Yes / The purpose of this paper is to demonstrate: 1) that silent substitution stimuli can be used generate electro-retinograms (ERGs) that effectively isolate rod photoreceptor function in humans without the need for dark adaptation and 2) that this approach constitutes a viable alternative to current clinical standard testing protocols. Rod-isolating and non-isolating sinusoidal flicker stimuli were generated on a 4 primary LED ganzfeld stimulator to elicit ERGs from non-dark adapted participants with normal and compromised rod function. Responses were subjected to Fourier analysis and the amplitude and phase of the fundamental were used to examine temporal frequency and retinal illuminance response characteristics. ERGs elicited by rod isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30Hz. Responses are optimal between 5 – 8 Hz and between 10-100 photopic Td. There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. Analysis of signal to noise ratios reveals significant differences between subjects with normal and compromised rod function. Silent substitution provides an effective method for the isolation of human rod photoreceptor function in subjects with normal as well as compromised rod function when stimuli are used within appropriate parameter ranges. Translational Relevance: This method of generating rod ERGs rod isolation can be achieved without time consuming periods of dark adaptation and provides improved isolation of rod- from cone-based activity and will lead to the development of faster clinical electro-physiological testing protocols with improved selectivity.

After over a decade of its discovery, the Electroretinogram (ERG) still remains the objective tool that is conventionally used in assessment of retinal function in health and disease. Although there is ongoing research in developing ERG recording techniques, interpretation and clinical applications, there is still a limited understanding on how each photoreceptor class contribute to the ERG waveform and their role and/or susceptibilities in various retinal diseases still remains unclear. Another limitation with currently used conventional testing protocols in a clinical setting is the requirement of an adaptation period which is time consuming. Furthermore, the ERG responses derived in this manner are recorded under different stimulus conditions, thus, making comparison of these signals difficult. To address these issues and develop a new testing method, we employed silent substitution paradigm in obtaining cone- and rod- isolating ERGs using sine- and square- wave temporal profiles. The ERGs achieved in this manner were shown to be photoreceptor-selective. Furthermore, these responses did not only provide the functional index of photoreceptors but their contributions to their successive postreceptoral pathways. We believe that the substitution stimuli used in this thesis could be a valuable tool in functional assessment of individual photoreceptor classes in normal and pathological conditions. Furthermore, we speculate that this method of cone/rod activity isolation could possibly be used in developing faster and efficient photoreceptor-selective testing protocols without the need of adaptation. / Bradford School of Optometry and Vision Sciences scholarship

Living elasmobranchs occupy every major aquatic ecosystem throughout the world (Compagno 2003; Compagno et al. 2005). Sensory ecology can be a good determinant in comprehending the processes occurring between an organism and its natural environment (Weissburg and Browman 2005). By utilizing ecophysiological tools, insight into the adaptive responses of the sensory systems to their ever-changing ecological niche can help explain behavioral and life history characteristics (Hueter 1991; Litherland 2009). Aquatic animals show structural and physiological adaptations in their visual sense specific to the ecological requirements of their habitat (Hart et al. 2004), implying that vision is an important modality. The visual system of the smooth dogfish (Mustelus canis, family Triakidae) was examined using corneal electrophysiological methods to determine the visual spectral range, irradiance sensitivity, and speed of vision (flicker fusion frequency, FFF). The smooth dogfish, a shallow water bottom feeder inhabiting inshore waters along the eastern United States, was found to be extremely sensitive to dim light (-3.1- 0.1 log light intensity), and have a slow FFF (13 Hz), thus being well adapted to the scotopic conditions of the turbid coastal inshore waters. This prompted a second set of experiments focusing on the chromatic adaptations of the photoreceptor cells and retina function following light adaptation. Light adaptation increased the photopic threshold by 2.0 log light units of intensity (LLI). However, the temporal resolution was not dramatically increased (to 17 Hz), indicating that the retinal integration time is very slow for this species under all circumstances. The spectral sensitivity peak for M. canis (470 nm) was found to be significantly blue-shifted in comparison to other members of the Triakidae family (Crescitelli et al. 1995; Sillman et al. 1996). Smooth dogfish appear to forgo high spatial and temporal resolution for the enhancement of photon capture. The sandbar shark inhabits the same inshore estuaries during the summer months but has a visual system with a higher temporal resolution (FFF, 54 Hz) and a brighter photopic threshold (1.2 LLI-50% max) (Litherland 2009). Furthermore, other elasmobranch or telelost species inhabiting similar photic environments also exhibit faster temporal resolution; little skate (FFF, 30 Hz), weakfish (FFF, 40 Hz), red drum (FFF, 50 Hz), spotted sea trout (FFF, 60 Hz), and Atlantic croaker (FFF, 58 Hz) (Horodysky et al. 2008; McComb et al. 2010). Coastal seas tend to contain more dissolved organics and particulates than the clear oceanic waters of the epipelagic and pelagic zones (McFarland 1986), therefore the retina of smooth dogfish has adapted to be extremely sensitive to dim light, has a long integration time, a low flicker fusion frequency and temporal resolution, and retinal cells that are able to adjust to changing light conditions. All of these factors contribute to the visual system to provide optimal visual ability to enable smooth dogfish to accurately exploit its surroundings.