My interest in ophthalmology started at a very early age, motivated by my own amblyopia and hyperopia. These led me to study physics and optics, with my first research experience at undergraduate and master’s level at the Applied Optics Group of the Universidad de la República in Uruguay. I then pursued my PhD work and a first postdoctoral position at the Photonics Group in Imperial College London, where I worked on instrumentation to study the topography of the tear film and adaptive optics (AO). The desire to advance AO for retinal imaging took me to the University of Rochester, where the interaction with patients affected by blinding conditions provided me with the determination to go beyond the proof-of-principle experiments after which many technologies are abandoned. Therefore, since starting my research group at the University of Rochester first, and at the Medical College of Wisconsin later and now at Stanford we have focused on the development and translation of AO and microscopy techniques into tools that can be used to address real clinical problems.
Honorary Lecturer of Ophthalmology, University College London (UK) (2013 - Present)
Associate Adjunct Professor of Ophthalmology, Medical College of Wisconsin (2016 - Present)
Boards, Advisory Committees, Professional Organizations
Member, The International Society for Optics and Photonics (2011 - Present)
Member, Association for Research in Vision and Ophthalmology (2001 - Present)
Member, Optical Society of America (2008 - Present)
PhD, Imperial College London, UK, Physics (2004)
MSc, Universidad de la República, Uruguay, Physics (2000)
BSc, Universidad de la República, Uruguay, Physics (1998)
Alfredo Dubra. "United States Patent 8,226,236 Method and apparatus for imaging in an eye", University Of Rochester, May 18, 2006
An Automated Reference Frame Selection (ARFS) Algorithm for Cone Imaging with Adaptive Optics Scanning Light Ophthalmoscopy.
Translational vision science & technology
2017; 6 (2): 9-?
To develop an automated reference frame selection (ARFS) algorithm to replace the subjective approach of manually selecting reference frames for processing adaptive optics scanning light ophthalmoscope (AOSLO) videos of cone photoreceptors.Relative distortion was measured within individual frames before conducting image-based motion tracking and sorting of frames into distinct spatial clusters. AOSLO images from nine healthy subjects were processed using ARFS and human-derived reference frames, then aligned to undistorted AO-flood images by nonlinear registration and the registration transformations were compared. The frequency at which humans selected reference frames that were rejected by ARFS was calculated in 35 datasets from healthy subjects, and subjects with achromatopsia, albinism, or retinitis pigmentosa. The level of distortion in this set of human-derived reference frames was assessed.The average transformation vector magnitude required for registration of AOSLO images to AO-flood images was significantly reduced from 3.33 ± 1.61 pixels when using manual reference frame selection to 2.75 ± 1.60 pixels (mean ± SD) when using ARFS (P = 0.0016). Between 5.16% and 39.22% of human-derived frames were rejected by ARFS. Only 2.71% to 7.73% of human-derived frames were ranked in the top 5% of least distorted frames.ARFS outperforms expert observers in selecting minimally distorted reference frames in AOSLO image sequences. The low success rate in human frame choice illustrates the difficulty in subjectively assessing image distortion.Manual reference frame selection represented a significant barrier to a fully automated image-processing pipeline (including montaging, cone identification, and metric extraction). The approach presented here will aid in the clinical translation of AOSLO imaging.
View details for DOI 10.1167/tvst.6.2.9
View details for PubMedID 28392976
Vision science and adaptive optics, the state of the field.
Adaptive optics is a relatively new field, yet it is spreading rapidly and allows new questions to be asked about how the visual system is organized. The editors of this feature issue have posed a series of question to scientists involved in using adaptive optics in vision science. The questions are focused on three main areas. In the first we investigate the use of adaptive optics for psychophysical measurements of visual system function and for improving the optics of the eye. In the second, we look at the applications and impact of adaptive optics on retinal imaging and its promise for basic and applied research. In the third, we explore how adaptive optics is being used to improve our understanding of the neurophysiology of the visual system.
View details for DOI 10.1016/j.visres.2017.01.006
View details for PubMedID 28212982
Multimodal Imaging of Photoreceptor Structure in Choroideremia
2016; 11 (12)
Choroideremia is a progressive X-linked recessive dystrophy, characterized by degeneration of the retinal pigment epithelium (RPE), choroid, choriocapillaris, and photoreceptors. We examined photoreceptor structure in a series of subjects with choroideremia with particular attention to areas bordering atrophic lesions.Twelve males with clinically-diagnosed choroideremia and confirmed hemizygous mutations in the CHM gene were examined. High-resolution images of the retina were obtained using spectral domain optical coherence tomography (SD-OCT) and both confocal and non-confocal split-detector adaptive optics scanning light ophthalmoscope (AOSLO) techniques.Eleven CHM gene mutations (3 novel) were identified; three subjects had the same mutation and one subject had two mutations. SD-OCT findings included interdigitation zone (IZ) attenuation or loss in 10/12 subjects, often in areas with intact ellipsoid zones; RPE thinning in all subjects; interlaminar bridges in the imaged areas of 10/12 subjects; and outer retinal tubulations (ORTs) in 10/12 subjects. Only split-detector AOSLO could reliably resolve cones near lesion borders, and such cones were abnormally heterogeneous in morphology, diameter and density. On split-detector imaging, the cone mosaic terminated sharply at lesion borders in 5/5 cases examined. Split-detector imaging detected remnant cone inner segments within ORTs, which were generally contiguous with a central patch of preserved retina.Early IZ dropout and RPE thinning on SD-OCT are consistent with previously published results. Evidence of remnant cone inner segments within ORTs and the continuity of the ORTs with preserved retina suggests that these may represent an intermediate state of retinal degeneration prior to complete atrophy. Taken together, these results supports a model of choroideremia in which the RPE degenerates before photoreceptors.
View details for DOI 10.1371/journal.pone.0167526
View details for Web of Science ID 000389587100115
View details for PubMedID 27936069
Noninvasive imaging of the photoreceptor mosaic response to light stimulation.
Proceedings of the National Academy of Sciences of the United States of America
View details for PubMedID 27810954