A practical implementation of the dynamic point shifting method as a corneal topographer is presented. A quadrangular OLED´s prism setup allows to change the target at will. This device has several advantages over the traditional commercial topographers using static target as those based in Placido disk. The target is displayed on the OLED screens as an image, by changing the image it is possible to change the spots position, but also, different targets can be used, for instance; B&W positive or negative, different colored targets, with square or radial arrays of spots, among other possibilities. Results of measurements obtained with calibration spheres as well as the first report of the qualitative evaluation of a corneal surface of a human volunteer using this device are presented.
We have been working in a method for testing fast aspheric convex surfaces with flat null screens in an array of LCD’s,
based on the null screen principles accordingly; i.e. we have demonstrated qualitatively that using three LCD’s forming a
triangular prism, we can evaluate aspheric fast surfaces instead of using the traditional test with a cylindrical null screen.
This setup of LCD’s has the advantage of display a series of 3 null screens for sampling an optical surface
simultaneously, where in the ideal case, the position of the drop-shaped spots should be forming a regular square array of
points in the image plane. However, due to typical problems of illumination and directionality with the transmitted light
through the LCD's, some spots on the image are missing which complicates the correspondence between centroids and
coordinates of the null screens; this is important for the numerical integration procedure used for the quantitative
evaluation . In this paper we propose the design of null screens with reference marks, which provide unambiguous
correspondence. Specific designs include some strategic color and position coding to ease the image spots identification.
We show the method as used during the quantitative evaluation of a spherical steel ball.
For obtaining the shape of the corneal surface through the Null Screen method, a numeric integration procedure must be
carried out; perhaps, the simplest integration method is the trapezoid rule. This method, however, is limited by the
truncation error. It has been shown previously [1-6] that the point shifting method allows the reduction of this error by
adding many more evaluation points so reducing the average spacing between evaluation points. To do so, an array of
LCD's must be used to display the moving Null Screen. In this paper we propose to use three LCD forming a triangular
prism, instead of a cylindrical Null Screen [3] for measuring the shape of the human corneas. The null screen design will
be described and some experimental results obtained with calibration spheres used to simulate the corneal surface will be
presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.