About

Dr. Robert J. Zawadzki is an Associate Professor in the Department of Ophthalmology & Vision Science at UC Davis Health. His research focuses on studying various types of retinal and optic nerve head (ONH) diseases. He is involved in the development of new instrumentation for high-resolution in vivo retina imaging, including techniques such as Optical Coherence Tomography (OCT), Scanning Laser Ophthalmoscopy (SLO), Adaptive Optics (AO), and their combinations. His work aims to visualize individual cellular structures within the retina and to understand the mechanisms underlying eye aging and retinal diseases. Dr. Zawadzki has a broad background in biomedical optics, biomedical engineering, and vision science. He is developing several novel in vivo retinal imaging modalities to study structural and functional changes of the retina over time at cellular resolution. These include multimodal adaptive optics enhanced clinical and basic science retinal imaging systems, as well as early-generation OCT handheld systems for pediatric clinical investigations. His research also involves creating new image acquisition and data processing schemes to quantify changes in the retina related to aging, disease progression, and therapy. Notably, he has contributed to the development of optoretinography (ORG), a functional retinal test that measures light-evoked signals from photoreceptors using OCT, similar to electroretinogram (ERG) assessments.

Research topics

• Computer Science
• Optics
• Physics
• Artificial Intelligence
• Neuroscience
• Biology
• Genetics
• Computer vision
• Telecommunications
• Medicine
• Ophthalmology

Selected publications

• Computational aberration correction for SD-OCT imaging of fish retina at 100 kHz A-scan rate

  2026-03-05

  articleSenior author

  While high axial resolution of Optical Coherence Tomography (OCT) provides cellular-level visualization of the retina layers, high-NA imaging is needed to visualize cellular level structures in en face plane. This, however, is often restricted by severe ocular aberrations present in imaging eye, including eyes of experimental animals, that preclude the attainment of diffraction-limited resolution. In this study, we propose a robust volumetric aberration correction framework integrated with a custom-built 100 kHz SD-OCT system for in vivo small animal retinal imaging. Instead of employing complex hardware-based adaptive optics, the proposed method utilizes a two-step computational optimization strategy: estimating a global wavefront map via Shannon entropy minimization on a representative structural layer and applying a depth-variant defocus model to the entire volume. The performance of this method is validated through a comparative intensity analysis and pixel intensity histograms, which demonstrate an enhancement in the signal intensity of individual photoreceptor cells. Furthermore, the enhancement of internal retinal structures is quantitatively confirmed through A-scan line profiling, showing marked improvements in signal contrast throughout the axial direction. This computational approach offers an efficient solution for high-speed volumetric imaging, facilitating high-resolution morphological studies of the small animal retina without additional hardware complexity.

  PublisherDOI

• Photopigment bleaching calculation and simulation notebook

  Open MIND · 2026-03-12 · 1 citations

  otherOpen access

  This notebook provides a quantitative framework for simulating retinal cone photopigment bleaching using photometric and radiometric formulations. This release includes minor updates to the photopigment bleaching worksheet notebook. Changes: Updated bleaching calculations Improved table headers Fixed typos and an error in the code for final table generation Updated README and citation information Authors Reddikumar Maddipatla$^{1,2}$, Yao Cai$^{1}$, Robert J. Zawadzki$^{1,2}$, and Ravi S. Jonnal$^{1}$ $^{1}$ Center for Human Ophthalmic Imaging Research (CHOIR), UC Davis Eye Center, Sacramento, CA 95817, USA $^{2}$ EyePOD Imaging Lab, Department of Cell Biology and Human Anatomy, University of California, Davis, CA 95616, USA

  PublisherDOI

• Dark adaptation of cone photoreceptor responses is revealed by optoretinography

  bioRxiv (Cold Spring Harbor Laboratory) · 2026-05-01

  articleOpen access

  Dark adaptation is the essential process that restores visual sensitivity following exposure to bright light, yet the underlying mechanisms remain incompletely understood. Here, we propose a method for assessing dark adaptation in cones using optoretinography (ORG) based on adaptive optics optical coherence tomography (AO-OCT). ORG quantifies cone functional response by monitoring nano-scale changes in the cone's outer segment occurring over hundreds of milliseconds after visible stimulation. This method consists of sequential measurements of stimulus-evoked cone responses over the course of minutes of dark adaptation. Each response captures optical path length changes in single photoreceptor outer segments over milliseconds during a multi-minute recovery period following a strong photopigment bleach. We parameterized cone ORG responses and proposed an exponential model linking ORG dynamics to pigment regeneration. Parameters of the ORG response exhibited exponential decay behavior during dark adaptation, and were thus fit with exponential functions and quantified by the resulting decay parameter τ. Parameters capturing the amplitude of the ORG responses recovered more slowly than those capturing temporal dynamics of the responses. This difference is consistent with distinct contributions from photopigment regeneration and downstream phototransduction processes. Recovery speed varied by two- to threefold among three normal subjects, suggesting substantial inter-subject physiological diversity. Processes within the cone, including pigment regeneration, are thought to underlie the gains in photopic visual sensitivity that occur in the dark. These findings highlight ORG as an objective and sensitive assay of those cellular mechanisms. While the ORG itself has shown promise as a biomarker of the health of the photoreceptor response to light, the results of this study show that it may also be useful for probing the health of the intra- and intercellular homeostatic mechanisms that support it.

  PublisherOA PDFDOI

• Clinical optoretinography for evaluating photoreceptor disease

  2026-03-05

  article

  Optoretinography (ORG) is an emerging method for parallel structural and functional assessment of the retina. Originally demonstrated using high-resolution and high-speed OCT systems, ORG has recently been implemented with clinical-grade OCT. Here we show that clinical-grade ORG is capable of measuring light-evoked photoreceptor responses in subjects without retinal disease, and also capable of revealing alterations in the photoreceptor responses of patients with inherited retinal disease, unexplained vision loss, and vitamin A deficiency.

  PublisherDOI

• Optoretinography (ORG): measurement of light-evoked changes in the optical properties of retinal neurons

  2026-03-05

  article1st authorCorresponding
  PublisherDOI

• Evaluation of phase-stability of optical coherence microscopy (OCM) system for high-resolution tissue imaging

  2026-01-19

  articleSenior author
  PublisherDOI

• Deep reinforcement learning for high resolution retinal imaging

  2026-03-05

  article
  PublisherDOI

• Adaptive optics OCT used to measure outer segment length dynamic equilibria in response to constant backgrounds

  2026-03-05

  article
  PublisherDOI

• Multiwavelength confocal fluorescence imaging of the age and disease-related pigmentary changes in the retinal pigment epithelium cells

  2026-03-05

  articleSenior author
  PublisherDOI

• Full-field swept source optical coherence tomography for structural and functional retinal imaging in mice

  2026-03-05

  articleSenior author

  We report a full-field swept-source optical coherence tomography (FF-SS-OCT) system with a ~ 20 million A-scan/s rate for the in vivo structural and functional imaging of the mouse retina. The FF-SS-OCT, configured as an on-axis Mach-Zehnder interferometer, employs a tunable wavelength source and a high-speed 2D CMOS camera. Optimized coherent illumination and detection strategies are implemented for an efficient full-field imaging of the mouse retina. The light-evoked experiments (Optoretinography-ORG) are performed using a single-flash stimulus to bleach controlled fractions of rhodopsin in individual experiments. Serial OCT volume acquisition facilitates the quantitative assessment of relative shifts in outer retinal layer positions and changes in the backscattering intensity post-stimuli.

  PublisherDOI

Recent grants

• Theranostics of Photoreceptor-RPE-Choroid Neurovascular Unit in Eye Diseases:

  NIH · $4.1M · 2017–2027

• Large Animal Core

  NIH · $18.3M · 1999–2029

• Full Field OCT for Cellular Level Structural and Functional Retinal Imaging

  NIH · $2.3M · 2020–2026

Frequent coauthors

• John S. Werner

  University of Lusaka

  242 shared

• Pengfei Zhang

  Shihezi University

  88 shared

• Edward N. Pugh

  University of California, Davis

  80 shared

• Ravi S. Jonnal

  University of California, Davis

  78 shared

• Stacey S. Choi

  The Ohio State University

  74 shared

• Marinko V. Šarunic

  University College London

  51 shared

• Yifan Jian

  Shenzhen University

  49 shared

• Susanna S. Park

  University of California, Davis

  49 shared

Awards & honors

• BrightFocus Foundation
• the Dr. Douglas H. Johnson Award (2021)
• Silver Fellow of The Association for Research in Vision and…
• Senior member of Optica (formerly known as The Optical Socie…
• R&D 100 Award for MEMS-based AO-SLO & MEMS-based AO-OCT (200…