R Díaz-Uribe | PubMed Health

PubMed2006

Testing a fast off-axis parabolic mirror by using tilted null screens.

We propose the design of tilted null screens for testing off-axis segments of conic surfaces. The tilt allows us to control the size of the screen and the sensitivity of the test. For positive tilt angles the sensitivity is increased while the size of the screen is reduced in the sagittal caustic region and vice versa in the tangential caustic region. Further analysis and preliminary experimental results are presented for a fast off-axis concave parabolic mirror with an elliptical aperture. An offset distance of X(C) = 25.4 mm yields radius of curvature at the vertex R = 20.4 mm; major axis of the mirror D(M) = 49.4 mm; and minor axis D(m) = 29.5 mm.

Journal Article↗

PubMed1999

Corneal shape evaluation by using laser keratopography.

Corneal topography assessment plays a fundamental role in the detection of keratoconus and the evaluation of the refractive surgery patient. The main drawbacks of the methods based on the use of Placido's disk (the most commonly used technique) have been pointed out recently, and new techniques are being sought that allow clinicians to be more confident about the measurement. Some years ago, we proposed a new technique based on a scan of the corneal surface with a low power HeNe laser beam; by measuring the deflection of the reflected beam, it is possible to compute the shape of the scanned cornea. In this paper, we explain the basic theory behind the method and present numerical simulations which show that errors in the surface heights of less than 1 microm may be obtained. In this work, we do not consider the effect of experimental errors. We discuss some possible extensions and improvements to the theory.

Cornea↗