RSS 1.0SUNY Optometry Masters Thesis Collection
Recent Submissions
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Cognitive Demand, Concurrent Viewing Distance, and Digital Eye StrainPurpose: Digital devices are now ubiquitous in modern daily life. Reports of digital eye strain (DES) symptoms are occurring frequently, particularly since the recent COVID-19 pandemic. Despite its prevalence, the mechanisms underlying DES have not been fully elucidated and there is currently no clinically proven treatment. Given that both mental effort and the accommodative and vergence demand have been associated with DES, the purpose of this study was to evaluate the relationship between the cognitive demand of the task, mode of presentation, working distance and symptoms of DES. Method: The study was performed on 30 young, normally-sighted individuals. Each participant completed four trials, each of which included a 30-minute reading task. The four conditions entailed: (1) a cognitively demanding task performed on a digital device (tablet) and (2) a less cognitively demanding task performed on the same digital device. Trials (3) and (4) were identical to (1) and (2) except that the tasks were performed on printed paper. Both prior to and immediately following each 30-minute task, subjects completed a 10 question DES symptom survey. For all four conditions, subjects wore a Clouclip, a spectacle-mounted device which uses infrared technology to monitor the working distance objectively every 5 seconds. Results: While all four 30-minute reading tasks induced symptoms of DES, the increase in symptoms was greater for the cognitively demanding tasks (p= <0.0001). However, there was no significant difference in symptoms between performing the tasks on paper versus the tablet computer (p=0.83). With regard to working distance, there was no difference between the four testing conditions (p=0.11). However, all tasks showed a similar significant reduction in working distance (p=0.001), on average from 32 to 30cm, over the first ten minutes of the task, with the working distance remaining relatively stable after this initial period. Conclusion: These results suggest that cognitive demand plays a greater role in DES than the mode of presentation. In addition, we found no evidence that working distance varies with cognitive demand or the method of presentation. However, it did decrease during the first 10 minutes of each trial. Further work is needed to explain the role of cognitive demand in DES.
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Effects of Test Flash Duration on the Photopic Negative Response (PhNR) of the Flash ElectroretinogramPurpose: The Photopic Negative Response (PhNR) of the cone mediated electroretinogram (ERG) is a slow potential with negative polarity that appears after the b-wave. The PhNR originates from the electrical activity of retinal ganglion cells (RGCS) and has clinical utility. The PhNR is typically recorded to a brief (<4ms) test flash, we explored the effect of increasing the stimulus duration on the PhNR amplitude of normal subjects in an ongoing attempt to optimize the stimulus conditions for its clinical use. Methods: ERGs were recorded with DTL electrodes from normal subjects (N=10) in the age range 23-53 years using the ColorBurst handheld ganzfeld stimulator and hardware from Diagnosys (Lowell, MA). The stimuli consisted of red test flashes on constant blue background (8 phot cd.s/m.sq). The test flashes were either brief stimuli (<4 ms duration) in the range of 0.00625 - 6.4 phot cd.s/m.sq or longer duration (20-80 ms) in the range of 0.125-1500 cd/m.sq. A new algorithm in the Espion software with objective sweep selection based on various noise and artifact identification criteria was used to average repeated responses at each test flash intensity. The PhNR amplitude of the averaged waveform was plotted as a function of test flash intensity and fitted with the standard Naka-Rushton equation. The saturated amplitude (Vmax), slope (n) and semisaturation constant (K) derived from the fits were analyzed. The student t-test was performed to compare the fit parameters across different test flash durations with correction for multiple comparisons using the Holm’s method. Results: Vmax for the brief stimulus was 20+7 microvolts and increased to 23+2 microvolts for 20 ms duration stimuli. With further increase in stimulus duration the PhNR Vmax was 34+8 v, 42+10 v and 37+10 v for 40 ms, 50 ms and 60ms duration stimuli and thereafter reduced to 29+7 v for an 80 ms stimulus duration. The Vmax amplitude differences between the brief and longer duration stimuli were statistically significant only for the 40 ms (p=0.04), 50 ms (p=0.001) and 60 ms (p=0.01) after correcting for multiple comparisons. Responses to stimulus durations up to 60 ms demonstrated a single PhNR trough and for longer duration stimuli two PhNR troughs were observed one following light onset after the b-wave and another following light offset. Conclusions: The saturated PhNR amplitude is larger for longer duration stimuli and is maximal in the range of 40-80 ms duration. The larger PhNR amplitude at the intermediate test flashes likely reflect the summation of the PhNR to stimulus onset and offset and could potentially have more value in assessing retinal ganglion cell function in patients with disease affecting the optic nerve and/or inner-retinal neurons.
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Accommodation over Time in Children Wearing Multifocal Soft Contact Lenses for Myopia ControlIntroduction The prevalence of myopia and its ocular complications increases each year worldwide and the complications of myopia are predicted to become the leading cause of blindness by 2050 (Holden Ophthamology 2016). Common therapies for myopia management include low-dose atropine, bifocals or Progressive Addition Lenses (PALs), orthokeratology (OK), and multifocal contact lenses (MFCL). One potential mechanism for OK and MFCLs to reduce myopia progression is by imposing peripheral myopic defocus on the retina. MFCL wear can reduce accommodation compared with single vision contact lenses (SVCL), potentially reducing peripheral myopic defocus and causing variable efficacies of MFCLs (Gong OVS 2017). The change in accommodation with MFCL use varies between MFCL designs. Auditory biofeedback training can decrease the accommodative lag during MFCL wear in young adults (Wagner Sci Rep 2020). We assessed: Differences in accommodative lag between children using low-dose atropine, OK, and MFCLs compared to a single vision spectacle control. Differences in accommodation between different MFCL designs. Differences in accommodation between viewing through SVCLs and MFCLs. The effect of biofeedback training on accommodation in children during MFCL wear. Methods Myopic children habitually using low-dose atropine, OK, or MFCLs as well as myopic children not undergoing myopia management (spectacle control) (19 male/ 24 female) were recruited from the Pediatric and Myopia Management Clinics at the University Eye Center, SUNY College of Optometry. Low dose atropine (n = 11), OK (n = 5), and spectacle control (n = 11) subjects’ accommodative lag was measured using an infrared (IR) photorefractor, using a stimulus at 0, 2.5, 3, and 4D. For the MFCL subjects (n = 17), accommodation through SVCLs and their habitual MFCLs before, after, and 1 week following biofeedback training were measured identically to the other subjects at the same distances. Differences in accommodative lag were measured using mixed effects multiple linear regression adjusting for accommodative stimuli. Results There was no significant difference between accommodation in the low-dose atropine (p = 0.8), OK (p = 0.3), and MFCL (p = 0.3) groups compared to the spectacle control. Eyes wearing MFCLs exhibited significantly increased lag of accommodation compared with SVCLs prior to the biofeedback training (SV vs. MFCL, p < 0.05). Specifically, eyes viewing through Biofinity MFCLs showed a significantly greater lag than MiSight (p < 0.05). Biofeedback training showed a tendency to decrease lag immediately following biofeedback training (p = 0.2) and significantly decreased lag 1 week later (p < 0.01). Both immediately and one week later, subjects that showed lower pretreatment accommodation had significantly greater decreases in lag following biofeedback training (p < 0.05). Conclusions Our findings show that pediatric subjects wearing MFCLs for myopia management show an increased accommodative lag compared to wearing SVCLs. The lag of accommodation while viewing with MFCLs differs between MFCL designs. Biofeedback training can significantly decrease lag in children during MFCL wear one week later, similar to previous findings (Wagner Sci Rep 2020). Subjects who displayed the greatest accommodative lag prior to the train showed the biggest improvements in accommodation before the biofeedback training, suggesting individuals with low accommodation while viewing through MFCLs use may yield the greatest benefit from biofeedback training. Biofeedback training may be effective in increasing the amount of peripheral myopic defocus during MFCL wear and thus increase the efficacy of MFCL wear for myopia management in children.
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Regional Differences in the Relationship Between Retinal Structure and ON-OFF Pathway Function in Myopic PatientsPurpose: The purpose of this study was to measure the effect of myopia on ON and OFF pathway asymmetries displayed between 5˚ to 30˚ of eccentricity and examine the structure-function relationship between retinal thickness and visibility of light and dark stimuli in eccentric quadrants of myopic eyes. Methods: Eighteen eyes were randomly selected from human subjects and all myopic subjects underwent testing with habitual soft contact lens correction. Subjects underwent ON-OFF perimetric testing in the test eye. The complete procedure is referenced and discussed in the body of the manuscript. Stimuli were presented at various contrasts across 30-degrees of the visual field and stimuli increased in size as a function of eccentricity. Structural and functional testing, including ultra-wide field macular optical coherence tomography (OCT), 30-2 static automated perimetry (SAP) mean sensitivity, peripheral autorefractive (AR) measurements, and axial length (AL), were also measured. All testing, except axial length measurements, were taken with subjects fully corrected in soft contact lenses. Results: There was a statistically significant positive correlation between AL and combined light and dark errors across the entire testing area of 5-30° (p=0.0019) as well as each eccentric range (5-10° p=0.0389; 11-20° p=0.0015; 21-30° p =0.0008). There was a statistically significant positive correlation between errors to light stimuli as a function of AL across the entire testing area of 5-30° (p=0.0251), 11-20° (p=0.0207) and 21-30° (p =0.0178). There was a statistically significant positive correlation between AL and dark stimuli errors across the entire testing area of 5-30° (p=0.0461), 11-20° (p=0.0424) and 21-30° (p =0.024). There was no statistically significant correlation when analyzing errors to light and dark stimuli separately at the 5-10° eccentricity. There was a statistically significant negative correlation between RE and combined light and dark errors across the entire testing area of 5-30° (p=0.0444) and a statistically significant negative correlation at the most peripheral eccentric range of 21-30° (p=0.0128). Subjects displayed higher errors to light stimuli over the entire testing area 5-30° (p=0.0166) and 21-30° (p=0.0007), but not at 5-10° or 11-20° (5-10° p=0.7043; 11-20° p=0.2572). The quadrant with the greatest average retinal thickness (IT) was associated with the lowest %errors (6.45 ± 6.56) and highest visual field mean sensitivity (VFMS, 30.9 ± 1.08 dB), whereas the quadrant with the least average retinal thickness (SN) was associated with the highest % errors (22.77 ± 15.93, p=8.91 x 10-9 for IT vs SN comparison) and among the lowest MS (29.43 ± 1.34, p=0.0020 for IT vs SN comparison). Conclusion: Higher levels of myopia are associated with greater response errors during ON-OFF perimetric testing, with higher error rates in response to light targets compared to dark targets. Both findings are most pronounced at the 21–30-degree eccentricity and have a stronger correlation with axial length compared to refractive error. Higher rates of error on ON-OFF perimetry correspond to thinner retinal thickness in the corresponding retinal quadrant. The highest average percent errors on ON-OFF perimetric testing were present in the superonasal visual field, which coincides with the thinnest total retinal thickness in the corresponding region of the retina (interotemporal). Better understanding of the structural and correspond to thinner retinal thickness in the corresponding retinal quadrant. The highest average percent errors on ON-OFF perimetric testing were present in the superonasal visual field, which coincides with the thinnest total retinal thickness in the corresponding region of the retina (interotemporal). Better understanding of the structural and corresponding functioning relationship between ON-OFF perimetric testing and retinal thickness may enhance our understanding of myopic refractive development.
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Effects of Scheduled Breaks on Digital Eye Strain and the 20-20-20 RulePurpose: The use of digital devices has increased substantially over the past two decades across all age groups, particularly during the recent pandemic, for both vocational and avocational purposes. Digital eye strain (DES) involves a range of visual and ocular symptoms that can be categorized into oculomotor/refractive abnormalities or dry eye symptoms. The so-called 20-20-20 rule, whereby individuals are advised to fixate an object at least 20 feet (6m) away for at least 20 seconds every 20 minutes is widely cited as a method for minimizing symptoms. Unfortunately, there is little or no peer-reviewed evidence to support this so-called rule. Accordingly, the aim of the present investigation was to determine whether 20-second breaks are indeed effective in reducing the adverse effects of digital device usage, and if so, then to identify the specific schedule that has the greatest success in controlling symptoms. Methods: The study was performed on 30 young, visually-normal subjects who performed a highly demanding 40-minute reading task from a tablet computer. The task required them to read random words and to identify which began with a specific letter chosen at random by the experimenter. The task was undertaken on four separate occasions, with 20-second breaks being allowed every 5, 10, 20 or 40 minutes (i.e., no break), respectively. Both before and immediately after each trial, subjects completed a questionnaire regarding ocular and visual symptoms experienced during the session. Additionally, both reading speed and task accuracy was quantified during the trial. Results: A significant increase in post-task symptoms (with respective to the pre-task value) was observed for all four trials (p<0.001). However, there was no significant effect of scheduled breaks on reported symptoms (p=0.70), reading speed (p=0.93) or task accuracy (p=0.55). Conclusions: While widely cited as a treatment option, these results do not support the proposal of using the 20-20-20 rule as a therapeutic intervention for DES. Future studies should look at alternative break schedules to determine their efficacy.
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Effects of Gingko biloba on Systemic and Retinal Blood CirculationIntroduction: The use of alternative medicine has increased in recent years due to its minimal side effects and holistic approach to healthcare. Ginkgo biloba extract (GBE) is a natural antioxidant derived from leaves of the Maidenhair tree and is known to improve blood vessel health. However, its effect on the retinal circulation is not fully understood. The purpose of this study is to examine the effect of GBE oral supplements on the retinal circulation. Methods: Blood pressure (Omron HEM-705CP), intraocular pressure (Canon T2 non-contact Tonometer), and blood flow velocities in the ophthalmic artery, central retinal artery, and short posterior ciliary arteries (Color Doppler imaging, Sequoia) were obtained from participants aged 22 to 36 with good ocular and systemic health. Measurements were performed between 12-5pm to control for circadian rhythm effects at 3 study visits: 1 week before baseline at pre-supplement visit (T-1), at baseline (T0) and after 4 weeks of 240mg/day GBE supplementation at post-supplement visit (T4). Ocular perfusion pressure (OPP) was calculated as OPP = 2/3 * (Mean Arterial Pressure – IOP). Results: Thirteen participants were recruited (5m, 8f; 25.54 ± 3.64 years). No significant changes in systemic blood pressure, OPP or retinal circulation were observed between pre-supplement visit (T-1) and baseline (T0) prior to GBE supplementation. However, the ophthalmic and short posterior ciliary arteries peak systolic velocities increased from baseline (T0) to post-treatment (T4) (ophthalmic artery baseline ave ± SD: 18.97 ± 6.67cm/s; post-treatment:24.33 ± 6.90cm/s; short posterior ciliary artery baseline: 10.56 ± 1.87cm/s; post-treatment: 11.58 ± 1.97cm/s; both p < 0.05). The increases in ophthalmic and short posterior ciliary arteries peak systolic velocities did not correlate with changes in systolic BP, diastolic BP, or OPP. Discussion: Our preliminary data suggests that 240mg/day of Ginkgo biloba extract (GBE) may increase blood flow in two major retinal ocular arteries. Such increase appears independent from changes in systemic blood pressure or OPP.
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Digital Eye Strain and Repeated Clinical Testing"Purpose: The use of digital devices has increased substantially over the past decades across all age groups for educational, career and leisure purposes. Although a high prevalence of Digital Eye Strain (DES) has been well established, especially during the recent pandemic, little is known about the association between repeated clinical testing and DES symptoms. The aim of this study was to determine whether symptoms of DES are associated with repeated measurements of standard clinical near-vision tests. Method: The study was performed on 30 young, normally-sighted individuals. Each participant completed 3 sessions to test accommodation (monocular facility, push-up amplitude), vergence (near point of convergence (NPC), near heterophoria) and accommodative-vergence interaction (AC/A ratio, binocular accommodative facility). Participants performed a cognitively demanding reading task from a tablet computer positioned at 33cm for 20 minutes. Repeated clinical measurements (3 readings) were taken both before and immediately after the reading task. Additionally, subjects completed a questionnaire regarding ocular and visual symptoms prior to and immediately after the reading period. Results: While a statistically significant difference in pre- and post-task DES symptom scores was observed (p < 0.01), no significant task-induced change in accommodation, vergence and accommodative-vergence measurements were found. Furthermore, there was no significant difference between the three consecutive readings for any of the pre- or post-task clinical parameters. Conclusion: These results indicate that repeated measurements of standard clinical near-vision tests are not associated with Digital Eye Strain (DES) symptoms. Additionally, no significant difference between the three repeated pre- or post-task measurements was found. "
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The Relationship Between Meibomian Gland Morphology, Dry Eye Disease, and Electronic Device Use in Pediatric Patients"Purpose: The purpose of this systematic study was to establish preliminary comparisons of various morphological and clinical parameters between dry eye and normal subjects in a pediatric cohort. Methods: Children aged 5-17 were recruited for the study with no previous clinical diagnosis of dry eye disease (DED) or meibomian gland dysfunction (MGD). Diagnostic criteria for DED consisted of positive scoring on at least two of three components; subjective symptoms, abnormal tear function, and vital staining. All subjects completed SPEED questionnaires to assess dry eye symptoms; scores above 5 indicated positive symptomology. Tear film and ocular surface integrity were inspected using fluorescein and lissamine green dye with slit lamp miscroscopy. Corneal fluorescein, as well as temporal and nasal conjunctival lissamine green staining was graded from 1-4 (0=no staining; 4=coalesced). A staining score of more than 4 points across all 3 sections indicated positive vital staining. Abnormal tear function was defined by a TBUT ≤5s. Meibomian gland morphology, lipid layer thickness, and blink patterns were evaluated with the use of a Lipiview Interferometer. The 5-point meiboscale for gland atrophy was used for dropout grading, while tortuosity was defined by number of glands with ≥45° angles. Tear volume assessment was completed with phenol red test. Questionnaires administered to both the child and family member were used to assess electronic device usage in order to screen for possible associations with average daily screen time and aforementioned parameters. Results: A total of 24 subjects participated in the study. Dry eye was found in 41.7% of the subjects. Presence of meibomian gland dropout and tortuosity were 70.8% and 87.5% respectively. Dropout was significantly higher in the dry eye group (p=0.016), although tortuosity was similar between both groups (p=0.93). Tear breakup times were significantly lower in the dry eye group (5.30s vs 9.66s; p<0.001) along with total staining scores (8.00 vs. 3.21; p=0.043). Blink behavior and measurements of lipid layer thickness (LLT) did not vary between the two groups; partial blink ratios were 0.62 and 0.67 for DED and normal groups respectively (p=0.76), and lipid layer thicknesses were 55.9nm and 57.43nm (p=0.84). Electronic device use did not vary significantly between the two groups (p=0.99). Screen time was significantly correlated with higher rate of partial blinks (r=0.84). Higher lipid layer thickness significantly predicted higher partial blink fraction in the left eye (p=0.39) and approached significance in the right eye (p=0.08). Conclusion: The present study provides a current baseline data on ocular surface characteristics and meibomian gland anatomy in healthy children with clinically dry eye vs. those without dry eye. Our results indicate that MGD and DED are highly inter-related at a much earlier age than previously acknowledged, and that the significant rise in pediatric variations of DED represent a worthwhile cause for investigation into long-term risk factors for disease progression. Better understanding of baseline ocular surface and tear film characteristics will be crucial to identify the impact increasingly prevalent risk factors, such as visual device use, myopia interventions, and other changing environmental factors might have on the pediatric population."
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Complexity of mental geometry for 3D pose perceptionBiological 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.
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Feasibility and applicability of a clinical assessment of both the ON and OFF pathways in patients with glaucoma and controls."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."
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Effects Of Correcting Fixation Disparity On Digital Eye StrainDigital 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.
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Gap Junctional Coupling between Retinal Amacrine and Ganglion Cells Underlies Coherent Spike Activity Integral to Global Object PerceptionCoherent 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.
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The Effect of Multifocal Contact Lenses on Accomodation and Phoria in a Pediatric PopulationThe 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.
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Exploring the veridicality of shape-from-shading for real 3D objectsDespite 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.
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Reading from an Electronic Reading Device versus Hardcopy TextThe 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.
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Triptolide Induces Increases in Migration via Mitogen-activated Protein Kinase Phosphatase-1 control of P38 and JNK MAPK ActivationPurpose 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.
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Nearwork-Induced Transient Myopia (NITM) Following Marked and Sustained, but Interrupted, Accommodation at NearPurpose: 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.
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Dynamic and Static Aspects of Accommodation in Mild Traumatic Brain InjuryPurpose: 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.
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Accommodation to wavefront vergence and chromatic aberration: color normal and deutan observersPurpose: 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).
