Abstract
Purpose :
To combine annular pupil illumination with sub-Airy disk diameter (ADD) confocal pinhole detection in adaptive optics scanning light ophthalmoscopy (AOSLO) to better resolve rod photoreceptors in the living human eye.
Methods :
Annular illumination enhances lateral resolution at the cost of axial resolution, resulting in a narrower but axially elongated point spread function (PSF) (BOE 3(7):1647-1661,2012). Sub-ADD detection rejects out-of-focus light and improves axial resolution (TVST 7(2):17, 2018), which can potentially be used to counteract the loss in axial resolution from annular illumination while further improving lateral resolution. To test this approach, 3D PSFs were simulated and compared to empirical measurements of PSFs after implementing both techniques. Empirical PSF measurements were taken using near-infrared fluorescent beads imaged in a near-infrared detection channel. Finally, to validate the applicability of this technique in the living human eye, three healthy subjects were recruited. Images were collected at a location of 10 degrees temporal using a 1-degree square field of view.
Results :
Empirical measurements of PSFs were consistent with simulations across different combinations of annular illumination patterns and confocal pinhole sizes. As predicted, annular illumination improved the lateral resolution but extended the focus axially. Sub-ADD detection recovered the loss in axial resolution with the additional benefit of further lateral resolution improvement. In the human eye, across all subjects, rod photoreceptors were better resolved in the confocal AOSLO with the combination of annular illumination and sub-ADD detection when compared to full pupil illumination. These observations were further corroborated by an enhanced peak in the power spectrum corresponding to the expected spatial frequency of rods. Interestingly, rods were also more clearly visible in the non-confocal split detection when using annular illumination.
Conclusions :
The combination of annular illumination with sub-ADD detection considerably improves the imaging of rod photoreceptors and can be readily implemented in AOSLO systems to improve lateral resolution while maintaining axial resolution.
This is a 2020 ARVO Annual Meeting abstract.