Design of 1300-nm spectral domain optical coherence tomography angiography system for iris microvascular imaging

Developing a high-resolution non-invasive optical coherence tomography angiography (OCTA) method for iris vasculature imaging is essential for diagnosing a wide range of ocular pathologies. However, the current iris-OCTA devices are still limited in imaging quality and penetration depth for dark-colored eyes ranging from brown to dark brown. A spectral domain iris-OCTA system is presented in this paper incorporating a 1300 nm wavelength for deeper tissue penetration, a linear-wavenumber spectrometer for better detection sensitivity, and an iris scan objective lens for better optical focusing across the entire iris over a 12 x 12 mm(2) scan field. The -6 dB fall-off range is similar to 3 mm, and the maximum sensitivity fall-off is -28.57 dB at 6.94 mm. The axial resolution is 15.1 +/- 3.2 mu m. The 40 mm focal-length iris scan objective is optimized based on the ocular parameters from 100 Asian participants' left eyes, and it has a diffraction-limited lateral resolution (14.14 mu m) for the iris, in general. OCT distortions were calibrated based on the average ocular parameters, and the maximum residual distortions in both the lateral and axial directions were <0.1 mm (2.0%) for all of the eyes. A pilot study on a constricted pupil was performed to demonstrate high-contrast, wide-field en face iris microvascular imaging by either a horizontal or vertical fast-scan protocol in a dark brown eye. The iris vessels are radially aligned, and each vessel is more visible when it has an angle of similar to 65 degrees-90 degrees with respect to the fast-scan direction. A new circular fast-scan protocol could improve image quality for better visualization of the iris features or integration with image-registration algorithms and an eye-tracking system for eye-motion compensation.