The Z axis tracker
Invention field
The present invention relates to a kind of method and apparatus of following the tracks of the body surface position.The present invention is specifically designed to the focus point of accurate locating laser in the surgery laser surgery, for example be applied in the refraction correction and phacoemulsification operation (phacoemulsifaction procedure) of peeling off (intrastromal ablation) operation, eyes in the substrate that comprises cornea, eye's lens was in a liquid state and was easy to remove in the phacoemulsification operation this moment.Though the present invention is applied as example with these and is described, be not subjected to their restriction.For example, be appreciated that to obtain that the present invention can be applicable to other need carry out the medical laser operation that the degree of depth is followed the tracks of.
Background technology
Intrastromal photorefractive keratectomy (substrate in PRK or IPRK) also is referred to as to peel off in the substrate, comprise with a branch of short pulse (<50ns), near-infrared or visible laser focus on the intracorneal point.Be different from excitation laser, the visible and near-infrared laser of short pulse can not fully be absorbed by the tissue of biological cells height, thus generation photodissociation or " peeling off ".And the mechanism that tissue is removed includes plasma media (plasma-mediated) photodisruption, and is attended by empty bubble and the generation of shock wave below the laser eyepiece district.If it is enough big that energy density reaches in tissue, so optical breakdown will take place, and have a small amount of tissue vaporization at the laser focus point place.
A large amount of research (for example referring to " the adopting neodymium-yttrium, lithium fluoride picosecond laser that the cat cornea is carried out near-sighted intrastromal photorefractive keratectomy " of being write by people such as Habib among " ophthalmology document " (1995) 113:499-505, or referring to " the adopting the Nd:YLF laser of 1053nm to carry out the picosecond laser in situ keratomileusis " of being write by people such as Hoi among " anaclasis operation periodical " (1996) 12:721-728) has been carried out in the feasibility aspect that adopts PRK in the substrate to proofread and correct the error of refraction of eyes.PRK makes the epithelial cell of cornea and endotheliocyte intact in the substrate, thereby prevents to produce the potential complication that for example infects, and is easy to cicatrize a wound.If in the cornea of cat, adopt ultrashort Nd:YLF laser, it seems that from the substrate area of cornea the influence of tissue is limited so, with fritter heat waste zone, and become normal collagen stroma shape (Habib, Speaker, Kaiser ﹠amp by six months post-operative recovery; Juhasz (1995)).Therefore PRK can provide more predictable refraction results in the substrate, and can reduce relatively and adopt the complication that conventional art produced.US5,112,328 have described a kind of method and apparatus that substrate interior angle film is peeled off of using.
Proposed to adopt an amount of tissue of technology removal in the substrate, thereby realized refraction correction and needn't produce flap (flap), perhaps in lasik surgery, cut flap in laser in situ keratomileusis (LASIK), to finish the similar mode of mode to those.The micro-keratome that is used at present in the refractive surgery of LASIK for example is a kind of like this mechanical devices, promptly has sizable fault potentiality, and the eyes to patient cause severe impairment sometimes.Adopt and peel off in LASIK, to produce flap in the substrate, realize that with peeling off in the substrate refraction change is much easier than attempting.The interior flap of substrate can make lasik surgery carry out saferly and be simpler, does not need to adopt a plurality of mechanical devices.
Have significant advantage although peel off the operation that for example reflects laser surgery in the employing substrate, have the difficulty in the reality when being registered to every kind of laser pulse on the intracorneal correction position, promptly mean and to implement the IPRK operation routinely.In lived eyes, every kind of pulsed laser deposition not only is strict with on the position of check point follows the tracks of eyes in the horizontal and vertical directions, also require leave or towards lasing light emitter vertically on (hereinafter being called " Z " direction) follow the tracks of eyes.At present also do not improve such technology, promptly adopt appropriate resolution when undergoing surgery, can on the Z direction, follow the tracks of the technology of eyes exactly.
U.S. Pat 5,162,641 have described a kind of eye tracking system, and this system is used for measuring the degree of depth motion in the ocular tissue based on the principle of confocal microscopy in laser surgery.This invention is provided with a branch of illumination light, a pin hole and a detector behind the optics of laser system, thereby monitors the degree of depth of reflection along optical axis.With this system layout become to make from the light of the maximum intensity of eye reflections can direct projection to this detector module.Eye tracker focuses on the reflecting surface of front, cornea tear layer (tear layer) for example, or one have the similar reference point of known connection to the target of laser beam, and needn't focus on this target itself.When histokinesis that laser beam focuses on, just reduced from the signal of photoelectric detector/pin hole structure.Then utilize the change of these signals to come the optics of driving laser system, so that compensate the motion of this tissue, the focus of locating laser thereby mobile objective lens is laid equal stress on.The focus monitoring also can realize by this pin hole of dither/photoelectric detector assembly, thereby determine the direction that signal increases.
U.S. Pat 5,336,215 (intelligent surgery laser) have proposed a kind of eye stabilizing mechanism shared with the computer control ophthalmic laser system, specifically, and in PRK or phacoemulsification are performed the operation in the substrate.This laser delivery system utilizes suction to fix eyes.The contact lens that has edge suction (limbal suction) has been got rid of the needs to noncontact eye tracker spare.A removable objective lens is controlled the position of laser focusing point on X and Y or Z direction by various ocular tissues.Even so, for example above-mentioned the sort of device is unsatisfactory with peeling off in the operation in the substrate: this is because they can add the interior pressure of oxeye, eyeball is deformed, and can cause patient uncomfortable.This contact lens also must be designed to consistent with the profile (topography) of independent patient's cornea.In addition, depending on that suction is fixed on device on the eyes also is the one of the main reasons that present micro-keratome leads to complications.
The current techique that can be used for the meter facial contour is optical coherence tomography imaging (OCT), also is referred to as the short-phase dry length interferometry.OCT generally includes from a low-coherence light source (for example superluminescent diode) and isolates light, and the part of this light is transmitted into observes object (for example cornea), and the part of remainder is transmitted into a reference surface (for example plane mirror).Then light concentrates on a detector place again.Only when apart from the distance of this reference surface with apart from the distance of observing object when consistent, just really take place to interfere mutually from the light beam of these two light paths, thereby form Strength Changes at this detector place.This reference surface is normally scanned by front and back, can adopt the easy detected signal of electronic filter thereby the Strength Changes at this detector place forms one.
U.S. Pat 5,465,147 have described a kind of general system and technology based on OCT, and this system and technology adopt the ccd array as detector to obtain the digital picture in a zone of object, thereby show interference figure.In this case, adopt one, and this bubbler does motion towards and away from beam splitter according to predetermined pattern, thereby produce the interference signal of a detectable variation with reference to bubbler rather than a plane mirror.Also propose this bubbler simultaneously and should be around an independent depth point (depth point) make back and forth vibration or dither, transversely provide a series of two dimensional images so that be in this independent depth point according to predetermined frequency.
U.S. Pat 5,644,642 have provided the tracking equipment of staring of a kind of OCT of employing.This equipment adopts the elevation information through the relevant eye feature of measuring, and improves the accuracy of following the tracks of eyes on X and Y direction.Adopt optical fiber with such radiation delivery to scan reference mechanism, i.e. this radiation has short moment coherence length, and is spatial coherence basically.This mechanism produces a radiating focus point, scans the pupil plane of laterally passing through pupil/iris boundary.Adopt the grating pattern or the coarse scanning pattern that characterize the some grid, and each the some place gather information on grid.Interfere from the radiation of eye reflections and light beam from reference path, this reference path has the known optical path length that intermittently changes.Then when the equal in length of the optical path length of this reflected radiation and this reference path, the output of OCT equipment has just produced.When the edge of pupil/iris is passed in scanning, just produce a discernible signal, thereby determine depth information.A computer checks that change in depth surpasses that position of scheduled volume.Then space coordinates and geometric equation formula are combined, thus the edge and the center of definite pupil.
In U.S. Pat 5491524, mention the application of OCT in other ophthalmology, comprised the imaging of intraocular structure, be used for determining corneal, iris, crystalline lens and anterior chamber's multiple measurement.This patent proposes a kind of OCT cornea mapping device, and this device utilizes the spiral of a rotation with reference to illuminator, thereby the cycle that produces the interference signal that detects changes.The height setting of this helical surface is become like this, and promptly the depth scan that is provided by the optical path length variation of the reference arm of interferometer has the order of magnitude of corneal thickness, thereby has reduced scanning amount and data acquisition time.In a specific embodiment, detect a signal peak and be in order to determine the degree of depth of specific cornea structure, be in order to follow the tracks of the radian with cornea and the reference path illuminator of shape and adopt successive like this peak value.
Thereby OCT provides cheap, the noncontact of a kind of definite ophthalmic depth point and has not had the method for infringement.But, OCT device of the prior art is usually from the upper and lower of the anterior corneal surface inside until eyes, come the scan reference surface around gamut that may signal, this OCT device is also in X, the enterprising line scanning of Y direction simultaneously, but this scanning also is not very effective as a tracking technique.And, the mechanism as a kind of accurate tracking of realization in ophthalmologic operation with OCT is not proposed as yet, this may be because it is too slow at this application medium velocity.
Therefore, the object of the present invention is to provide a kind of improved tracking and device, this tracking and device can be followed the tracks of the motion of object on axial or Z direction, and so advantageous applications in ophthalmologic operation.
The brief introduction of invention
The present invention mainly provides a kind of method of following the tracks of the body surface position, this method is included between the light beam with short moment coherence length and produces an interference signal, and this light beam comprises respectively from the elementary beam (primary beam) and the reference beam of body surface reflection or scattering.The reference surface that scans in the light path of this reference beam carries out around the position that produces interference signal, thereby the position of this reference surface indicates the position of body surface.In one aspect of the invention, control the position of this reference surface, thus in the indicating positions place keeps sweep limits a predetermined point.On the other hand, this interference signal be adopt characteristic predetermined repeat to change carry out synthetic.
The present invention also provides the device that is used for following the tracks of the body surface position, this device comprises interferometer arrangement, this interferometer arrangement is used for producing an interference signal between the light beam with short moment coherence length, and this light beam comprises respectively from the elementary beam and the reference beam of object reflection or scattering.A reference surface is arranged in the light path of this reference beam, and this device also further comprises a kind of like this equipment simultaneously, promptly is used for scanning this reference surface around the position that produces interference signal, and the position of this reference surface indicates the position of body surface.On the one hand, this device comprises the equipment of controlling this reference surface position, thereby predetermined point in the sweep limits is remained on this indicating positions place.
On the other hand, this device comprises the characteristic predetermined equipment that comes the interferometric modulator signal that repeats to change that utilizes.
This reference surface preferably includes the equipment of reflection or scattering.It is favourable realizing modulating by the position of this reference surface of dither extraly.
Preferably realize control like this: promptly come this reference surface of dither, and described predetermined point is remained on this indicating positions place according to this peak interference signal around the position of detection peak interference signal to this reference surface position.
In a favourable application, this object is eye's cornea or iris.
The present invention also provides a kind of method of performing surgical operation at an in-house sequence of points place, and wherein, the correction position of point is to keep by the position of following the tracks of the object correlation surface according to the method described above.This surgical operation can be a kind of surgery laser operation, wherein focuses on laser beam one by one at in-house a plurality of somes place.This surgical operation can comprise intrafascicular one or more of the laser optics decay in intrastromal photorefractive keratectomy, laser in situ keratomileusis or the phacoemulsification.
Described laser eye surgery preferably includes IPRK, excises flap in lasik surgery or phacoemulsification operation.
Described laser eye surgery preferably includes by short laser pulse and cause optical breakdown in the tissue of eyes.
Brief description of drawings
The invention will be further elaborated in conjunction with example below with reference to accompanying drawings, this accompanying drawing is the sketch map of OCT Z axle eye tracking apparatus according to a preferred embodiment of the present invention, thereby arrange the aligning of this OCT Z axle eye tracking apparatus control laser beam, wherein laser beam is used for patient's eyes is performed surgical operation.
The description of preferred embodiment
In OCT tracking means with figure explanation, have short moment coherence length and the light beam 2 that produces by light source 4 by beam splitter 6 direct projections.This light source 4 is suitably a superluminescent diode, produces a kind of visible or near infrared light beam.This beam splitter 6 is divided into the reference beam 8 of reflection and the elementary beam 10 of transmission with light beam.These elementary beam 10 direct projections to a suitable surface 12 of the eyes that will be treated, the front surface of cornea for example, and reference beam 8 direct projections are to the reflection reference surface of plane mirror 14 forms.Carry out front and back scanning by 15 pairs of these illuminators 14 of sweep mechanism on the direction of reference beam 8, this sweep mechanism 15 has a Master Scanner 18 and a secondary dither scanning device 16.
When making by Master Scanner 18 when being subjected to vibrating with reference to illuminator 14, just interfere from the light of these illuminator 14 reflections, and produce a characteristic interference signal with reflected light from anterior corneal surface 12, this signal can detect at photoelectric detector 20 places and obtain.
Scan or vibrate the position of this illuminator 14, thereby change the optical path length of reference beam 8: when total optical path length of elementary beam and reference beam equates, come the output signal of self-detector 20 (and sending filter 22 to) to reach maximum intensity.Thereby, the intensity of delivering to the signal of telecommunication of filter 22 just depends on the position of reflecting anterior corneal surface 12, therefore and depend on and the degree of depth of point of observation (the point of interest) in the cornea will focus on a beam treatment laser beam 30 in this given viewpoint, be used for realizing the interior PRK of substrate.Can analyze the signal of this detection with respect to the position of illuminator 14, thus signal peak definite and surperficial 12 position consistency.
Illuminator 14 needs not to be an optical surface or has optical characteristics, and to reach such situation be favourable, and promptly the order of magnitude of the reflected signal at beam splitter 6 places is all similar.For example, usually the order of magnitude of the inverse signal of a detected cornea approximately is 4% of an incoming signal, and it is preferably in the reflection reference signal of interference and is consistent.
In order more effectively and more accurately to follow the tracks of, secondary dither scanning device 16 is set, thereby it is 18 predetermined around scanning device, make illuminator 14 dithers with 12 corresponding positions, surface, and adopt detected peak interference signal, side-play amount is set for the position of scanning device 16 by scanning device 18, thereby makes the reflecting surface of illuminator 14 be in the central authorities in dither zone.This dither scanning device 16 is scheduled to repeat to change introduce detected interference signal with characteristic, is realized effectively tracking thereby this interference signal can filter.This modulation to this interference signal can realize best tracking velocity and follow the tracks of accuracy, can select surface location with very little noise.For example, can advantageously adopt phase-sensitive detection.
The character of scanning device 16,18 does not play a decisive role in the present invention, and for the person of ordinary skill of the art, it is easy making suitable selection in wide region.Wherein a kind of selection is the spin cam, and wherein reference surface is a face of cylinder, vibrates in light path by an eccentric rotating cam that is driven by adjacent motor.
Controller 32 these tracking means of control, explain filtering detection signal, detection peak interference signal, and control two scanning devices 16,18, and this controller 32 links to each other with a surgical laser system 35, this surgical laser system 35 produces treatment light beam 30, thereby this light beam 30 can be aimed at intracorneal successive point according to the tracking on corneal surface.For the those of ordinary skill in tracking and control appliance field, will find out the form and the structure of this controller 32 and its circuit and firmware easily significantly.
By adopting suitable optics, usually along light beam 30 being sent to eyes with the shared optical axis of former tracking light beam 10.Certainly also can understand and obtain, the structure of optics can be different from fully illustrated like that, here only be for explaining that principle of the present invention provides simple index path.
Described structure can realize the eyes inner surface is followed the tracks of accurately, in real time and also resolution high.This device only centers on and from the corresponding position of the electrical signal peak of filter 22 illuminator 14 is scanned.Sweep limits be around anterior corneal surface ± 1 micron to ± 10 microns.Therefore this structure can be on the Z direction (towards eyes) so that the response time provides very sensitive depth survey fast.The preferred secondary dither scanning device that uses helps fast reaction, and helps overcoming previously mentioned defective traditionally, and promptly OCT speed for present application is too slow.In surgical operation, a controller is explained signal and instruction is sent to surgical laser system, thereby adjusts laser focus point according to the motion of patient's eyes.
OCT method and apparatus of the present invention can provide the information of relevant corneal axis to the position, makes peeling off in substrate for example or in LASIK in the operation of excision flap, can make to degrade laser and focus on exactly on the intracorneal point.But, even if there has been the Z axle to follow the tracks of, the motion of eyes on X and Y direction still can influence the location of laser beam.Therefore, the second preferred embodiment (not shown) of the present invention comprises the tracking means of staring of the transverse movement that can follow the tracks of eyes.Can adopt any suitable level and the eye-tracking device of vertical direction, detecting the variation of pupil center's coordinate, thereby demonstrate the eye motion that level or vertical direction have taken place.Therefore can adjust the laser focusing point in any direction according to the motion of patient's eyes.
Also can select infrared ray to carry out the tracking of eye gaze in the horizontal and vertical directions.