Motion artefacts in traditional scanning spot optical coherence tomography (OCT) anterior-segment imaging can hamper the application of OCT to the determination of refractive properties of ocular interfaces. To overcome this problem, we have developed a Hyperparallel spectral domain approach (HP-OCT) for high speed volumetric imaging (up to 300k Ascan/ s). We demonstrate a repeatability of better than 0.1 Diopters for in-vivo anterior and posterior corneal power measurements as well as providing biometric measurements such as axial length, pachymetry, lens thickness and curvature, anterior chamber depth and axial length.
We present a proof-of-concept experiment utilizing a novel “snap-shot” spectral domain OCT technique that captures a
phase coherent volume in a single frame. The sample is illuminated with a collimated beam of 75 μm diameter and the
back-reflected light is analyzed by a 2-D matrix of spectral interferograms. A key challenge that is addressed is
simultaneously maintaining lateral and spectral phase coherence over the imaged volume in the presence of sample
motion. Digital focusing is demonstrated for 5.0 μm lateral resolution over an 800 μm axial range.
Accurate metrology of the anterior chamber of the eye is useful for a number of diagnostic and clinical applications. In particular, accurate corneal topography and corneal thickness data is desirable for fitting contact lenses, screening for diseases and monitoring corneal changes. Anterior OCT systems can be used to measure anterior chamber surfaces, however accurate curvature measurements for single point scanning systems are known to be very sensitive to patient movement. To overcome this problem we have developed a parallel 3D spectral metrology system that captures simultaneous A-scans on a 2D lateral grid. This approach enables estimates of the elevation and curvature of anterior and posterior corneal surfaces that are robust to sample movement. Furthermore, multiple simultaneous surface measurements greatly improve the ability to register consecutive frames and enable aggregate measurements over a finer lateral grid. A key element of our approach has been to exploit standard low cost optical components including lenslet arrays and a 2D sensor to provide a path towards low cost implementation. We demonstrate first prototypes based on 6 Mpixel sensor using a 250 μm pitch lenslet array with 300 sample beams to achieve an RMS elevation accuracy of 1μm with 95 dB sensitivity and a 7.0 mm range. Initial tests on Porcine eyes, model eyes and calibration spheres demonstrate the validity of the concept. With the next iteration of designs we expect to be able to achieve over 1000 simultaneous A-scans in excess of 75 frames per second.