Adaptive optics (AO) is an advanced technology used to improve the clarity and resolution of images taken through systems that suffer from optical distortions. Originally developed for astronomical telescopes to correct for the blurring effects of Earth’s atmosphere, adaptive optics has since found applications in microscopy, ophthalmology, laser communication, and deep-space imaging. In simple terms, an adaptive optics system senses distortions in an optical wavefront—in other words, the “shape” of light as it travels—and then rapidly adjusts a deformable mirror (or another correcting element) to cancel out those distortions. This process happens many hundreds or thousands of times per second, allowing instruments to capture sharp, high-contrast images that would otherwise appear blurred or distorted.
At its core, an AO system has three main components: a wavefront sensor, which measures how the incoming light has been distorted; a control computer, which calculates the correction needed; and a correcting element (often a deformable mirror), which physically reshapes the outgoing light to counteract the distortion. By closing this loop at high speed, adaptive optics “undoes” the blur in real time, revealing details that would be impossible to see with an uncorrected system.
Light traveling through any media other than vacuum undergoes aberrations due to changes in the refractive index and interface of the medium.[rx] Similarly, rays exiting the eye also have wavefront aberrations contributed by the differences in the refractive index of ocular tissues. The wavefront aberrations are classified as chromatic and monochromatic aberrations.[rx]
The monochromatic aberrations are further classified as lower order (contribute to about 90% of total aberrations) and higher order aberrations (10% of total aberrations). Spherical and cylindrical lenses correct the lower-order aberrations. The higher-order aberrations responsible for limiting the lateral resolution of devices are unique to each patient’s eye and were deemed un-rectifiable until recently.[rx] In 1971, the Shack-Hartmann wavefront sensor (SHWS) measured the eye’s possible optical aberrations.rx4]
Types of Adaptive Optics
1. Classical (Single-Conjugate) AO
Classical AO uses one deformable mirror conjugated to a single altitude layer—typically the telescope’s pupil plane. This configuration corrects distortions introduced along a single optical path, yielding significant image sharpening for a narrow field of view.
2. Multi-Conjugate AO (MCAO)
MCAO employs multiple deformable mirrors conjugated to different atmospheric layers. By sampling and correcting at several altitudes, MCAO expands the corrected field of view, enabling sharp images over a larger area of sky.
3. Ground-Layer AO (GLAO)
GLAO focuses on correcting turbulence near the ground, where most atmospheric distortion occurs. Using fewer mirrors and simpler control, GLAO offers moderate correction across very wide fields—ideal for survey telescopes.
4. Extreme AO (XAO)
Extreme AO systems push correction speed and precision to the highest levels, employing thousands of actuators on the deformable mirror and very fast wavefront sensors. XAO is crucial for directly imaging exoplanets, which demand extremely high contrast.
5. Laser Tomography AO (LTAO)
LTAO uses multiple laser guide stars to probe the three-dimensional structure of atmospheric turbulence. By tomographically reconstructing the turbulence, LTAO delivers enhanced correction for single-object observations, even when natural guide stars are dim or absent.
Anatomy and Physiology
The retina is the innermost coat of the eyeball, responsible for processing light energy and generating visual information. The three major types of cells in the retina are the photoreceptors, glial cells, and neuronal cells.[rx] The rods are the predominant photoreceptors in the retina and are concentrated more in the retinal peripheries. They are sensitive to photons of light and help in scotopic vision. The cones comprise only 5 to 6 % of the photoreceptors and are concentrated primarily in the center of the macula, the fovea. They are sensitive to a specific wavelength of light and help in photopic and color vision.[rx]
The retinal ganglion cells are second-order neurons that relay image-forming and non-image-forming information from the bipolar cells to the lateral geniculate body. Multiple rods converge onto a single ganglion cell, whereas a single cone is connected to a single ganglion cell. At least twenty different types of retinal ganglion cells receive excitatory and inhibitive impulses from the amacrine and bipolar cells.[rx]
The retinal pigment epithelium is the outermost layer of the retina, which is made up of a single layer of regularly arranged cells with a polygonal shape. It has many roles, like phagocytosis of photoreceptor outer segments, barrier function, transport of substrates, and protection against phototoxicity, as it contains pigments like melanin and lipofuscin.[rx]
Indications
Adaptive optics helps visualize individual cellular components in vivo and demonstrates individual photoreceptors, retinal pigment epithelial cells, ganglion cells, and retinal microvasculature in various acquired and inherited retinochoroidal pathologies. This helps in understanding the basic pathophysiology of these disorders, screening and diagnosing them at the subclinical stage, formulating newer therapeutic interventions, and monitoring cellular-level responses to therapeutic interventions.[rx]
The various indications include retinal vascular disorders like hypertensive retinopathy, retinal vasculitis, intraocular inflammation, diabetic retinopathy, macular pathologies like central serous chorioretinopathy, and age-related macular degeneration, inherited retinal dystrophies, drug-induced maculopathies, choroidal pathologies, and glaucoma.[rx][rx][rx]
Contraindications
There are no contraindications to this procedure. Various factors limit the usage of adaptive optics in routine practice.[rx] Firstly, studies employing adaptive optics for various retinal pathologies have a limited sample size. Large patient cohorts are essential to generate a normative database comparable to gender, ethnicity, and age. Good-quality image acquisition in patients with nystagmus, corneal opacities, and cataracts is challenging. Poor fixation poses a significant challenge in capturing a good-quality image.
A small area of the retina is imaged, and the time required for imaging is significantly more. It may be difficult for uncooperative and anxious patients. Incorporating eye-tracking software may help acquire better quality information in these patients. Analysis of acquired images is manual and may be laborious and time-consuming. Automated interpretation or development of artificial intelligence software may simplify grading. The enormous cost of the equipment and size has limited its location in research labs. More compact hardware will make its installation and operation practical.
Equipment
Components of the Machine
Adaptive optics equipment has four main components.[rx] These are the following:
- A wavefront sensor to detect and measure the optical aberrations in the light rays reflected from the eye. It consists of a lenslet array, each of which samples a part of the light wave. Shack- Hartmann wavefront sensor (SHWS) is commonly used.[rx]
- A deformable mirror to correct the detected aberrations. The actuator receives inputs from the wavefront sensor and modifies the surface of these mirrors. This helps correct the higher-order and any significant lower-order aberrations in the light beam.[rx]
- A control system to calculate the required correction level and receive feedback, and
- Image acquisition and processing device to capture the corrected waveform and generate an image.
Adaptive optics is not a stand-alone technology and has been combined with pre-existing imaging equipment, like the fundus camera, optical coherence tomography, and scanning laser ophthalmoscope.[rx]
Adaptive Optics flood Illumination Technology (AO FI)
AO components like the SHWS and deformable mirrors are combined with a high-resolution fundus camera. This setup helps image the spacing and directionality of the cones and pick up any fluctuations in cone reflectance. Since it uses an incoherent light source, the exposure time is brief, reducing the time required for image capture. However, this system is limited by its reduced axial resolution.[rx]
Adaptive Optics Scanning Laser Ophthalmoscope (AO SLO)
Dreher et al. were the first to combine AO with SLO devices in 1989.[rx] The system offers a retinal image and video with unparalleled lateral and axial resolution. The high-resolution video imaging helps demonstrate the movement of blood columns in retinal capillaries. By using a confocal pinhole, the different retinal layers can be visualized. It is equipped with eye-tracking software and laser-assisted stimulus delivery to the retina.[rx]
Adaptive Optics Optical Coherence Tomography (AO-OCT)
This system overcomes monochromatic aberrations and helps in the reduction of speckle size. This enables three-dimensional imaging of individual photoreceptors, ganglion cells, retinal pigment epithelium, lamina cribrosa, and nerve fiber layer.[rx]
Personnel
Any trained ophthalmologist, vitreoretinal surgeon, optometrist, or ophthalmic imaging technician can perform this procedure. In addition, technicians and ophthalmologists need to be trained in grading and interpreting images.
Preparation
Adaptive optics is a non-invasive retinal imaging procedure. The procedure of image acquisition is clearly explained to the patient. A pupillary diameter of at least 4 mm is recommended.
Technique or Treatment
The patient is positioned comfortably in a traditional chin rest. They are asked to focus on an internal fixation target, which is mobilized depending on the area of interest. The type of imaging is enface reflectance imaging. Once the site of interest appears on the graphic display in the user interface, the cones are brought into focus. Images are acquired over a 4-degree * 4-degree area at 9.5 frames/ second using a low noise-charged coupled device (CCD) camera. The illumination source is a near-infrared (850 nm) light-emitting diode (LED).
The software acquires 40 images, of which 20 with the best Sobel contrast are chosen. They are summed together using an auto-correlation algorithm to generate a single image with a good signal-to-noise ratio. The final image is obtained by subtracting the computed image from the background image. The brightness and contrast of the resultant image are adjusted while saturating the bright pixels. Every averaged image finally undergoes visual checks to rule out apparent artifacts. Automatic image alignment may be used to track the same retinal area with accuracy in microns for the progression of the disease, the natural history of the disease, or the response to therapy.
Complications
There are no complications associated with Adaptive optics imaging as it is a non-invasive procedure. However, patients with cervical spine pathologies, anxious patients, debilitated individuals, and patients with low vision and ocular motility disorders may find it challenging to maintain fixation for longer.
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The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members
Last Updated: July 10, 2025.
