Abstract
We implemented a Lagrange-multiplier (LM)-based damped least-squares (DLS) control algorithm in a woofer-tweeter dual deformable-mirror (DM) adaptive optics scanning laser ophthalmoscope (AOSLO). The algorithm uses data from a single Shack-Hartmann wavefront sensor to simultaneously correct large-amplitude low-order aberrations by a woofer DM and small-amplitude higher-order aberrations by a tweeter DM. We measured the in vivo performance of high resolution retinal imaging with the dual DM AOSLO. We compared the simultaneous LM-based DLS dual DM controller with both single DM controller, and a successive dual DM controller. We evaluated performance using both wavefront (RMS) and image quality metrics including brightness and power spectrum. The simultaneous LM-based dual DM AO can consistently provide near diffraction-limited in vivo routine imaging of human retina.
Highlights
The retina is a thin layer of neural and support cells lining the inside of the eye
In 2008, we proposed the construction of a composite influence matrix for both deformable mirror (DM) using a Lagrange-Multiplier (LM) method, and employing the damped least-squares (DLS) method to suppress the correlation between the two DMs [31]
Wavefront RMS was reduced from 5 to 6 μm to less than 0.1 μm for a large defocus correction, or from 0.7 μm to around 0.025 μm for small aberrations correction which corresponds to a Strehl ratio of 0.97 for wavelength at 840 nm. This confirms that the wavefront control accuracy of the dual DM adaptive optics scanning laser ophthalmoscope (AOSLO) for the model eye enables diffraction-limited imaging in the near infrared
Summary
The retina is a thin layer of neural and support cells lining the inside of the eye. Due to the aberrations of the eye’s optics, it is difficult to image the fine details of the retina in a living subject. Adaptive optics (AO) allows the aberrations of the eye to be corrected, providing the potential to in vivo image the retina at cellular level [1]. Almost all systems used a wavefront sensor to measure wavefront aberrations of the eye and the system, and corrected the wavefront errors with a deformable mirror (DM). There are two major approaches to quantifying how well these AO retinal imaging systems are correcting the wavefront aberrations. One common approach is to use a wavefront-based metric, typically the residual wavefront root-mean-square (RMS) error estimated from the wavefront sensor. For published single deformable mirror (DM) AO correction, the wavefront residual aberration in RMS was reported to be 0.07-0.08 μm at best for in-vivo human subjects [4,5,9], and generally it was around 0.1-0.2 μm. The best resolution was reported for an AOSLO system as being approximately 2.5 μm [11], precise details vary with pupil size, wavelength and boundary conditions [12]
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