Surgery – Instruments – Electrical application
Reexamination Certificate
2000-10-17
2003-08-19
Walberg, Teresa (Department: 3742)
Surgery
Instruments
Electrical application
C606S005000, C606S010000, C351S212000
Reexamination Certificate
active
06607527
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed at a precision ophthalmic surgical laser method and system and includes an active eyetracker system and method for accurate and efficient eyetracking which takes into consideration eye tilt, and laser delivery systems and methods well suited for accommodating eye tilt during laser application.
BACKGROUND OF THE INVENTION
Roughly two decades ago, surgical techniques were introduced in an effort to permanently correct shortsightedness and astigmatism. The radial keratotomy procedure used a diamond blade to make incisions into the cornea, the front surface or “window of the eye”. Although this technique worked relatively well, there have been problems with long term stability of vision and weakening of the cornea as a result of the cuts often having to be made up to 95% of the corneal thickness.
More recently, these older techniques have been replaced with laser treatment techniques which have replaced the surgeon's blade with a computer controlled laser that gently re-sculptures the shape of the cornea without cutting or, for most applications, weakening the eye. These laser techniques are typically carried out with a photoablation process using an excimer laser.
An excimer laser's extreme accuracy and low thermal effect makes it well suited as an eye laser. Many eye lasers are extremely accurate and remove only 0.25 microns (1/4000
th
millimeter) of tissue per pulse. During corneal re-sculpturing, the excimer laser gently “evaporates” or vaporizes tissue; there is no burning or cutting involved. In the normal eye, light rays entering the eye are accurately focused on the retina and a clear image is formed. Most of the bending or focusing of the light rays occurs at the cornea, with the natural lens inside the eye being responsible for fine adjustments. If light is not focused on the retina, then the eye is said to have a refractive error. Common refractive errors include: myopia or shortsightedness, hyperopia or farsightedness, and astigmatism. The excimer laser has been used to re-sculpture the cornea in myopia, hyperopia and astigmatism corrections in an effort to make the curvature of the cornea focus light rays normally on the retina.
Presbyopia is a problem considered to be due to an aging process occurring in the natural lens of the eye, and thus does not fall under the same category as the refractive errors of myopia, astigmatism and hyperopia noted above, although combinations of presbyopia and one or more of the refractive errors are possible. U.S. Pat. Nos. 5,533,997 and 5,928,129 to Dr. Luis A. Ruiz describe presbyopia corrective apparatus and methods which involve the use of a laser system to remove tissue from the eye in presbyopic corrective patterns discovered to be effective by Dr. Ruiz. These two patents are incorporated herein by reference. Reference is also made to PCT Publication No. WO 00/27324 for International Application No. PCT/US99/26242 filed on Nov. 8, 1999, directed at improvement in presbyopia “LASIK” surgery. This PCT publication is also incorporated herein by reference and represents further improvement in addressing presbyopia by way of laser surgery.
Also, the corneal surface is not a very smooth body and has topographical irregularities which can be both large and small. Under prior art laser systems these surface irregularities are not fully taken into consideration in the standard formulas and patterns designed to correct defects such as hyperopia, myopia and astigmatism. Accordingly, the final ablation profile formed in the eye deviates to some extent from what was predetermined by the surgeon to be the final resultant profile of the eye, and this is particularly true with respect to eyes with highly irregular surfaces wherein the defect can be simply shifted to a lower corneal altitude and thus create a new defect which is often unpredictable under the prior art systems. Reference is made to U.S. Pat. No. 6,129,722 which issued on Oct. 10, 2000 and is incorporated herein by reference. U.S. Pat. No. 6,129,722 describes improvements in eye ablation volume formation in laser eye surgery that takes into consideration the topographic irregularities in the eye being ablated, while also allowing for the input of the surgeons expertise.
Reference is also made to co-pending U.S. Ser. Nos. 09/598,226 and 09/598,227 each filed on Jun. 21, 2000 to Dr. Luis Ruiz and Eduardo Matallana which are incorporated by reference herein. These applications describe means for enhancing accuracy, registration and desired beam density application to conform the applied ablation volume pattern with the desired vision enhancements through use of an active mask in the path of the laser beam.
Despite the above described improvements in determining the desired ablation volume to be applied and providing a laser system capable of achieving high precision with respect to the desired ablation volume pattern, if the laser can not keep up with movement of the eye, including eye tilt about its normal axis, than all the enhancements in these other areas will be lost or degraded in the final result.
Efforts have been made in the prior art to improve the tracking response of a laser with eye movements. Laser systems without an eyetracker system rely on having patients fixate their gaze upon a fixation light. This technique does not, however, prevent rapid movements of the eye. Further, a momentary lapse in fixation can result in an ablation shot far from the intended shot location. As an alternative, physical fixation devices have been used which immobilize the eye by physically connecting to the eye, thereby holding it steady. This technique can lead to increased patent discomfort and a further cluttering of the surgical area.
More recent techniques involve computer aided eyetracking devices. These tracking devices are typically optical or topographic location systems that use a video camera to either optically or topographically locate and track the center of the eye. Examples of such systems can be found in U.S. Pat. No. 5,602,436 to Lang et al., U.S. Pat. No. 5,098,426 to Sklar et al., U.S. Pat. No. 5,162,641 to Fountain and U.S. Pat. No. 4,848,340 to Bille. These systems use various techniques to track the center of the eye, such as a computer mapped digital image from a video camera. For example, U.S. Pat. No. 5,098,426, to Sklar, et al., hereby incorporated by reference, describes an eyetracking system that generates a three dimensional profile of the eye and tracks movement by noting changes in that profile. The Sklar patent shows an eyetracker using a slow control loop and a fast control loop. The slow control loop relies on a video camera to provide topographical information that the eyetracker then uses to aim the system optics.
An alternate eyetracking system is shown in U.S. Pat. No. 4,848,340 to Bille, also incorporated by reference. The Bille patent shows a strictly optical, rather than topographical, based system that tracks a reference grid which has been ablated into the eye. U.S. Pat. No. 5,980,513 to Frey et al. illustrates another example of an eyetracking system and relies on substantial mirror movement requirements.
Some prior art eyetracking systems use infrared light to illuminate the pupil of the eye in an effort to facilitate tracking. One example is found in U.S. Pat. No. 5,620,436 which utilizes an eyetracker system relying on a non coaxial infrared heat source located on a side of a patient for the detection of an infrared heat target normally being the center of the pupil.
The above described systems tend to be either invasive, not particularly accurate and/or complicated, in the sense that they require actual physical markings to be made on the eye ( as shown in the Bille patient), or require highly complex and often not highly accurate topographical location systems and multiple feedback loops for locating the center of the eye. Also, those systems relying on infrared heat sources are very sensitive to changes in the illumination and infrared spectrum contaminations generated by
Matallana Eduardo
Narvaez Arnoldo
Ruiz Luis Antonio
Dahbour Fadi H.
Smith Gambrell & Russell
Walberg Teresa
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