Frequency modulation as an alternative for local phase in 3D corneal topography

Bertho A. Th. Stultiens; Franciscus H. M. Jongsma

doi:10.1117/12.178553

23 June 1994 Frequency modulation as an alternative for local phase in 3D corneal topography

Bertho A. Th. Stultiens, Franciscus H. M. Jongsma

Proceedings Volume 2126, Ophthalmic Technologies IV; (1994) https://doi.org/10.1117/12.178553
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

Abstract

There is little time for acquiring coherent data in corneal topography. Especially in height contouring, only a single flash exposure excludes movement artifacts. Starting with a single flash image, from a projected low frequency line grating on a fluorescein stained cornea, there are basically two ways of analyzing the acquired data. First by locating the local phase of the grating which is not very accurate and second, a straight forward frequency demodulation on the complete recorded image. The frequency demodulation had one great advantage, all points were both horizontally and vertically correlated. One major problem was the sensitivity to noise in the amplitude of the recorded image. This problem was solved by limiting the maximum allowable slope in the measured object to +/- 60 degree(s) and using steep digital filters in both spatial and frequency domains. With these improvements we could reconstruct the corneal height image with a lateral resolution of approximately 30 $umm and an axial resolution of +/- 3 micrometers . The accurate information of the entire corneal surface that became available, gave us reasons to doubt the reliability of some commonly used parameters; e.g., the radius of curvature assumes one optical axis but the calculated vectors from the corneal surface do not point to one axis. Because of the nonspherical shape, there probably is a focal volume instead of a focal point.

Citation Download Citation

Bertho A. Th. Stultiens and Franciscus H. M. Jongsma "Frequency modulation as an alternative for local phase in 3D corneal topography", Proc. SPIE 2126, Ophthalmic Technologies IV, (23 June 1994); https://doi.org/10.1117/12.178553

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

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.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available