Investigation Of A New Method Of Subjective Refraction
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Investigation Of A New Method Of Subjective Refraction
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Author : Lary G. McAtee
language : en
Publisher:
Release Date : 1957
Investigation Of A New Method Of Subjective Refraction written by Lary G. McAtee and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1957 with Eye categories.
Clinical Validation Of A Fast Binocular Subjective Refraction Algorithm
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Author : Rocío García García
language : en
Publisher:
Release Date : 2017
Clinical Validation Of A Fast Binocular Subjective Refraction Algorithm written by Rocío García García and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
The purpose of this study is to investigate a new algorithm to perform an automated non-cycloplegic refraction in adults. In order to carry on the study fifty healthy subjects were measured twice (test-retest) with the new automated subjective refraction (ASR) method and with the conventional clinician subjective refraction (CSR) procedure. Objective refraction (OR) is also measured with the autorefractor Grand Seiko WAM-5500. The new subjective refraction procedure is mainly based on the root finding bisection algorithm and on the Euclidean distances among power vectors. The algorithm is implemented on a computer that is synchronized with a custom-made motorized phoropter. Main outcome measures: spherical equivalent (M) and Jackson cross-cylinder (J0 and J45). Repeatability is assessed with the within-subject standard deviation (Sw) and agreement is assessed with the limits of agreement. The results showed that the first implementation of the algorithm is a potential novel method of performing non-cycloplegic subjective refraction in adults without clinician support. Although it presents some limitations that warrant further research and it still should be tested in a wider population in terms of age, refraction and different ocular conditions, this method can contribute to improve the access to primary eye care services in developing countries.
New Method Of Subjective Refraction Involving Identical Technics In Static And Dynamic Tests
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Author : Matthew Luckiesh
language : en
Publisher:
Release Date : 1940
New Method Of Subjective Refraction Involving Identical Technics In Static And Dynamic Tests written by Matthew Luckiesh and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1940 with categories.
Lens Based Technologies To Study Accommodation And Refraction
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Author : Carles Otero Molins
language : ca
Publisher:
Release Date : 2018
Lens Based Technologies To Study Accommodation And Refraction written by Carles Otero Molins and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
A visual stimulus can be presented in free space or through lens-based systems. Interestingly, it has been reported many times in the past that some subjects have poorer accommodative responses when optically stimulated, with no aparent reason. However, this limitation has not precluded the use of lens-based systems in ophthalmic devices, virtual reality displays or research setups, probably because it is outweighed by some advantages such as the computer-control of the focal plane of the stimuli. Under this general context, the objective of this thesis is to apply lens-based technologies (from computer-controlled electró-optical lenses to Badal Systems) to study accommodation and refraction. The methodology of this thesis is structured in 6 studies. The first three studies investigate the response of the accommodative system when optically-stimulated with a Badal optometer. The remaining 3 studies take advantage of electro-optical varifocal systems to investigate new methodologies related to the automated subjective refraction and the accommodative facility test. Concretely, the fourth study is a clinical validation of a new automated refraction algorithm and is the only study thatworks specifically on eye¿s refraction. The fifth and sixth studies use an electro-optical liquid lens to present a repeated step-like stimulus at different accommodative distances. The fifth study validates a new accommodative facility test that integrates both the far and near accommodative facility testwith random changes of accommodative stimulus and, the sixth study explores how the predictability of a stimulus affects the accommodation dynamics. The results of the first three studies show that previously reported differences in accommodative response when using lens-based methods compared to free space viewing may be explained by the effect of other factors such as the refractive error or field of view rather than the method to stimulate accommodation. It is also shown that the most accurate accommodative responses are obtained for fields between 8o and 10o which suggests that there may be an optimum peripheral retinal image size for accommodation stimulation. Also, it is shown that the only factor that in isolation significantly affects the accuracy of the accommodative responses is the type of refractive error. And finally, it is also shown that the accuracy of the accommodation response generally improves with a 2-dimensional stimulus with apparent depth cues and simulated out-of-focus blur in a relatively large field of view. Even though these conditions may not be adequate for all individuals, they can be used to improve the overall visual comfort in those virtual reality systems that use a varifocal optical system to change the focal plane of a 2-dimensional surface or visual simulators. The results of the study 4 show the first implementation of a potential novel method of performing non1cycloplegic subjective refraction in adults without clinician suport. Although this method has some limitations thatwarrant further research and it should be tested in a wider population in terms of age4 refraction and different ocular conditions4 it is precise and more accurate than objective refraction methods and it has the potential to be incorporated in novel lens1based technologies to improve primary eye care services in developing countries. And finally, the last two studies showed also the first implementation of a new accommodative facility test that integrates both the far and near accommodative facility testwith random changes of accommodative stimulus. This new methodology is a faster test than performing both the near and far accommodative tests and it provides more information than conventional accommodative facility tests. Additionally these two studies showed that the prediction operator does not exist in accommodation and the unpredictability of the stimulus does not affect the accommodation dynamics.
A Comparative Study Of The Relationship Of Four Clinical Subjective Refraction Methods With The Laser Subjective Refraction Method
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Author : Michael Hatfield
language : en
Publisher:
Release Date : 1966
A Comparative Study Of The Relationship Of Four Clinical Subjective Refraction Methods With The Laser Subjective Refraction Method written by Michael Hatfield and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1966 with Eye categories.
Evaluation Of Meridional Refraction Techniques
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Author : Jennifer Nicole Chlam
language : en
Publisher:
Release Date : 2022
Evaluation Of Meridional Refraction Techniques written by Jennifer Nicole Chlam and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Eye categories.
Purpose: To evaluate subjective and objective refraction methods based on oriented grating targets. Methods: Subjective and objective meridional refraction was performed on 21 young normally-sighted subjects. Both the subjective and objective refraction methods were performed with and without cycloplegia. Targets for refraction were Gaussian-attenuated square wave gratings at four orientations (00, 450, 900, 1350), with a bar width equal to 2x the subject’s threshold letter size (i.e. for 20/20, 10 minarc/bar width, or 3 cycles/degree). The endpoint of the refraction was the spherical lens power to achieve maximum grating contrast. Lens power at each grating orientation was determined twice, and the sphero-cylindrical correction was derived from the dioptric power for those four orientations. The objective refractive correction was based on a measurement of ocular aberrations. In both the cyclopleged and non-cyclopleged conditions, aberration coefficients were transformed from those for the measured pupil diameter to a 3.5 mm pupil. As in the subjective method, the dioptric power to maximize grating contrast was found for each orientation, and the sphero-cylindrical correction was derived from those powers. Visual acuity was measured with the result of each refraction using an adaptive, maximum-likelihood method. Visual acuities with the result of the cycloplegic refraction were measured at a second visit, at least one day after the refraction visit. Results: Intra-session repeatability of M, J0, and J45 of dry subjective refraction was not significantly different from those found in a previous similar study (2-sample Kolmogorov-Smirnov test, p>.10). The standard deviations of M, J0, and J45 were 0.20D, 0.29D, and 0.22D, respectively, and is comparable to repeatability of standard methods of subjective refraction. Agreement between the different types of refraction was evaluated by examining differences in M, J0, J45, and in total dioptric power. Wet and dry objective refraction agreed most closely: the median dioptric difference in 3D dioptric power space was 0.16D. Pairwise comparison across all refraction methods had median values of at least twice that value. Mean visual acuity achieved with the results of each type of refraction ranged from logMAR -0.15 for dry subjective refraction to -0.19 for dry objective refraction. Differences in visual acuity between all four refraction methods were not significantly different (2-way ANOVA, p>0.5). Conclusions: In this sample of young normal subjects, these refraction methods based on oriented meridional targets yield results with repeatability similar to published values for standard methods of refraction. In future studies, we will examine the performance of these refraction methods in more highly aberrated eyes. We hypothesize that the subjective task could be simpler, and therefore more consistent, with these oriented targets, as the judgement is primarily of grating contrast, and is less confounded by changes in contrast and phase at multiple simultaneous orientations.
The Pediatric Eye Exam Quick Reference Guide Office And Emergency Room Procedures
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Author : Zhu-Tam, Lily
language : en
Publisher: IGI Global
Release Date : 2022-02-18
The Pediatric Eye Exam Quick Reference Guide Office And Emergency Room Procedures written by Zhu-Tam, Lily and has been published by IGI Global this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022-02-18 with Medical categories.
There is a need for comprehensive books that provide crucial information in a clear and direct manner, particularly in the medical field. Currently, there are limited resources available to students and clinicians that provide step-by-step procedures with pictures on how to examine the eye in the pediatric population. The Pediatric Eye Exam Quick Reference Guide: Office and Emergency Room Procedures is a clinical procedure book to provide step-by-step pediatric eye care examination techniques and is an important addition to the field of eye care. The chapters are written by leading pediatric optometrists and ophthalmologists in the field. Years of academic and clinical experiences from schools of optometry, hospital-based eye care, and private practice are all presented in a user-friendly format with clinical pearls and insights that will help any clinician perform a pediatric eye exam easily and efficiently. Covering a range of critical topics such as pupil examination, visual field testing, refraction, and ocular emergencies and providing pictures, it is ideal for all students, residents, academicians, trainers, and novel and seasoned clinicians who are interested in learning how to examine a pediatric patient and staying on top of the latest pediatric eye care procedures.
Meridional Subjective Refraction With Dynamic Optometer Instrumentation
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Author : Denis Humphreys
language : en
Publisher:
Release Date : 1974
Meridional Subjective Refraction With Dynamic Optometer Instrumentation written by Denis Humphreys and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1974 with Eye categories.
Comparative Analysis Of Fotometer Vs Subjective Refraction Data In A Clinical Population
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Author : Darya Inozemtseva
language : en
Publisher:
Release Date : 2014
Comparative Analysis Of Fotometer Vs Subjective Refraction Data In A Clinical Population written by Darya Inozemtseva and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with Eye categories.
Uncorrected refractive errors (URE) such as hyperopia, myopia, astigmatism and presbyopia are the main causes of visual impairment in the world, affecting all ages, ethnicities, and both genders. We investigated the validity of an alternative refractive method that does not rely on electricity, extensive training or high cost to determine URE in areas of the world with limited eye care. The refractive error of 60 patients of monte Cristi (Dominican Republic) was measured using a portable Badal optometer (fotometer). The results were compared to the refractive errors measured by a standard optometric refraction by experienced optometrists using portable phoropters. The mean spherical equivalent and mean spheres values measured with the focometer were within 0.50D from those obtained in the standard refraction. The focometer values were less positive and reflected less prevalence of astigmatism than the standard refraction. The study indicates that the focometer is moderately useful in determining refractive errors in developing communities.
Clinical Visual Optics
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Author : Arthur George Bennett
language : en
Publisher: Butterworth-Heinemann
Release Date : 1989
Clinical Visual Optics written by Arthur George Bennett and has been published by Butterworth-Heinemann this book supported file pdf, txt, epub, kindle and other format this book has been release on 1989 with Medical categories.