Why use adaptive optics (A.O) ?

Diagnosing illnesses of the eye requires high resolution images of the retina. Unfortunately, the images taken by conventional instruments are not of sufficient quality because of aberrations introduced by the eye itself. Adaptive optics offers a promising technique for recovering excellent image quality. In addition, adaptive optics might be used to create a vision simulator.

ALPAO has developed a new deformable mirrors technology destined to be integrated into the majority of ophthalmic instruments. Thanks to very large strokes, excellent linearity and high bandwidth, these deformable mirrors achieve excellent results in a variety of configurations (AO-SLO, AO-OCT, etc.). In addition, thanks to ALPAO's Core Engine architecture, the use of adaptive optics has never been so easy.

Deformable mirrors: record stroke and exceptional temporal stability in a compact casing.

Correct most of the images thanks to unrivalled strokes (+/-45µm focus and astigmatism)

ALPAO has developed an exclusive deformable mirrors technology for ophthalmological applications. Thanks to the mirrors of ALPAO's Hi-Speed Magnetic Deformable Mirrors range, you will be able to construct an instrument covering a very large part of the population. Indeed, the aberrations of more than 95% of the population can be corrected thanks to a mirror able of generating up to +/-45µm of focus and astigmatism.

The figure on the right shows the typical Zernike modes that are achievable with the Hi-Speed DM97-15 (wavefront peak-to-valley amplitude). The quality of the optical correction depends on the number of actuators.

Build compact instruments thanks to the small pitch

Thanks to the low distance between actuators (1.5mm), it is possible to construct compact instruments. Thus, with a size of 9.0mm, the Hi-Speed DM52-15 includes 52 actuators. With a low 1.5 magnification factor (for a 6.0mm eye pupil), it is possible to construct a compact instrument that will introduce few instrumental aberrations.

Get better correction thanks to outstanding temporal responses

Typical step response for generating a pure focus (30µm) with the Hi-Speed DM97-15

The excellent temporal performance of ALPAO's Hi-Speed deformable mirrors also allows a reduction in the temporal errors traditionally present in large-stroke mirrors. The rise time for a step response is typically equal to 1ms.

Even if the aberrations present in the eye develop slowly (a few Hz), it is necessary to use a rapid and stable deformable mirror for at least two reasons:

• The vibration of the mirror during the wavefront sensor's measurement time distorts the measurement. A mirror taking time to stabilise itself thus reduces the gain from adaptive optics. Typically, correcting aberrations of up to 5Hz requires an adaptive optics loop operating at 50Hz. Consequently, the mirror only has 20ms to stabilise itself. If the mirror stabilises itself in 10ms, it will be measuring a bad signal during 50% of the time.
• Imaging instruments are sensitive to the back-and-forth produced by overshoot and residual oscillations.

With a stabilisation time in the order of a millisecond, the Hi-Speed DM mirrors from ALPAO meet these expectations perfectly, allowing very large aberrations to be corrected in a very short time.

The characteristics of the Hi-Speed DM Series range of mirrors for ophthalmology are summarised in table 1. For more information you can contact us via the site (click here) or by telephone or you can download the information brochure in the Downloads section.

	Hi-Speed DM52-15	Hi-Speed DM69-15	Hi-Speed DM97-15	Hi-Speed DM277-15
Distance between actuators	1.5mm
Number of actuators	52	69	97	277
Diameter	9.0mm	10.5mm	13.5mm	24.5mm
Best flat errors (1)	<7 nm RMS
Tip/tilt stroke (wavefront)	+/- 60 µm
Inter-actuator stroke (wavefront)	> 3.0 µm
3x3 stroke (wavefront)	> 30 µm			> 14 µm
Bandwidth (2)	>750 Hz			>500 Hz
Non linearity errors	< 3%
Hysteresis errors	< 1%
Coating	Protected silver (3)
Operating temperature	10 - 35 °C

(1) in closed loop

(2) first resonance of the membrane

(3) Other metallic coatings are available

 

Wavefront Sensor

Page under construction

Open control software which is easy to integrate

The development and the integration of adaptive optics systems requires open and flexible systems that adapt to the application. An AO Flood Illumination system, for example, has different requirements from an AO-SLO system.

The proprietary ALPAO Core Engine (ACE) architecture is the perfect solution in this situation thanks to its open and modular architecture (represented in figure 1). As this is an adaptive optics toolbox for Matlab®, it speeds up the development of a system.

The flexibility of the ACE thus makes it possible to exploit all the potential of adaptive optics by integrating it into the system you want to build (AO-SLO, AO-OCT, etc.).

Our expertise in the optics field allows us to develop specific systems according to the specifications of the client. Complementing this offer, ALPAO offers two standard adaptive optics systems for user that want to study adaptive optics with a produt ready right out of the box:

• AOS-0: system optimised for R&D
• AOS-1: closed-loop system with exceptional performance (500Hz frame rate, low-noise camera, mirror with 241 actuators).

ALPAO AOS-0: Open and flexible system for teaching and R&D

This plug-and-play system has been specially designed for:

1. engineers and scientists studying adaptive optics, the laws of control and real-time processing,
2. the teaching of adaptive optics.

The AOS-0 workbench includes all the components necessary to simulate a complete adaptive optics system:

• a Hi-Speed ALPAO DM52-15 mirror (including the control electronics)
• a wavefront sensor
• an imaging camera
• a rotating turbulence screen
• an optical source
• the opto-mechanical parts
• Matlab® software to control the system.
• a Matlab® licence (if the user doesn't have one).

Thanks to the ALPAO CORE ENGINE (ACE) architecture and the AOS-0 workbench, it is possible to develop control methods going from the simple law of integration right up to the most advanced solutions such as Kalman filtering. The real-time access to all data (residual errors, wavefront, camera images,.) facilitates the development of your project.

The choice of Matlab® allows the user to benefit from the support of the very large user community and the numerous forums associated with it.

Thanks to the AOS-0, you don't need to be a specialist to do adaptive optics but you can become one if you want to!

For more information you can contact us via the site (click here) or you can download the information brochure in the Downloads section.

> Click here for more information

AOS-1: high-performance adaptive optics loop

The AOS-1 system is based on:

• a Hi-Speed DM241-25 with 241 actuators spread across a diameter of 40mm (17 x 17 matrix).
• an ultra-sensitive wavefront sensor manufactured by ALPAO and based on an EMCCD camera (16x16 micro-lenses for a Fried configuration)
• a real-time computer operating at 500 fps and based on the ALPAO Core Engine (ACE).

For more information you can contact us via the site (click here) or you can download the information brochure in the Downloads section.

> Click here for more information

References & Examples

Journal papers

Articles written by ALPAO users in scientific journals:

• Robert J. Zawadzki, Steven M. Jones, Suman Pilli, Sandra Balderas-Mata, Dae Yu Kim, Scot S. Olivier, and John S. Werner, "Integrated adaptive optics optical coherence tomography and adaptive optics scanning laser ophthalmoscope system for simultaneous cellular resolution in vivo retinal imaging," Biomed. Opt. Express 2 , 1674-1686 (2011)
• Alfredo Dubra and Yusufu Sulai, "Reflective afocal broadband adaptive optics scanning ophthalmoscope," Biomed. Opt. Express 2 , 1757-1768 (2011)
• Alfredo Dubra, Yusufu Sulai, Jennifer L. Norris, Robert F. Cooper, Adam M. Dubis, David R. Williams, and Joseph Carroll, "Noninvasive imaging of the human rod photoreceptor mosaic using a confocal adaptive optics scanning ophthalmoscope," Biomed. Opt. Express 2 , 1864-1876 (2011)
• Robert F. Cooper, Adam M. Dubis, Ashavini Pavaskar, Jungtae Rha, Alfredo Dubra, and Joseph Carroll, "Spatial and temporal variation of rod photoreceptor reflectance in the human retina," Biomed. Opt. Express 2 , 2577-2589 (2011)
• Jennifer J. Hunter, Benjamin Masella, Alfredo Dubra, Robin Sharma, Lu Yin, William H. Merigan, Grazyna Palczewska, Krzysztof Palczewski, and David R. Williams, "Images of photoreceptors in living primate eyes using adaptive optics two-photon ophthalmoscopy," Biomed. Opt. Express 2 , 139-148 (2011)

Conference papers

Articles written by ALPAO users and presented during conferences:

• J.A. Croskrey, B. Schroeder, J. Rha, A.M. Dubis, J. Carroll, D.P. Han, "In vivo imaging of the human photoreceptos with adaptive optics and SD-OCT after short duration PASCAL™ Macular Grid an Panretinal Laser Photocoagulation", ARVO 2011, publication number 732
• A.M. Dubis, B.R. Hansen, R.F. Cooper, J. Beringer, Y. Sulai, A. Dubra, J. Carroll, "The Relationship between the foveal avascular zone and foveal pit morphology", ARVO 2011, publication number 1045
• R.F. Cooper, J. Rha, A. Dubra, J. Carroll, "Examining DFT and Direct Counting Estimates of Photoreceptor Density in Adaptive Optics Retinal Imaging", ARVO 2011, publication number 1321
• J. Carroll, A.M. Dubis, S.Sayeram, P. Sommer, T. Patitucci, J.T. McAllister, K.E. Stepien, M.H. Brilliant, T.B. Connor Jr, C.G. Summers, " Variability in Fovel Morphology in albinism assessed with SD-OCT", ARVO 2011, publication number 2175
• D. Masella, J.J. Hunter, L. Yin, J. Strazzeri, A. Dubra, W. H. Merigan, D. R. Williams, "No Loss of Photopigment Kinetics or Contrast Sensitivity seen after Photochemical Insult to the Retinal Pigment Epithelium", ARVO 2011, publication number 3199
• E. Blanco, X. Wang, Y. Zhang, Evaluate and Optimize the Performance of Adaptive Optics for Retinal Imaging, ARVO 2011, pPublication number 4059
• J.S. Werner, S.M. Jones, Q. Yang, A. Capp, S. Pilli, D. Kim, D.W. Arathorn, C.R. Vogel, S.S. Olivier, R.J. Zawadski, "Cellular Resolution in vivo Retinal Imaging with Motion Artifact-Free Adaptive Optics - Optical Coherence Tomography", ARVO 2011,
  publication number 4064
• J. Neitz, M. Wagner-Schuman, A. Dubra, S.A. Sjoberg, A.T. Moore, T.L. Young, M. Neitz, J. Carroll and M. Michaelides, "Cone mosaic disruption caused by L/M opsin mutations in Bornholm eye disease", ARVO 2011, publication number 4896
• J. Rha, MA. Genead, D.M. Bonci, A.M. Dubis, B. Schroeder, M. Neits, G.A. Fishman, J. Carroll, "Imaging Photoreceptor structure in achromatopsia patients using adaptive optics and spectral- domain optical coherence Tomography", ARVO 2011, publication number: 4897
• M.M. chung, E.A. Rossi, H. Song, A. Dubra, M.O. Gonzalez, E.M. Stone, J. Riley, D.R. Williams, " In vivo adaptive optics imaging of the cone photoreceptor mosaic in autosomal dominant cone rod dystrophy (AD-CRD) in a three-generation family carrying the I143NT mutation in the guanylate cyclase activator A1A (BUCA1A) Gene", ARVO 2011, publication number 5002
• Y. Geng, R. Sharma, A. Dubra, K. Ahmad, T. Twietmeyer, B. Masella, J.J. Hunter, R.T. Libby, D. R. Williams, " High Resolution In Vivo Imaging Of The Mouse Retina Using an Adaptive Optics Scanning Laser Ophtalmoscope", ARVO 2011, publication number 5871
• A. Dubra, Y. Sulai, D.R. Williams, J. Carroll, "In Vivo Imaging of The Rod Photoreceptor Mosaic", ARVO 2011, publication number 5872
• K.E. Stepien, W.M. Martinez, A.M. Dubis, R.F. Cooper, A. Dubra, J. Carroll, "Detection of Photoreceptor Disruption After Commotio Retinae Using Adaptive Optics Scanning Laser Ophthalmoscopy", ARVO 2011, publication number 6657