Adaptive Optics (AO) describes the use of deformable mirrors and wavefront sensors to reduce aberrations from visual systems. While this technique was originally developed to reduce aberrations in Earth's atmosphere when gazing at the night sky, it has been modified and optimized for the visualization of retinal structures in vivo. Given its utility in retinal imaging, AO is currently under research for optimization in viewing cone photoreceptors (PR), retinal pigmented epithelial cells (RPE), retinal ganglion cells, blood vessels, and the optic nerve, among others. This article will evaluate different types of Adaptive Optics machines, analyzing advantages and disadvantages and the potential applications of each.
AO is often paired with retinal imaging technology to aid in visualization of the posterior segment. Because AO modifies other optical systems, it has been paired with a number of existing modalities for ophthalmic imaging including flood illumination ophthalmoscopy (FIO), optical coherence tomography (OCT), and scanning laser ophthalmoscopy (SLO). Some of its applications include, but are not limited to, the visualization of cone photoreceptors and cellular monitoring of healthy eyes, those with age-related macular degeneration (AMD), and those with inherited retinal diseases; the study of vasculature in patients with diabetic retinopathy; the tracking of leukocyte migration through retinal vasculature; and the imaging of retinal ganglion cells, particularly in patients with glaucoma. 
The techniques for clinical use of AO vary based on the combined imaging modality.
AOFIO can be performed with the commercially available device, rtx1, developed by Imagine Eyes (Orsay, France) and approved for clinical use in Europe but not in the United States. This machine functions by optimizing en face imaging of the subject eye with AO. Pupils may either be dilated or undilated for this procedure. The patients chin rests in the chin rest with forehead up against the plastic bar. Working distance is approximately 50cm. The patient fixates on a yellow cross, which may be adjusted horizontally to alter the view of the retina. Image depth may be altered from 0 to -80 microns by the technician to focus on various retinal structures. A numerical value during the imaging indicates the relative correction of optical aberrations in real time. 
Imaging with AOOCT follows a similar protocol of OCT imaging with the addition of AO.
For AOSLO, the patient sits facing the the machine with his or her chin on the chin rest and forehead braced against a plastic ribbon to steady the head. In order to optimize the consistency of the procedure and to mitigate blinking in the first frame, the patient fixates on a point and initiates the system with a button. The machine begins by rapidly assessing optical aberrations and correcting them with AO until they fall below a designated threshold. At this point, the camera collects an image. This sequence of aberration correction and image collection continues until a sufficient number of images are gathered.
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