Academic literature on the topic 'Peripheral Refraction'
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Journal articles on the topic "Peripheral Refraction"
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Bezdetko, P., and R. Parkhomets. "STUDY OF PERIPHERAL REFRACTION IN CHILDREN WITH MYOPIA WITH ORTHOKERATOLOGY LENSES OF COMBINED DESIGN." East European Scientific Journal 2, no. 4(68) (May 14, 2021): 38–46. http://dx.doi.org/10.31618/essa.2782-1994.2021.2.68.19.
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Progressive myopia is a leading problem in modern optometry and ophthalmology in general. In recent years, refractive therapy with orthokeratology lenses has gained popularity among methods to control myopia progression. The aim: To study peripheral refraction in children with myopia with the use of orthokeratology lenses (OKL) of combined design. Methods. We followed up 60 children (117 eyes) diagnosed with uncomplicated mild to moderate myopia. All children underwent a complete ophthalmological examination as well as corneal keratotopography and peripheral refraction determination. Statistical analysis of correlations between peripheral corneal refraction under the influence of OKL, peripheral defocus, and axial length growth gradient was performed. Results. An inverse correlation relationship of -0.2 (p=0.03) was obtained between corneal differential power in the return 6 mm zone and peripheral refraction in its corresponding peripheral refraction of 23° on the temporal side. A positive correlation with a correlation coefficient of 0.21 (p=0.026) was obtained between the defocus in the temporal part and the gradient of myopia progression over one year, while the same result was obtained in the nasal part with a correlation coefficient of 0.2 (p=0.036). Concluсions. Difference corneal power at the periphery may be prognostic in relation to the course of myopia in OКL users. With an aboveaverage pupil diameter, combined design orthokeratology lenses are more effective in controlling myopia due to the greater influence of the formed corneal refractive ring on peripheral refraction.
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Marcellán, Maria Concepción, Francisco J. Ávila, Jorge Ares, and Laura Remón. "Peripheral Refraction of Two Myopia Control Contact Lens Models in a Young Myopic Population." International Journal of Environmental Research and Public Health 20, no. 2 (January 10, 2023): 1258. http://dx.doi.org/10.3390/ijerph20021258.
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Peripheral refraction can lead to the development of myopia. The aim of this study was to compare relative peripheral refraction (RPR) in the same cohort of uncorrected (WCL) and corrected eyes with two different soft contact lenses (CL) designed for myopia control, and to analyze RPR depending on the patient’s refraction. A total of 228 myopic eyes (114 healthy adult subjects) (−0.25 D to −10.00 D) were included. Open-field autorefraction was used to measure on- and off- axis refractions when uncorrected and corrected with the two CLs (dual focus (DF) and extended depth of focus (EDOF)). The RPR was measured every 10° out to 30° in a temporal-nasal orientation and analyzed as a component of the power vector (M). The average RPR for all subjects was hyperopic when WCL and when corrected with EDOF CL design, but changed to a myopic RPR when corrected with DF design. Significant differences were found between RPR curves with both CLs in all the eccentricities (Bonferroni correction p < 0.008, except 10°N). An incremental relationship between relative peripheral refraction at 30 degrees and myopia level was found. It is concluded that the two CLs work differently at the periphery in order to achieve myopia control.
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Fritschi, Alina, Chloe Gerber, Damian Eggler, and Martin Loertscher. "Simultaneous Myopic Defocus for Myopia Control: Effect on Accommodation, Peripheral Refraction and Retinal Image Quality in Non-Presbyopic Patients." Optics 2, no. 4 (September 30, 2021): 200–215. http://dx.doi.org/10.3390/opt2040019.
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Exposing the retina to a simultaneous myopic defocus is an optical method that has shown a promising effect in slowing the progression of myopia. Optical treatments applying a simultaneous defocus are available in the form of soft contact lenses or multifocal lenses originally designed to correct presbyopia. Orthokeratology is another optical method that slows down the progression of myopia. With orthokeratology, it is hypothesized that a change in peripheral refraction could slow the progression of myopia. We aimed to measure the accommodation response between monofocal and multifocal contact lenses in young subjects. Additionally, we performed a ray-tracing simulation to visualize the quality of the retinal image and the refractive status in the retinal periphery. The accommodation and pupil size measurements were performed on 29 participants aged 24.03 ± 2.73 years with a refractive error (spherical equivalent) of −1.78 ± 1.06 D. With the multifocal lens in situ, our participants showed less accommodation in comparison to the monofocal contact lens (mean difference, 0.576 ± 0.36 D, p > 0.001) when focusing on a near target at 40 cm. Pupil size became smaller in both contact lens groups during an accommodation of 0.29 ± 0.69 mm, p ≤ 0.001 and 0.39 ± 0.46 mm, p ≤ 0.001 for monofocal and multifocal contact lenses, respectively. The ray-tracing model showed a degradation for central and peripheral vision with the multifocal contact lens. The peripheral refraction was relatively myopic in both contact lens conditions up to 30°. Even if the accommodation ability is without fault, parts of simultaneous myopic defocus are used for the near task. The peripheral refraction in the ray-tracing model was not different between the two contact lenses. This is contrary to the proposed hypothesis that myopic peripheral refraction slows down the progression of myopia in current optical methods.
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Tarutta, E. P., E. N. Iomdina, N. G. Kvaratskheliya, S. V. Milash, and G. V. Kruzhkova. "Peripheral refraction: cause or effect of refraction development?" Vestnik oftal'mologii 133, no. 1 (2017): 70. http://dx.doi.org/10.17116/oftalma2017133170-74.
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Sng, Chelvin C. A., Xiao-Yu Lin, Gus Gazzard, Benjamin Chang, Mohamed Dirani, Audrey Chia, Prabakaran Selvaraj, et al. "Peripheral Refraction and Refractive Error in Singapore Chinese Children." Investigative Opthalmology & Visual Science 52, no. 2 (February 28, 2011): 1181. http://dx.doi.org/10.1167/iovs.10-5601.
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Sun, Han-Yin, Wei-Yang Lu, Jhen-Yu You, and Hui-Ying Kuo. "Peripheral Refraction in Myopic Children with and without Atropine Usage." Journal of Ophthalmology 2020 (May 12, 2020): 1–10. http://dx.doi.org/10.1155/2020/4919154.
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Purpose. To compare the patterns of relative peripheral refractions of myopic children who were currently on atropine treatment for myopia control and myopic children who did not use atropine. Methods. Chinese children (n = 209) aged 7 to 12 years participated in the study, 106 used atropine and 103 did not. Participants were also classified into three groups: emmetropes (SE: +0.50 to −0.50 D), low myopes (SE: −0.50 to −3.00 D), and moderate myopes (SE: −3.00 to −6.00 D). The central and peripheral refractions along the horizontal meridians (for both nasal and temporal fields) were measured in 10-degree steps to 30 degrees. Results. There were no statistically significant differences in spherical equivalent and astigmatism of the three refractive groups in either the nasal or temporal retina. The atropine group showed a significant relative myopia in the temporal 30° field in spherical equivalent compared to the emmetropic group (t49 = 3.36, P=0.02). In eyes with low myopia, the atropine group had significant relative myopia in the nasal 30° and temporal 30° fields (t118 = 2.59, P=0.01; t118 = 2.06, P=0.04), and it is also observed at 20° and 30° of the nasal field for the moderate myopic group (t36 = 2.37, P=0.02; t2.84 = 2.84, P=0.01). Conclusion. Significant differences in relative peripheral refraction were found between the atropine group and its controls. The findings suggested that the eyes that received atropine may have a less prolate shape and thus explain why using atropine is effective in controlling myopia progression.
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Kuo, Hui-Ying, John Ching-Jen Hsiao, Jing-Jie Chen, Chi-Hung Lee, Chun-Chao Chuang, and Han-Yin Sun. "The Correlations between Horizontal and Vertical Peripheral Refractions and Human Eye Shape Using Magnetic Resonance Imaging in Highly Myopic Eyes." Healthcare 9, no. 8 (July 30, 2021): 966. http://dx.doi.org/10.3390/healthcare9080966.
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The aim of this study was to determine the relationship between relative peripheral refraction and retinal shape by 2-D magnetic resonance imaging in high myopes. Thirty-five young adults aged 20 to 30 years participated in this study with 16 high myopes (spherical equivalent < −6.00 D) and 19 emmetropes (+0.50 to −0.50 D). An open field autorefractor was used to measure refractions from the center out to 60° in the horizontal meridian and out to around 20° in the vertical meridian, with a step of 3 degrees. Axial length was measured by using A-scan ultrasonography. In addition, images of axial, sagittal, and tangential sections were obtained using 2-D magnetic resonance imaging. The highly myopic group had a significantly relative peripheral hyperopic refraction and showed a prolate ocular shape compared to the emmetropic group. The highly myopic group had relative peripheral hyperopic refraction and showed a prolate ocular form. Significant differences in the ratios of height/axial (1.01 ± 0.02 vs. 0.94 ± 0.03) and width/axial (0.99 ± 0.17 vs. 0.93 ± 0.04) were found from the MRI images between the emmetropic and the highly myopic eyes (p < 0.001). There was a negative correlation between the retina’s curvature and relative peripheral refraction for both temporal (Pearson r = −0.459; p < 0.01) and nasal (Pearson r = −0.277; p = 0.011) retina. For the highly myopic eyes, the amount of peripheral hyperopic defocus is correlated to its ocular shape deformation. This could be the first study investigating the relationship between peripheral refraction and ocular dimension in high myopes, and it is hoped to provide useful knowledge of how the development of myopia changes human eye shape.
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Allinjawi, Kareem, Sharanjeet-Kaur Sharanjeet-Kaur, Saadah Mohamed Akhir, and Haliza Abdul Mutalib. "Peripheral refraction with different designs of progressive soft contact lenses in myopes." F1000Research 5 (November 22, 2016): 2742. http://dx.doi.org/10.12688/f1000research.9971.1.
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Aim: The purpose of this study was to compare the changes in relative peripheral refractive error produced by two different designs of progressive soft contact lenses in myopic schoolchildren. Methods: Twenty-seven myopic schoolchildren age between 13 to 15 years were included in this study. The measurements of central and peripheral refraction were made using a Grand-Seiko WR-5100K open-field autorefractometer without correction (baseline), and two different designs of progressive contact lenses (PCLs) (Multistage from SEED & Proclear from Cooper Vision) with an addition power of +1.50 D. Refractive power was measured at center and at eccentricities between 35º temporal to 35º nasal visual field (in 5º steps). Results: Both PCLs showed a reduction in hyperopic defocus at periphery. However, this reduction was only significant for the Multistage PCL (p= 0.015), (Proclear PCL p= 0.830). Conclusion: Multistage PCLs showed greater reduction in peripheral retinal hyperopic defocus among myopic schoolchildren in comparison to Proclear PCLs.
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Kang, Pauline, Paul Gifford, Philomena McNamara, Jenny Wu, Stephanie Yeo, Bonney Vong, and Helen Swarbrick. "Peripheral Refraction in Different Ethnicities." Investigative Opthalmology & Visual Science 51, no. 11 (November 1, 2010): 6059. http://dx.doi.org/10.1167/iovs.09-4747.
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CHARMAN, W. NEIL, JOHN MOUNTFORD, DAVID A. ATCHISON, and EMMA L. MARKWELL. "Peripheral Refraction in Orthokeratology Patients." Optometry and Vision Science 83, no. 9 (September 2006): 641–48. http://dx.doi.org/10.1097/01.opx.0000232840.66716.af.
Full textDissertations / Theses on the topic "Peripheral Refraction"
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Hartwig, Andreas. "The influence of optics, peripheral refraction and posture on refractive error development." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-optics-peripheral-refraction-and-posture-on-refractive-error-development(f0382767-3194-4631-8cab-d473d64900bd).html.
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The aim of the present project was to analyse the link between peripheral posture, optics, optics and refractive error progression. Preliminary studies were conducted to ensure that peripheral aberrometry is valid for further analysis. The repeatability of the IRX-3 for peripheral aberrometry was asgood as for central measurements and the recalculation of elliptical pupils did not seem to be necessary for measurements up to 20 degrees eccentricity. Higher order aberration measurements werecomparable to other studies. Eye and head movements as well as working distance did not differ significantly between myopes and non-myopes. However, there was some evidence, that forward bending of the head during reading increases in association with higher refractive error progression rates. The link between central higher order aberrations and refractive error development was analysed by comparing higher order aberrations between isometropes and anisometropes. This analysisdid not show any significant association of higher order aberrations on the development, as no major differences were found between the two groups. For central vision, changes in biometric parameters during accommodation were analysed. It was found that biometric parameters change similarly in myopes and non-myopes. Peripheral accommodation was found to differ between myopes and emmetropes indicating that there might be an influence of peripheral refraction on myopisation. However, associationbetween peripheral refraction or peripheral aberrations and refractive error progression were not significant. The reason for this observation might be the low refractive error progression (0.04± 0.29 D in myopes and -0.12 ± 0.38 D in emmetropes) during one year in the study population.
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Mathur, Ankit. "Peripheral ocular monochromatic aberrations." Queensland University of Technology, 2009. http://eprints.qut.edu.au/30384/.
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Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.
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Harper, Justine. "Ocular biometric correlates of early-and late-onset myopia." Thesis, Aston University, 2001. http://publications.aston.ac.uk/14536/.
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Myopia is a refractive condition and develops because either the optical power of the eye is abnormally great or the eye is abnormally long, the optical consequences being that the focal length of the eye is too short for the physical length of the eye. The increase in axial length has been shown to match closely the dioptric error of the eye, in that a lmm increase in axial length usually generates 2 to 3D of myopia. The most common form of myopia is early-onset myopia (EO M) which occurs between 6 to 14 years of age. The second most common form of myopia is late-onset myopia (LOM) which emerges in late teens or early twenties, at a time when the eye should have ceased growing. The prevalence of LOM is increasing and research has indicated a link with excessive and sustained nearwork. The aim of this thesis was to examine the ocular biometric correlates associated with LOM and EOM development and progression. Biometric data was recorded on SO subjects, aged 16 to 26 years. The group was divided into 26 emmetropic subjects and 24 myopic subjects. Keratometry, corneal topography, ultrasonography, lens shape, central and peripheral refractive error, ocular blood flow and assessment of accommodation were measured on three occasions during an ISmonth to 2-year longitudinal study. Retinal contours were derived using a specially derived computer program. The thesis shows that myopia progression is related to an increase in vitreous chamber depth, a finding which supports previous work. The myopes exhibited hyperopic relative peripheral refractive error (PRE) and the emmetropes exhibited myopic relative PRE. Myopes demonstrated a prolate retinal shape and the retina became more prolate with myopia progression. The results show that a longitudinal, rather than equatorial, increase in the posterior segment is the principal structural correlate of myopia. Retinal shape, relative PRE and the ratio of axial length to corneal curvature have been indicated, in this thesis, as predictive factors for myopia onset and development. Data from this thesis demonstrates that myopia progression in the LOM group is the result of an increase in anterior segment power, owing to an increase in lens thickness, in conjunction with posterior segment elongation. Myopia progression in the EOM group is the product of a long posterior segment, which over-compensates for a weak anterior segment power. The weak anterior segment power in the EOM group is related to a combination of crystalline lens thinning and surface flattening. The results presented in this thesis confirm that posterior segment elongation is the main structural correlate in both EOM and LOM progression. The techniques and computer programs employed in the thesis are reproducible and robust providing a valuable framework for further myopia research and assessment of predictive factors.
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Cagnolati, Bastian. "Central and peripheral refraction in children and young adults : a longitudinal study." Thesis, Glasgow Caledonian University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636812.
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The development of refractive errors remains of scientific and clinical interest down to the present day. This applies in particular to myopia which at higher levels is associated with an increased risk of ocular disease. In urban areas of Asia the prevalence of myopia has increased over the last few decades such that numbers have reached epidemic proportions. Multidisciplinary research efforts on the aetiology of myopia are ongoing. Among those the role of the retinal periphery in myopia has seen renewed interest in the past decade. This thesis describes a 4-year longitudinal study of refractive development in children and young adults that aimed to investigate factors associated with refractive error progression, particularly the relationship of central refraction with peripheral refractive state and ocular shape. For this project 140 subjects between 5 and 20 years were recruited. Their history and activities were assessed using a questionnaire. Non-cycloplegic central and peripheral (250 temporal) refraction as well as accuracy of accommodation were determined with the Shin-Nippon NVision-K 5001 autorefractor. Ocular dimensions were quantified with the Zeiss IOLMaster. This included peripheral ocular length measurements (190 superior, inferior, temporal, nasal) to infer ocular shape. Additionally amplitude of accommodation, dissociated heterophoria, visual acuity, contrast sensitivity, body height and pupillary distance were also determined.
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Ehsaei, Asieh. "An investigation of the relationship between the structure and function of the myopic eye : correlating the optical, functional and structural aspects of ametropia in young adult humans." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5524.
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The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.
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Jaisankar, Durgasri. "Influence of testing methods on the evaluation of peripheral ocular optics and peripheral visual performance." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/226479/1/Durgasri%20Jaisankar%20Thesis.pdf.
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Peripheral (out-to-the-side) vision is important for general mobility and tasks such as driving. This study evaluated appropriateness of testing methods used to measure peripheral optics and visual performance. Peripheral optics measurements depended on the instrument used to measure them. The choice of either head or eye movements to set up peripheral optics measurements was not critical, even when contact lenses were worn. The nature of targets, in terms of size and abrupt or gradual loss of contrast near the edge, affected peripheral detection. To measure peripheral contrast detection accurately in the presence of blur, fine spatial frequency sampling was required.
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Rojo, Badenas Pilar. "Generalized ray tracing method for the calculation of the peripheral refraction induced by an ophthalmic lens." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/322554.
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This thesis proposes a method to evaluate and quantify in a precise way the peripheral refraction induced by an ophthalmic lens. The motivation for this work stems from the progression of myopia and its possible causes; two of them are particularly key for this PhD: (a) Peripheral refraction of the eye may have an important role in the progression of myopia and (b) ophthalmic lenses are the compensating element more used in children and teenagers. These two elements fully justify the need for a reliable method to quantify the induced peripheral refraction by an ophthalmic lens. This method is based on two pillars: first, it must accurately assess the design of the ophthalmic lens and, second, it should consider what peripheral refractive pattern is acting, that is, without compensating element. The proposed method takes the advantages provided by the ray tracing strategies used in the classic design of ophthalmic lenses but applying them in parallel with amendments to evaluate the peripheral refraction. Thus, the simple scheme used in the classic design of ophthalmic lenses containing a remote sphere and a small aperture at the center of rotation of the eye becomes a scheme where the retina conjugate surface (RCS) and the nodal point of the eye play equivalent roles. In our case, the reference for ray tracing is the nodal point of the eye and the reference for measuring the induced peripheral refraction is the RCS. Ray tracing is based on a finite ray tracing (FRT) from the image space to the object space and on a generalized ray tracing (GRT) from object space to image space. Both have been implemented in a Matlab program and validated to provide a powerful tool for our purpose. GRT allows a quick and accurate assessment of the oblique astigmatism, ie the tangential and sagittal focal lens, in wide field of view considering accurately the lens design. This considers that each ray has a small wavefront associated traveling perpendicular to it. By GRT we are able to know how the wavefront shape changes when is propagated and refracted. Therefore, it is mandatory to have a locally description of the geometry of both the wavefront and the refractive surface at the point where the ray arrives to the refractive surface. This local description is determined by the normal and by the principal curvatures and directions of these surfaces at the point of interest; they can be obtained from a parametric description of the surface and then using Gaussian fundamental forms. This ray tracing procedure has been developed for the general case of any geometry to the surfaces of the ophthalmic lens and has been detailed for the case of an astigmatic lens. For calculating the induced peripheral refraction, a surface is modeled reflecting the peripheral refractive initial values before entering the lens; this is the aforementioned RCS. Two methods have been proposed to model this RCS. One is based on the trends observed in the different studies and uses three-dimensional surfaces power vectors associated with peripheral refraction. The second method uses experimental measurements obtained along four meridians of the retina to interpolate a surface. The expression of these surfaces by power vectors can easily be combined with the results obtained by tracing rays through the lens for the calculation of the induced peripheral refraction. We present in this manuscript some specific examples of how variations on the lens geometry modified the induced peripheral refraction. This opens up the possibility of custom designs ophthalmic lenses to prevent the progression of myopia.Esta Tesis tiene como objetivo la propuesta de un método para la evaluación cuantitativa de la refracción periférica inducida en el ojo de un paciente por una lente oftálmica. La motivación del trabajo radica en la importancia de este fenómeno en el progresión de la miopía y sus causas. La existencia de una refracción periférica hipermetrópica se ha relacionado directamente con la progresión de la miopía, y las lentes oftálmicas son el elemento compensador preferenteen niños y adolescentes, los sujetos más relevantes en cuanto al control de la progresión de l amiopía, en sí misma y como antesala d eotros problemas oculares más graves. Hasta la realización de esta Tesis no existía un método preciso, próximo a los métodos convencionales del diseño de lentes oftálmicas, que permitiera el cálculo de la refracción periférica inducida por la lente oftálmica y el análisi de los diseños de lente utilizados. Dicho diseño debe considerar tanto los efectos asociados a a óptica y la geometría del ojo, como al propio diseño de la lente compensadora. El método que se propone sigue una metodologia próxima a la del diseño convencional de lentes oftálmicas, sustituyendo el rol del centro de rotación del ojo por el de su punto nodal, y el rol de la esfera del remoto por lo qque se ha denominado la superfície conjugada de la retina (RCS, de retinal conjugate surface, en el texto). Con este enfoque se han implementado algoritmos detallados de trazado de rayos finito y generalizado que permiten el trazado detallado de rayos en un conjunto de direcciones alrededor de la fóvea. Los algoritmos de trazado generalizado permiten el análisis de lentes oftálmicas de manera más eficiente que el trazado intensivo típico del software de diseño óptico, utilizando el concepto de trazado de frente d eonda, que analiza las deformaciones del frente de onda que acompaña a un rayo principal. Dichos algoritmos se han implementado y validado para un conjunto de lentes oftálmicas de diferentes geometrías en un software científico estándard (Matlab(R)) como parte de los trabajos desarrollados en esta Tesis. Mediante el uso de los algoritmos descritos es posible calcular la superficie refractada que induceuna lente oftálmica. A continuación se hen desarrollado modelos teóricos y experimentales para la RCS que permiten tener en cuanta la variabilidad de patrones de refracción periférica existente, y se ha propuesto el uso de vectores de potencia (M J0 y J45) para el cálculo de la refracción periférica inducida por la lente, mediante la combinación de la superficie refractada por la lente y la modelada para una determinada RCS. Se presentan casos para lentes esféricas, asféricas y astigmáticas, para ojos miopes y emétropes, y en condiciones de infra y sobre refracción, mostrando la potencialidad del método propuesto para diseñar lentes que compensen simultáneamente la refracción foveal y la periférica, que mediante el método propuesto podrán optimizarse simultáneamente.
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Berntsen, David A. "Accommodative lag, peripheral aberrations, and myopia in children." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243829481.
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Martinez, Aldo A. Optometry & Vision Science Faculty of Science UNSW. "On and off-axis monochromatic aberrations and myopia in young children." Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/33676.
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Purpose: To study ???on??? and ???off-axis??? wavefront aberration of eyes of children and to determine the relationship with refractive error development. Methods: On and off-axis ocular aberrations of cyclopleged eyes of children (mostly 12 year olds) were measured and compared to data obtained from a group of mostly 6 year old children. Only data from the right eyes were analysed (pupil diameter=5 mm) and categorised into refractive error groups based on ???M???. Differences in ???on??? and ???off-axis??? aberrations between refractive and ethnic groups were analysed using univariate and multivariate analyses of variance with adjustment for multiple comparisons. Off-axis refraction was analysed using skiagrams and mean relative spherical equivalent. Results: Data from 1,636 12 year old children (mean age 12.6 ?? 0.4 years) was analysed. Lower order aberrations were the largest and higher order aberrations contributed to only 25% of the wavefront. There were no differences in the amount of total higher orders between refractive groups. Of the individual higher orders, spherical aberration was greater in hyperopic eyes (0.07 ?? 0.06 ??m) in comparison to emmetropic and myopic eyes (0.05 ?? 0.04 ??m and 0.05 ?? 0.04 ??m) (p<0.001). Myopic eyes had more positive values of Z(3,-1) (p<0.05). Similar results were obtained for the 1,364 6 year old children (mean age 6.7 ??? 0.4 years). Despite East Asian children being more myopic than other ethnic groups (p<0.01), there were no differences in higher orders except for low hyperopic East Asian eyes presenting with higher levels of positive spherical aberrations (p<0.001). When compared to the fovea, off-axis myopic eyes had hyperopia (0.55 to 1.66 D) and emmetropes and hyperopes had myopia (0.10 to -2.00 D). Astigmatism and defocus were the dominant off-axis aberrations. The magnitude of higher order aberrations (mostly 3rd orders) increased with eccentricity but was similar across refractive error groups. Conclusions: Myopic eyes do not have abnormal or excessive levels of on and off-axis higher order aberrations but had patterns of off-axis refraction that may be associated with progression. Considerable inter-subject variability in higher order aberrations was seen for all refractive groups. However, their magnitude was small and suggests that any impact on the optical quality of the eye is negligible.
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Noble, Andrew G. "The Repeatability of Peripheral Axial Length Measurements." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330654198.
Full textBooks on the topic "Peripheral Refraction"
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Cleary, Georgia, Allon Barsam, and Stephen Tuft. Cornea and conjunctiva. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780199672516.003.0002.
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This chapter focuses on the cornea and conjunctiva. It first discusses corneal anatomy and physiology, corneal nutrition, and conjunctival anatomy and physiology. Next, it outlines history taking for anterior segment disease. It then discusses clinical knowledge areas, including blepharitis, staphylococcal hypersensitivity disorders, dry eye disease, conjunctivitis, cicatrizing conjunctival disease, conjunctival degeneration, conjunctival neoplasia, corneal degeneration, infectious keratitis (bacterial, fungal, and viral), interstitial keratitis, peripheral ulcerative keratitis, metabolic and drug induced keratopathies, corneal dystrophies, contact lenses, corneal ectasia, keratoplasty, anterior uveal tumours, anterior segment trauma, chemical injury, and refractive surgery. Practical skills, such as the removal of a corneal foreign body, and corneal sutures, are also discussed.
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Goyal, Saurabh, Allon Barsam, and Stephen Tuft. External eye disease. Oxford University Press, 2012. http://dx.doi.org/10.1093/med/9780199237593.003.0001.
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This chapter covers corneal and conjunctival basic science, before covering clinical skills (history taking for anterior segment disease and examination of the anterior segment). The chapter then covers blepharitis, staphylococcal hypersensitivity disorders, dry eye disease, conjunctivitis, cicatrizing conjunctival disease, conjunctival degeneration, conjunctival neoplasia, corneal degeneration, infectious keratitis, interstitial keratitis, peripheral ulcerative keratitis, metabolic and drug-induced keratopathies, corneal dystrophies, contact lenses, corneal ectasia, keratoplasty, complications of keratoplasty and graft rejection, anterior uveal tumours, anterior segment trauma, chemical injury, and refractive surgery. Practical skills are then covered, including corneal glue, removal of corneal sutures, removal of corneal foreign bodies, corneal topography, and corneal pachymetry. The chapter concludes with three case-based discussions, on chemical injury, Herpes zoster keratitis, and bacterial keratitis.
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Liyanage, Sidath E., Fred K. Chen, and James W. Bainbridge. Vitreoretinal surgery. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780199672516.003.0005.
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This chapter explores vitreoretinal surgery. It starts off with a detailed examination of retinal anatomy, including a discussion of retinal embryology, and then discusses the physiology of the retina. Next, it outlines the clinical skills of posterior segment history taking and examination. It then discusses the use of diagnostic lenses, which enable visualization of the fundus by neutralizing the optical power of the eye (direct lenses) or increasing the refractive power of the eye to create an inverted real image of the fundus anterior to the eye (indirect lenses). It then continues with a discussion of the practical skills of optical coherence tomography, ultrasonography, and retinal photocoagulation. The chapter also outlines clinical knowledge areas of vitreous disorders, retinal detachment, peripheral retinal abnormalities, macular surgery, submacular surgery, retinal tumours, choroidal tumours, vitreoretinopathies, and posterior segment trauma.
Book chapters on the topic "Peripheral Refraction"
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Fechtner, Robert D., and Albert S. Khouri. "Early Vision Loss After Trabeculectomy." In Complications of Glaucoma Surgery. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780195382365.003.0027.
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“This surgery is designed to help you preserve the vision you have. If we are completely successful, you will not see worse once we are done.” Hardly an encouraging message we give to patients needing glaucoma surgery. An experienced glaucoma surgeon knows that aqueous diversion procedures are fraught with complications, including the ever terrifying loss of vision. Early complications of trabeculectomy that can lead to vision loss can be categorized as refractive, inflammatory/infectious, hemorrhagic, and other. It is important to recognize these complications promptly and understand the appropriate time to intervene. Thoughtful preoperative planning, meticulous technique, and a dose of good luck can help prevent these complications. It is the ability to anticipate, avoid, and manage complications that distinguishes the successful and satisfied glaucoma surgeon from a frustrated one. Trabeculectomy may induce new spherical and cylindrical aberrations. When intraocular pressure (IOP) is reduced, and particularly if there is overfiltration, the lens-iris diaphragm moves forward, and the anterior chamber shallows. These combined actions usually induce a spherical refractive error (myopic shift). The clinical signs of a myopic shift will be a shallow anterior chamber and visual acuity that will improve with a pinhole occluder or refraction. Interestingly, should the overfiltration be accompanied by macular edema, the myopic effect may be counteracted by a hyperopic shift due to macular elevation and shortening of axial length, and the patient may not have any change in refraction or may even have a hyperopic shift. For more information about axial length and changes in refraction, including after trabeculectomy, see Chapter 41. Astigmatic shift can have several origins. If a trabeculectomy flap is dissected too far anteriorly into the peripheral cornea and not sutured securely back to its origin, “against the rule” astigmatism can be induced. If a superiorly located flap is sutured with too much tension, astigmatism can be induced along the axis of the tightest suture(s), usually “with the rule.” (See Chapter 26.) Additionally, uneven suture tension in the conjunctival closure (whether limbus- or fornix-based) can affect the degree of postoperative astigmatism.
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Kim, Soyang Ella, and Stephen Tuft. "Cornea and conjunctiva." In Training in Ophthalmology, C2—C2.P1543. 3rd ed. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/med/9780198871590.003.0002.
Full textAbstract:
Abstract This chapter focuses on the cornea and conjunctiva. It first discusses corneal anatomy and physiology, corneal nutrition, and conjunctival anatomy and physiology. Next, it outlines history taking for anterior segment disease. It then discusses clinical knowledge areas, including blepharitis, staphylococcal hypersensitivity disorders, dry eye disease, conjunctivitis, cicatrizing conjunctival disease, conjunctival degeneration, conjunctival neoplasia, corneal degeneration, infectious keratitis (bacterial, fungal, and viral), interstitial keratitis, peripheral ulcerative keratitis, metabolic and drug-induced keratopathies, corneal dystrophies, contact lenses, corneal ectasia, keratoplasty, anterior uveal tumours, anterior segment trauma, chemical injury, and refractive surgery. Practical skills, such as the removal of a corneal foreign body, and corneal sutures, are also discussed.
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Mehat, Manjit, and James Bainbridge. "Vitreoretinal surgery." In Training in Ophthalmology, C5–222. 3rd ed. Oxford University PressOxford, 2022. http://dx.doi.org/10.1093/med/9780198871590.003.0005.
Full textAbstract:
Abstract This chapter explores vitreoretinal surgery. It starts off with a detailed examination of retinal anatomy, including a discussion of retinal embryology, and then discusses the physiology of the retina. Next, it outlines the clinical skills of posterior segment history taking and examination. It then discusses the use of diagnostic lenses, which enable visualization of the fundus by neutralizing the optical power of the eye (direct lenses) or increasing the refractive power of the eye to create an inverted real image of the fundus anterior to the eye (indirect lenses). It continues with a discussion of the practical skills of optical coherence tomography, ultrasonography, and retinal photocoagulation. The chapter also outlines clinical knowledge areas of vitreous disorders, retinal detachment, peripheral retinal abnormalities, macular surgery, submacular surgery, retinal tumours, choroidal tumours, vitreoretinopathies, and posterior segment trauma.
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Rao, Rahul. "Epilogue." In Out of Time, 213–24. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190865511.003.0007.
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This chapter returns to a puzzle running through the book, namely how to account for the ways in which queerness mutates to become a metonym for imperialism/anti-imperialism, paganism/Christianity, whiteness, embourgeoisement, and backwardness in different institutional configurations of power. Using Hortense Spillers’s historically informed notion of the ‘grammar’ of a state, the chapter argues that these mutations result from a refraction of queerness through the foundational grammar of the institutions being investigated in each chapter. Both states and their antagonists speak in these grammars, making their engagements what Achille Mbembe calls ‘convivial’. The chapter illustrates this with reference to the politics of Uganda. It then summarises its claims about the global frictions surrounding the Anti Homosexuality Act, reiterating the ways in which these frictions illustrate the mutual constitution of core and periphery. It suggests that this insight offers a possible strategy for disorienting orientalism
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Brinton, Daniel A., and Charles P. Wilkinson. "Ophthalmoscopy." In Retinal Detachment. Oxford University Press, 2009. http://dx.doi.org/10.1093/oso/9780195330823.003.0007.
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Indirect viewing systems, including the binocular indirect ophthalmoscope and slit lamp biomicroscopy through an indirect lens, have become the standard of care for management of retinal detachments. Comparison with direct ophthalmoscopy illustrates the capabilities of indirect systems. The technique of indirect ophthalmoscopy with scleral depression is presente The characteristics of direct and indirect ophthalmoscopy are compared in Table 3–1. Figure 3–1A shows the optical principles of direct ophthalmoscopy, and Figure 3–1B illustrates the optics of the indirect method. Substantial clinical differences between the two methods are due to the differences in optical characteristics. The direct ophthalmoscope offers 14X magnification compared with 3X with the indirect using the usual +20 diopter lens. However, this does not mean the direct device has an equal advantage in resolution. Resolution is a function of how close together two points can be and remain distinguished as separate when viewed through an optical system. The visualization of detail that an optical system permits is a function of its resolving power and not its magnifi cation. Resolution is a function of the light available at the points to be resolved and of the quality of the optical components of the system. Magnification plays a role only if the resolution of the optical system exceeds the resolution of the observing human eye at a given level of magnification. Too much magnification of a poorly resolved image results in a loss of detail, such as if one were to examine a halftone newspaper photograph under a microscope. With the direct method, the greater the degree of myopia, the higher the magnification of the fundus image and the smaller the field of view. In very high myopes, the field of view with the direct instrument becomes very limited. High cylindric errors strongly and adversely affect the image of direct ophthalmoscopy because the high magnification of the system also magnifies the effects of refractive errors on the image. With the indirect method, the lower magnification minimizes this effect. Furthermore, the condensing lens can be tilted slightly to overcome astigmatic aberrations. Examination of the retinal periphery entails the travel of light obliquely through the cornea and lens, introducing cylindrical aberrations that are likewise problematic with the direct ophthalmoscope and easily overcome with the indirect.
Conference papers on the topic "Peripheral Refraction"
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Calabuig, Alejandro, Ajay Pinate, Nikolai Suchkov, and Siegfried Wahl. "Model eye assessment by 3D fast-scanning peripheral refraction wavefront sensor." In Unconventional Optical Imaging III, edited by Marc P. Georges, Gabriel Popescu, and Nicolas Verrier. SPIE, 2022. http://dx.doi.org/10.1117/12.2621558.
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Ho, Arthur, Frederik Zimmermann, Andrew Whatham, Aldo Martinez, Stephanie Delgado, Percy Lazon de la Jara, and Padmaja Sankaridurg. "Change in peripheral refraction and curvature of field of the human eye with accommodation." In SPIE BiOS: Biomedical Optics, edited by Fabrice Manns, Per G. Söderberg, and Arthur Ho. SPIE, 2009. http://dx.doi.org/10.1117/12.812110.
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Tabernero, Juan, and Frank Schaeffel. "A new Fast Scanning Infrared Photoretinoscope to measure peripheral refraction as a function of accommodation." In Frontiers in Optics. Washington, D.C.: OSA, 2009. http://dx.doi.org/10.1364/fio.2009.jwc80.
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Арутюнян, А. Г. "О НЕКОТОРЫХ ВОПРОСАХ ИЗУЧЕНИЯ СОВРЕМЕННОГО МУЗЫКАЛЬНОГО ФОЛЬКЛОРА." In Proceedings of the XXIII International Scientific and Practical Conference. RS Global Sp. z O.O., 2020. http://dx.doi.org/10.31435/rsglobal_conf/25112020/7245.
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The modern stage in the development of ethnomusicology is marked by the emergence of large-scale fundamental research. However, the problems of ethnomusicology are essentially not discussed in them, being peripheral for the authors. In this regard, it seems timely to analyze the refraction of ideas and methods of ethnomusicology in the research of scientists - representatives of various regional scientific centers and schools. The lack of interest in the study of modern processes and dynamics of culture is partly due to objective circumstances. Scientists do not always have collections of materials collected in previous periods of the development of science. However, it should be noted that such a trend is characteristic of ethnomusicology, while linguists, for example, are constantly studying and monitoring the transformation of the everyday, scientific language, studying the languages of corporate and information communities, new forms of written culture.
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Smith, George, and David A. Atchison. "Correcting peripheral refractive errors with ophthalmic lenses." In Vision Science and its Applications. Washington, D.C.: OSA, 2000. http://dx.doi.org/10.1364/vsia.2000.mb3.
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Yoshida, Kenji, Tomoya Adachi, Isao Kataoka, Hiroyuki Horiki, Akira Yoneya, Toshimitsu Kaji, and Kiyoshi Horii. "Hydrodynamic Behavior of Swirling Liquid Film Flow on Rotating Disc." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45184.
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Experimental and analytical studies have been carried out on the hydrodynamic behavior of swirling liquid film flow on a rotating disc. Film flow formation and swirling waves on the liquid film were analyzed through observation using high speed video. Liquid film thickness was measured using the Laser refraction method and compared with prediction. The rotating disc is 200 mm in diameter and was made of Silicon (Silicon wafer in industrial use). The rotating speed is up to 100 rad/sec (2000 rotations per min.) Water is supplied to the center of the disc at a flow rate of 8.3 × 10−6 m3/s (500 cc/min). The film flow is divided into three regimes depending upon rotating speed. For the lower rotating speed (up to 10 rad/sec), formation of liquid film flow is incomplete and some part of the peripheral region of the disc is not completely covered by liquid film. For the intermediate rotating speed (15–25 rad/sec), laminar film flow covered the whole disc. Furthermore, there are swirling waves on the liquid film. This wave is considered to be a continuity wave arising at the center portion of disc due to the water flow rate variation form the nozzle. Wave propagation speed and behavior of these swirling waves were well explained by the theory of continuity wave. For the high rotating speed (more than 30 rad/sec), the liquid film flow changed its flow regime from laminar flow to turbulent flow. The estimated film Reynolds number at transition is about 1200 which is consistent with turbulent flow transition for pipe flow and film flow on non-rotating surface. Three dimensional turbulent waves were observed on this turbulent liquid film. The behavior of such three dimensional turbulent waves were quite random in time and space. Measured film thicknesses ranged from 50 to 300 micron. Film thickness and its fluctuation decreased as the rotation speed of disc increased and distance from disc center increased. The analysis was made on the film thickness based on the force balance between shear stress and centrifugal force acting on the film. The predicted film thickness agreed well with the measured value.
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Coughlan, Mark F., Conor J. Sheil, and Alexander V. Goncharov. "A young eye model to investigate the influence of a gradient-index lens on peripheral refractive errors." In Frontiers in Optics. Washington, D.C.: OSA, 2020. http://dx.doi.org/10.1364/fio.2020.jm6b.17.
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Lu, Yuan, Joseph Katz, and Andrea Prosperetti. "Generation and Transport of Bubbles in Intense Ultrasonic Fields." In ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72286.
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This paper examines cavitation phenomena generated by a 500 kHz, high-intensity focused ultrasonic (HIFU) beam, with pressure amplitude in the focal zone of up to 19 atm, in quiescent water and at the exit of a jet. The pressure field and cavitation are visualized using high-speed digital in-line holography. The spatial distribution of the acoustic pressure is determined form the variations in the water density and refractive index. A partial standing wave is generated by the reflection of the sound from the wall of the test chamber. Several cavitation phenomena are observed. At low to moderate sound levels, bubbly layers form in the pressure nodes of the standing wave, in the periphery of the focal zone. At high sound levels, clouds of vapor bubbles are generated in the antinodes, and migrate in the direction of the acoustic beam at speeds in the 1–4 m/s range. Both the cloud size and velocity oscillate, with the size peaking in the nodes and the velocity in the antinodes. A model for the cloud dynamics shows that the periodic velocity variation is dominated by the balance between the primary Bjerknes force and the drag. The secondary Bjerknes force involving interactions among the bubbles within the cloud is a likely cause for the size oscillations.
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Tsuritani, Hiroyuki, Toshihiko Sayama, Yoshiyuki Okamoto, Takeshi Takayanagi, Kentaro Uesugi, and Takao Mori. "Nondestructive Evaluation of Thermal Fatigue Crack Propagation in Sn-Ag-Cu Solder Joints by Synchrotron Radiation X-Ray Micro-Tomography." In ASME 2009 InterPACK Conference collocated with the ASME 2009 Summer Heat Transfer Conference and the ASME 2009 3rd International Conference on Energy Sustainability. ASMEDC, 2009. http://dx.doi.org/10.1115/interpack2009-89155.
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An X-ray micro-tomography system called SP-μCT, which has a spatial resolution of 1 μm, has been developed in SPring-8, the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied to the nondestructive evaluation of micro-crack propagation appearing as thermal fatigue damage in lead-free solder joints. The observed specimens include two typical micro-joint structures by Sn-3.0wt%Ag-0.5wt%Cu lead-free solder. The first is an FBGA (Fine pitch Ball Grid Array) joint specimen in which an LSI package is connected to a substrate by solder bumps 360 μm in diameter, while the second is a chip joint specimen in which chip type resistors 1.6 mm in length and 0.8 mm. in width are mounted on a substrate. A thermal cycle test was carried out, and the specimens were picked up at fixed cycle numbers. The same solder joints were observed repeatedly using SP-μCT at beamline BL20XU in SPring-8. An X-ray energy of 29.0 keV was selected to obtain CT (Computed Tomography) images with high contrast among some components, and a refraction-contrast imaging technique was also applied to the visualization of fatigue cracks in the solder joints. In the FBGA type specimens, fatigue cracks appeared at the periphery of the interfaces between the solder and the UBM (Under Bump Metallization) on the LSI package. As the thermal cycle proceeds, the cracks propagate gradually to the inner region of the solder bumps in the vicinity of the interface. On the basis of the three-dimensional crack images, the fatigue crack propagation lifetime was accurately estimated by means of the average crack propagation rate. On the other hand, in the chip joint specimens, fatigue cracks appeared and propagated through the thin solder layer between the chip and substrate. In contrast to the FBGA specimen, many small voids roughly 5 to 10 μm in length were formed in the solder layer. The important observed fact is that these voids deform and connect to each other due to the thermal cyclic loading prior to crack propagation. Consequently, the obtained CT images clearly show the process of crack propagation due to the thermal cyclic loading of the same solder joint. In contrast, such information has not been obtained, whatsoever by industrially employed X-ray CT systems.
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Miorini, Rinaldo L., Huixuan Wu, David Tan, and Joseph Katz. "Three-Dimensional Structure and Turbulence Within the Tip Leakage Vortex of an Axial Waterjet Pump." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-06052.
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The flow structure and dynamics of turbulence are investigated by means of three-dimensional stereo particle image velocimetry (Stereo-PIV) measurements within the tip leakage vortex (TLV) of an axial waterjet pump rotor. Both the blades and casing of the pump are transparent and their optical refractive indices are matched with that of the pumped fluid, providing unobstructed optical access to the sample area without image distortion. Data are acquired on selected meridional planes in the rotor passage as well as in three-dimensional domains obtained by stacking closely-spaced planes situated within the rotor passage. Presented data have been sampled in one of these 3D regions, at 67% of the blade tip chordlength. All components of velocity and vorticity are calculated, together with the whole strain-rate and Reynolds stress tensors. The entire set of contributors to the turbulence production-rate is also available. The TLV and associated flow structures are completely 3D and change significantly along the blade tip chordwise direction. The vortex originates from the rollup of a multi-layered tip leakage flow, and propagates within the rotor passage towards the neighboring blade. Because of layered backflow rollup, vorticity entrained in the TLV is convected along different paths and re-oriented several times within the vortex. As a result, the TLV consists of a core surrounded by a tube of three-dimensional vorticity that wraps around it helically. Propagation of tip leakage backflow into the passage and subsequent TLV rollup also cause flow separation at the casing endwall with ejection of boundary layer vorticity that is finally entrained into the outer perimeter of the TLV. This complex TLV flow dominates the tip region of the rotor and involves non-uniform distributions of strain-rate and Reynolds stresses resulting in well-defined peaks of turbulence production-rate. For instance, turbulence is produced locally both at the flow contraction point near the region of aforementioned endwall separation and in the shear layer that connects the vortex with the suction side corner of the blade tip. The spatial inhomogeneity of turbulent kinetic energy (TKE) distribution within the TLV, and the mismatch between locations of TKE and production-rate peaks can be explained by analyzing the 3D mean flow advection of turbulence, for example from the region of endwall boundary layer separation towards the outer region of the TLV. In addition to being spatially non-uniform, turbulence is also anisotropic in both the shear layer and periphery of the TLV. Conversely, turbulence is intense and relatively isotropic near the TLV core, as well as monotonically increasing along the vortex centerline. This trend cannot be described solely in terms of local production of turbulence; it must also involve slow turbulence dissipation associated with the meandering of relatively large-size, interlaced vortex filaments in the TLV core region.