• Gap Junctional Coupling between Retinal Amacrine and Ganglion Cells Underlies Coherent Spike Activity Integral to Global Object Perception

      Roy, Kaushambi (2017-08)
      Coherent spike activity between neighboring cells is a ubiquitous phenomenon exhibited by ensembles of neurons throughout the central nervous system, including the retina. In addition to the robust coherent activity between neighboring retinal ganglion cells (RGCs), there is evidence that widely separated RGCs can also show correlated spiking. These long range correlations can be evoked by large, contiguous light stimuli, but not to smaller, discontinuous objects. It has thus been posited that long range spike correlations between distant RGCs encode information critical to global object perception. Since the wide separation of the RGCs precludes common excitatory drive from bipolar cells, the mechanism underlying long range concerted activity has remained elusive. Most RGCs show gap junctional coupling to polyaxonal amacrine cells (PACs), which maintain extensive axonal arbors that can extend >1mm across the retina. The electrical coupling between RGCs and PACs thereby form a plausible circuit that can underlie long range correlated activity in the retina. In the current study we tested this hypothesis by targeting and recording from pairs of widely separated ON α-RGCs in the mouse retina, which are coupled indirectly through intermediary PACs. Pharmacological blockade of gap junctions or genetic ablation of connexin36 (Cx36) subunits eliminated the long range correlated spiking between the α-RGCs. These data indicated that electrical coupling between RGCs and PACs was responsible for the long range spike activity. In contrast, I found that direct, serial RGC-RGC coupling was incapable of supporting long range spike correlations. Finally, behavioral experiments were performed to test whether blockade of retinal gap junctions or ablation of Cx36 attenuates the ability of mice to discriminate large, global objects from small, disjointed stimuli. I found that Cx36 knockout mice indeed have significantly reduced ability to discriminate global objects from smaller discontinuous stimuli as compared to wild type littermates. This reduced perception of global objects was not due to a general reduction in spatial acuity that measured in knockout animals was similar to that for wild type mice. Taken together, our results indicate that long range concerted firing between RGCs, derived from electrical coupling with amacrine cells, encodes information critical to global object perception.
    • Mild Traumatic Brain Injury (mTBI) and Photosensitivity: Objective Pupillometric Findings

      Truong, James Q. (2016-06)
      Background Given the extensive neural network of the human, binocular, pupillary system including its sympathetic and parasympathetic innervation, it is plausible that a mild traumatic brain injury (mTBI) could compromise pupillary control, thus causing pupillary asymmetry and dysfunction. Furthermore, presence of such pupillary abnormalities could exacerbate mTBI-related visual symptomatology, such as photosensitivity. There have only been two studies in the area, and they both used monocular pupillometry with only one test condition; hence they were limited. Furthermore, their results were in part equivocal. There remain many unanswered questions (i.e., gaps) in this important field of study including: 1) does mTBI affect the pupillary light reflex (PLR)?, 2) is there an increase in inter-ocular pupillary asymmetry (IOPA) in mTBI?, and 3) are there PLR differences related to one of the most prominent and prevalent dysfunctions resulting from mTBI, namely photosensitivity? Aim The overall aim of the present dissertation was twofold. First, to evaluate comprehensively the effect of mTBI on the human pupillary system, and furthermore to determine if pupillometry could be used as an objective visual biomarker for mTBI. Second, to evaluate comprehensively the effect of photosensitivity on the human pupillary system, and furthermore to determine if pupillometry could be used as an objective biomarker for photosensitivity. Methods The binocular pupillary light reflex was evaluated in mTBI, and it was compared to normal individuals, with and without photosensitivity, under a range of test conditions. Nine pupillary parameters (maximum, minimum, and final pupillary diameter; latency; amplitude; and peak and average constriction and dilation velocities) and 6 stimulus conditions (dim pulse, dim step, bright pulse, bright step, bright red step, and bright blue step) were assessed in 32 adults with mTBI (21-60 years of age) and compared to 40 normals (22-56 years of age). The Neuroptics, infrared, DP-2000 binocular pupillometer was used (30Hz sampling rate; 0.05mm resolution) with binocular stimulation and recording. Results and Discussion 1. Inter-ocular pupillary asymmetry: There were no statistical differences in either static or dynamic inter-ocular pupillary asymmetry (IOPA) between the normal and mTBI groups. Thus, the pupillary effects of mTBI appear to be symmetrical rather than asymmetrical in nature, which suggests post-chiasmal involvement. The mean average (across groups) static IOPA was 0.26 + 0.20mm or 4.17 + 3.29%. The mean average dynamic IOPA was dependent on the light stimulus condition, with the average across all test conditions and groups being 0.11 + 0.10mm or 1.84 + 1.70%. 2. Pupillometry in mTBI: mTBI has been reported to cause the pupillary light reflex (PLR) to be globally attenuated (i.e., slower in onset and more sluggish in response dynamics). The present results showed that there were many statistically significant differences (p < 0.05) in the PLR parameters between the mTBI and normal groups. Furthermore, different test conditions allowed for discrimination of different parameters between the two groups. For any of the given six test conditions, 5 to 8 of the 9 pupillary parameters were statistically different (p < 0.05) between the two groups. The overall trends revealed that the mTBI cohort had longer constriction latency, slower constriction and dilation velocities, and smaller pupillary diameters (baseline, minimum, and 6PSPD). The most consistent and robust pupillary parameters that differentiated between the two groups were the pupillary diameters (maximum, minimum, and 6SPSD; p < 0.01 under all 6 test conditions), and peak dilation velocity (p < 0.02, under all applicable conditions). This suggests that mTBI adversely affects both the sympathetic and parasympathetic systems, however, the effect appears to be greater on the sympathetic system. 3. Pupillometry in photosensitivity: There were statistically significant differences (p < 0.05) in the PLR parameters of those with versus without photosensitivity in both groups. Interestingly, these differences depended upon whether the photosensitivity was mTBI related. Those with mTBI and photosensitivity manifested six significant differences (p < 0.05) as compared with those with mTBI cohort without photosensitivity: larger baseline diameter, larger minimum diameter, faster peak dilation velocity, faster T50 and T75 recovery times, and a larger pupil diameter at 6 seconds post-stimulus. Normal (non-mTBI) subjects with photosensitivity exhibited four significant differences (p < 0.05) as compared with their normal cohort without photosensitivity: larger constriction amplitude, faster average constriction
    • Nearwork-Induced Transient Myopia (NITM) Following Marked and Sustained, but Interrupted, Accommodation at Near

      Arunthavaraja, Mathangi (2010-07-16)
      Purpose: It has been speculated that non-decayed NITM (accommodatively-based nearwork-induced transient myopia) may be myopigenic in nature. Thus, the purpose of the present investigation was to determine objectively the initial magnitude and decay of NITM, and its potential additivity, following successive but interrupted periods of marked, sustained accommodation at near in asymptomatic young-adult myopic subjects. Methods: Fifteen visually-normal, asymptomatic young adults (ages 18 – 28 years) were tested with full distance refractive correction. They included 9 early-onset (EOM) and 6 late-onset (LOM) myopic subjects. Accommodation was assessed objectively with a Canon R-1, open-field, infrared auto-refractor under monocular viewing conditions (RE). The distance refractive state was measured immediately before and after a ten minute period of focusing upon a moderate contrast (50%), very near target (12 cm; 8D) subtending a visual angle of 1 degree. The task was repeated twice with a 5-minute inter-task rest period of imposed far viewing. NITM was defined as the post-task minus pre-task change in distance refractive state immediately following each task. Results: Significant amounts of NITM were generated following nearly each trial in each subject. These ranged from 0.11 to 0.71D, with a mean of 0.31D. The group mean NITM was 0.32, 0.29, and 0.31D for trials 1, 2, and 3, respectively. For the EOMs subgroup, NITM was 0.28, 0.30, and 0.34D, while for the LOMs subgroup, it was 0.38, 0.29, and 0.26D, for for trials 1, 2, and 3, respectively. Decay of NITM was prolonged in many of the subjects (67%). However, additivity of NITM was not found following the sequences of interrupted near tasks. Conclusions: There was no evidence of NITM additivity following a marked and sustained, but interrupted, near task. Although NITM has been reported to be additive following long periods of uninterrupted and sustained reading at lower dioptric levels, providing rest periods between each near task trial appears to prevent a cumulative effect (i.e., additivity effect). These findings support the idea of far viewing being protective in nature from myopia development.
    • Objective Assessment of Retinal Ganglion Cell Function in Glaucoma

      Joshi, Nabin (2017-09-25)
      Glaucoma refers to a group of diseases causing progressive degeneration of the retinal ganglion cells. It is a clinical diagnosis based on the evidence of structural damage of the optic nerve head with corresponding visual field loss. Structural damage is assessed by visualization of the optic nerve head (ONH) through various imaging and observational techniques, while the behavioral loss of sensitivity is assessed with an automated perimeter. However, given the subjective nature of visual field assessment in patients, visual function examination suffers from high variability as well as patient and operator- related biases. To overcome these drawbacks, past research has focused on the use of objective methods of quantifying retinal function in patients with glaucoma such as electroretinograms, visually evoked potentials, pupillometry etc. Electroretinograms are objective, non-invasive method of assessing retinal function, and careful manipulation of the visual input or stimulus can result in extraction of signals particular to select classes of the retinal cells, and photopic negative response (PhNR) is a component of ERG that reflects primarily the retinal ganglion cell function. On the other hand, pupillary response to light, measured objectively with a pupillometer, also indicates the functional state of the retina and the pupillary pathway. Hence, the study of both ERGs and pupillary response to light provide an objective avenue of research towards understanding the mechanisms of neurodegeneration in glaucoma, possibly affecting the clinical care of the patients in the long run.
    • Objective assessment of visual dysfunction in the acquired brain injury (ABI) population using the visual-evoked potential (VEP)

      Yadav, Naveen K. (2014-07-09)
      Purpose: To assess quantitatively and objectively selected visual dysfunctions in patients with mild traumatic brain injury (mTBI) (i.e., increased abnormal visual motion sensitivity (VMS), attentional deficits) and stroke (i.e., hemianopic visual field defects) by using empirically-derived, optimized pattern visual evoked potential (VEP) parameters derived from our laboratory. Furthermore, the goal was to develop simple and reliable clinical VEP protocols to assess the aforementioned visual dysfunctions in acquired brain injury. Methods: Four experiments were performed binocularly with full refractive correction using an objective, pattern VEP technique. Experiments #1-3 included both visually-normal (VN) adults and adults with mTBI, all ages 18-70 years. Experiment #4 included adult patients with stroke and hemianopic visual field defects, all ages 18-70 years. The following tests and stimulus conditions were used in Experiments #1-4: Experiment #1 – central field VEP with 10, 20, and 40 min arc check sizes at low (20%) and high (85%) contrast levels; Experiment #2 – central field VEP (baseline), binasal occlusion only (BNO), base-in prism (BI) only (4 pd total), and BNO with 4 pd BI; Experiment #3 – central field VEP (eyes open (EO), baseline), eyes-closed (EC, “relaxed”), and eyes-closed number counting (ECNC, “increased attentional state”); Experiment #4 – central field VEP, intact hemi-field only, and hemianopic field only. Results: The followings results were found: Experiment #1 – The 20 min arc check size provided the largest VEP amplitude and normative latency values at both contrast levels in both the VN and mTBI groups. These optimal parameters were then used to measure VEP responses in Experiments #2-4. Experiment #2 – With BNO alone, the VEP amplitude was larger in individuals with mTBI (90%) and smaller in the VN (100%) groups, as compared to other two test conditions and baseline. In addition, with BNO only, those with mTBI demonstrated improvement in their visual impressions and in performing specific sensorimotor tasks. Experiment #3 – Objectively-based alpha attenuation ratio (AR = EC ÷ EO, ECNC ÷ EC) was able to detect, assess, and differentiate between mTBI with versus without an attentional deficits, as well as between VNs. These objective AR findings were correlated with the subjective Adult ADHD Self-Report Scale (ASRS) questionnaire scores. Experiment #4 – The group and individual VEP findings showed that the central field and the intact hemi-field VEP amplitudes were larger than found in the hemianopic field. Moreover, these objective findings were correlated with the subjective clinical perimetric results. Conclusions: The optimized VEP parameters provided quantitative, rapid, reliable, and repeatable responsivity in all experiments. These findings demonstrated that the conventional pattern VEP could be beneficial for researchers in general, as well as clinicians to differentiate between mTBI versus the VN group with a high probability, and also between mTBI with versus without an attentional deficit. In addition, the VEP could be used clinically to detect and assess hemianopic visual field defects in patients with stroke. Based on these findings, the VEP has the potential to be used as an objective visual system biomarker for the diagnosis of mTBI/concussion, and also as an objective adjunct clinical tool to detect visual field defects in patients with stroke.
    • Oculomotor rehabilitation for reading dysfunction in mild traumatic brain injury

      Thiagarajan, Preethi (2013-06-04)
      Abstract: Aim Considering the extensive neural network of the oculomotor subsystems, global damage as a result of traumatic brain injury could compromise precise oculomotor control, thus causing reading dysfunction. The aim of the present thesis was to evaluate comprehensively the effect of oculomotor-based vision rehabilitation in symptomatic individuals with respect to nearwork and reading and having a mild traumatic brain injury (mTBI). A wide range of laboratory and clinical parameters related to reading involving vergence, accommodation, and version were tested. Methods Twelve subjects with documented mTBI and nearvision-related symptoms participated in the study. A cross-over, interventional experimental design was used involving true “oculomotor” training and “SHAM” training. Each training protocol was performed for 6 weeks, 2 sessions a week, 45 minutes of actual training per session. During each training session, all three oculomotor subsystems (vergence/accommodation/version) were trained for 15 minutes each in a randomized order. All laboratory and clinical parameters were measured before (baseline) and after true oculomotor (post-OMT) and SHAM (post-SHAM) training. In addition, nearvision-related symptoms were assessed using the Convergence Insufficiency Symptom Survey (CISS) scale. Lastly, subjective attention was measured using the Visual Search and Attention Test (VSAT). iv Results Following true oculomotor training, there was a marked improvement in various laboratory and clinical parameters assessed. Over 80% of the abnormal parameters found at baseline testing were found to significantly improve with training. Dynamics of vergence and accommodation, along with clinically assessed maximum amplitudes, improved markedly. Versional saccadic eye movements demonstrated improved rhythmicity and accuracy. These results together had a significant positive impact on overall reading ability. The improved reading-related oculomotor behavior was reflected in reduction of symptoms. In addition, subjective attention was found to also improve with true oculomotor training. In contrast, none of the aforementioned parameters changed with SHAM training. Conclusions Oculomotor-based vision rehabilitation had a strong positive effect on reading-related oculomotor control. This oculomotor learning effect is suggestive of intact neuroplasticity mechanisms in a compromised brain following TBI.
    • Reading from an Electronic Reading Device versus Hardcopy Text

      Hue, Jennifer E. (2013-06-24)
      The use of electronic reading devices has become more prevalent. Many individuals of all ages are using personal electronic readers (e.g., Kindle, Nook, E-Reader) in place of hardcopy printed materials. Previous work in our laboratory has demonstrated that symptoms when reading from a computer screen are significantly greater than those experienced when reading printed text. Accordingly, the aim of the present study was to examine both symptoms and task performance when reading from a Kindle e-reading device, and to compare the findings with those from hardcopy, printed materials.
    • Roles of Calcium Signaling and Protein Kinase C Activation in Mediating Receptor Control of Corneal Epithelial Renewal

      Zhang, Fan (2007-06-26)
      Epidermal growth factor, EGF, is one of the essential growth factors that stimulates injury-induced corneal epithelial healing rates. Cell signaling contributors mediating this response include capacitative calcium entry (CCE) activation and protein kinase C (PKC) isoform stimulation. This study shows in human corneal epithelial cells, HCEC, that CCE is preferentially activated by the PKC isoforms  and . Moreover such activation requires increases in plasma membrane Ca2+ influx through store-operated channels. Therefore, EGF-induced stimulation of cell proliferation and migration may depend on unique effects mediated by six different PKC isoforms identified in HCEC. TRPV1 is a vanilloid subtype of the transient receptor potential protein superfamily. This isoform is a subunit of a non-selective cation channel mediating downstream responses to heat, low pH, or noxious stimuli. TRPV1 expression has been recently described in some epithelial tissues and induces proinflammatory cytokine release through mitogen-activated protein kinase (MAPK) superfamily stimulation. This study describes in HCEC the signaling pathways mediating TRPV1-induced increases in proinflammatory cytokine release. It suggests that epithelial TRPV1 receptor activation by noxious stimuli contributes in-vivo to mounting proinflammatory reactions.
    • The Effect of Multifocal Contact Lenses on Accomodation and Phoria in a Pediatric Population

      Gong, Celia (2017)
      The increasing prevalence of the use of distance-centered multifocal (MF) contact lenses as a method of myopia control in the pediatric population calls for a better understanding of binocularity and accommodation in children wearing these lenses. This was a prospective, randomized, crossover, single visit study that enrolled myopic children with normal accommodation and binocular vision and no history of myopia control treatment. All subjects were fitted with Coopervision Biofinity single vision (SV) and MF (+2.50D center distance add) contact lenses. Accommodative responses (photorefraction) and phorias (Modified Thorington) were measured at 4 distances (>3m, 100cm, 40cm, 25cm). Secondary measures included high and low contrast logMAR acuity, accommodative amplitude, and accommodative facility. Differences between MF and SV contact lenses were analyzed using repeated measures regression and paired t-tests. A total of 16 subjects, aged 10-15 years, completed the study. There was a small decrease in high (SV: -0.08, MF: +0.01) and low illumination (SV:-0.03, MF: +0.08) (both p<0.01) visual acuity, and contrast sensitivity (SV: 2.0 log units, MF: 1.9, p=0.015) with MFs. Subjects were more exophoric at 40cm (SV: -0.41 Δ, MF: -2.06 Δ) and 25cm (SV: -0.83 Δ, MF: -4.30 Δ) (both p<0.01). With MFs, subjects had decreased accommodative responses at distance (SV: -0.04 D; MF: -0.37 D, p=0.02), 100 cm (SV: +0.37 D; MF: -0.35 D, p<0.01), 40 cm (SV: +1.82 D; MF: +0.62 D, p<0.01), and 25 cm (SV: +3.38 D; MF: +1.75 D, p<0.01). There were no significant differences in accommodative amplitude (p=0.66) or accommodative facility (p=0.54). Children wearing MF contact lenses exhibited reduced accommodative responses and more exophoria at increasingly higher accommodative demands than with SV contact lenses. This suggests that children may be relaxing their accommodation and using the positive addition or increased depth of focus from added spherical aberration of the MF lenses. Further studies are needed to evaluate other lens designs, different amounts of positive addition and aberrations, and long-term adaptation to lenses.
    • Triptolide Induces Increases in Migration via Mitogen-activated Protein Kinase Phosphatase-1 control of P38 and JNK MAPK Activation

      Parekh, Nili M. (2010-07-16)
      Purpose Triptolide is a Chinese herbal extract known for its anti-inflammatory and immunosuppressive effects in treating chronic inflammatory diseases and tumors. As these attributes promote wound healing, we determined if triptolide enhances corneal wound healing by stimulating human corneal epithelial cell (HCEC) migration through changes in negative feedback regulation by a dual specificity protein Phosphatase (DUSP1) of MAPK signaling mediated effect. Methods SV40-adenovirus-immortalized HCEC were maintained in DMEM/F12. Specific shRNA for MKP-1(DUSP1) and c-jun NH2- terminal kinase JNK-1 were transduced to establish stable cell lines deficient in their respective gene expression. Scratch wound assay was employed to assess cell migration rates by taking time-dependent serial photographs of cells following wound creation. Hydroxyurea (2.5 mM) was also added to the medium to inhibit cell proliferation during the experiment. Cell Titer-Glo® luminescent cell viability assay was used to evaluate cell viability by measuring ATP production by HCEC. Results Triptolide did not affect cell viability up to 10nM and stimulated wound closure through increases in migration. Maximal responses occurred at 1nM. These increases in migration were suppressed below that in the untreated control when p38 or JNK MAPK activation was inhibited. In the MKP-1 knockdown cells, migration was stimulated relative to the control and triptolide failed to augment this response. In JNK-1 knockdown cells, migration is comparable to SV40 wild type cells. In JNK-1 knockdown cells, triptolide mediated increases are diminished completely in the presence of p38 inhibition. Conclusions Triptolide at concentrations up to 10 nM promotes cell migration without compromising cell survival. Such promotion is mediated by loss of MKP-1 negative feedback control of p38 and JNK activation. Therefore, triptolide stimulates cell migration through inhibition of MKP-1 (DUSP1) stabilization induced by kinase mediated phosphorylation.