Bio


My interest in optics started during undergraduate education. During my Ph.D. at the Indian Institute of Science, Bengaluru, India, I was introduced to a technology called adaptive optics that is used to compensate for the image degradation caused by atmospheric turbulence in large ground-based astronomical telescopes. As a postdoc at the School of Physics, University College Dublin, Ireland, we developed novel adaptive optics methods using spatial light modulators and applied them to microscopy and ophthalmology. During my second postdoctoral fellowship at the Institute of Optics in Madrid, Spain, we engineered the working principles of a new clinical device for prospective refractive and cataract surgery patients called SimVis, which facilitates the prescription of intraocular lenses and contact lenses.

Current Role at Stanford


My role is to advance the development of next-generation clinically relevant adaptive optics ocular imaging devices to allow early disease diagnosis and monitoring through a non-invasive visualization of subcellular structures in the eye.

Honors & Awards


  • Qualcomm Distinguished Poster Award, SCIEN Industry Affiliates Meeting, Stanford University (2020)
  • Senior Member, Optical Society of America (2019)
  • Outstanding Reviewer Recognition, Optical Society of America (2016)
  • MARIE SKŁODOWSKA-CURIE Co-fund Advanced Fellowship (MVISION), European Union and Communidad de Madrid (2014)
  • Robert S. Hilbert Memorial Student Travel Grant, Optical Society of America and Optical Research Associates (2011)
  • Student foreign travel grant, Council of Scientific and Industrial Research, India (2011)
  • Student travel grant, Optical Society of America (2011)
  • Silver medal, ACEEE, India (2011)
  • Student travel grant, SPIE, the international society for optics and photonics (2010)
  • First prize paper of a session, International conference on advanced computing, India (2009)
  • Second prize paper, International conference on advanced computing, India (2009)
  • J. N. Sapru scholarship and gold medal, Bhadrachalam Public School and Junior College, India (2001)
  • Gayathri Meritorious Award, Bhadrachalam Public School and Junior College, India (2000)

Education & Certifications


  • Ph.D., Indian Institute of Science (2012)
  • Master of Science, Sri Sathya Sai Institute of Higher Learning (2006)
  • Bachelor of Science, Sri Sathya Sai Institute of Higher Learning (2004)

Work Experience


  • Senior Post Doctoral Researcher, Instituto de Optica (IO-CSIC) (December 22, 2014 - February 13, 2018)

    Location

    Madrid, Spain

  • Post Doctoral Researcher, University College Dublin (March 14, 2012 - August 31, 2014)

    Location

    Dublin, Ireland

Professional Affiliations and Activities


  • Lifetime Member, SPIE—The International Society for Optical Engineering (2021 - Present)
  • Senior Member, Optical Society of America (2019 - Present)
  • Chair, Vision Technical Group, Optical Society of America (2019 - 2021)
  • Committee Member, Optical Society of America (Optical Metrology Technical Group) (2014 - 2018)

All Publications


  • Multi-layer Shack-Hartmann wavefront sensing in the point source regime Biomedical Optics Express Akondi, V., Dubra, A. 2021; 12 (1): 409-432

    View details for DOI 10.1364/BOE.411189

  • A two-layer Shack-Hartmann wavefront sensor model of the human and mouse retinas Akondi, V., Dubra, A. 2021

    View details for DOI 10.1117/12.2583667

  • Shack-Hartmann wavefront sensor optical dynamic range Optics Express Akondi, V., Dubra, A. 2021; 29 (6): 8417-8429

    Abstract

    The widely used lenslet-bound definition of the Shack-Hartmann wavefront sensor (SHWS) dynamic range is based on the permanent association between groups of pixels and individual lenslets. Here, we formalize an alternative definition that we term optical dynamic range, based on avoiding the overlap of lenslet images. The comparison of both definitions for Zernike polynomials up to the third order plus spherical aberration shows that the optical dynamic range is larger by a factor proportional to the number of lenslets across the SHWS pupil. Finally, a pre-centroiding algorithm to facilitate lenslet image location in the presence of defocus and astigmatism is proposed. This approach, based on the SHWS image periodicity, is demonstrated using optometric lenses that translate lenslet images outside the projected lenslet boundaries.

    View details for DOI 10.1364/OE.419311

  • Wavefront distortions in an oscillating resonant galvanometric optical scanner Computational Optical Sensing and Imaging Akondi, V., Kowalski, B., Sredar, N., Dubra, A. 2020: JW2A. 48
  • Dynamic distortion in resonant galvanometric optical scanners. Optica Akondi, V., Kowalski, B., Burns, S. A., Dubra, A. 2020; 7 (11): 1506-1513

    Abstract

    High-speed optical systems are revolutionizing biomedical imaging in microscopy, DNA sequencing, and flow cytometry, as well as numerous other applications, including data storage, display technologies, printing, and autonomous vehicles. These systems often achieve the necessary imaging or sensing speed through the use of resonant galvanometric optical scanners. Here, we show that the optical performance of these devices suffers due to the dynamic mirror distortion that arises from the variation in torque with angular displacement. In one of two scanners tested, these distortions result in a variation of signal-to-noise (Strehl) ratio by an order of magnitude across the field of view, degrading transverse resolution by more than a factor of 2. This mirror distortion could be mitigated through the use of stiffer materials, such as beryllium or silicon carbide, at the expense of surface roughness, as these cannot be polished to the same degree of smoothness as common optical glasses. The repeatability of the dynamic distortion indicates that computational and optical corrective methods are also possible.

    View details for DOI 10.1364/optica.405187

    View details for PubMedID 34368405

    View details for PubMedCentralID PMC8345821

  • Optical and Visual Quality With Physical and Visually Simulated Presbyopic Multifocal Contact Lenses Translational Vision Science & Technology Vinas, M., Aissati, S., Gonzalez-Ramos, A., Romero, M., Sawides, L., Akondi, V., Gambra, E., Dorronsoro, C., Karkkainen, T., Nankivil, D., Marcos, S. 2020; 9 (20): 1-16

    View details for DOI 10.1167/tvst.9.10.20

  • Average gradient of Zernike polynomials over polygons Optics Express Akondi, V., Dubra, A. 2020; 28 (13): 18876-18886

    View details for DOI 10.1364/OE.393223

  • In vivo quantification of Bruch's membrane in humans with visible light OCT Zhang, T., Kho, A., Akondi, V., Dubra, A., Srinivasan, V. 2020

    View details for DOI 10.1117/12.2546437

  • Perceptual and physical limits to temporal multiplexing simulation of multifocal corrections Dorronsoro, C., Rodriguez-Lopez, V., Barcala, X., Gambra, E., Akondi, V., Sawides, L., Marrakchi, Y., Lage, E., Geisler, W. S., Marcos, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Shack-Hartmann wavefront sensor bias at the pupil boundary: problem and solution Akondi, V., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Chromatic Shack-Hartmann wavefront sensor with adaptive optics correction of monochromatic aberrations Steven, S., Akondi, V., Dubra, A. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Optical and visual quality with physical and visually simulated presbyopic multifocal contact lenses Vinas, M., Aissati, S., Gonzalez-Ramos, A., Romero, M., Sawides, L., Akondi, V., Gambra, E., Dorronsoro, C., Martinez-Enriquez, E., Karkkainen, T., Nankivil, D., Marcos, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2019
  • Accounting for focal shift in the Shack-Hartmann wavefront sensor Optics Letters Akondi, V., Dubra, A. 2019; 44 (17): 4151-4154

    Abstract

    The Shack-Hartmann wavefront sensor samples a beam of light using an array of lenslets, each of which creates an image onto a pixelated sensor. These images translate from their nominal position by a distance proportional to the average wavefront slope over the corresponding lenslet. This principle fails in partially and/or non-uniformly illuminated lenslets when the lenslet array is focused to maximize peak intensity, leading to image centroid bias. Here, we show that this bias is due to the low Fresnel number of the lenslets, which shifts the diffraction focus away from the geometrical focus. We then demonstrate how the geometrical focus can be empirically found by minimizing the bias in partially illuminated lenslets.

    View details for DOI 10.1364/OL.44.004151

  • Tunable lenses: dynamic characterization and fine-tuned control for high-speed applications Optics Express Dorronsoro, C., Barcala, X., Gambra, E., Akondi, V., Sawides, L., Marrakchi, Y., Rodriguez-Lopez, V., Benedi-Garcia, C., Vinas, M., Lage, E., Marcos, S. 2019; 27 (3): 2085-2100

    Abstract

    Tunable lenses are becoming ubiquitous, in applications including microscopy, optical coherence tomography, computer vision, quality control, and presbyopic corrections. Many applications require an accurate control of the optical power of the lens in response to a time-dependent input waveform. We present a fast focimeter (3.8 KHz) to characterize the dynamic response of tunable lenses, which was demonstrated on different lens models. We found that the temporal response is repetitive and linear, which allowed the development of a robust compensation strategy based on the optimization of the input wave, using a linear time-invariant model. To our knowledge, this work presents the first procedure for a direct characterization of the transient response of tunable lenses and for compensation of their temporal distortions, and broadens the potential of tunable lenses also in high-speed applications.

    View details for DOI 10.1364/OE.27.002085

  • Visual simulators replicate vision with multifocal lenses. Scientific reports Vinas, M. n., Benedi-Garcia, C. n., Aissati, S. n., Pascual, D. n., Akondi, V. n., Dorronsoro, C. n., Marcos, S. n. 2019; 9 (1): 1539

    Abstract

    Adaptive optics (AO) visual simulators based on deformable mirrors, spatial light modulators or optotunable lenses are increasingly used to simulate vision through different multifocal lens designs. However, the correspondence of this simulation with that obtained through real intraocular lenses (IOLs) tested on the same eyes has not been, to our knowledge, demonstrated. We compare through-focus (TF) optical and visual quality produced by real multifocal IOLs (M-IOLs) -bifocal refractive and trifocal diffractive- projected on the subiect's eye with those same designs simulated with a spatial light modulator (SLM) or an optotunable lens working in temporal multiplexing mode (SimVis technology). Measurements were performed on 7 cyclopleged subjects using a custom-made multichannel 3-active-optical-elements polychromatic AO Visual Simulator in monochromatic light. The same system was used to demonstrate performance of the real IOLs, SLM and SimVis technology simulations on bench using double-pass imaging on an artificial eye. Results show a general good correspondence between the TF performance with the real and simulated M-IOLs, both optically (on bench) and visually (measured visual acuity in patients). We demonstrate that visual simulations in an AO environment capture to a large extent the individual optical and visual performance obtained with real M-IOLs, both in absolute values and in the shape of through-focus curves.

    View details for PubMedID 30733540

    View details for PubMedCentralID PMC6367467

  • Centroid error due to non-uniform lenslet illumination in the Shack-Hartmann wavefront sensor Optics Letters Akondi, V., Steven, S., Dubra, A. 2019; 44 (17): 4167-4170

    Abstract

    Images formed by individual Shack-Hartmann wavefront sensor lenslets are displaced proportionally to the average wavefront slope over their aperture. This principle fails when the lenslet illumination is non-uniform. Here we demonstrate that the resulting error is proportional to the linear component of the illumination intensity, the quadratic wavefront component, and the lenslet size. For illustrative purposes, we compare the error due to centered Gaussian illumination decaying by 30% at the pupil edge against the error due to assuming the wavefront at the lenslet center being equal to the wavefront average across each lenslet. When testing up to ninth-order Zernike polynomial wavefronts and simulating nine lenslets across the pupil, the maximum centroid errors due to non-uniform illumination and sampling are 1.4% and 21%, respectively, and 0.5% and 6.7% when considering 25 lenslets across the pupil in the absence of other sources of error.

    View details for DOI 10.1364/OL.44.004167

  • Comparison of multifocal visual simulations in patients before and after implantation of diffractive trifocal lenses Vinas, M., Romero, M., Aissati, S., Luis Mendez-Gonzalez, J., Benedi, C., Gambra, E., Akondi, V., Garzon, N., Poyales, F., Dorronsoro, C., Marcos, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2018
  • Experimental validations of a tunable-lens-based visual demonstrator of multifocal corrections. Biomedical optics express Akondi, V. n., Sawides, L. n., Marrakchi, Y. n., Gambra, E. n., Marcos, S. n., Dorronsoro, C. n. 2018; 9 (12): 6302–17

    Abstract

    The Simultaneous Vision simulator (SimVis) is a visual demonstrator of multifocal lens designs for prospective intraocular lens replacement surgery patients and contact lens wearers. This programmable device employs a fast tunable lens and works on the principle of temporal multiplexing. The SimVis input signal is tailored to mimic the optical quality of the multifocal lens using the theoretical SimVis temporal profile, which is evaluated from the through-focus Visual Strehl ratio metric of the multifocal lens. In this paper, for the first time, focimeter-verified on-bench validations of multifocal simulations using SimVis are presented. Two steps are identified as being critical to accurate SimVis simulations. Firstly, a new iterative approach is presented that improves the accuracy of the theoretical SimVis temporal profile for three different multifocal intraocular lens designs - diffractive trifocal, refractive segmented bifocal, and refractive extended depth of focus, while retaining a low sampling. Secondly, a fast focimeter is used to measure the step response of the tunable lens, and the input signal is corrected to include the effects of the transient behavior of the tunable lens. It was found that the root-mean-square of the difference between the estimated through-focus Visual Strehl ratio of the multifocal lens and SimVis is not greater than 0.02 for all the tested multifocal designs.

    View details for PubMedID 31065430

    View details for PubMedCentralID PMC6490999

  • On-bench validations of tunable lens based multifocal visual simulations Imaging and Applied Optics Akondi, V., Sawides, L., Marrakchi, Y., Gambra, E., Barcala, X., Marcos, S., Dorronsoro, C. 2018

    View details for DOI 10.1364/AIO.2018.AW2A.1

  • Simulating multifocal intraocular lenses with a spatial light modulator and a tunable lens: a computational evaluation Akondi, V., Gambra, E., Vinas, M., Aissati, S., Dorronsoro, C., Pascual, D., Marcos, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2017
  • Visual simulations of real multifocal lenses in a multi-channel Adaptive Optics system Marcos, S., Vinas, M., Benedi, C., Aissati, S., Akondi, V., Barcala, X., Gambra, E. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2017
  • In vivo measurement of longitudinal chromatic aberration with multifocal diffractive intraocular lenses. Vinas, M., Gonzalez-Ramos, A., Dorronsoro, C., Akondi, V., Garzon, N., Poyales, F., Marcos, S. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2017
  • Temporal multiplexing to simulate multifocal intraocular lenses: theoretical considerations Biomedical Optics Express Akondi, V., Dorronsoro, C., Gambra, E., Marcos, S. 2017; 8 (7): 3410-3425

    View details for DOI 10.1364/BOE.8.003410

  • In Vivo Measurement of Longitudinal Chromatic Aberration in Patients Implanted With Trifocal Diffractive Intraocular Lenses Journal of Refractive Surgery Vinas, M., Gonzalez-Ramos, A., Dorronsoro, C., Akondi, V., Garzon, N., Poyales, F., Marcos, S. 2017; 33 (11): 736-742
  • Evaluation of the true wavefront aberrations in eyes implanted with a rotationally asymmetric multifocal intraocular lens Journal of Refractive Surgery Akondi, V., Pérez-Merino, P., Martinez-Enriquez, E., Dorronsoro, C., Alejandre, N., Jiménez-Alfaro, I., Marcos, S. 2017; 33 (4): 257-265
  • Virtual pyramid wavefront sensor for phase unwrapping Applied optics Akondi, V., Vohnsen, B., Marcos, S. 2016; 55 (29): 8363-8367

    View details for DOI 10.1364/AO.55.008363

  • Temporal multiplexing and simulation of multifocal intraocular lenses Frontiers in Optics Akondi, V., Dorronsoro, C., Gambra, E., Vinas, M., Pascual, D., Aissati, S., Marcos, S. 2016

    View details for DOI 10.1364/FIO.2016.FW2A.3

  • Phase unwrapping with a virtual Hartmann-Shack wavefront sensor Optics Express Akondi, V., Falldorf, C., Marcos, S., Vohnsen, B. 2015; 23 (20): 25425-25439

    View details for DOI 10.1364/OE.23.025425

  • Phase estimation in digital phase-shifting point diffraction interferometry using a virtual Hartmann-Shack wavefront sensor Adaptive Optics: Analysis, Methods & Systems Akondi, V., Marcos, S., Vohnsen, B. 2015
  • Optimization of sensing parameters for a confocal signal-based wavefront corrector in microscopy Journal of Modern Optics Jewel, A. R., Akondi, V., Vohnsen, B. 2015; 62 (10): 786-792
  • Closed-loop adaptive optics using a spatial light modulator for sensing and compensating of optical aberrations in ophthalmic applications Journal of Biomedical Optics Akondi, V., Jewel, A. R., Vohnsen, B. 2014; 19 (9): 096014-096014
  • 3-D Analysis of Pinhole Size Optimization for a Confocal Signal-based Wavefront Sensor Frontiers in Optics Jewel, M. R., Akondi, V., Vohnsen, B. 2014

    View details for DOI 10.1364/FIO.2014.JW3A.40

  • Multi-faceted digital pyramid wavefront sensor Optics Communications Akondi, V., Castillo, S., Vohnsen, B. 2014; 323: 77-86
  • Digital phase-shifting point diffraction interferometer Optics Letters Akondi, V., Jewel, A. R., Vohnsen, B. 2014; 39 (6): 1641-1644

    View details for DOI 10.1364/OL.39.001641

  • Myopic aberrations: Simulation based comparison of curvature and Hartmann Shack wavefront sensors Optics Communications Basavaraju, R. M., Akondi, V., Weddell, S. J., Budihal, R. P. 2014; 312: 23-30
  • A direct comparison between a MEMS deformable mirror and a liquid crystal spatial light modulator in signal-based wavefront sensing Journal of the European Optical Society-Rapid publications Jewel, A. R., Akondi, V., Vohnsen, B. 2013; 8: 13073-1 - 13073-10

    View details for DOI 10.2971/jeos.2013.13073

  • Digital pyramid wavefront sensor Adaptive Optics: Methods, Analysis and Applications Akondi, V., Castillo, S., Jewel, M. R., Vohnsen, B. 2013

    View details for DOI 10.1364/AOPT.2013.OM2A.3

  • On pinhole size optimization in wavefront sensorless adaptive optics Adaptive Optics: Methods, Analysis and Applications Jewel, M. R., Akondi, V., Vohnsen, B. 2013
  • A review of atmospheric wind speed measurement techniques with Shack Hartmann wavefront imaging sensor in adaptive optics Journal of the Indian Institute of Science Mysore Basavaraju, R., Akondi, V., Budihal, R. 2013; 93 (1): 67-84
  • Digital pyramid wavefront sensor with tunable modulation Optics Express Akondi, V., Castillo, S., Vohnsen, B. 2013; 21 (15): 18261-18272

    View details for DOI 10.1364/OE.21.018261

  • Myopic aberrations: impact of centroiding noise in Hartmann Shack wavefront sensing Ophthalmic and Physiological Optics Akondi, V., Vohnsen, B. 2013; 33 (4): 434-443

    View details for DOI 10.1111/opo.12076

  • X-ray attenuation coefficient of mixtures: Inputs for dual-energy CT Medical Physics Haghighi, R. R., Chatterjee, S., Akondi, V., Kumar, P., Thulkar, S. 2011; 38 (10): 5270–5279

    View details for DOI 10.1118/1.3626572

  • Multi-dither Shack Hartmann sensor for large telescopes: A numerical performance evaluation Adaptive Optics: Methods, Analysis and Applications Akondi, V., Basavaraju, R. M., Budihal, R. 2011

    View details for DOI 10.1364/AOPT.2011.ATuA4

  • Towards Low Cost turbulence generator for AO testing: Utility, control and stability Adaptive Optics: Methods, Analysis and Applications Basavaraju, R. M., Akondi, V., Krishnan, A., Ram, S., Shankar Sai, S., Budihal, R. 2011

    View details for DOI 10.1364/AOPT.2011.JMB5

  • Grid size optimization for atmospheric turbulence phase screen simulations Adaptive Optics: Methods, Analysis and Applications Basavaraju, R. M., Akondi, V., Budihal, R. 2011

    View details for DOI 10.1364/AOPT.2011.JMB3

  • Automated ROI selection and calibration of a microlens array using a MEMS CDM Adaptive Optics: Methods, Analysis and Applications Basavaraju, R. M., Akondi, V., Budihal, R. 2011

    View details for DOI 10.1364/AOPT.2011.ATuA5

  • Evaluation of the performance of centroiding algorithms with varying spot size : case of WFS calibration for the TMT NFIRAOS Adaptive Optics: Methods, Analysis and Applications Akondi, V., Ellerbroek, B. L., Basavaraju, R. M., Anderson, D. R., Budihal, R. 2011

    View details for DOI 10.1364/AOPT.2011.ATuA1

  • Intensity Weighted Noise Reduction in MEMS Based Deformable Mirror Images Vyas, A., Roopshree, M. B., Prasad, B., Predeep, P., Thakur, M., Varma, M. K. AMER INST PHYSICS. 2011

    View details for DOI 10.1063/1.3643545

    View details for Web of Science ID 000302007600102

  • Experimental evaluation of centroiding algorithms at different light intensity and noise levels Roopashree, M. B., Vyas, A., Prasad, B., Predeep, P., Thakur, M., Varma, M. K. AMER INST PHYSICS. 2011

    View details for DOI 10.1063/1.3643533

    View details for Web of Science ID 000302007600090

  • Influence Function Measurement of Continuous Membrane Deformable Mirror Actuators Using Shack Hartmann Sensor Roopashree, M. B., Vyas, A., Prasad, B., Predeep, P., Thakur, M., Varma, M. K. AMER INST PHYSICS. 2011

    View details for DOI 10.1063/1.3643577

    View details for Web of Science ID 000302007600134

  • Noise reduction in the centroiding of laser guide star spot pattern using thresholded Zernike reconstructor Vyas, A., Roopashree, M. B., Prasad, B., Ellerbroek, B. L., Hart, M., Hubin, N., Wizinowich, P. L. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.856640

    View details for Web of Science ID 000285506400148

  • Dither based sensor for improved consistency of adaptive optics system Vyas, A., Roopashree, M. B., Prasad, B., AtadEttedgui, E., Lemke, D. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.856636

    View details for Web of Science ID 000285833700073

  • Multilayered temporally evolving phase screens based on statistical interpolation Roopashree, M. B., Vyas, A., Prasad, B., Ellerbroek, B. L., Hart, M., Hubin, N., Wizinowich, P. L. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.856814

    View details for Web of Science ID 000285506400133

  • Real-time wind speed measurement using wavefront sensor data Roopashree, M. B., Vyas, A., Prasad, B., Korotkova, O. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.841333

    View details for Web of Science ID 000284396600009

  • Improved Iteratively Weighted Centroiding for accurate spot detection in Laser Guide Star based Shack Hartmann Sensor Vyas, A., Roopashree, M. B., Prasad, B., Korotkova, O. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.841331

    View details for Web of Science ID 000284396600005

  • Optimizing the modal index of Zernike polynomials for regulated phase screen simulation Vyas, A., Roopashree, M. B., Prasad, B., Ellerbroek, B. L., Hart, M., Hubin, N., Wizinowich, P. L. SPIE-INT SOC OPTICAL ENGINEERING. 2010

    View details for DOI 10.1117/12.856816

    View details for Web of Science ID 000285506400134

  • Performance of Centroiding Algorithms at Low Light Level Conditions in Adaptive Optics Vyas, A., Roopashree, M. B., Prasad, B. R., Vyas, A., IEEE IEEE. 2009: 366-+