On improving pyramid wavefront sensor based AO-OCT

Abstract

Purpose : Non-modulated pyramid wavefront sensor (P-WFS) based adaptive optics (AO) has shown excellent and highly reliable performance for posterior layer imaging in healthy volunteers. To widen the range of ophthalmic applications of the P-WFS, the stability of the closed-loop focus shifting, and the AO update rate need to be improved. This study introduces a novel method for focus shifting and demonstrates the robustness and versatility of the P-WFS for AO optical coherence tomography (OCT) imaging, specifically of anterior retinal layers.

Methods : The system at hand is a spectral domain AO-OCT setup using a four-sided P-WFS. It provides a 250kHz A-scan rate and an axial resolution of 4.5μm at 840nm central wavelength. To achieve a stable placement of the focus of the imaging beam in the desired retinal layer, a new concept for focus shifting is introduced which uses an in vivo calibration routine (time: ~150ms) that is performed prior to image recording in each subject (image data cf. Fig.1a). To minimize the effect of accommodation and eye motion on the calibration, the AO loop bandwidth was increased from 6 to 30Hz update rate. Retinal images were recorded with a field of view (FoV) of 4°x4° along the superior vascular arcade of healthy subjects and patients suffering from diabetic retinopathy (DR).

Results : With the fast P-WFS based AO, excellent imaging performance is achieved throughout the extended FoV. The fast update rate of the AO reduced field aberrations along the slow scanning axis. Representative image data recorded in a patient with moderate DR is shown in Fig.1b. The intensity variations in the P-WFS pupil images introduced by cataract (cf. Fig.1b) do not influence the in vivo calibration of the focus shifting routine. Vessel walls of arteries and veins are visualised in the enface and B-scan images over a large FoV. One additional asset of the P-WFS is the assessment of the pupil plane by providing information about the exact pupil location and the presence of artificial lenses, cataracts, shadowing, etc.

Conclusions : An adapted version of the P-WFS based AO correction method for retinal imaging is presented and demonstrated in vivo with AO-OCT. The new method for closed-loop focus shifting provides stable focus placement in healthy as well as pathological eyes. A faster AO-loop improves large FoV measurements and the good performance of the P-WFS based AO in patient imaging indicates good clinical applicability of the technology.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.