Using Pancorrection to Approach Isotropic Ultra-High Resolution in Optical Coherence Tomography

Abstract

Purpose: : To approach an isotropic resolution of ~2 µm using ultra-high resolution optical coherence tomography using the simultaneous correction of the chromatic and monochromatic aberrations of the eye.

Methods: : The light source is a Ti:Sapphire laser emitting a spectrum of 140 nm full width at half maximum, centred at 800 nm. The longitudinal chromatic aberration of the eye presents a ~0.4 D focal shift between 700 and 900 nm. An achromatizing lens has been developed to compensate for the chromatic aberrations of the eye. To achieve a high transverse resolution, large (~6 mm) pupil diameters are used, but the monochromatic aberrations of the eye greatly deteriorates the retinal image at larger pupil sizes. The monochromatic aberrations are dynamically estimated and corrected with adaptive optics using a Hartmann-Shack wavefront sensor and a novel magnetic deformable mirror (MIRAO 52, Imagine Eyes) providing a substantial 100 µm stroke. Changes to the system include intended improvements in the axial resolution by increasing the bandwidth from 140 nm to 240 nm, and to reduce motion artefacts by increasing the line scan from 10 kHz to 100 kHz.

Results: : A near isotropic resolution of 2-3 µm has been achieved in the living human retina, showing an unprecedented amount of detail. 3D ultrahigh resolution images from a human eye have been obtained and it has been possible to distinguish the inner and outer segments of the photoreceptors. The width of the cones has been estimated to be 3-4 µm, in agreement with ranges obtained ex vivo.

Conclusions: : Using pancorrection - the simultaneous correction of the monochromatic and chromatic aberrations of the eye, lateral resolutions between 2-3 µm have been achieved. With ultra-high axial and transverse resolutions, it has been possible to visualize retinal morphology with detail comparable to that obtained with histology.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • photoreceptors