Electric heating – Metal heating – By arc
Reexamination Certificate
1999-10-05
2001-04-10
Ryan, Patrick (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690, C219S121670, C219S121730
Reexamination Certificate
active
06215096
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for determining a required shape for at least one surface of an artificial or natural part of the eye which is intersected by a path of rays through the pupil of the eye. The invention also relates to a device for the manufacture of an artificial lens.
The cornea and lens are natural parts of an eye which are intersected by a path of rays passing through the pupil of an eye. In addition to this however, optical fittings can be placed or surgically attached to the surface of the cornea, implants can be inserted into the inner cornea to vary the shape of the cornea, and further fittings can be placed into the anterior section or into the internal part of the eye to refract the path of rays passing through the eye.
The shape of the intersected surfaces is of great importance because the refraction power of the eye is altered by changing the shape of a surface that is intersected by the path of rays. The success of measures for the treatment of natural parts or artificially inserted or attached parts of the eye should be accurately determinable beforehand.
Major problems exist in predicting the success actually achieved, in particular for the coordination of several measures which alter the refraction power of the eye.
It is for example already known when manufacturing an artificial lens, to scan the curvature of the cornea of the eye at 4 points using keratometry, and to determine the approximate curvature of the total cornea surface area using extrapolation. In addition the distances between the anterior surface of the cornea, lens and retina are scanned using biometry to determine the curvature and refraction power of the lens respectively by means of the average curvature of the cornea in such a way that rays which are incident to the cornea, intersect at one point on the retina.
This method is suitable for a cornea with a very uniform curvature. In certain areas of the cornea, incident rays are in practice not focused at the attainable point because the curvature of the cornea, however, is as a rule different over the total area.
In addition, this method is only suitable for determining the surface of an artificial lens.
SUMMARY OF THE INVENTION
The invention faces therefore the task of proposing a method which allows it to determine the required shape of any surface that is intersected by a path of rays through the pupil of an eye, in such a way that an image is created as accurately as possible inside the eye.
This task is resolved using a method through which the refraction performance is measured along the path of rays for a multitude of ray paths which are distributed across the surface, each originating from one point, or is given based on empirically established values, and through which the distances between the surfaces intersected by the path of rays are measured along the path of the incident rays or are given based on empirically established values, and the required shape of at least one surface intersected by the paths of rays is calculated based on those values in such a way that the paths of rays possibly intersect in one point.
The method according to the invention offers the advantage that any number of points can be scanned on a surface intersected by a path of rays through the pupil of the eye in order to increase the accuracy for the shaping of the surface. In especially important areas such as the central area, a lot of points can be calculated whereas in the border area the calculation of only a few points may be sufficient. Also deformations of the cornea or of any other area of the eye that are detected during the scanning or even earlier, can be taken into account using the method according to the invention by scanning in particular many points in this specific area. The required shape determined by this method is therefore adapted accurately to the individual eye and can consequently compensate deformations or irregularities in another part of the eye.
The method is especially suited for the simulation of eye operations. For example, the total surface area of a contact lens placed on the eye surface can be calculated. The use of a contact lens is suitable when the necessary refraction performance of the contact lens is approximately equal on rings which are concentric to the center of the contact lens. Otherwise another measure has to be employed or the surface areas that show discrepancies have to be compensated for by using a further method. This example shows that the method according to the invention can be used as a one stage procedure to determine the required shape of the surface. However, as many required shapes cannot be manufactured due to technical or surgical reasons the refraction performance along the paths of rays is measured again in these cases utilizing a second procedural stage which takes the first measure into account, in order to specify the required shape of another surface based on the measured values.
The different operations for which the accurate determination of the required shape of a surface is of great importance, include—apart from contact lenses - epikeratophakia, photorefractive keratectomy, radiary keratotomy and thermokeratoplastic, intracorneal inlays, intracorneal rings, the lens implantation into the phaco-eye and the use of intraocular lenses.
It is advantageous to choose, in addition to determining the required shape of the surface based on the calculated values, the material of a part of the eye according to its refraction. While the thickness of the substance intersected by the path of rays is taken into account by this method for determining the required shape of the surface, selecting the materials of parts which are artificially inserted into the eye causes a particular refraction performance. The method according to the invention allows it therefore to vary the materials for the parts utilized and to determine the respective shape of the intersected surfaces for different materials. For example, an artificial lens offers a different refraction performance depending on the material used, and another required shape will therefore be specified according to the material utilized using the method according to the invention.
A preferred area of application for this method is presented when attempting to create a device for the manufacture of an artificial lens. The lens manufactured using this method is adapted exactly to the individual cornea of that particular eye and is therefore capable of compensating for deformations on the cornea.
The number of scanned points at which the refraction performance is measured can be increased at will. Preferably more than 20 points should be scanned to achieve an acceptable result.
In order to scan a large number of points it is recommended that the refraction performance at the cornea is analyzed topometrically. The topometry permits a very accurate scanning of the entire cornea surface and is therefore especially suited for the method according to the invention.
The distances along the path of the incident rays between the surfaces intersected by the path of rays such as the cornea, lens and retina, are preferably measured biometrically. This is a simplistic, well researched and particularly precise method for scans such as these.
As it is known that the thickness of the cornea also varies across the surface, it is advantageous to measure the cornea thickness at several points. Normally the thickness of the cornea will not especially be taken into account for the manufacture and also the implantation of artificial lenses. The scanning of the cornea thickness leads however to a further increase in accuracy, for example for the manufacture of artificial lenses.
Depending on the calculation, the point of intersection of the paths of rays can be situated in front of or behind the retina. It is advantageous for the point of intersection to lie on the retina, preferably within the yellow spot.
Principally it is sufficient to calculate a surface to the highest accuracy and reshape it accordingly in order to achieve
Neuhann Thomas
Von Wallfeld Herbert
Day Ursula B.
Elve M. Alexandra
Feiereisen Henry M.
Ryan Patrick
Technomed Gesellschaft für Med. und Med.-Techn. Systeme mbH
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