
object without a significant delay. Tracking and following the eye
movement during a laser eye surgery is an example of such
applications.
[0004] Many eye-tracking devices have been developed for eye
surgery with lasers, in particular, for photo-refractive surgery. A
typical photo-refractive surgery scans an UV laser beam on the
cornea to sculpture the profile of the corneal outer surface, one
layer at a time. This procedure can correct various refractive
disorders of the eye, including nearsightedness, farsightedness,
and astigmatism.
[0005] Any eye movement during the surgery may adversely affect the
outcome of refractive correction. Immobilizing the eye movement
during a surgery has been proven difficult in practice. A device
automatically tracking and compensating the eye movement is an
attractive approach. For the nature of photo-refractive surgery,
the tracking device needs to be fast, accurate, and reliable.
[0006] U.S. Pat. No. 5,620,436 discloses use of a video camera to
monitor the eye's movement and to determine the position of an
aiming beam on the eye. U.S. Pat. No. 5,632,742 teaches projecting
four laser spots on the eye and using a set of peak-and-hold
circuits to determine the position of the eye. In these designs, a
ring shape reference is used for determining the eye position, and
spatial stationary infrared beams are applied to illuminate the
reference. Sophisticated imaging system and electronics, such as a
CCD camera or four peak-and-hold circuits are implemented to
determine the position of the reference. The ring shape references
are practically either the limbus or the iris of the eye and the
whole ring is needed as the reference for determining the eye
position.
SUMMARY
[0007] Generally, any optically identifiable reference mark or
indicator affix to an object can be used to indicate the position
and movement of the object. The devices and methods disclosed
herein apply an optical probe beam scanning repeatedly and rapidly
over such a reference mark. A change in the position of the
reference mark can then be determined by measuring the change in
the delay between a predetermined reference time and the detected
time at which the optical probe beam intercepts the reference mark.
The reference mark can be artificially formed on the object, or
alternatively, can be an inherent mark on the object.
[0008] For the application of eye tracking, a reference mark may be
the limbus of the eye, which is the natural boundary between the
transparent cornea and the white sclera. Optical scattering changes
from one side of the limbus to the other significantly. Therefore
the position of the limbus can be detected by measuring the timing
of the change in the scattered light of the probe beam as the probe
beam scans across the limbus. The devices and methods of the
present disclosure will be described by examples of eye tracking
using a section of the limbus as the reference mark.
[0009] In one embodiment, a section of the limbus is used as the
reference mark and the x-y positions of the limbus are determined
by two sets of linear positioning devices. The two linear
positioning devices are set for measurement along two mutually
orthogonal axes.
[0010] Each linear positioning device consists of a scanning beam
generator, a detection assembly, and a processing electronics. The
scanning-beam generator projects an infrared probe beam onto the
eye and scans the probe beam across a section of the limbus
repetitively. The detection assembly detects the infrared light
scattered from the eye. The detected scattered-light signal is a
time-resolved signal and has a sequence of sharp steps
corresponding to the probe beam repeatedly across the limbus. The
timing of each sharp step depends on the limbus position at the
corresponding scan. The processing electronics converts the timing
of the sharp steps into the positioning signal indicating the
position of the eye.
[0011] With the positioning signal, a system computer can then
generate a control signal to steer the surgical laser beam to
follow the movement of the eye. Hence, accurate laser surgery can
be achieved even though the eye may move during the surgery.
[0012] In this embodiment, about a quart of the limbus is used to
determine the x and y positions of the eye. This is particularly
important for a new type of refractive surgery so called LASIK, in
which part of the limbus is obstructed during the surgery. This
embodiment can use the limbus section that is not blocked and thus
it can use the limbus as a reliable reference mark for LASIK.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram showing one embodiment of an
open-loop optical monitoring and tracking system;
[0014] FIG. 1a shows timing diagrams of the scattered-light signal
from the eye and the reference signal generated by a scanning beam
generator.
[0015] FIG. 2 is a schematic diagram showing an embodiment of a
close-loop optical monitoring and tracking system;
[0016] FIG. 3a is a schematic diagram showing one embodiment of a
scanning-beam generator;
[0017] FIG. 3b is a schematic diagram showing another embodiment of
a scanning-beam generator;
[0018] FIG. 3c is a schematic diagram showing a third embodiment of
a scanning-beam generator;
[0019] FIG. 4 is a block diagram showing a processing electronics
for the optical monitoring and tracking systems of FIGS. 1 and
2;
[0020] FIG. 5a is a schematic diagram illustrating simultaneous
tracking of an eye in two different directions by two scanning
probe beams projected on the limbus.
[0021] FIG. 5b shows two scanning probe beams projected on a
partially obscured limbus to track the eye movement in two
different directions in a LASIK surgery.
DETAILED DESCRIPTION
[0022] FIG. 1 shows a schematic diagram of one embodiment of an
optical monitoring and tracking system 100 for an eye 10. The
system 100 implements an open loop configuration that includes a
position sensing module 101, a system computer 80, and a beam
steering module 60 (e.g., a x-y scanner). The position-sensing
module 101 projects a scanning probe beam 4 and monitors the
position of the eye 10. The system computer 80 controls the beam
steering module 60 to guide a surgical laser beam 62 to a desired
position on the eye 10. As an open loop configuration, the scanning
probe beam 4 dose not follow the movement of the eye 10 and only
one beam steering module 60 is required.
[0023] For illustration purpose, the position-sensing module 101
shown in FIG. 1 is only a linear positioning device and is for
monitoring one-dimensional eye movement only (e.g., along
x-direction). To determine the eye's movement in two dimensions, a
second set of linear positioning device is needed to monitor the
movement of the eye 10 along a second different direction, e.g.,
the y-direction orthogonal to the x-direction.
[0024] The position-sensing module 101 comprises a scanning beam
generator 30, a collection lens 6, a photo-detector 7, and a
processing electronics 50. The limbus 11 of the eye 10 is used as a
reference mark 20. The scanning-beam generator 30 projects a
scanning probe beam 4 across the reference mark 20. The scanning
probe beam 4 may repeatedly start from a fixed point and is scanned
at a constant speed over a predetermined tracking range. The
scanning-beam generator 30 also produces a reference signal 31 to
indicate a reference point of the scanning.
[0025] The lens 6 is disposed at a proper position relative to the
eye 10 to collect the scattered light 5. The photo-detector 7
receives and converts the scattered light 5 into an electrical
signal, i.e., the scattered-light signal 8. The scattering from the
sclera side 13 of the eye 10 is approximately 20 times stronger
than that from the transparent cornea side 14. Hence, the intensity
of the scattered light 5 exhibits a significant change when the
probe beam 4 scans across the limbus 11. This intensity change of
the scattered light 5, in turn, generates a sharp step in the
scattered-light signal 8. The timing of this sharp step depends on
the position of the eye 10.
[0026] In one implementation, an infrared laser beam (at 830 nm) of
about 100 .mu.W is used as the scanning probe beam 4 and the
collection lens 6 having an aperture of about 18 mm is located
about 30 cm away from the eye 10. Detector 7 receives a
scattered-light power of about 20 nW when the probe beam 4 is on
the sclera side.
[0027] FIG. 1a shows timing diagrams of the scattered-light signal
8 and the reference signal 31. The scattered-light signal 8 has a
sequence of sharp steps and each sharp step 9 corresponds to a scan
of the probe beam 4 across the limbus 11. The sharp step 9 has a
time delay Td with respect to the reference point 31s of the
scanning. This time delay Td depends on the position of the limbus
11 and varies as the eye 10 moves. The processing electronics 50,
which may include a microprocessor, processes the reference signal
31 and the scattered-light signal 8 to determine this time delay Td
for each scan. This time delay Td is then used to determine the
position of the limbus 11. The lines Vth represent the threshold
voltage for triggering.
[0028] To operate the tracking device 100, an initial time delay
Td.sub.0 or eye position is first registered and stored in the
system computer 80. The time delay Td.sub.0 of subsequent scans is
then compared with the initial time delay Td.sub.0 to calculate a
displacement of the eye 10. With this calculated displacement, the
system computer 80 can generate a control signal 81 to drive the
beam steering module 60 to steer the surgical laser beam 62 to
follow the movement of the eye 10.
[0029] As an open loop device, the scanning probe beam 4 does not
move with the eye 10. The beam steering module 60 can be used
simultaneously to compensate the eye movement and to scan the
surgical laser beam 62 on the eye 10. In this case, the control
signal 81 may consist of a scanning signal and an offset signal.
The scanning signal scans the surgical laser beam 62 in a
predetermined pattern while the offset signal offsets the scanning
to compensate for the eye movement. This open-loop device is
relatively simple and is good for tracking small movement of the
eye 10.
[0030] FIG. 2 shows a schematic diagram of a close-loop tracking
device 200. In the close-loop configuration, both the scanning beam
4 and the surgical beam 62 are steered to the eye 10 by a common
steering module 60. Consequently, both the scanning probe beam 4
and the surgical laser beam 62 follow the movement of the eye
10.
[0031] In implementation, the scanning probe beam 4 is directed
into the beam steering module 60 and reflected onto the reference
mark 20 (i.e. the limbus 11). A dichromatic mirror 70 is placed in
the path of the scanning probe beam 4 to couple the surgical laser
beam 62 into the beam steering module 60. The dichromatic mirror 70
reflects light at the wavelength of the surgical laser beam 62 but
transmits light at the wavelength of the scanning probe beam 4. The
surgical laser beam 62 is reflected from the beam steering module
60 and projected onto the eye 10.
[0032] Again, the scattered light 5 from the reference mark 20 is
collected by a lens 6 and detected by a photo-detector 7, which
produces an output of scattered-light signal 8. Similar to the open
loop device 100, the scatted-light signal 8 has a sharp step 9
corresponding to each scan of the probe beam 4 across the boundary
of the reference mark 20. The sharp step 9 has a time delay Td with
respect to the reference point 31s of corresponding scan. A
processing electronics 50 determines this time delay Td for each
scan.
[0033] To operate the tracking device 200, an initial time delay
Td.sub.0 or eye position is first registered and stored by the
system computer 80. The time delay Td of later scans is then
compared with the initial time delay Td.sub.0. Any deviation of Td
from Td.sub.0 is used as an error signal to drive the beam steering
module 60 such that to bring the error signal toward zero. Through
this process, the beam steering module 60 deflects the scanning
probe beam 4 to follow the movement of the eye 10. Seeing the same
deflection as the scanning probe beam 4, the surgical laser beam 62
can thus impinge on any predetermined position of the eye 10 as if
the eye remains stationary.
[0034] As a close loop device, the relative position between the
trace of the scanning probe beam 4 and the reference mark 20 is
kept constant during the operation. The beam steering module 60 is
thus used solely for compensating the eye movement. A second beam
steering module 90 is required to scan the surgical laser beam 62
on the eye 10 for surgery purpose. In this case, the control signal
81 to beam steering module 60 is simply the driving signal to
compensate the eye movement. The control signal 82 to beam steering
module 90 is simply the programmable signal to scan the surgical
laser beam 62. The close loop device 200 is relatively more
complicate but it can track a relative large displacement of the
eye 10.
[0035] FIG. 3a shows one embodiment of a scanning-beam generator
30a that produces a scanning probe beam 4a. The generator 30a
includes an infrared-light source 32a, which produces an
infrared-light beam 33a projected onto a rotating blade 35a. The
blade 35a has a set of pinholes 36a evenly distributed on a circle.
A motor 34a drives the blade 35a at a constant rotation speed. The
pinholes 36a are thus scanned across the infrared-light beam 33a at
a constant speed.
[0036] A lens 37a focuses onto a reference ring 20 (i.e. the
reference mark) the infrared-light beam 38a that is transmitted
through the pinhole 36a. As the pinhole 36a is scanned across the
infrared beam 33a, the image of the pinhole 36a is scanned across
the reference ring 20. Thus, the transmitted infrared beam 38a may
serve as the scanning probe beam 4 of FIG. 1.
[0037] A beam splitter 39a directs a small portion of the beam 38a
onto a reference photo-detector 40a. This reference photo-detector
40a has a tiny light-sensitive area and the detected signal is thus
a sequence of spikes as the split beam scans across the reference
detector repetitively. The output signal from the photo-detector
40a defines a reference point of the scanning and serves as the
reference signal 31 of FIG. 1.
[0038] In this embodiment, the infrared-light source 32a can be
simply a light emitted diode. The repetition rate of the scanning
probe beam 4 can be up to the kilohertz range. For example, the
motor 34a may run at 100 rotation per second and the blade 35a may
have 10 pinholes 36a on it.
[0039] FIG. 3b shows another embodiment of a scanning-beam
generator 30b producing a scanning probe beam 4. The generator 30b
includes an infrared-light source 32b, which produces an
infrared-light beam 33b directed onto a disk 35b. The disk 35b
holds a set of identical lenses 36b evenly distributed on a circle.
A motor 34b rotates the disk 35b and the lenses 36b are scanned
across the infrared-light beam 33b at a constant speed.
[0040] The infrared-light beam 38b transmitted through a lens 36b
is focused onto a reference ring 20. As the lens 36b is scanned
across the infrared-light beam 33b, the focused beam 38b is scanned
across the reference ring 20. Thus, the focused infrared-light beam
38b may serve as the scanning probe beam 4 of FIG. 1.
[0041] Again, a beam splitter 39b directs a small portion of the
beam 38b onto a reference photo-detector 40b. The output signal
from the photo-detector 40b defines a reference point of the
scanning and serves as the reference signal 31 of FIG. 1. In this
embodiment, the infrared-light source 32b is preferably either a
pre-focused beam or a point source.
[0042] FIG. 3c is a schematic diagram showing a third embodiment of
a scanning-beam generator 30c producing a scanning probe beam 4.
The generator 30c includes an infrared-light source 32c, which
produces an infrared-light beam 33c directed into a lens 37c. The
transmitted infrared beam 38c is reflected by a mirror 36c and
focused onto a reference ring 20. The mirror 36c is driven by a
scanner head 34c to scan the infrared beam 38c across the reference
ring 20. Thus, the transmitted infrared beam 38a may serve as the
scanning infrared beam 4 of FIG. 1.
[0043] Similarly, a beam splitter 39c directs a small portion of
the beam 38c onto a reference photo-detector 40c. The output signal
from the photo-detector 40c defines the reference point of the
scanning and serves as the reference signal 31 of FIG. 1. The
scanner 34c scans the beam 38c back and forth. A synchronized
signal from the scanner 34c can also be used as a reference point
of the scanning. In this embodiment, the infrared-light source 32c
can be either a collimated beam or a point source.
[0044] FIG. 4 is a block diagram showing one embodiment of the
processing electronics 50. This processing electronics 50 includes
a first trigger circuit 52, a second trigger circuit 54, and a
microprocessor 58. The reference signal 31 from the scanning beam
generator 30 is fed into the first trigger circuit 52 to produce a
TTL output signal 53 carrying the timing of the reference signal
31. The scattered-light signal 8 from the photo-detector 7 is fed
into the second trigger circuit 54 to produce a TTL output signal
55 carrying the timing of the scattered-light signal 8.
[0045] The microprocessor 58 reads in the signal 53 and signal 55
to calculate a time delay Td between the two signals. This time
delay Td indicates the relative position of the reference mark 20
to the scanning probe beam 4. This delay Td can be compared with an
initial delay Td.sub.0 registered and stored by the system computer
80 at the very beginning of the tracking.
[0046] For an open loop device 100, any change of the delay Td from
its initial value Td.sub.0 can be used to determine a displacement
of the eye 10 from its initial position. The determined
displacement can then be converted into an offset signal combined
in the control signal 81 to deflect the surgical laser beam 62 to
follow the movement of the eye 10.
[0047] For a close loop device 200, any deviation of the delay Td
from its initial value Td.sub.0 is used as an error signal to drive
the beam steering module 60 such that to bring the error signal
toward zero. The beam steering module 60 thus deflects both of the
scanning probe beam 4 and the surgical laser beam 62 to follow the
movement of the eye 10.
[0048] The above-described operation of the processing electronics
50 is repetitively for every scan of the probe beam 4. The first
trigger circuit 52 and the second trigger circuit 54 should be
reset automatically after the signal 53 and signal 55 are read by
the microprocessor 58.
[0049] The processing electronics 50 shown in FIG. 4 is for one
axis tracking. To track the two-dimensional movement of the eye 10,
another pair of the trigger circuit should be used.
[0050] FIG. 5a shows schematically two scanning probe beams 4x and
4y projected on a reference ring 20 (the limbus 11) for
two-dimension positioning detection. The two scanning probe beams
4x and 4y are set along two approximately perpendicular directions
and occupy about one quart of the limbus 11.
[0051] FIG. 5b shows how the tracking device remains full
performance for LASIK. In a LASIK surgery, a disk shape flap is
laminated from the cornea and about one quart of the perimeter is
uncut to maintain the flap attached to the cornea. The flap is
folded over during the surgery to allow laser ablation on the
corneal bed. The folded flap 15 covers about one third of the
limbus 11 and may disable those eye tracking devices which rely on
the whole limbus as the reference. The corneal bed after the flap
is folded becomes less smooth and the scattered light from the
corneal bed may disturb those tracking devices that use the pupil
as a reference.
[0052] As illustrated in FIG. 5b, the two scanning beams 4x and 4y
use only the limbus section that is not covered by the cornea flap
15. Therefore, the limbus 11 remains as a good reference for the
tracking device of the present invention.
[0053] In all the above description, the tracking device is to
steer a surgical laser beam 62 to follow the eye movement.
Obviously, the same tracking mechanism can guide any other light
beam or simply an optical path to follow the eye movement.
Therefore, the above technique can be used to other surgical or
diagnosis application in which compensating the eye movement is
desirable.
[0054] Although the above embodiments are described with a specific
reference to eye tracking, the techniques can be generally used to
track lateral movement of other object with an optical reference
mark. Various modifications can be made without departing from the
scopes of the appended claims.
* * * * *