Axial eye-length measurement by wavelength-shift interferometry.

A simplified noncontact measuring technique for axial eye length was developed. According to this method, the wavelength shift of a single-mode laser-diode beam that is irradiated onto the eyeball causes a phase shift in the interference fringes of reflections from the retina and the cornea. Then the optical distance between the cornea and the retina is obtained from the phase-shift measurement. High-speed axial eye-length measurements can be performed by using a laser diode on a pulse-modulation drive and signals from the reference light path as an analog-to-digital-conversion trigger. Compared with the technique that uses partially coherent light, this technique is inferior in terms of measurement accuracy but superior in its wide, measurable range of 16-32 mm. The results of measurements of 21 adults showed that 2 standard deviations of measurement was 2 sigma = +/- 0.11 mm.