Corneal topography via two-wavelength holography

An interferometric, holographic instrument has been developed by the authors which can precisely characterize the entire corneal surface with submicron accuracy. An air-cooled argon ion laser was run at all wavelengths to construct the hologram and an interference filter picked out a single wavelength for reconstruction and viewing. The holograms were recorded by a holographic camera on a thermoplastic recording medium. The laser and optics were layed out in a modified Twyman-Green interferometer setup. A CCD camera imaged the resulting hologram on a video screen and fringe analysis software subsequently digitized and analyzed the data. Head and eye movement were minimized by the use of a rigid head and chin rest, a fixation light, and a short exposure time. This technique was completely noninvasive in that no physical alien surface made contact with the corneal surface. The amount of optical radiation which entered the eye was orders of magnitude lower than the exposure limit standards set by ANSI Z-136.1 guidelines.