High-resolution retinal phase gradient imaging using line-scanning laser ophthalmoscopy

Abstract

Simultaneous dual-channel offset imaging provides isotropic images of retinal microstructures that enable phase imaging in the living eye with enhanced visualization contrast. Phase imaging is widely used in microscopy and biomedical imaging to reveal structures not visible in standard imaging due to their low scattering properties. We implement the technique in a line-scanning approach using a high-speed 2D camera to visualize microstructures in the living eye with enhanced contrast, that were only visible with other modalities, such as flying-spot scanning laser ophthalmoscopy (SLO). A simplified phase imaging system has the potential to be quantitative, with diagnostic value for retinal diseases, and may enable monitoring treatment. Methods for super-resolution reconstruction were explored to break the diffraction limit.SLO phase imaging exploits forward-scatter through phase objects in the retina and subsequent reflection (rescatter) of intensity-encoded diffuse reflections for detection; line-scan ophthalmoscopy (LSO) phase imaging works in the opposite way, in which the offset line-beam produces oblique back-illumination enabling the diffractive/refractive effects of phase objects in the inner retina to be imaged in transmission. The former scrambles optical phase information, the latter preserves it. This design has several advantages over conventional SLOs: 1) the LSO has a reduced number of optical elements, which results in a short optical path and compact design, 2) only one moving part, thus hardware and electronics are simplified, and 3) the LSO is inherently safer because the beam is focused in only one dimension on the retina.