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Spectroscopic measurement of light that is reflected from biological tissue in vivo is being investigated for various clinical applications. One special object of investigation using optical methods is the human ocular fundus. A fundus reflectometer that enables the simultaneous acquisition of up to 192 spectra arranged in a horizontal line across the fundus is described. The underlying optical principle of the device is the confocal imaging of an illuminated narrow, slitlike field at the fundus to the entrance slit of a spectrograph. This is imaged by the grating of the spectrograph onto a two-dimensional CCD chip that records the local distribution of ocular fundus reflectance spectra within a wavelength range of 400 up to 710 nm with a resolution better than 2 nm and a local resolution of 23 m in a field dimension of 1.5 mm. The performance of the device was investigated, the effects of confocal and nonconfocal imaging are discussed, and some representative measurements are presented.

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In the past, new techniques to measure axial eye length using partial coherent light or wavelength-tuned light have been developed. They are based on the interference ofthe light reflected at the cornea and the retina ofthe eye. This method has the advantage ofmeasuring independently ofaxial eye movements. However the light is reflected from the retina and the cornea with different divergencies. These divergencies have to be matched to collect as much light as possible in order to achieve a sucient interference signal.We have employed a diffractive optical element which focuses one part ofthe light onto the cornea while the other part ofthe light remains uninfluenced and is focused onto the retina by the optical system ofthe eye.As shown by measurements on model and on living eyes the signal-to-noise-ratio and the sensitivity ofthe dual beam partial coherence interferometry was improved. IntroductionIn the past various techniques ofwhite light interferometry were investigated to produce images and length measurements of living eyes structures in a non-contact manner.High resolution images obtained by optical coherence tomography (OCT) " are based on the interference of partial coherent light in a Michelson interferometer with the eye under evaluation in one interferometer arm and a reference mirror in the other (OCDR-technique).3 Interference occurs only when the reference arm length is equal to the distance of any reflecting surface in the eye within the source coherence length While moving the reference mirror with a constant velocity, the interference is detected at the Doppler frequency corresponding to the velocity of movement. The envelope of the interference signal due to the reflectance of the eye media is recorded as a function of the position of the reference mirror. Two or three-dimensional images are generated by a thither transverse scan of the beam across the object.Because the reflectivity of the reference mirror is much higher than that of the eye media, the signals are limited by shot noise of the light returning from the reference path: A dynamic range of more than 90 dB was achieved at a power incident to the eye of 30 J.LW with a wavelength of 800 mn, a scanning velocity of 40 mm/s and a detection bandwidth of 9 kHz4. * now with Hewlett Packard, Palo Alto, CA, USA O-8194-2332-7/96/$6.OQ SPIE Vol. 2930 / 175 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/16/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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