Measurements of the posterior structures of the human eye in vivo by partial coherence interferometry using diffractive optics

In the past ten years, the dual beam version of partial coherence interferometry has been developed for measuring intraocular distances in vivo with a precision on the order of 0.3 to 3 mu m. This technique has now been further improved by using diffractive optics. A special diffractive optical element focuses part of the laser beam on the vertex of the cornea and lets the other collimated parallel part of the beam pass through. The beams remitted from the eye will thereby be converted into parallel beams. The light power oscillations in the corresponding interferograms are much stronger than those of the narrow interference fringes obtained without that technique what significantly improves the signal to noise ratio. This makes it possible to clearly differentiate signals from different fundus layers. High precision in vivo fundus measurements have been performed at various positions on the human retina in order to obtain fundus profiles. These measurements have been synthesized to tomographic images of the human eye fundus. In order to localize the exact measurement point on the retina simultaneously to the fundus scans, a fundus camera has been implemented into the partial coherence interferometry system that allows a clear identification of the individual A-scan positions.