Surgery – Instruments – Light application
Reexamination Certificate
2002-07-30
2004-05-18
Gibson, Roy D. (Department: 3739)
Surgery
Instruments
Light application
C128S898000, C606S004000
Reexamination Certificate
active
06736806
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a controllable liquid crystal matrix (patternable) mask for controlling ultraviolet laser energy, and a system which involves the use of the controllable liquid crystal matrix mask for use in, for example, an ophthalmic surgical system such as an excimer laser system for contouring the cornea through controlled ablation of the cornea with penetration into the stroma and volumetric removal of corneal tissue whereby the ablated corneal surface is characterized by a sculptured new curvature having improved optical properties.
BACKGROUND OF THE INVENTION
Various surgical techniques for reprofiling of the corneal surface have been proposed as described in, for example, L'Esperance, U.S. Pat. No. 4,732,14; J. T. Lin, U.S. Pat. No. 5,520,679; David F Muller, U.S. Pat. No. 4,856,513; Kristian Hohla, U.S. Pat. No. 5,520,679. Each of these patents is incorporated by reference herein.
In practice there are two basic techniques to ablate and remove a set volume of tissue in the cornea and they are:
1) a scanning technique that uses a small flying laser spot between 1-2 mm in diameter and requires thousands of pulses to do the surgery; and
2), a large spot beam technique wherein a laser beam of around 8 mm in cross-section is used in conjunction with an erodible mask or a moving, blocking mask to ablate and which generally requires, on average, a few hundred pulses to achieve the desired ablation.
The main advantage of a flying laser spot technique is the ability to readily execute irregular patterns. However, the flying laser spot technique suffers from the drawback of generally requiring longer surgical times to execute the desired ablation pattern both from the standpoint of the number of pulses required and the overlapping requirement to ensure coverage of the ablated area. Any increase in the length of time required to carry out the laser ablation process can lead to longer corneal exposure time and corresponding medical concerns such as cornea dehydration which can lead to poorer healing, poorer visual acuity and, in general, longer post operative recovery times. A longer time period in which a laser is operated per patient also leads to a decrease in the useful life of the laser and an increase in service requirements. In addition to the time delay associated with a flying spot laser technique, there is also the problem of ridges and valleys being formed due to overlapping that will prevent a highly smooth and polished ablation. Flying laser spot techniques place greater stress on the laser cavity and the optical train components due to high repetition and rate requirements.
A large beam spot system does allow for more rapid application of the desired energy (including the avoidance of the degree of overlapping involved in a randomly or non-randomly applied, partially overlapping flying spot system) and typically places less strain on the laser equipment, but does not have the irregular pattern versatility provided with a flying spot system. Also, if mechanically moving components are relied upon as the means for blocking or allowing through the laser beam (e.g., an iris or rotating or sliding aperture plate), then the problems of mechanical wear, potential jamming or breakdown arise.
Attempts have been made to provide masks that operate with a large beam application including EP 0 417 952 to Rose et al. which uses a stacked set of binarily weighted masks (A to H) on a cornea intended for sculpturing. A proposed system such as this one suffers from a variety of drawbacks such as the time consumption involved in stacking and developing the mask sets and the increased potential for error brought about by a system using so many different stacked mask components.
Another example of the use of large beam application is found in U.S. Pat. No. 4,994,058 which describes a supported or contact type mask presenting a predetermined resistance to the beam such as through use of a different height erodible mask or by varying the composition of the plastic material making up the mask. A mask arrangement such as this avoids the complications of a scanning laser, but is very limited from the standpoint of having to prepare a new mask for each patient and, with respect to an erodible mask, not having the benefit of being able to test the pattern on a test strip or the like without destroying the mask. In use of an erodible mask there is also heavy reliance on chosen material consistency.
SUMMARY OF THE INVENTION
The present invention is directed at providing a controllable, patternable liquid crystal mask that is particularly well suited for use with ultraviolet electromagnetic energy utilized in an ophthamological surgical procedure such as a photo refractive keratectomy (PRK); photo therapeutic karatectomy (PTK); and a laser in-situ keratomileusis (LASIK) surgical procedure for resculpturing the exposed cornea of an eye. Accordingly, the present invention is directed at providing a controllable patternable mask system, an ophthalmic laser surgery system with said controllable mask system, and a method of using the same. The apparatus and method of the present invention is particularly well suited for ablating a corneal surface using a laser in the ultraviolet spectrum to achieve extremely smooth and precise ablation surfaces with a mask system that can be repeatedly used for different patient ablation requirements. The mask is used with a large beam spot (e.g., 6-8 mm) which covers the entire projected surface on a cornea and thus avoids the time delays associated with a flying spot beam as well as ridge and valley formation. In addition to multi-patient use, the present invention avoids the delays associated with the prior art with respect to forming or assembling the mask. Moreover, the present invention provides a system which can achieve repeated high precision or registration between the planned or predetermined ablation volume to be removed and the actual ablation volume removed so as to better enable a surgeon to achieve desired levels of eyesight corrections. Also, the volumetric ablation patterns to be removed can involve highly irregular or regular configurations, as an object of the present invention is to provide a system which facilitates the execution of a surgical procedure on highly irregular individual customized patterns on a patient's cornea in addition to more regular volumetric patterns.
Furthermore, the arrangement of the present invention provides a system that can achieve a customized volumetric ablation pattern based on, for example, a stored, ophthamological patient data set (e.g., an ablation data set as described in U.S. patent application Ser. No. 09/267,926 filed Mar. 10, 1999 by Dr. Luis Ruiz which application is incorporated herein) which data set is developed by a measuring instrument such as a topographer or aberrometer and, under the present invention, is provided to a processor for input to the mask system via a digital interface, for example. The matrix mask system of the present invention includes an active liquid crystal matrix mask which receives expanded, polarized laser energy and, based on the processed patient data, controls the energy pattern that exits in the mask for sculpturing the desired ablation pattern on the cornea.
Under the present invention, the ablation pattern data set is processed by a processor such as the laser's main computer which communicates with the mask via an interface or the like to provide corresponding commands to activate the matrix mask. For example, in one embodiment of the invention, the transmission pixel pattern of the mask is individually controlled by the computer and is synchronized with the pulse rate of the main excimer laser. In this way, any regular or irregular ablation volume can be removed by ablating with each pulse of the large beam a set depth (based to the laser characteristics such as laser energy and density) corresponding with the matrix pattern set for that pulse. By changing the mask's matrix pixel pattern with each large beam
Matallana Eduardo
Ruiz Luis Antonio
Gibson Roy D.
Johnson, III Henry M.
Smith Gambrell & Russell
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