A new method has been developed for determining intraocular distances. It is based on interferometry methods in conjunction with the laser Doppler technique, using partially coherent light. In a first approach two distances are measured: the axial eye length (distance cornea -retina) and the thickness of the retina. An accuracy of 10 pm for optical distances is achieved.Comparisons with the usual ultrasound technique show a good agreement also for geometrical distances. 1 . INTRODUCTION A precise knowledge of intraocular distances, especially of the axial length of the eye, is needed in several cases. As an example, the most important of the present applications is the determination of refractivity of intraocular lenses after cataract surgery. Today the standard technique for this purpose is the ultrasonic echo-impulse technique (US technique). Recently, some new optical methods for the measurement of intraocular distances were reported on. The femtosecond optical ranging technique was used to determine the thickness of the cornea in anesthesized rabbit eyes [1]. A modification of the slit lamp technology was proposed to measure the thickness of the human retina [2]. The axial length of the human eye was measured by interferometry with partially coherent light [3,Li]. This work reports on improvements and extensions of this latter technique and presents comparisons with the US-technique. 2 . METHODS Figure 1 shows a sketch of the interferometer used in this work. A multimode semiconductor laser diode (MMLD) emits a light beam (wavelength 780 nm, power 0.25 mW) with high spatial coherence but short coherence length CL. (The HeNe Laser and the single mode laser diode (SMLD), as well as the IR scope, are only used for alignment purposes.) This beam passes a Michelson interferometer MI which splits the beam in two parallel, coaxial beams: a reference beam 1, and a measuring beam 2 which is retarded with respect to beam 1 by twice the difference d of the interferometer arm lengths. Additionally, the interferometer mirror of the measuring beam is shifted with constant speed causing a Doppler shift of beam 2. Both beams illuminate the eye via a beam splitter cube BSC and are reflected at the cornea and the other intraocular interfaces. This introduces an additional 46 / SPIE Vol. 1423 Ophthalmic Technologies(199 1) 0-8194-0513-2/91 /$4.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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