12 mm Depth Range, 1.25 kHz A–line Rate Optical–Frequency–Domain Optical Coherence Tomography for Imaging of Anterior Segment of Eyes

Abstract

Abstract: : Purpose:Conventional Optical Coherence Tomography (OCT) based on time–domain principle at a wavelength region near 800 nm has been proven as an extremely useful tool to investigate retinal histology and diseases in vivo human eyes. However, a short depth range of about 2.5 mm and strong decay in sclera due to scattering precluded its effective use for anterior segment of eye. The purpose of this work is to develop an OCT based on a novel principle, which enables full depth transscleral measurements of anterior segment of eyes in relatively high speed. Methods: An OCT based on discretely scanned optical–frequency–domain reflectometry (OFDR–OCT) has been developed using an SSG–DBR laser. The laser emits cw coherent light at equal frequency interval Δf = 6.25GHz at a speed of 1 µs/1 frequency, which enables ranging depth of Δz=c/4Δf=12 mm (c; velocity of light) and A–line rate of 1.25 kHz with axial 800 samples, respectively. The A–line rate eliminates most of motion artifacts for in vivo measurements. The longer wavelength region from 1.53 to 1.57 nm (corresponds to 20 µµ axial resolution in eye tissues) of the light source reduces tissue scattering compared to shorter wavelength region, enabling deep transscleral measurements of angle region of eyes. A slitlamp–adapted OCT system with a x–y scanning mirror module enabled in vivo measurements of human eyes with an arbitrary direction of cross sectioning. Results:We applied our system to enucleated pig eyes and found that the angle region is clearly seen including feature of the ciliary body. We extended measurements to in vivo volunteer human eyes and found simultaneous measurements of angle, iris and cornea are possible with little motion artifacts. At the presentation, we shall report on : anterior chamber angle measurements including effects of iridotomy ; pre– and post–operative pachymetric analysis in relation to PRK, LASIK, and LTP; real time iris motion and deformation in response to exposed light intensity and dose. Conclusions: A new OCT modality has been developed for anterior segment of eyes which enable measurement of 12 mm depth range at 1.25 kHz A–line rate, enabling transscleral measurements of whole anterior chambers.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • anterior segment • anterior chamber