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3D OCT kit scans eye in record time

05 Nov 2003

An OCT system records a 3D image of the retina in just 1.2 seconds.

Scientists in Austria and the US claim to have developed an OCT that acquires a 3D image of the retina in just 1.2 seconds. The team says its instrument is the fastest retinal three-dimensional optical coherence tomography (OCT) system developed to date. (Optics Express 11 2753).

“The main advantage of our OCT system is the image acquisition speed,” Christoph Hitzenberger from the University of Vienna told Optics.org. “It records a full 3D data set in around 1 second. This is one to two orders of magnitude faster than presently available in commercial retinal OCT systems.”

Conventional OCT systems scan in the z (depth) direction, a so-called A-scan. In contrast, Hitzenberger and colleagues’ system scans across the surface of the eye, essentially imaging a slice of the retina. The process, which is known as a C-scan, is repeated 64 times at different depths to create a 3D image of the retina.

Hitzenberger and colleagues tested their system by acquiring images of the fovea and optic nerve head in ten volunteers. The images contain 256 (x) x 128 (y) pixels. According to Hitzenberger the system can probe to a depth of around 1 mm, has a depth resolution of 12 microns and a transversal resolution of 15 – 20 microns.

The system relies on a continuous wave super luminescent diode emitting at 840 nm. Light from the diode enters an interferometer where it is split into a reference beam and a sample beam. The reference beam is sent through an acoustic-optic modulator, which shifts its frequency. The sample beam interacts with the retina.

After probing the eye and reflecting off a reference mirror respectively, the sample and reference beams recombine and interfere. This produces a set of fringes which is detected and passed to a PC for processing.

“The reference arm length is initially adjusted so that the depth position from which the interferometric signals are obtained is slightly in front of the retina,” explains Hitzenberger. “Then an x-y scanning mirror pair raster scans the sample beam over a complete x-y plain and the interferometric signal is recorded as a function of position.”

After recording the complete x-y plane, the reference arm length is changed to probe deeper into the retina. This process is repeated until the entire retina has been imaged.

The team is now working on doubling the depth scan range and is hoping to image more patients to quantify the repeatability of its system.

Hitzenberger was partnered by Qienyuan Zhou and co-workers from Laser Diagnostic Technologies, San Diego, US, where the prototype instrument was constructed

Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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