416 research outputs found
Optical and biomechanical factors, associated with near work and myopia
No full textNear work may play an important role in the development of myopia in the younger population. The prevalence of myopia has also been found to be higher in occupations that involve substantial near work tasks, for example in microscopists and textile workers. When nearwork is performed, it typically involves accommodation, convergence and downward gaze. A number of previous studies have examined the effects of accommodation and convergence on changes in the optics and biometrics of the eye in primary gaze. However, little is known about the influence of accommodation on the eye in downward gaze. This thesis is primarily concerned with investigating the changes in the eye during near work in downward gaze under natural viewing conditions.\ud
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To measure wavefront aberrations in downward gaze under natural viewing conditions, we modified a commercial Shack-Hartmann wavefront sensor by adding a relay lens system to allow on-axis ocular aberration measurements in primary gaze and downward gaze, with binocular fixation. Measurements with the modified wavefront sensor in primary and downward gaze were validated against a conventional aberrometer using both a model eye and in 9 human subjects.\ud
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We then conducted an experiment to investigate changes in ocular aberrations associated with accommodation in downward gaze over 10 mins in groups of both myopes (n = 14) and emmetropes (n =12) using the modified Shack-Hartmann wavefront sensor. During the distance accommodation task, small but significant changes in refractive power (myopic shift) and higher order aberrations were observed in downward gaze compared to primary gaze. Accommodation caused greater changes in higher order aberrations (in particular coma and spherical aberration) in downward gaze than primary gaze, and there was evidence that the changes in certain aberrations with accommodation over time were different in downward gaze compared to primary gaze. There were no obvious systematic differences in higher order aberrations between refractive error groups during accommodation or downward gaze for fixed pupils. However, myopes exhibited a significantly greater change in higher order aberrations (in particular spherical aberration) than emmetropes for natural pupils after 10 mins of a near task (5 D accommodation) in downward gaze.\ud
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These findings indicated that ocular aberrations change from primary to downward gaze, particularly with accommodation. To understand the mechanism underlying these changes in greater detail, we then extended this work to examine the characteristics of the corneal optics, internal optics, anterior biometrics and axial length of the eye during a near task, in downward gaze, over 10 mins. Twenty young adult subjects (10 emmetropes and 10 myopes) participated in this study. To measure corneal topography and ocular biometrics in downward gaze, a rotating Scheimpflug camera and an optical biometer were inclined on a custom built, height and tilt adjustable table. We found that both corneal optics and internal optics change with downward gaze, resulting in a myopic shift (~0.10 D) in the spherical power of the eye. The changes in corneal optics appear to be due to eyelid pressure on the anterior surface of the cornea, whereas the changes in the internal optics (an increase in axial length and a decrease in anterior chamber depth) may be associated with movement of the crystalline lens, under the action of gravity, and the influence of altered biomechanical forces from the extraocular muscles on the globe with downward gaze. Changes in axial length with accommodation were significantly greater in downward gaze than primary gaze (p < 0.05), indicating an increased effect of the mechanical forces from the ciliary muscle and extraocular muscles.\ud
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A subsequent study was conducted to investigate the changes in anterior biometrics, axial length and choroidal thickness in nine cardinal gaze directions under the actions of the extraocular muscles. Ocular biometry measurements were obtained from 30 young adults (10 emmetropes, 10 low myopes and 10 moderate myopes) through a rotating prism with 15° deviation, along the foveal axis, using a non-contact optical biometer in each of nine different cardinal directions of gaze, over 5 mins. There was a significant influence of gaze angle and time on axial length (both p < 0.001), with the greatest axial elongation (+18 ± 8 μm) occurring with infero-nasal gaze (p < 0.001) and a slight decrease in axial length in superior gaze (−12 ± 17 μm) compared with primary gaze (p < 0.001). There was a significant correlation between refractive error (spherical equivalent refraction) and the mean change in axial length in the infero-nasal gaze direction (Pearson's R2 = 0.71, p < 0.001).\ud
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To further investigate the relative effect of gravity and extraocular muscle force on the axial length, we measured axial length in 15° and 25° downward gaze with the biometer inclined on a tilting table that allowed gaze shifts to occur with either full head turn but no eye turn (reflects the effect of gravity), or full eye turn with no head turn (reflects the effect of extraocular muscle forces). We observed a significant axial elongation in 15° and 25° downward gaze in the full eye turn condition. However, axial length did not change significantly in downward gaze over 5 mins (p > 0.05) in the full head turn condition. The elongation of the axial length in downward gaze appears to be due to the influence of the extraocular muscles, since the effect was not present when head turn was used instead of eye turn.\ud
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The findings of these experiments collectively show the dynamic characteristics of the optics and biometrics of the eye in downward gaze during a near task, over time. These were small but significant differences between myopic and emmetropic eyes in both the optical and biomechanical changes associated with shifts of gaze direction. These differences between myopes and emmetropes could arise as a consequence of excessive eye growth associated with myopia. However the potentially additive effects of repeated or long lasting near work activities employing infero-nasal gaze could also act to promote elongation of the eye due to optical and/or biomechanical stimuli
Game theory in economics : a response
No full textIn the article, “Non-cooperative Game Theory and Pay-off” (EPW, 28 January 2017), Atanu Sengupta and Abhijit Ghosh question the contributions of game theory to economics. They do this by setting up examples to show how game theory is case-specifi c, and thus cannot be generalised
Measurement of ocular aberrations in downward gaze using a modified clinical aberrometer
No full text*This article is free to read on the publisher's website*\ud
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Changes in corneal optics have been measured after downward gaze. However, ocular aberrations during downward gaze have not been previously measured. A commercial Shack-Hartmann aberrometer (COAS-HD) was modified by adding a relay lens system and a rotatable beam splitter to allow on-axis aberration measurements in primary gaze and downward gaze with binocular fixation. Measurements with the modified aberrometer (COAS-HD relay system) in primary and downward gaze were validated against a conventional aberrometer. In human eyes, there were significant changes (p<0.05) in defocus C(2,0), primary astigmatism C(2,2) and vertical coma C(3,−1) in downward gaze (25 degrees) compared to primary gaze, indicating the potential influence of biomechanical forces on the optics of the eye in downward gaze. To demonstrate a further clinical application of this modified aberrometer, we measured ocular aberrations when wearing a progressive addition lens (PAL) in primary gaze (0 degree), 15 degrees downward gaze and 25 degrees downward gaze
Towards the rapid network-wide deployment of new application specific network protocols, using application level active networking
No full textIn this thesis I try to show that traditional transport protocols (such as TCP) poorly match the requirements of today's applications. Firstly, I develop two new user level protocols using Application Layer Framing (ALF) [20] concepts in order to test this hypothesis. A simple remote login program and a protocol to deliver mailing lists using multicast. In both cases I am able to show that application level protocols utilise less network resources than their traditional counterparts as well as providing improved responsiveness to the user. The development and deployment of new protocols is both difficult and time consuming. I consider a new mechanism for the deployment of protocols. Rather than attempting to deploy them in the end systems, new protocols entities are dynamically deployed into the network. These protocol entities are called proxylets and are written in the programming language Java. A whole infrastructure funnelWeb, [34], has been built to allow the deployment of proxylets. A number of diverse applications are then built around proxylets to show benefits which can be derived from such a scheme. In order to make the funnelWeb infrastructure useful, when globally deployed, a routing infrastructure is designed and partially built
Planar Core and Macrocyclic Shell Stabilized Atomically Precise Copper Nanocluster Catalyst for Efficient Hydroboration of C–C Multiple Bond
No full textThe influence of downward gaze and accommodation on ocular aberrations over time
No full text*This article is free to read on the publisher's website*\ud
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A Shack–Hartmann wavefront sensor was modified to allow measurement of ocular aberrations in downward gaze with binocular fixation. Subjects first performed a control task prior to four different trials involving a distance task or a near task (accommodative demand of 2.5 D) performed in primary and downward gaze (25°). Immediately after beginning and then again 5 and 10 min after the commencement of each trial, ocular aberrations were measured. To observe the recovery in ocular aberrations following each test condition, subjects again viewed a distance target in primary gaze and aberration measurements were taken at 0, 5, and 10 min. During the distance task, small but significant changes in refractive power and higher order aberrations were observed in downward gaze compared to primary gaze. The changes in ocular aberrations that occurred in downward gaze recovered almost immediately after shifting gaze from downward back to primary gaze. During the accommodation tasks, there was a significant influence of gaze for changes in primary spherical aberration C(4, 0) [p = 0.004] and secondary spherical aberration C(6, 0) [p = 0.02]. There was also a significant gaze by time interaction (p = 0.04) for changes in C(6, 0). These findings show that ocular aberrations change from primary to downward gaze, particularly during accommodation
LIGAND-FIELD PHOTOPHYSICS OF COBALT(III) POLYPYRIDYL COMPLEXES
No full textThesis (Ph.D.)--Michigan State University. Chemistry - Doctor of Philosophy, 2025Fundamental research has consistently driven major technological advancements since the early twentieth century. A notable example is the photophysical investigation of transition metal complexes, which has led to breakthroughs in solar energy conversion technologies, including dye-sensitized solar cells and photocatalysis. Over the past two decades, d6 second- and third-row transition metal complexes have served as workhorses for light-driven applications due to their long-lived charge-transfer excited states and synthetic tunability. However, recent focus has shifted toward earth-abundant first-row transition metals, which not only offer a more sustainable alternative route for efficient energy conversion but also present unique opportunities to uncover unprecedented photophysical and photochemical behavior.First-row transition metal complexes often suffer from rapid deactivation of charge-transfer excited states to lower-energy ligand-field states due to their weaker ligand fields. This deactivation has limited their utility in applications that require long-lived charge-separated excited states. Among low-spin d6 first-row metals, Fe(II) has been extensively studied, but direct observation of ultrafast ligand-field crossover remains challenging due to the short lifetimes of their metal-to-ligand charge-transfer (MLCT) states in addition to inability to directly access their ligand-field states. Isoelectronic Co(III) complexes, in contrast, offer the ability to directly photoexcite into low-energy, spin-allowed ligand-field excited states owing to their energetically demanding ligand-to-metal charge-transfer (LMCT) transitions. This dissertation leverages this unique property of Co(III) polypyridyl complexes to elucidate their excited-state dynamics within the ligand-field manifold after photoexcitation into the lowest energy spin-allowed ligand-field band, bypassing charge-transfer excitation. This thesis takes a systematic molecular approach to investigate ligand-field excited state deactivation mechanism and ways to control energy flow in such excited states through employing a wide array of tools including ultrafast optical spectroscopy, synthesis, computational modeling, multi-dimensional NMR, and chemical intuition. The findings presented throughout the dissertation advance fundamental understanding of ligand-field photophysics and highlight their potential in future light-driven technologies.Description based on online resource. Title from PDF t.p. (Michigan State University Fedora Repository, viewed ).Includes bibliographical references
Axial elongation associated with biomechanical factors during near work
No full textPurpose: To investigate the changes occurring in the axial length, choroidal thickness and anterior biometrics of the eye during a 10 minute near task performed in downward gaze. \ud
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Methods: Twenty young adult subjects (10 emmetropes and 10 myopes) participated in this study. To measure ocular biometrics in downward gaze, an optical biometer was inclined on a custom built, height and tilt adjustable table. Baseline measures were collected after each subject performed a distance primary gaze control task for 10 mins, to provide wash-out period for prior visual tasks before each of three different accommodation/gaze conditions. These other three conditions included a near task (2.5 D) in primary gaze, and a near (2.5 D) and a far (0 D) accommodative task in downward gaze (25°), all for 10 mins duration. Immediately after, and then 5 and 10 mins from the commencement of each trial, measurements of ocular biometrics (e.g. anterior biometrics, axial length, choroidal thickness and retinal thickness) were obtained. \ud
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Results: Axial length increased with accommodation and was significantly greater for downward gaze with accommodation (mean change ± SD 23 ± 13 µm at 10 mins) compared to primary gaze with accommodation (mean change 8 ± 15 µm at 10 mins) (p < 0.05). A small amount of choroidal thinning was also found during accommodation that was statistically significant in downward gaze (13 ± 14 µm at 10 mins, p < 0.05). Accommodation in downward gaze also caused greater changes in anterior chamber depth and lens thickness compared to accommodation in primary gaze.\ud
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Conclusion: Axial length, choroidal thickness and anterior eye biometrics change significantly during accommodation in downward gaze as a function of time. These changes appear to be due to the combined influence of biomechanical factors (i.e. extraocular muscle forces, ciliary muscle contraction) associated with near tasks in downward gaze
Changes in ocular biometrics and refraction during near work in downward gaze over time
No full textPURPOSE\ud
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To investigate changes in the characteristics of the corneal optics, total optics, anterior biometrics and axial length of the eye during a near task, in downward gaze, over 10 min. \ud
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METHODS\ud
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Ten emmetropes (mean - 0.14 ± 0.24 DS) and 10 myopes (mean - 2.26 ± 1.42 DS) aged from 18 to 30 years were recruited. To measure ocular biometrics and corneal topography in downward gaze, an optical biometer (Lenstar LS900) and a rotating Scheimpflug camera (Pentacam HR) were inclined on a custom built, height and tilt adjustable table. The total optics of the eye were measured in downward gaze with binocular fixation using a modified Shack-Hartmann wavefront sensor. Initially, subjects performed a distance viewing task at primary gaze for 10 min to provide a "wash-out" period for prior visual tasks. A distance task (watching video at 6 m) in downward gaze (25°) and a near task (watching video on a portable LCD screen with 2.5 D accommodation demand) in primary gaze and 25°downward gaze were then carried out, each for 10 min in a randomized order. During measurements, in dichoptic view, a Maltese cross was fixated with the right (untested) eye and the instrument’s fixation target was fixated with the subject’s tested left eye. Immediately after (0 min), 5 and 10 min from the commencement of each trial, measurements of ocular parameters were acquired in downward gaze. \ud
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RESULTS\ud
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Axial length exhibited a significant increase with downward gaze and accommodation over time (p<0.05). The greatest axial elongation was observed in downward gaze with 2.5 D accommodation after 10 min (mean change from baseline 23±3 µm). Downward gaze also caused greater changes in anterior chamber depth (ACD) and lens thickness (LT) with accommodation (ACD mean change -163±12µm at 10 min; LT mean change 173±17 µm at 10 min) compared to primary gaze with accommodation (ACD mean change -138±12µm at 10 min; LT mean change 131±15 µm at 10 min). Both corneal power and total ocular power changed by a small but significant amount with downward gaze (p<0.05), resulting in a myopic shift (~0.10 D) in the spherical power of the eye compared with primary gaze. \ud
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CONCLUSION\ud
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The axial length, anterior biometrics and ocular refraction change significantly with accommodation in downward gaze as a function of time. These findings provide new insights into the optical and bio-mechanical changes of the eye during typical near tasks
Axial length changes with shifts of gaze direction in myopes and emmetropes
No full textPurpose. The purpose of the study was to investigate the changes in axial length occurring with shifts in gaze direction. \ud
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Methods. Axial length measurements were obtained from the left eye of 30 young adults (10 emmetropes, 10 low myopes, and 10 moderate myopes) through a rotating prism with 15° deviation, along the foveal axis, using a noncontact optical biometer in each of the nine different cardinal directions of gaze over 5 minutes. The subject's fellow eye fixated on an external distance (6 m) target to control accommodation, also with 15° deviation. Axial length measurements were also performed in 15° and 25° downward gaze with the biometer inclined on a tilting table, allowing gaze shifts to be achieved with either full head turn but no eye turn, or full eye turn with no head turn. \ud
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Results. There was a significant influence of gaze angle and time on axial length (both P < 0.001), with the greatest axial elongation (+18 ± 8 μm) occurring with inferonasal gaze (P < 0.001) and a slight decrease in axial length in superior gaze (−12 ± 17 μm) compared with primary gaze (P < 0.001). In downward gaze, a significant axial elongation occurred when eye turn was used (P < 0.001), but not when head turn was used to shift gaze (P > 0.05). \ud
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Conclusions. The angle of gaze has a small but significant short-term effect on axial length, with greatest elongation occurring in inferonasal gaze. The elongation of the eye appears to be due to the influence of the extraocular muscles, in particular the oblique muscles
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