Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2001-10-02
2003-07-01
Lateef, Marvin M. (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
C264S400000, C623S006110
Reexamination Certificate
active
06585375
ABSTRACT:
The present invention relates to a method of producing an intra-ocular lens or a contact lens.
BACKGROUND OF THE INVENTION
Intra-ocular lenses (IOLs) are artificial eye lenses consisting e.g. of acrylic glass, in particular “Plexiglas”, or polymethyl methacrylate (PMMA), in particular in the form of a material offered under the name of Acrysoft (trademark). Also silicone is used as a material for IOLs.
Intra-ocular lenses serve to correct refractive errors of the eye, often after a removal of the natural lens. IOIs are also used for correcting high-order visual defects. Also for remedying aphakia IOLs are becoming increasingly important.
The implantation of an IOL is a microsurgical operation carried out either in one session (primary implantation) or in more than one session with insertion of the lens into the apha-kial eye.
Hundreds of different types of intra-ocular lenses are known. These lenses are normally roughly classified according to the positioning of the IOL and its fixation in the eye. A distinction is made between “anterior chamber lenses”; “iris clip lenses”; “posterior chamber lenses fixed in the sulcus (posterior chamber angle)”; and “posterior chamber lenses fixed in the capsular sac”. The present invention relates in particular to all these intra-ocular lenses.
Furthermore, the present invention also relates to contact lenses, i.e. optical lenses acting as a visual aid in contact with the eye. A contact lens is optimally adapted to the individual shape of the front section of the eye with its inner surface facing the eye. It serves to correct visual defects and irregular refractive errors, normally refractive errors of the cornea of the eye. Materials which are adapted to be used for contact lenses are in particular PMMA and modifications thereof, CAB (cellulose acetobutyrate), silicone methacrylates, fluorosilicone acrylates, fluorocarbons, HEMA hydrogels, etc.
In the prior art, intra-ocular lenses as well as contact lenses are normally formed at the manufacturer's, then delivered to the hospital or the ophthalmologist where they are inserted in or attached to the patient's eye, i.e. the lenses are mechanically formed and, optionally, polished, packed in a sterile condition and then delivered to the hospital or the ophthalmologist who inserts the respective lens in the patient's eye.
Intra-ocular lenses especially serve to correct myopia, hyperopia, and astigmatism. For this purpose, the so-called refraction data of the patient's eye are measured, i.e. the dioptric value measured for the patient's eye determines the shape of the lens. In accordance with this measurement, the ophthalmologist then orders or takes from a stock a specific intra-ocular lens corresponding to this dioptric value of the patient. It follows that this conventional method is in this sense an “overall correction” of lower-order visual defects insofar as the correction is based on the “overall” dioptric value of the eye.
Optical image formation in the eye is, however, not only impaired by the above-mentioned lower-order visual defects but also by so-called higher-order image errors. Such higher-order image errors occur especially after operations on the cornea and within the eye (cataract operations). Such optical aberrations may be the cause for the fact that, in spite of a medical correction of lower-order defects, the full visus is not achieved. P.Mierdel, H.-E. Krinke, W. Wigand, M. Kaemmerer and T. Seiler describe in “DER OPHTHALMOLOGE”, No. 6, 1997, p. 441, a measuring set-up for determining the aberration of the human eye. By means of such a measuring set-up, aberrations (imaging errors) for monochromatic light can be measured. The aberrations that can be measured are not only aberrations caused by the cornea, but what can be measured are the imaging errors caused by the whole ocular image-forming system of the eye, said measurements being carried out in a position-dependent manner, i.e. for given locations within the pupil of the eye it can be determined with a specific resolution how large the imaging error of the whole optical system of the eye to be corrected is at this location. Such imaging errors of the eye are mathematically described in the above-cited paper of P. Mierdel et al. as so-called wave-front aberration. A wave-front aberration is the three-dimensional profile of the distance between a real light wave front of a central spot of light and a reference surface, e.g. an ideal spherical shape, i.e. the system used as a spatial reference system is e.g. the spherical surface of the ideal wave front. It is, in principle, also known in the prior art to choose a plane as a reference system for the aberration measurement, in cases in which the ideal wave front to be measured is flat.
BRIEF SUMMARY OF THE INVENTION
When realizing the present invention, the measurement principle according to the above-mentioned paper of P. Mierdel, T. Seiler et al. can also be used as an initial step. The essential features here are that a parallel bundle of light of sufficient diameter is subdivided into separate parallel single rays by a perforated mask. These single rays pass through a collective lens (a so-called aberroscope lens) and are thus focussed in front of the retina at a specific distance therefrom in the case of an emmetropic eye. This leads to easily visible projections of the mask holes on the retina. This retinal light spot pattern is imaged on the sensor area of a CCD video camera according to the principle of indirect ophthalmoscopy. In the aberrationfree ideal eye the imaged light spot pattern is orthoscopic and corresponds precisely to the perforated mask pattern. If, however, an aberration exists, this will result in individual displacements of each pattern spot, since each single ray passes through a specific area of the cornea and pupil, respectively, and undergoes a deviation from the ideal path in accordance with the irregular optical effect. From the retinal pattern spot displacements, the wave-front aberration is finally determined with an approximation method as a local function over the pupil area. The above-cited prior art also describes the mathematical representation of this wave-front aberration in the form of a so-called “wave-front aberration mountain”. This wave-front aberration mountain indicates over each pupil location (x-y coordinates) a value for the wave-front aberration W(x, y) which is then plotted as height against the x-y coordinates. The higher the “mountain”, the higher the imaging distortions in the eye at the respective pupil location. For each incident light beam there is a proportionality between the measured deviation of the respective retinal light spot from its ideal position and the steepness of the “wave-front aberration mountain” in a first approximation. It follows that the wave-front aberration can be determined therefrom as a local function related to an arbitrary reference value on the optical axis of the system. Ideal, normally undistorted light spot positions on the retina, which can provide the reference value, are e.g. four central, closely spaced spots. Such spots represent a central cornea-pupil zone having a diameter of approx. 1 to 2 mm; from previous experience, it can be assumed that this zone is largely free from higher-order image errors.
The “wave-front aberration mountain” can be mathematically represented in different ways with the aid of a complete term (a function). Terms which can be used for this purpose are e.g. approximations in the form of a sum of Taylor polynomials or especially also Zernike polynomials. The Zernike polynomials have the advantage that their coefficients are directly related to the generally known image errors (spherical aberration, coma, astigmatism, distortion). The Zernike polynomials are a set of fully orthogonal functions. In a paper of J. Liang, B. Grimm, S. Goelz and J. F. Bille, “Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor,
Optical Society of America
, 11(7): 1949-1957, July 1994, it is sho
Donitzky Christof
Reindl Maximilian
Browning Clifford W.
Lateef Marvin M.
Sanders John R
Wavelight Laser Technologies AG
Woodard Emhardt Moriarty McNett & Henry LLP
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