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Abstract
We have developed an improved adaptive optics - optical coherence tomography (AO-OCT) system and evaluated its performance for in vivo imaging of normal and pathologic retina. The instrument provides unprecedented image quality at the retina with isotropic 3D resolution of 3.5 x 3.5 x 3.5 microm(3). Critical to the instrument's resolution is a customized achromatizing lens that corrects for the eye's longitudinal chromatic aberration and an ultra broadband light source (Delta lambda=112 nm lambda(0)= approximately 836 nm). The eye's transverse chromatic aberrations is modeled and predicted to be sufficiently small for the imaging conditions considered. The achromatizing lens was strategically placed at the light input of the AO-OCT sample arm. This location simplifies use of the achromatizing lens and allows straightforward implementation into existing OCT systems. Lateral resolution was achieved with an AO system that cascades two wavefront correctors, a large stroke bimorph deformable mirror (DM) and a micro-electromechanical system (MEMS) DM with a high number of actuators. This combination yielded diffraction-limited imaging in the eyes examined. An added benefit of the broadband light source is the reduction of speckle size in the axial dimension. Additionally, speckle contrast was reduced by averaging multiple B-scans of the same proximal patch of retina. The combination of improved micron-scale 3D resolution, and reduced speckle size and contrast were found to significantly improve visibility of microscopic structures in the retina.
Highlights
The use of optical coherence tomography (OCT) [1,2,3,4,5,6,7,8] has revolutionized treatment and monitoring of retinal diseases in everyday clinical settings
Improvements in lateral resolution have been demonstrated by incorporation of wavefront correctors in various retinal imaging systems starting with a flood illuminated ophthalmoscope [10] followed by scanning laser ophthalmoscopes [11], and recently into many variations of OCT systems [12,13,14,15,16,17,18,19,20,21]
adaptive optics - optical coherence tomography (AO-OCT) vs. AO-UHR-OCT—To test the improvement achieved with our new UHRAO-OCT system two light sources have been used consecutively
Summary
The use of optical coherence tomography (OCT) [1,2,3,4,5,6,7,8] has revolutionized treatment and monitoring of retinal diseases in everyday clinical settings. To other imaging techniques, lateral resolution and, quality of the OCT imaging is reduced by imperfections in the eye's optics. A short overview of different configurations and corrector types implemented in those AO-OCT systems has recently been published by Pircher and Zawadzki [22] While each of these AOOCT cameras reduces the degrading impact of the ocular aberrations, full compensation of both low- and high-order aberrations of the eye has not been achieved. This becomes a limiting factor when AO-OCT systems are used in clinical settings, where most patients are known to have moderate amounts of refractive error. This two-DM AO system was integrated into the ultrahigh-resolution (UHR) OCT system (AO-UHR-OCT) presented in this paper
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