Now showing items 1-20 of 26

    • Complexity of mental geometry for 3D pose perception

      Guo, Crystal (2022-06-13)
      Biological visual systems rely on pose estimation of three-dimensional (3D) objects to understand and navigate the surrounding environment, but the neural computations and mechanisms for inferring 3D poses from 2D retinal images are only partially understood, especially for conditions where stereo information is insufficient. We previously presented evidence that humans use the geometrical back-transform from retinal images to infer the poses of 3D objects lying centered on the ground. This model explained the almost veridical estimation of poses in real scenes and the illusory rotation of poses in obliquely viewed pictures, including the pointing at you phenomenon. Here we test this model for 3D objects in more varied configurations and find that it needs to be augmented. Five observers estimated poses of inclined, floating, or off-center 3D sticks in each of 16 different poses displayed on a monitor viewed straight or obliquely. Pose estimates in scenes and pictures showed remarkable accuracy and agreement between observers, but with a systematic fronto-parallel bias for oblique poses. When one end of an object is on the ground while the other is inclined up, the projected retinal orientation changes substantially as a function of inclination, so the back-transform derived from the object’s projection to the retina is not unique unless the angle of inclination is known. We show that observers’ pose estimates can be explained by the back-transform from retinal orientation only if it is derived for close to the correct inclination. The same back-transform explanation applies to obliquely viewed pictures. There is less change in retinal orientations when objects are floated or placed off-center but pose estimates can be explained by the same model, making it more likely that observers use internalized perspective geometry to make 3D pose inferences while actively incorporating inferences about other aspects of object placement.
    • Feasibility and applicability of a clinical assessment of both the ON and OFF pathways in patients with glaucoma and controls.

      Moore-Stoll, Veronica (2022-05-03)
      "Purpose: To assess the feasibility and clinical utility of a head-mounted, On/Off perimetry test and to investigate the effect of early to moderate glaucoma on reaction time and accuracy to ON and OFF perimetric stimuli. Methods: We tested one eye each of 9 patients with early to moderate primary open angle glaucoma (mean = 71.88 years, std = 5.17), 9 visually-normal control patients of a similar age (mean = 63.88 years, std = 5.17 ) , and 9 visually-normal optometry students (ages 22-25 years). We used a head mounted display equipped with an eye tracker (HTC VIVE embedded Tobii). Custom software (Unity, version 2017) was used to create the stimuli and a library provided by Tobii Pro was used to measure eye movements at 120 Hz. Stimulus size changed as a function of eccentricity using a power law relationship: stimulus size= minimum scale*(eccentricity/5)^α. Eye movements were restricted to a central circle with a 2.5 degree radius. Stimulus contrast was initially set to 100%. A single test comprised of 579 trials, including 51 catch trials, presented at 90 different positions in the visual field. Each test location was repeated 3 times for both light and dark stimuli, with 6 repeats in each of two blind spot positions. Results: Our results demonstrate asymmetry between the two achromatic visual transduction pathways. These results support previous findings that dark targets elicit a faster and more accurate response than light targets, when presented on binary background noise. Our results extend previous work by demonstrating that the two pathways remain asymmetrical in eccentricities up to 30 degree from fixation. We also show that the relationship between the percentage of correct responses for ON pathway and OFF pathway stimuli follows a power function, wherein glaucoma and controls overlap (R2=0.842) . This overlap decreases when we quantify only the subthreshold (unseen) increment targets in a linear relationship (R2=0.7074). All controls had less than 12% of subthreshold increment targets whereas the percentage of subthreshold targets was higher for 75% of the glaucoma subjects, even in early stages of the disease. CONCLUSION We have demonstrated that ON/OFF perimetry is feasible in a VR environment and confirmed an asymmetry between the ON and OFF pathways in patients with glaucoma and control patients in both central and peripheral visual fields. We measured on-pathway deficits in patients with limited loss of visual sensitivity which may improve detection of early disease. Future work will focus on optimizing stimulus parameters to improve the sensitivity and specificity of this test."
    • Effects Of Correcting Fixation Disparity On Digital Eye Strain

      Saksena, Sanjana (2022-04-20)
      Digital Eye Strain (DES) is a widespread and highly prevalent condition whose incidence appears to be rising during the present pandemic. It comprises a range of visual and ocular symptoms which occur after viewing a digital screen for an extended period of time. Previous work from our laboratory has shown the magnitude of fixation disparity to be the only clinical parameter that is significantly correlated with DES symptoms. Therefore, this study sought to determine whether correcting the underlying fixation disparity will significantly reduce DES symptoms. Thirty young, visually-normal students were required to read randomly generated words from a digital tablet device for 20 minutes. Three different trials were performed, with the subject wearing either: (i) the prism that corrected their fixation disparity, (ii) the same magnitude of prism as for condition (i) but with the opposite base direction or (iii) a near addition lens that corrected the fixation disparity. Immediately after the reading task, subjects rated their ocular and visual symptoms on a questionnaire. There was no significant difference between the mean symptom scores for the three conditions. However, this may be due, in part, to the small number of subjects encountered with large values of fixation disparity. Future studies should further examine the range of oculomotor responses associated with DES in order to provide appropriate treatment options.
    • Library renovation: From setbacks to success.

      Wells, Elaine (Research Caucus of the Medical Library Association, 2021-02-25)
      The journey started at a 2016 meeting of the college’s Learning Resources Committee, which I chair as Library Director, A student representative casually commented that our Library looked “dated”. Not that we actually WERE dated, we have electronic resources, 24/7 remote access, printers, scanners, wireless, and a state-of-the-art Library Management System. However, through the eyes of our young student, the Library looked “like something from the 1970s.” Anyone who has lived through that decade’s will know that was not meant as a compliment. The student’s criticism prompted the Dean of Academic Affairs, who sat in on the meeting, to ask when the Library had had its last “facelift.” That was an easy one to answer - as far as I knew…never. And I’ve been here over 20 years. Just like that, a renovation was born. How hard could this be? I would query the students on what a suitable update might look like, get a budget, buy some new furniture, and go back to the business of being a librarian rather than an interior designer. Spoiler alert: not so fast.
    • Color Transparency: Geometry, Motion, Color, Scission, and Induction

      Huang, Zhehao (2024-03-30)
      Objects that pass light through are considered transparent, and we generally expect that the light coming out will match the perceived color of the object. However, when the object is placed on a colored surface, the light coming back to our eyes becomes a composite of surface, illumination, and transparency properties. Despite that, we can often perceive separate overlaid and overlaying layers differing in colors. How neurons separate the information to extract the transparent layer remains unknown, but physical characteristics of transparent filters generate geometrical and color features in retinal images which could provide cues for separating layers. We estimated the relative importance of such cues in a perceptual scale for transparency, using stimuli in which X or T-junctions, different relative motions, and color consistency, cooperated or competed in forced-preference psychophysics experiments. Maximum-likelihood Thurstone scaling revealed some new results: moving X-junctions increased transparency compared to static X-junctions, but moving T-junctions decreased transparency compared to static T-junctions by creating the percept of an opaque patch. However, if the motion of a filter uncovered a dynamically changing but stationary pattern, sharing common fate with the surround but forming T-junctions, the probability of seeing transparency was almost as high as for moving X-junctions, despite the stimulus being physically improbable. In addition, geometric cues overrode color inconsistency to a great degree. Finally, a linear model of transparency perception as a function of relative motions between filter, overlay, and surround layers, contour continuation, and color consistency, quantified a hierarchy of latent influences on when the filter is seen as a separate transparent layer. Previous measurements of color scission have limitations. The color adjustment to match the target color is relatively accurate but time consuming and suffers from long time adaptation bias. Force-choice judgment is quick and free from adaptation effect, but the selection of choices can be the source of bias. We examine the observers’ ability to estimate filter color with transparency with our improved method: we ask observers to make a judgement of the transparency region being red or green (or, blue/yellow). By doing this we found the neutral point of the filter that the observers think colorless. The result showed that, in color consistent conditions, though biased by the background or individual preference, the observers’ measured neutral filter settings were close to the colorless filter, showing relatively good color scission. In the color inconsistent conditions, the observers matched the overlaid region to a neutral color, as if the observers were attributing the average color of the overlaid region completely to the transparency. Veridicality of scission varied little in the color consistent conditions, despite the large variation in degree of perceived transparency. An exception to the rule that only one color is seen at every retinotopic location happens when a bounded colored transparency or spotlight is seen on a differently colored surface. Despite the spectrum of the light from each retinotopic location being an inextricable multiplication of illumination, transmission, and reflectance spectra, we seem to be able to scission the information into background and transparency/spotlight colors. Visual cues to separating overlay and overlaid layers have been enumerated, but neural mechanisms that extract veridical colors for overlays have not been identified. Here, we demonstrate that spatial induction contributes to color scission by shifting the color of the overlay toward the actual color of the filter. By alternating filter and illumination spectra, we present naturalistic simulations where isomeric disks appear to be covered by filters/spotlights of near veridical colors, depending solely on the surrounding illumination.
    • 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.
    • 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.
    • 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.
    • 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
    • Exploring the veridicality of shape-from-shading for real 3D objects

      Bartov, Jenny (2016-05)
      Despite the large number of shape-from-shading studies, the degree of veridicality with which observers perceive real 3D objects from shading cues has not been examined. Six observers viewed semicircular, triangular and trapezoidal corrugations in depth made from gray cardboard of approximately uniform reflectance, presented in a fronto-parallel plane. The object, placed inside a box, was illuminated solely from its top-left or left by a point light source. The corrugations were seen through an aperture that masked their terminating contours and the light source. Observers were asked to draw the depth profile of the object as if it were seen from above. Using a computer mouse, they drew on a computer screen placed just below the object. They also indicated the orientation of the object and the location of the light source. In the first condition, the objects were viewed monocularly; in the second, a white matte sphere was placed in front of the objects to help in locating the light; in the third, the task was repeated with binocular viewing. Drawings revealed that observers were quite accurate in inferring the objects’ shapes when viewing binocularly. There was more variability among the observers when objects were viewed monocularly, with some systematic trends: 1. Most observers were able to recreate the veridical shapes despite monocular viewing. 2. The drawn shapes often differed from the shape of the luminance variations across the objects, thus rejecting heuristics such as “dark is deeper”. 3. In the absence of cues to light direction, observers did not tend to resort to a “light from above” prior. 4. While binocularity heavily aided the extraction of the true shapes, knowledge of the illuminant direction did not. However, even though the exact location of the light source did not aid in extracting 3D shape, when oriented at a horizontal level, the light source did aid in perceiving 3D orientation.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • Dynamic and Static Aspects of Accommodation in Mild Traumatic Brain Injury

      Green, Wesley (2009-05-18)
      Purpose: To assess static and dynamic parameters of accommodation in a group of patients with mild traumatic brain injury (mTBI) that reported symptoms associated with near work. Methods: A range of laboratory and clinical measurements of accommodative function were assessed in 12 patients with mTBI, as well as in 10 visually-normal control subjects. Static parameters included push-up and minus-lens accommodative amplitude, positive and negative relative accommodation (PRA/NRA), horizontal and vertical near heterophoria, accommodative convergence-to-accommodation (AC/A) ratio, accommodative stimulus/response function (AS/R), and tonic accommodation. Dynamic parameters included time constant, peak velocity, gain, steady-state response level, steady-state response variability, and accommodative flipper facility rate, including changes in flipper rate after a three-minute fatigue session. Results: All individuals with mTBI manifested a multitude of abnormal accommodative response characteristics. With respect to dynamic parameters, abnormal responses in those with mTBI were found for time constant, peak velocity, accommodative flipper facility fatigue, and steady-state response variability. With respect to static parameters, abnormal values in those with mTBI were found for accommodative amplitude, AC/A ratio, PRA/NRA, and horizontal near heterophoria. Conclusions: The results of the present study provide further evidence that there is a substantial impact of mTBI on accommodative function. With the global nature of the brain insult, it may be presumed that accommodation would be affected by disturbances in various cortical, cerebellar, and/or brainstem areas and along related axonal pathways. Specifically, the reduced peak velocity and related increased time constant found in the mTBI group could be due to damage of neurons carrying accommodative velocity information (i.e., burst cells). This could result in a decrease in either their firing rate or the number of activated cells. The resultant symptoms at near, such as transient blur, can have a negative impact on the overall quality of life and functional capabilities.
    • Accommodation to wavefront vergence and chromatic aberration: color normal and deutan observers

      Wang, Yinan (2009-05-18)
      Purpose: Longitudinal chromatic aberration (LCA) provides a cue to accommodation with small pupils. However, large pupils increase monochromatic aberrations, which may obscure chromatic blur (McLellan, Marcos, Prieto, & Burns, 2002). We examined the effect of pupil size and LCA on accommodation in color normal and deutan observers. Methods: Participants were nine normal trichromats, three deuteranomalous trichromats, and two deuteranopic dichromats (anomaloscope and D-15). Accommodation was recorded by infrared optometer (100 Hz) and pupil by video-camera (30 frames/s) while observers viewed a sinusoidally moving Maltese cross target (1-3 D at .2 Hz) in a Badal stimulus system. There were two illumination conditions: white (3000 K; 20 cd/m2) and monochromatic (550 nm with 10 nm bandwidth; 20 cd/m2) and two artificial pupil conditions (3 mm and 5.7 mm). Separately, static measurements of wavefront aberration were made with the eye accommodating to targets between zero and 4 D (COAS, Wavefront Sciences). Results: Dynamic gain to vergence modulation increased significantly with pupil size in monochromatic (p=.005) but not white light (p=.12), and gain increased significantly with addition of LCA at both pupil sizes (5.7 mm, p=.004; 3 mm, p=.02). Mean RMS higher order aberration increased from .23 m with small pupils (3 mm) to .48 m with large pupils (5.7 mm). There were no significant differences in dynamic accommodation between color normal and deutan individuals for any condition (.68≤p≤.96). Normals and deutan observers showed large individual differences in dynamic gain to both vergence and LCA. Mean responses also varied among individuals, but deuteranomalous observers over-accommodated compared to color normal observers (.06≤p≤.12). Conclusions: Large individual differences in accommodation to wavefront vergence and to LCA are a hallmark of accommodation in normal and deutan observers. LCA continues to provide a signal at large pupil sizes despite higher levels of monochromatic aberrations. Monochromatic aberrations may defend against chromatic blur at high spatial frequencies, but accommodation responds best at 3 c/deg where blur from higher order aberrations is less (Mathews, 1998; Mathews & Kruger, 1994).
    • Accommodation to wavefront vergence: adapting ‘averse channels’

      Chen, Angela (2008-06-02)
      Purpose: Accommodation responds to wavefront vergence, but the mechanisms for vergence detection are unknown. One possibility is that accommodation responds to the angle of incidence of light at edges blurred by defocus. ‘Averse channels’ that sample light from opposite sides of the pupil were hypothesized by Makous (1968, 1977). Makous named the phenomenon a “transient” Stiles-Crawford effect because he found that there was a reduction in sensitivity to light entering one side of the pupil that lasts for a short period of time. Such ‘averse channels’ that sample modulation across the pupil are a possible mechanism for detecting the sign of defocus. The purpose of the present experiment is to determine whether such ‘averse channels’ can operate separately of each other to specify the sign of defocus for accommodation. Method: Accommodation was monitored continuously while subjects viewed a vertical monochromatic (548nm) luminance edge (1.0 contrast) that stepped either to a far or near direction in a Badal optometer. Various levels of adapting field were used to reduce the contrast of the edge (0.48, 0.36, 0.26, or 0.17 contrast) to determine the contrast threshold for accommodation. In a final experiment, an adapting field entered the eye through the nasal or temporal side of the pupil, to selectively adapt nasally or temporally tuned ‘channels’, while the target stepped randomly toward or away from the eye. The orientation of the vertical edge was either bright on the right side or bright on the left. Results: In a preliminary experiment, only five out of twenty-six subjects showed reliable and consistent responses, with gains >0.5 for both positive and negative step change in vergence. The contrast threshold for accommodation to step changes in target vergence was approximately 26%. Data from three subjects who accommodated reliably to both directions of step changes in vergence do not support the claim that ‘channels’ sample light separately from opposite sides of the pupil to determine the sign of defocus. Conclusion: Potential factors that account for the poor accommodative responses in the present study include: 1) the target was illuminated with monochromatic light, 2) the target was a simplified stimulus in which the blur was in only one direction (one spatial phase), 3) the target was viewed monocularly, 4) the 3mm artificial pupil increased depth-of-focus and removed the normal dynamic behavior of the pupil, 5) our subjects were untrained. The negative results suggest alternate hypotheses: 1)‘averse channels’ work in conjunction with each other, not separately, to detect vergence, 2) ‘averse channels’ can function separately to detect vergence, but the signal was undetectable using the current method, and 3) ‘averse channels’ do not mediate vergence detection.
    • Critical Flicker Frequency in Traumatic Brain Injury

      Chang, Tina T. (2008-05-19)
      Primary Objective: To determine whether critical flicker frequency (CFF) thresholds are elevated in individuals with traumatic brain injury (TBI) and correlated with the degree of motion and light sensitivity. Methods and procedures: The foveal CFF threshold was assessed in individuals with TBI (n=18) having varying degrees of light and motion sensitivity. Mean CFF values were obtained using the ascending and descending psychophysical method of limits with binocular viewing at 40 cm. A rating-scale questionnaire was used to assess the degree of light sensitivity and motion sensitivity. These parameters were also assessed in a visually-normal cohort. Main outcomes and results: CFF in the TBI group was not significantly different across age groups from the visually- normal cohort. However, mean CFF among the TBI subjects was significantly higher for the “light sensitive” and “motion sensitive” subgroups when compared to the “not light sensitive” and “not motion sensitive” subgroups. The majority of TBI subjects had both light and motion sensitivity. Conclusion: An elevated CFF among a subgroup of TBI subjects may be related to the symptoms of light and motion sensitivity that many TBI patients experience. Underlying mechanisms involving disinhibition of the magnocellular pathway as a result of brain injury may be causal of the hypersensitivity to light and motion. CFF thresholds can potentially aid clinicians in determining methods of treatment for TBI patients.