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Al-Hafeez Dhalla, Derek Nankivil, Theresa Bustamante, Hansford C. Hendargo, Ryan P. McNabb, Anthony N. Kuo, Joseph A. Izatt; Simultaneous Swept Source Optical Coherence Tomography of the Anterior Segment and Retina. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3126.
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© ARVO (1962-2015); The Authors (2016-present)
OCT has the potential to provide comprehensive quantitative biometry of the human eye, including measurements of corneal refractive power, corneal thickness, anterior chamber depth, lens optical power, lens thickness and eye length. Acquisition of these parameters is important for calculation of IOL power for cataract surgery, would enable customized ray-traced modeling of patient eyes to improve refractive surgical interventions, and would enable correction of optical artifacts resulting from distortions in retinal OCT diagnostics due to unknown upstream optics. We describe a novel OCT system design capable of imaging both the retina and the anterior segment simultaneously. This design employs polarization-encoding and interference revival-based heterodyning to eliminate any potential crosstalk between anterior and posterior channels. This also allows for independent, optimized optical designs to be employed in each path.
A full-depth SSOCT system was built using an Axsun Technologies laser (1040nm, 100 kHz sweep rate) and a polarization-encoded sample arm. Heterodyning was achieved using interference revival, which allows multiple imaging depths to be encoded at different temporal frequencies by carefully mismatching the interferometer pathlengths. The retinal path was matched to the reference path, enabling conventional imaging; the anterior segment path was offset from the reference path by the laser cavity length, which encoded the anterior segment image with a carrier frequency, to avoid overlap with the retinal images, while also resolving the complex conjugate artifact. The system was used to simultaneously image the anterior segment and retina of healthy humanvolunteers.
Both imaging depths achieved a sensitivity of ~95dB. Axial resolution for both paths was ~10µm; transverse resolution was ~30µm for the anterior segment, and limited by patient optics for the retina. The total imaging range in the anterior segment was 14mm transverse and 10mm axial in air (7.5mm in tissue); the retinal imaging range was 12o lateral by 5.5mm axial (4.1mm in tissue). High quality imaging of the anterior segments and retinas of healthy human volunteers was achieved at a 100Hz frame rate for 1000 (lateral) x 2304 (axial) pixel images. Volumetric imaging was also performed at 1 volume/second for 1000 x 100 x 2304 voxel volumes.
We have demonstrated the use of a novel SSOCT system design that enables simultaneous imaging of the anterior and posterior eye. This technology has applications in IOL and refractive surgery planning, image distortion correction, and may also aid in future studies of accommodation dynamics.
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