Adaptive optics (AO) and optical coherence tomography (OCT) can provide information on cellular and sub-cellular structures in the live eye. OCT uses low-coherence interferometry to de-link axial resolution from the diffraction-limited depth-of-field for generation of micron-level axial resolution optical depth sections. AO is a technique to enhance the transverse resolution and depth sectioning capabilities by detection and correction of ocular aberrations. It has been integrated into instruments for full-field fundus imaging, scanning laser ophthalmoscopy (SLO), and Fourier domain (FD) OCT.
AO has also become a staple for vision researchers as a tool to explore the structural and functional aspects of vision and its disruption by disease. While AO has yet to make a full transition from research lab to clinic, OCT is now a standard diagnostic procedure for glaucoma, macular holes, macula edema, retinal detachments, and other retinal pathologies. FDOCT has now supplanted time domain (TD) OCT because of its advantages of higher speeds (near video rate), higher signal-to-noise ratio via simultaneous multiplexed acquisition of depth voxels, and lower phase noise. Clinical FDOCT systems are available commercially from several companies.
FDOCT comes in two basic varieties depending upon whether the source arm (swept source, SS) or the detection arm (spectral domain, SD) of the interferometer is altered. Each technique has advantages and disadvantages, but in general, SDOCT systems have slightly better axial resolution and SSOCT systems have increased depth range and accessibility to longer wavelengths. Ophthalmic OCT research systems at 1 μm, including initial reports configured with AO have shown significantly improved choroidal penetration compared to 850 nm systems. In addition to increased penetration, ocular dispersion is less at 1 μm than at 850 nm.
SLO and OCT are complementary tools for imaging the retina. OCT is an interferometric technique, whose fast 2-D frame axis is cross-sectional (i.e., lateral-axial) with micron level axial resolution that yields excellent sectioning capability. OCT is therefore better suited for visualization of retinal layers. SLO is a confocal technique whose fast 2-D frame axis is en-face (i.e. lateral-lateral) with sensitivity to multiply-scattered light. SLO is therefore better able to resolve photoreceptors, blood flow, and capillaries with higher contrast than OCT. Also, SLO systems can be configured to collect fluorescence signals.