ABSTRACT
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
The AOSLO [1] is an advanced imaging modality for the living eye. In most applications the
imaging target of the AOSLO is the retina, a thin, transparent, multi-layered neural tissue lining the
inner surface of the eye that initiates and processes visual signals at the earliest stage [2-4]. The
retina is actually a piece of brain tissue, and one of a few parts of the central nervous system (CNS)
that can be visualized non-invasively [5]. Direct assessment of the retinal structure and function at
the single cell level in the living eye is important for both basic science research and clinical research
on the retina; this task may be facilitated by advanced retinal imaging technology. The scanning
laser ophthalmoscopy (SLO) [6, 7] is a retinal imaging modality that was developed in the early
1980s. Like most ophthalmic imaging instruments, the SLO works essentially with the principle of
the ophthalmoscope that was invented by Charles Babbage in 1847 and Hermann von Helmholtz in
1851 [8, 9], i.e., shining the light into the eye to illuminate the retina and (simultaneously) record-
Biophotonics:
ing the light scattering back to form the image. The SLO is a confocal imaging system; thus it has
the potential for enhanced spatial resolution, improved image contrast, and fine optical sectioning
ability, which are the fundamental merits of the confocal imaging mechanism [10, 11]. However,
the SLO must use the optical system of the human eye, including the cornea, lens, and vitreous;
hence, the human eye is an essential component of the SLO and plays the role of the objective lens
in a microscope. Unfortunately, the optics of the human eye, although exquisitely designed, are
not perfect. Theoretically, when the pupil of the human eye measures 6 mm in diameter, the cone
photoreceptors in the central region of the retina should be resolved; but this was not achieved until
Liang et al. introduced adaptive optics (AO) to compensate for the optical defects of the human eye
in a flood illuminated ophthalmoscope [12]. In 2002, Roorda et al. reported the first AO assisted
SLO [1], which provided video rate retinal images with unprecedented resolution and contrast. The
invention of the AOSLO represented an important advance in high-resolution ophthalmoscopy. In
the decade since the first AOSLO was reported, AOSLO has gained significant progress in engi-
neering, in basic science, and in clinical application. Many fundamental advantages of the confocal
imaging nature of the SLO have been realized or capitalized, but the AOSLO is still at an early
stage. This chapter will be dedicated to describing this emerging technology. First, we will briefly
review the structural and optical properties of the human eye and the retina to describe the major
challenges to in vivo high-resolution retinal imaging; then, we will review the SLO working princi-
ple and the spatial and temporal properties of the human eye’s optical defects, which will elucidate
the requirements of the ophthalmic AO system. Next, we will discuss the AOSLO including the
design of the optical system, the selection of the light sources, the optimization of photon detection,
and image acquisition as well as image processing. We will present specific examples of AOSLO
imaging of the retinal structure and function. Finally, we will summarize and discuss the emerging
trend and applications.
