Doctor of Philosophy, The Ohio State University, 2024, Vision Science

Purpose: To characterize any differences in the vasculature, cone photoreceptor packing geometry (CPG), retinal ganglion cell (RGC) packing and inner plexiform layer (IPL) thickness measures between subjects with diabetes mellitus (DM) without/no diabetic retinopathy (NDR) and age-similar healthy control subjects. Methods: Both NDR and healthy cohorts were enrolled. Optical coherence tomography angiography (OCTA) was used to assess vasculature at the macula. The following parameters were quantified; vessel density, vessel length density, and vessel density index (VDI) in three vascular plexuses, namely, the superficial vascular plexus, intermediate capillary plexus, and deep capillary plexus (DCP). The choriocapillaris (CC) flow deficit (FD) was also measured. OCTA images were binarized and processed to extrapolate the parafovea and parafoveal quadrants and the OCTA indices mentioned above. The CC was processed with six different radii to quantify FD. Adaptive optics (AO) - scanning laser ophthalmoscopy images were used to characterize cones based on five CPG indices, namely, cone density (CD), cone-to-cone spacing (CS), linear dispersion index (LDi), heterogeneity packing index (HPi) and percent of cells with six neighbors (hexagonal) at 3.6⁰ in the temporal retina (TR). AO - optical coherence tomography images were used to quantify integrity of the inner retina based on five neural indices, namely, RGC density (RGCD), RGC spacing (RGCS), IPL full thickness (IPLFT), IPL sublamina A thickness (SAT) and IPL sublamina B thickness (SBT) at 5⁰ in the TR. Results: No significant differences were found between the cohorts in the parafovea or parafoveal quadrants for any of the OCTA indices, although generally the NDR had reduced vasculature. In all eyes, statistically significant differences were found in the parafoveal FD across the six radii (p < 0.001). There were no significant differences in any of the CPG indices or IPL thickness indices between the cohort (open full item for complete abstract)

Committee: Stacey Choi (Advisor); Nathan Doble (Advisor); Deyue Yu (Committee Member); Matthew Reilly (Committee Member); Thomas Raasch (Committee Member); Colleen Cebulla (Committee Member) Subjects: Ophthalmology; Optics

Doctor of Philosophy, University of Akron, 2020, Integrated Bioscience

Visual processing begins with phototransduction when rod and cone photoreceptors in the outer retina transform incident photons into electrochemical potentials. The unique spectral sensitives of the expressed light-sensitive opsin (s) as well as several other factors shape an individual photoreceptors response properties. Subsequently, photoreceptor outputs distribute amongst distinct postsynaptic partners establishing parallel intraretinal channels for information flow. Furthermore, light-evoked responses in the mouse retina are known to increase significantly after eye-opening between postnatal days 12-14 (P12-14). This correlates with activities of the inner retina, confirming that outer retinal function increases after eye-opening and stabilizes around P30 (maturity). Previous in-vivo electroretinogram (ERG) studies have demonstrated light-evoked photoreceptor activity at P10. Such responses coincide with initial synaptogenesis between photoreceptors and second-order bipolar cells. However, this is a full 2-3 days after synaptogenesis of bipolar cells and third-order ganglion cells that relay retinal outputs to higher-order visual system regions. Moreover, various developmental factors determine the onset of photoreceptor responsivity, one being the gradual increase in phototransduction-specific genes and proteins. In partial disagreement with previous electrophysiological findings, molecular analyses indicate that much of the machinery for cone phototransduction is present before P10 and just before eye-opening in rods. Therefore, it was hypothesized that photoreceptors are responsive and second-order bipolar cells can respond to photoreceptor output days before eye-opening in mice. It was found that photoreceptor-evoked a-waves were detected in response to both green and UV flashes of light at P8 and bipolar cell-evoked b-waves were responsive within the 24 hours to follow using ex-vivo electroretinograms (ERGs). Furthermore, seminal studies have demonstrated (open full item for complete abstract)

Committee: Jordan Renna (Advisor); Qin Liu (Committee Member); Adam Smith (Committee Member); Merri Rosen (Committee Member); Yong Lu (Committee Member) Subjects: Biology; Biophysics; Cellular Biology; Evolution and Development; Molecular Biology; Neurobiology; Neurosciences; Optics; Physiology

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2019, Photochemical Sciences

The primary event in vision is induced by the ultrafast photoisomerization of rhodopsin, the dim-light visual pigment of vertebrates. While spectroscopic and theoretical studies have identified certain vibrationally coherent atomic motions to promote the rhodopsin photoisomerization, how exactly and to what degree such coherence is biologically related with its isomerizing efficiency (i.e. the photoisomerization quantum yield) remains unknown. In fact, in the past, the computational cost limited the simulation of the rhodopsin photoisomerization dynamics, which could be carried out only for a single molecule or a small set of molecules, therefore lacking the necessary statistical description of a molecular population motion. In this Dissertation I apply a hybrid quantum mechanics/molecular mechanics (QM/MM) models of bovine rhodopsin, the verterbrate visual pigment, to tackle the basic issues mentioned above. Accordingly, my work has been developing along three different lines comprising the development, testing and application of new tools for population dynamics simulation: (I) Development of a suitable protocol to investigate the excited state population dynamics of rhodopsins at room temperature. (II) A correlation between the phase of a hydrogen-out-of-plane (HOOP) motion at the decay point and the outcome of the rhodopsin photoisomerization. (III) A population “splitting” mechanism adopted by the protein to maximize its quantum yield and, therefore, light sensitivity. In conclusion, my Dissertation reports, for the first time, a connection between the initial coherent motion of a population of rhodopsin molecules and the quantum efficiency of their isomerization. The photoisomerization efficiency is ultimately determined by the way in which the degree of coherence of the excited state population motion is modulated by the protein sequence and conformation.

Committee: Massimo Olivucci Ph.D (Advisor); Andrew Gregory Ph.D (Other); Hong Lu Ph.D (Committee Member); Alexey Zayak Ph.D (Committee Member) Subjects: Biochemistry; Chemistry

Master of Science, University of Akron, 2007, Biology

During embryogenesis, tissue differentiation and organ development require cells expressing specific molecules that cue migration, aggregation and differentiation. One group of molecules involved in such processes is cadherin molecules, which are defined as calcium dependant adhesion molecules. This study is intended to investigate the role of cadherin-6 in the development of zebrafish pineal gland and retinal photoreceptors. Cadherin expression in the central nervous system (CNS) has been investigated in various vertebrate animals, but there is little information on cadherin function in retinal photoreceptor differentiation, and scarcer knowledge on cadherin function in the pineal gland development. My results showed that cadherin-6 affected retinal development more than the development of the pineal gland

Committee: Qin Liu (Advisor) Subjects: Biology, Animal Physiology

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2013, Photochemical Sciences

Visual sensitivity in vertebrae depends on the photochemical and thermal processes occurring in visual pigments of the retina. Indeed, the efficiency of the primary event in vision, the cis-trans photoinduced isomerization of the chromophore embedded inside visual pigments, must be high to achieve such sensitivity. Meanwhile, thermal processes are responsible for generating spontaneous electrical signals even in the absence of light, thus imposing a limit on visual sensitivity. While the photochemical process in visual pigments has been extensively studied both experimentally and computationally, there are fewer studies targeting the thermal process, and such studies are often conflicting. However, the observation of a relationship between the maximum absorption wavelength (λmax), a photochemical property, and the activation kinetic constant (k), a thermal property, of visual pigments suggests that the thermal and photochemical processes are related. The understanding of these processes has been largely aided by computational studies. Indeed, computer simulations can be used to investigate certain features of the potential energy surfaces (PESs) driving these processes. However, a quantitative (or even qualitative) description of these PESs requires computational methods capable of correctly describing the ground (S0) and excited (S1) state regions of concern. Therefore, in the following, we first employ a reduced model of the chromophore of visual pigments (the penta-2,4-dieniminium cation) to design a stringent test of the performance of quantum mechanical methods along regions of interest on the S0 and S1 PESs. We then select a suitable method and employ it in a full hybrid quantum mechanical / molecular mechanical model of the prototypal bovine rod pigment, rhodopsin, to provide a molecular-level understanding of the thermal process in such pigments and its relation to the photochemical isomerization mechanism. We find that the transition state mediating ther (open full item for complete abstract)

Committee: Massimo Olivucci Ph.D (Advisor); Ksenija Glusac Ph.D (Committee Member); H. Peter Lu Ph.D (Committee Member); Paul Morris Ph.D (Committee Member) Subjects: Biochemistry; Chemistry; Physical Chemistry

Bachelor of Sciences, Ohio University, 2013, Biological Sciences

The formation of the actin-rich apical surface structures of Drosophila photoreceptor cells, the rhabdomeres, is a tightly regulated process involving many protein interactions. Moesin, the sole Ezrin/Radixin/Moesin (ERM) protein in Drosophila, serves to anchor F-actin microfilaments to the cellular membrane and is subject to many regulatory interactions. Moesin must bind to PIP2 and then be phosphorylated by the Sterile20 (Ste20) kinase Slik to be activated and serve as a cytoskeletal anchor. Conversely, it is deactivated by dephosphorylation by the PP1 phosphatase PP1-87B. Here I show that the sole CLIC family protein in Drosophila, Clic, is also intimately involved with moesin and PP1-87B in establishing the architecture of rhabdomeres. Disruption in the function of these important proteins has adverse effects on microvilli formation within the rhabdomeres and induces a loss of epithelial integrity and organization within the photoreceptor cells. A knockdown of moesin function causes the loss of three rhabdomeres, two of which can be recovered in a Clic loss-of-function mutant background. This suggests an antagonistic role between Clic and moesin. Masking of the phenotype induced by a knockdown of PP1-87B by the Clic loss-of-function mutation suggests that Clic works upstream of PP1-87B to antagonize moesin function. Our current model is that Clic facilitates the transfer of active moesin from PIP2 to a membrane protein. Once this transaction is complete, PP1-87B gains access to moesin for dephosphorylation and subsequent deactivation. Thus, I present a model of a novel role for Clic in rhabdomere morphogenesis via genetic interaction with moesin and PP1-87B.

Committee: Soichi Tanda D.Sc. (Advisor) Subjects: Biology; Cellular Biology; Molecular Biology

PhD, University of Cincinnati, 2012, Arts and Sciences: Biological Sciences

Uca pugilator are semi-terrestrial brachyuran fiddler crabs that inhabit inter-tidal sand and mud flats. They are social animals that rely exclusively on visual information during several of their behaviors that include mate choice, predator avoidance, burrow surveillance, courtship and territorial interactions. Through several behavioral and optical experiments, it has been previously shown that they have 360° viewing angle on each eye, high spatial resolution along their eye's midline, improved resolution on the vertical axes and posses excellent optomotor stabilization mechanism. Such understanding of their retinal design has helped us realize that the eyes of fiddler crabs are adapted for specific visual tasks in their geometrically structured habitat. However, the physiological capabilities of this retina are not yet completely understood, especially at the photoreceptor level. The objective of my thesis has been to fill this gap in knowledge, and specifically determine the spatial, temporal and spectral properties of photoreceptor cells through an integrative approach, using several molecular and electrophysiological techniques. Through these experiments, I have shown that the spatial resolution of the eye is best along the eye´s midline (~1°), photoreceptor cells are capable of perceiving up to ~45Hz of flickering light stimuli and that they are capable of perceiving color cues including in the ultra-violet.

Committee: John Layne PhD (Committee Chair); Elke Buschbeck PhD (Committee Member); Tiffany Cook PhD (Committee Member); Edwin Griff PhD (Committee Member); Stephanie Rollmann PhD (Committee Member) Subjects: Biology