Processing of keratoscopic images using local spatial phase

Details Processing of keratoscopic images using local spatial phase Processing of keratoscopic images using local spatial phase

A - Human Necessities

61

B

A61B 3/107 (2006.01) A61B 3/15 (2006.01) G01B 11/255 (2006.01)

Patent

CA 2172284

Quantitative measurement of corneal surface topography is obtained by processing a two-dimensional image of the surface (6) which reflects a quasi-periodic illuminated pattern, such as a series of concentric rings (13), from a Placido disk source. The local spatial phases exhibited by the image of the illuminated pattern when reflected from the corneal surface and when reflected from standard specular surfaces are obtained by processing the images (42). The distances at which predetermined local spatial phases are observed in the image from the cornea are compared (42) with the distances at which these same phases are observed in the images of the standard surfaces. The distances are also compared (42) with certain corresponding distances on the source and converted to reveal the dioptric powers of refraction of the corneal surface without the need for parametric interpolation. During processing, any mislocation of the apex of the corneal surface along the optical axis is compensated for.

On obtient une mesure quantitative topographique de la surface cornéenne en traitant une image bidimensionnelle de la surface (6) qui réfléchit un motif éclairé quasi périodique, tel qu'une série d'anneaux concentriques (13), à partir d'une source à disque de Placido. On obtient les phases spatiales locales présentées par l'image du motif éclairé renvoyé depuis la surface cornéenne et depuis des surfaces spéculaires standard en traitant les images (42). On compare (42) les distances auxquelles sont observées les phases spatiales locales prédéterminées dans l'image provenant de la cornée avec les distances auxquelles ces mêmes phases sont observées dans les images des surfaces standard. On compare (42) également les distances avec certaines distances correspondantes sur ladite source et on les convertit pour révéler les puissances dioptriques de réfraction de la surface cornéenne sans avoir recours à une interpolation paramétrique. Au cours du traitement, on compense toute erreur d'emplacement de l'apex de la surface cornéenne le long de l'axe optique.

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