Application of a new high-speed magnetic deformable mirror for in-vivo retinal imaging

Abstract

Nowadays in ophthalmologic practice several commercial instruments are available to image patient retinas in vivo. Many modern fundus cameras and confocal scanning laser ophthalmoscopes allow acquisition of two dimensional <i>en face</i> images of the retina with both back reflected as well as fluorescent light. Additionally, optical coherence tomography systems allow non-invasive probing of three-dimensional retinal morphology. For all of these instruments the available lateral resolution is limited by optical quality of the human eye used as the imaging objective. To improve lateral resolution and achieve diffraction-limited imaging, adaptive optics (AO) can be implemented with any of these imaging systems to correct both static and dynamic aberrations inherent in human eyes. Most of the wavefront correctors used previously in AO systems have limited dynamic range and an insufficient number of actuators to achieve diffraction-limited correction of most human eyes. Thus, additional corrections were necessary, either by trial lenses or additional deformable mirrors (DMs). The UC Davis AO flood-illuminated fundus camera system described in this paper has been previously used to acquire in vivo images of the photoreceptor mosaic and for psychophysical studies on normal and diseased retinas. These results were acquired using a DM manufactured by Litton ITEK (DM109), which has 109 actuators arranged in a hexagonal array below a continuous front-surface mirror. It has an approximate surface actuator stroke of &plusmn;2&#956;m. Here we present results with a new hi-speed magnetic DM manufactured by ALPAO (DM97, voice coil technology), which has 97 actuators and similar inter-actuator stroke (&gt;3&#956;m, mirror surface) but much higher low-order aberration correction (defocus stroke of at least &plusmn;30&#956;m) than the previous one. In this paper we report results of testing performance of the ALPAO DM for the correction of human eye aberrations. Additionally changes made to our AO flood illuminated system are presented along with images of the model eye retina and in-vivo human retina acquired with this system.