Wavelength-tuning interferometry of intraocular distances

Abstract

We describe basic principles of wavelength-tuning interferometry and demonstrate its application in ophthalmology. The advantage of this technique compared with conventional low-coherence interferometry ranging is the simultaneous measurement of the object structure without the need for a moving reference mirror. Shifting the wavelength of an external-cavity tunable laser diode causes intensity oscillations in the interference pattern of light beams remitted from the intraocular structure. A Fourier transform of the corresponding wave-number-dependent photodetector signal yields the distribution of the scattering potential along the light beam illuminating the eye. We use an external interferometer to linearize the wave-number axis. We obtain high resolution in a model eye by slow tuning over a wide wavelength range. With lower resolution we demonstrate the simultaneous measurement of anterior segment length, vitreous chamber depth, and axial eye length in human eyes in vivo with data-acquisition times in the millisecond range.

Sensitivity advantage of swept source and Fourier domain optical coherence tomography

“…The first, Fourier-domain OCT (FD-OCT) [2][3][4][5] uses a broadband light source and achieves spectral discrimination with a dispersive spectrometer in the detector arm. The second method, sweptsource OCT (SS-OCT) [2,[6][7][8][9], time-encodes wavenumber by rapidly tuning a narrowband source through a broad optical bandwidth. Until recently, it has been unclear how the performance of SD-OCT techniques compares with TD-OCT. A recently published work [10] demonstrated superior sensitivity (defined as the signal-to-noise ratio for a perfect sample reflector) of an FD-OCT implementation over TD-OCT.…”

Spectral- and time-domain optical coherence tomography measurements of macular thickness in normal eyes and in eyes with diabetic macular edema

“…An alternative to TD detection for OCT is a technique known as Fourier or frequency-domain detection. 2,3 Spectral/Fourier-domain OCT (SD-OCT) detects all echoes of light simultaneously. The elimination of the moving reference mirror (present in TD-OCT) allows a dramatic increase in line rate (A-scan rate) in SD-OCT. [4][5][6] Multiple SD-OCT devices are commercially available; Heidelberg's SPECTRALIS (Heidelberg Engineering Inc., Vista, CA, USA) is one of the commonly used devices in this category.…”

Adolf Friedrich Fercher: a pioneer of biomedical optics

“…Again, Fercher and his group were ahead of their time. (It should be mentioned in this context that the lack of suitable swept sources also delayed the development of SS-OCT; the first papers demonstrating SS-OCT in phantoms and in vitro were published in 1996 by Haberland et al 35 and, with improved resolution, by Chinn et al in 1997, 36 and the first paper demonstrating in vivo SS-PCI for axial eye length measurements in 1997 by Lexer et al 37 However, the tunable lasers used in these papers suffered from slow speed and/or a very narrow tuning range; it took more than a decade until swept sources with sufficient speed and bandwidth became commercially available).…”