Surgery – Instruments – Light application
Reexamination Certificate
1999-07-23
2001-11-27
Cohen, Lee (Department: 3739)
Surgery
Instruments
Light application
C606S010000, C606S011000, C606S012000, C128S898000, C219S121600, C250S252100, C356S302000, C356S307000
Reexamination Certificate
active
06322555
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to laser surgery apparatus and methods and more particularly to the monitoring of laser systems used in ophthalmic laser surgery.
BACKGROUND OF THE INVENTION
Laser systems have been used in ophthalmic surgery for modifying the cornea of the patient. Systems such as shown in U.S. Pat. No. 4,729,372 to L'Esperance contemplate the controlled ablation of the cornea of the patient with a pulsed excimer laser. Operations performed with the system include corneal transplants and keratotomies.
The application of laser light to the cornea may be controlled by spot scanning of the cornea or by the use of masks. As shown in U.S. Pat. No. 5,108,388 to Trokel, the masks may, for example, employ slits or holes. Repeated scanning or pulsing through properly selected masks are employed to reshape or reprofile the curvature of the cornea to treat myopic or hyperopic conditions. The system can also be used, for example, to remove corneal sections for corneal replacements or transplants.
A system used by applicant for performing ophthalmic laser surgery is shown in FIG.
1
. The system includes an Excimer laser
10
such as a COMPex
201
Excimer laser. An optical rail
12
contains optical elements for controlling the laser pulses and delivers spatially modulated pulses to a shuttling device
14
, which acts as a selectively positionable turning mirror, for directing the laser pulses to a selected one of the two surgical stations,
16
and
18
. The system allows surgery to be performed on one patient while a second patient is readied, and improves the utilization efficiency of the operating room, laser and optical rail.
FIGS.
2
(
a
) and (
b
) are vertical and horizontal cross-sectional views and ray traces of an optical path which may be used in the system of
FIG. 1
to deliver pulses from the laser
10
′ to the cornea of the patient at
20
. A light beam from the laser is shaped and focused by a series of lenses
22
,
24
and
26
. A beam homogenizer
28
is located next in the optical path as shown. A spatial modulator
30
provides beam dimensions and orientations in accordance with predetermined treatment parameters appropriate for the surgery required by the patient. The spatial modulator may include a conventional iris and variable, slit mask(s) as well as controls for changing the axis of orientation of the mask(s). These systems are motor driven on command from a treatment computer containing a treatment algorithm into which the treatment parameters have been programmed.
The shuttling turning mirror
32
selectively directs the laser beam to one or the other surgical stations along one of the system arms
34
or
36
shown in FIG.
1
. An imaging lens
38
is located in each arm. Pulses from the imaging lens are reflected by end turning mirror
40
toward the target area
42
on the patient's cornea.
It is important that pulses delivered to the cornea have the appropriate energy to ensure that the reprofiling, cutting or ablation produced is consistent with the prescribed treatment for the patient. Systems of the type shown in
FIG. 2
have employed photo detectors selectively positionable in the main optical path of the system at the end turning mirror for the purpose of calibrating or adjusting the energy delivered by the system during a preliminary calibration phase. See U.S. Pat. No. 5,772,656 to Kloptek.
Other control systems have been proposed such as disclosed in U.S. Pat. No. 4,941,093 to Marshall et al., which includes a measurement device to measure the cornea surface profile and a feedback control system to control the laser operation in accordance with the measured and desired profiles. U.S. Pat. No. 5,423,801 to Marshall et al. discloses further control of the laser by a measurement signal from a beam-shaping means and/or cornea while it is exposed to irradiation by the laser. U.S. Pat. No. 4,973,330 to Azema et al. discloses a photo detector associated with a semi-transparent mirror, which is intended to furnish a treatment computer with information relative to the energy of the pulses exiting the laser before the laser beam reaches the controlling device. A laser calibration device is shown in U.S. Pat. No. 5,464,960 to Hall et al. which employs a phantom cornea with superimposed thin films of alternating colors.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a more efficient and reliable technique for monitoring laser surgery.
It is another object of the present invention to monitor the energy of actual laser pulses used in the ophthalmic laser surgery after spatial modulation.
It is another object of the present invention to monitor a sequence of laser pulses of varying beam dimensions used in ophthalmic laser surgery.
It is another object of the present invention to provide a parallel, fail-safe system for detecting discrepancies between a programmed treatment and the laser pulses actually administered to the cornea of the patient.
These and other objects and features will be apparent from the following description of the present invention contained herein.
The present invention relates to methods for laser surgery and particularly for the modification of the cornea of a patient with a laser system in accordance with treatment parameters appropriate for the patient and for continuously verifying that a predetermined sequence of laser pulses of correct energy are being delivered to the cornea of the patient. In practicing the method, pulses of laser light are generated and controlled. The controlled pulses are simultaneously directed to the cornea of the patient and to a photo detector. An output signal of the photo detector is converted into a value representative of the light energy delivered to the cornea of the patient.
The light energy value may be compared to a reference value derived from system calibration information and from the treatment parameters for the patient. An indication of the performance of the laser system is provided in response to this comparison.
In preferred embodiments of the method, the pulses of laser light are produced by a laser triggered by a triggering signal from a treatment computer. The pulses of laser light may be spatially modulated responsive to signals from the treatment computer. The treatment computer is programmed with the treatment parameters appropriate for the patient.
In this embodiment, the reference value is produced by a monitoring computer separately programmed with the treatment parameters appropriate for the patient. The double entry of treatment parameters helps expose data entry errors in the treatment computer, since such an error will create a discrepancy between the light energy value and the reference value. The comparison may be initiated by the monitoring computer responsive to the laser triggering signal. When the light energy value of a predetermined number of pulses deviates a predetermined amount from the corresponding reference values, the system may produce an alarm signal or shut down the system.
In another preferred embodiment of the present invention, the simultaneous directing of the spatially modulated pulses is performed by beam-splitting the pulses to direct a portion of electromagnetic energy from the pulse to a photo detector. The directed portion of electromagnetic energy of the laser pulse is converted to fluorescent light which is detected by the photo detector. One or more neutral density filters may be employed to filter the fluorescent light so that the photo detector and associated amplifier are operated in a generally linear response mode across a range of expected incident radiation energies.
The present invention also includes an apparatus for producing a predetermined treatment sequence of laser pulses of predetermined energy and for monitoring the energy of the pulses as the pulses are being delivered to the patient. Such an apparatus may include an excimer, pulsed laser, and a beam homogenizer and a spatial modulator in the optical path of the laser. First electronic circuit
Burns Doane Swecker & Mathis L.L.P.
Cohen Lee
Farah A.
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