Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1998-07-13
2000-02-15
Manuel, George
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
356376, A61B 310
Patent
active
060244496
ABSTRACT:
Forming an image on a CCD of a grid pattern projected on a target surface and detecting the positional coordinates of the image by correlating voltage peaks in the CCD output voltage during pixel readout synchronized with the count of pulses from a master clock. Topography is calculated by knowing the equations of the rays comprising the projection pattern and the rays from the determined CCD positional coordinates and solving for the 3D coordinates formed by the intersections of the two sets of rays. Means are provided for: blocking the specular component of reflected light from the target surface while passing the diffuse component; forming the rays of the projected grid pattern so that fluctuations in the target surface position do not cause measurement error; adequate focussing of the full grid pattern on the CCD; differentiating the CCD output voltage and detecting a zero crossing for precise timing of count capture at the instant of a peak. In a preferred embodiment, the target surface is a cornea undergoing PRK and a laser projection source pulsed at a high enough rate to provide real time differential topographical display and feedback to the photoablation means. Alternate embodiments include: using the uv photoablating laser as also the projection source in conjunction with a uv sensitive CCD; an adjunct CCD type sensor in the 8 micron region for monitoring corneal sector temperatures during PRK concurrent with the topography measurement.
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