Marquette University e-Publications@Marquette Dissertations (2009 -) Dissertations, Theses, and Professional Projects Noninvasive Assessment of Photoreceptor Structure and Function in the Human Retina Robert Francis Cooper Marquette University Recommended Citation Cooper, Robert Francis, "Noninvasive Assessment of Photoreceptor Structure and Function in the Human Retina" (2015). Dissertations (2009 -). 590. https://epublications.marquette.edu/dissertations_mu/590 NONINVASIVE ASSESSMENT OF PHOTORECEPTOR STRUCTURE AND FUNCTION IN THE HUMAN RETINA By Robert F Cooper, B.S. A Dissertation submitted to the Faculty of the Graduate School, Marquette University, in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Milwaukee, Wisconsin December 2015 i ABSTRACT NONINVASIVE ASSESSMENT OF PHOTORECEPTOR STRUCTURE AND FUNCTION IN THE HUMAN RETINA Robert F Cooper, B.S. Marquette University, 2015 The human photoreceptor mosaic underlies the first steps of vision; thus, even subtle defects in the mosaic can result in severe vision loss. The retina can be examined directly using clinical tools; however these devices lack the resolution necessary to visualize the photoreceptor mosaic. The primary limiting factor of these devices is the optical aberrations of the human eye. These aberrations are surmountable with the incorporation of adaptive optics (AO) to ophthalmoscopes, enabling imaging of the photoreceptor mosaic with cellular resolution. Despite the potential of AO imaging, much work remains before this technology can be translated to the clinic. Metrics used in the analysis of AO images are not standardized and are rarely subjected to validation, limiting the ability to reliably track structural changes in the photoreceptor mosaic geometry. Preceding the extraction of measurements, photoreceptors must be identified within the retinal image itself. This introduces error from both incorrectly identified cells and image distortion. We developed a novel method to extract measures of cell spacing from AO images that does not require identification of individual cells. In addition, we examined the sensitivity of various metrics in detecting changes in the mosaic and assessed the absolute accuracy of measurements made in the presence of image distortion. We also developed novel metrics for describing the mosaic, which may offer advantages over more traditional metrics of density and spacing. These studies provide a valuable basis for monitoring the photoreceptor mosaic longitudinally. As part of this work, we developed software (Mosaic Analytics) that can be used to standardize analytical efforts across different research groups. In addition, one of the more salient features of the appearance of individual cone photoreceptors is that they vary considerably in their reflectance. It has been proposed that this reflectance signal could be used as a surrogate measure of cone health. As a first step to understanding the cellular origin of these changes, we examined the reflectance properties of the rod photoreceptor mosaic. The observed variation in rod reflectivity over time suggests a common governing physiological process between rods and cones. ii TABLE OF CONTENTS List of Abbreviations ........................................................................................................ v List of Figures ................................................................................................................ vii List of Tables ................................................................................................................... x Chapter One: General introduction ................................................................................. 1 The Human Visual System .......................................................................................... 1 The Human Photoreceptor Mosaic .............................................................................. 5 Photoreceptor Structure and Function ......................................................................... 6 Adaptive Optics Imaging of the Human Retina In Vivo ................................................ 9 Assessing Adaptive Optics Images of the Photoreceptor Mosaic ...............................13 Summary of Dissertation Aims ...................................................................................16 Chapter Two: General methodology ..............................................................................18 Human Subjects ........................................................................................................18 Imaging the Human Photoreceptor Mosaic ................................................................18 AO Image Scaling ......................................................................................................22 Image Post-Processing ..............................................................................................24 Chapter Three: Assessing the performance of metrics describing the human cone mosaic ...........................................................................................................................32 Introduction ................................................................................................................33 Methods .....................................................................................................................35 Results .......................................................................................................................41 Discussion .................................................................................................................47 iii Chapter Four: Methods for investigating the local spatial anisotropy and the preferred orientation of the cone mosaic in adaptive optics retinal images ....................................51 Introduction ................................................................................................................52 Methods .....................................................................................................................54 Results .......................................................................................................................62 Discussion .................................................................................................................68 Chapter Five: Automatic detection of modal spacing (Yellott’s ring) in adaptive optics scanning light ophthalmoscope images .........................................................................73 Introduction ................................................................................................................74 Methods .....................................................................................................................75 Results .......................................................................................................................81 Discussion .................................................................................................................88 Chapter Six: Effects of intra-frame distortion on measures of cone mosaic geometry from adaptive optics scanning light ophthalmoscopy .............................................................91 Introduction ................................................................................................................92 Methods .....................................................................................................................94 Results ..................................................................................................................... 100 Discussion ............................................................................................................... 107 Chapter Seven: Spatial and temporal variation of rod photoreceptor reflectance in the human retina ............................................................................................................... 112 Introduction .............................................................................................................. 113 Methods ................................................................................................................... 115 Results ..................................................................................................................... 123 Discussion ............................................................................................................... 128 iv Bibliography ............................................................................................................. 131 v LIST OF ABBREVIATIONS AOIP – Advanced Ocular Imaging Program AOSLO – Adaptive Optics Scanning Light Ophthalmoscope AO – Adaptive Optics API – Application Programming Interface CCD – Charge-Coupled Device cGMP – Cyclic Guanosine-Monophosphate CHC – Cumulative Histogram Comparisons CI – Confidence Interval DFT – Discrete Fourier Transform DM – Deformable Mirror DRP – Density Recovery Profile DRPD – Density Recovery Profile Distance ERG – Electroretinogram FFT – Fast Fourier Transform FOV – Field of View GDP – Guanosine-Diphosphate GMP – Guanosine-Monophosphate GTP – Guanosine-Triphosphate GUI – Graphical User Interface ICC – Intra-class Correlation Coefficient ICD – Inter-Cell Distance IS – Inner Segment LC – Liquid Crystal vi LGN – Lateral Geniculate Nucleus LSO – Line-Scan Ophthalmoscope NCC – Normalized Cross-Correlation NND – Nearest Neighbor Distance NNR – Nearest Neighbor Regularity NoNR