Conoscopic system for real-time corneal topography
First Claim
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1. A conoscopic topographer for obtaining topographic measurements of a substantially spherical target surface at a fixed position, comprising:
- an illuminating device, producing a collimated probe beam to said target surface, said probe beam being of a probe wavelength to which said target surface is reflective;
a collecting lens disposed relative to said target surface at a predetermined distance, for receiving a reflected probe beam including said target surface, said reflected probe beam encoded with surface phase information indicative of said target surface;
an optical birefringent medium having a single optic axis, positioned relative to said collecting lens and oriented to form a tilted angle between a direction of said reflected probe beam and said optic axis, said birefringent medium splitting said reflected probe beam into an ordinary probe beam and an extraordinary probe beam which interfere with each other to form a conoscopic interference pattern;
a first polarizer, located in an optical path of said probe beam between said light source and said birefringent medium, operating to polarize said reflected probe beam in a first polarization direction;
an imager, receiving said conoscopic interference pattern and producing an electrical representation of said interference pattern; and
a microprocessor, processing said electrical representation of said interference pattern to extract a topographic shape of said target surface.
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Abstract
A corneal topographer based on conoscopic holography with partially coherent illumination. Corneal topographic measurements can be accomplished at a processing rate higher than the standard video rate of 30 Hz. The conoscopic measurements can be used in an opto-electronic servo to control a photorefractive keratectomy system in real time for an improved accuracy in laser ablation of a corneal surface.
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Citations
16 Claims
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1. A conoscopic topographer for obtaining topographic measurements of a substantially spherical target surface at a fixed position, comprising:
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an illuminating device, producing a collimated probe beam to said target surface, said probe beam being of a probe wavelength to which said target surface is reflective; a collecting lens disposed relative to said target surface at a predetermined distance, for receiving a reflected probe beam including said target surface, said reflected probe beam encoded with surface phase information indicative of said target surface; an optical birefringent medium having a single optic axis, positioned relative to said collecting lens and oriented to form a tilted angle between a direction of said reflected probe beam and said optic axis, said birefringent medium splitting said reflected probe beam into an ordinary probe beam and an extraordinary probe beam which interfere with each other to form a conoscopic interference pattern; a first polarizer, located in an optical path of said probe beam between said light source and said birefringent medium, operating to polarize said reflected probe beam in a first polarization direction; an imager, receiving said conoscopic interference pattern and producing an electrical representation of said interference pattern; and a microprocessor, processing said electrical representation of said interference pattern to extract a topographic shape of said target surface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A photorefractive keratectomy surgical system, comprising:
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a pulsed laser with a pulse repetition rate, producing an ablating laser beam at a wavelength at which a cornea is absorptive, said ablating laser beam having a fluence sufficient to ablate cornea tissue; a beam steering system, located relative to said laser and guiding said ablating laser beam to a target eye which is at a fixed location; a conoscopic topographer disposed relative to said fixed location, producing a probe beam to illuminate said target eye and receiving a reflected probe beam from said target eye, said topographer operable to measure a corneal shape of said target eye based on a conoscopic interference of said reflected probe beam; and a system controller having a microprocessor, electrically connected to said laser, said beam steering system, and said topographer, said controller controlling said topographer to achieve a corneal topographic measurement of said target eye at a processing rate higher than said pulse repetition rate. - View Dependent Claims (10, 11, 12, 13)
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14. A method for performing a topographic measurement of a spherical surface that is illuminated with a collimated probe beam, comprising:
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imprinting a phase information of said spherical surface onto a reflected probe beam produced by said illumination of said probe beam; generating a conoscopic interference pattern by using a uniaxial birefringent crystal to produce an ordinary beam and an extraordinary beam from said reflected probe beam; determining a phase difference between said ordinary and extraordinary beams; detecting a two-dimensional positioning representation of said spherical surface according to positioning coordinates in said conoscopic interference pattern; extracting said phase information of said spherical surface based on said phase difference; and determining a three-dimensional representation of said spherical surface. - View Dependent Claims (15, 16)
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Specification