Surgery – Truss – Pad
Patent
1995-07-21
1997-06-24
Lateef, Marvin M.
Surgery
Truss
Pad
1286531, 128665, 128745, 351211, 351212, A61B 3107, G01B 1124
Patent
active
056409621
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a process and apparatus for determining the surface topography of a reflecting surface according to the preamble of claims 1 to 13.
Processes of this type, especially for measuring the cornea based upon a Moire pattern projection method are known under the designation video keratometry. What is meant thereby is the projection of the so-called placido disk, i.e. a pattern of concentric alternating black and white rings upon the human cornea. The reflections from the corneal surface are registered by a video camera for computation. Of particular interest are the distances or distortions of the structure of the reflection pattern compared to a standard of measurement.
In case of measuring a cornea, the standard of measurement is formed by a known surface which is required for a correct evaluation/assessment of the corneal surface. The analysis of stated distortions from the standard of measurement yields informations about the radius of the corneal curvature as well as deviations from a spherical surface, as encountered in astigmatism.
Processes of this type are known for example from U.S. Pat. Nos. 4,978,213, 4,863,260 and 4,772,115.
In this process, the association of the reflection pattern to the scanned-in projection rings has often proven difficult and resulted not infrequently in errors. The association becomes particular difficult when the corneal surface is defective and causes gaps in the reflection pattern of an initially closed ring that is projected upon the cornea. The erroneous association of unrelated structures of a reflection pattern to a particular scanned-in projection ring results in grave errors, for example in form of an incorrect determination of the corneal radius or in form of an incorrect determination of the distortions of the corneal surfaces from the desired spherical surface.
In addition to the imaging of a ring-shaped projection pattern, the use of a grid-shaped line pattern is known. This, however, could not eliminate the above-stated problems.
Moreover, hitherto conventional processes are extremely sensitive with regard to misalignments of the eye in the Z-axis, i.e. in the connection axis between the corneal apex and the image detection unit.
It is thus the object of the present invention to propose a process for determining the topography of a reflecting surface and especially of the cornea, which ensures an unambiguous and reliable association of the structures of the reflection pattern reflected from the surface to those of the scanned-in projection pattern.
Further, it is desired to provide a suitable device for carrying out the process.
This object is attained by a process and by a device based upon the above-stated type by the characterizing features of claims 1 and 13. The features recited in the subclaims enable additional advantageous further developments and improvements of the invention.
In accordance with the invention, at least three distinguishable recognition marks are used within the projection pattern projected onto the surface for characterizing the structures of the projection pattern. This can be achieved by e.g. an additional recognition mark which is distinguishable from black/white and bright/dark marks. This utilization of specially designated zones within the projection pattern generates together with e.g. bright and dark zones an additional criteria of association of the structures of the image pattern specularly reflected from the reflecting surface with regard to the projection pattern projected onto the surface. Certainly, the number of criteria of association is increased by employing several such recognition marks so that this association becomes further improved. When using at least three marks with colors that are distinguishable from each other, black-white marks can be omitted altogether.
In accordance with a particularly advantageous embodiment, at least one color marking is used as recognition mark. The provision of such color markings allows an easy association of the structures of the reflection pattern to the res
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Bende Thomas
Jean Benedikt
Matallana-Kielmann Michael
Feiereisen Henry M.
Lateef Marvin M.
Shaw Shawna J.
Technomed Gesellschaft fur Med. und Med. Techn. Systeme mbH
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