Surgery – Instruments – Light application
Reexamination Certificate
1999-04-08
2001-09-18
Cohen, Lee (Department: 3739)
Surgery
Instruments
Light application
C606S011000, C606S017000, C607S089000
Reexamination Certificate
active
06290695
ABSTRACT:
BACKGROUND
The invention relates to a process and device for shaping surfaces, in particular lenses, by laser ablation of the surfaces, particularly but not exclusively, surfaces of biological material. The invention preferably is applied in photorefractive keratectomy (PRK) and in ophthalmological precision shaping of contact lenses.
The known state of art will be described hereinafter with reference to processes and devices for shaping surfaces relating to the correction of deficiency of sight and and which are most relevant to the present invention. The ablation processes in the treatment of deficiencies of sight of the human eye which have been carried out since the middle 1980's are all based on formulas for calculating the required flattening and steepening, respectively, of the cornea as first described by Munnerlin. When correcting myopia and according to the above calculation, more corneal tissue is ablated in the center of the cornea than in the peripheral ranges of the cornea. When correcting hyperopia, more tissue is ablated in the periphery of the cornea than in the center of the cornea. The enhanced or reduced effect caused in this manner with respect to the power refraction of the cornea surface corresponds to that of a contact lens.
In previous processes closely related to the present invention, the ablation of a respective amount of cornea is carried out in individual successive ranges of constantly varying areas. In the theoretically simplest case, namely the correction of myopia, the areas are described by successive circles of continuously decreasing or increasing diameters. To obtain an optimal result of treatment, it is necessary to completely ablate all layers in a series. In the presently known procedures, such series are worked off in a continuously increasing or decreasing sequence from the beginning to the end. When, while performing such procedures, there is an unintentional break-off of the treatment, anomalous cornea surfaces will result which generally lead to a considerable deterioration of eyesight. Regrettably, such defects of sight can be removed only partially or not at all by conventional means such as glasses or contact lenses. The only way to correct the situation will be to continue treatment at exactly that point where it was interrupted. When the exact point cannot be found or the patient is not ready to undergo a further treatment, a permanent deterioration of the eyesight will result.
A detailed description of the state of art is disclosed in European Patent Application No. 90308709.6 (corresponding to German Patent Publication No. DE 690 24 558 T2).
U.S. Pat. No. 5,520,679 describes an ophthalmic surgery method using a spot scanning laser in which the cornea ablation is achieved by setting single laser spots. This method, which operates like the ablation processes mentioned hereinbefore, tries to achieve an ablation as uniform as possible by setting laser spots in close timely succession with a defined overlap rate. This, however, involves an increased thermal stress to individual ranges of area, in particular, when an erbium laser is employed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process and device for shaping surfaces, in particular lenses and, more particularly, surfaces of biological material, by using lasers of pulsed laser output beams, which ensure that, at a sudden desired or undesired break-off of the surface shaping, at least an acceptable partial correction of the surface to be shaped is obtained which represents an improvement compared to the initial state.
It is a further object of the invention to substantially reduced the thermal stress of the surface to be shaped, in particular, when employing an erbium laser.
The objects are realized by a device and process for shaping surfaces by laser ablation in which required coordinates of individual laser shots for entirely ablating the surface are determined, the laser shots are associated together into blocks of laser shots, each block including laser shots for ablating an ablation area in a single layer of the surface and then the blocks are combined into block sequences, each block sequence including specific blocks of laser shots effective to achieve a complete partial correction of the entire surface. Control data is generated for controlling a laser deviation unit and a beam formation unit based on the block sequences such that the complete partial correction of the entire surface is obtainable for each block sequence. The laser, the beam formation unit and the laser deviation unit are then controlled to obtain the complete partial correction of the entire surface for each block sequence.
According to the process and device used in accordance with the invention, the individual layers of a surface to be shaped are ablated in a predetermined sequence in order to minimize the risk of a deterioration of eyesight upon an unexpected breaking-off, i.e., interruption, of treatment. Instead of a shaping which, only at the end, provides an optically correct spherical cornea surface including the desired complete correction, the process according to the invention using the device in accordance with the invention produces as many partial corrections of acceptable intermediate results as feasible. Thus, upon a sudden breaking-off of treatment, there never will result severely irregularly shaped surfaces. Though in such a case, the desired complete correction intended by the shaping is not achieved, it is feasible, however, to remove the remaining defect of sight considerably more easily with glasses or contact lenses. Moreover, a new PRK can be carried out with considerably fewer complications at a later time even using devices performing different methods.
The device and the shaping process described herein are adapted to be used with all presently applied PRK-methods, such as area ablation, slit scanning, and small spot scanning, in ablations of the cornea surface as well as in intra-stromatic ablations of tissue in connection with the LASIK-method or lasers of the picosecond range.
The process in accordance with the invention differs from the multi-pass method occasionally used with devices operating on the area ablation principle in that the present invention intentionally produces a number of partial corrections which are as small as possible. The multi-pass method typically provides only a division into two to three partial corrections. Moreover, the multi-pass technique tries to reduce certain side-effects typically present for area ablation procedures, such as too strong a drying-out, too strong a heating of tissue, and the development of “Central Islands”.
REFERENCES:
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Kuhnert Jurgen
Mäusezahl Holger
Pieger Stefan
Schroeder Eckhard
Aesculap Meditech GmbH
Cohen Lee
Jordan and Hamburg LLP
Ruddy David M.
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