Chromatic dependence of first-order optical properties of the eye
- Authors: Evans, Tanya
- Date: 2015
- Subjects: Optical properties , Chromatic dispersion , Optometry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/17506 , uj:15892
- Description: Abstract: Many first-order optical properties depend on chromatic dispersion and, hence, on frequency of light. The purpose of this theoretical study is to investigate the dependence of first-order optical properties of model eyes on frequency. In this study we are purposefully not concerned with subjective measurements. Instead, definitions are obtained that are general for optical systems that have astigmatic and decentred elements, and then simplified for Gaussian systems. In linear optics the transference is a matrix that is a complete representation of the effects of the system on a ray traversing it. Almost all of the familiar optical properties of the system can be obtained from the transference. From the transference S we obtain the four fundamental properties namely dilation A, disjugacy B, divergence C and divarication D, submatrices of S. Transferences are symplectic and do not define a linear space. Linear spaces are amenable to statistical analyses and therefore a number of mappings to linear spaces are investigated, including the Cayley and logarithmic mappings to Hamiltonian space and the four characteristic matrices. In each case, the individual entries of the transform are studied for their dependence on frequency and then the chromatic dependence relationship between the entries is compared graphically. , M.Phil. (Optometry)
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- Authors: Evans, Tanya
- Date: 2015
- Subjects: Optical properties , Chromatic dispersion , Optometry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/17506 , uj:15892
- Description: Abstract: Many first-order optical properties depend on chromatic dispersion and, hence, on frequency of light. The purpose of this theoretical study is to investigate the dependence of first-order optical properties of model eyes on frequency. In this study we are purposefully not concerned with subjective measurements. Instead, definitions are obtained that are general for optical systems that have astigmatic and decentred elements, and then simplified for Gaussian systems. In linear optics the transference is a matrix that is a complete representation of the effects of the system on a ray traversing it. Almost all of the familiar optical properties of the system can be obtained from the transference. From the transference S we obtain the four fundamental properties namely dilation A, disjugacy B, divergence C and divarication D, submatrices of S. Transferences are symplectic and do not define a linear space. Linear spaces are amenable to statistical analyses and therefore a number of mappings to linear spaces are investigated, including the Cayley and logarithmic mappings to Hamiltonian space and the four characteristic matrices. In each case, the individual entries of the transform are studied for their dependence on frequency and then the chromatic dependence relationship between the entries is compared graphically. , M.Phil. (Optometry)
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Lens internal curvature effects on age-related eye model and lens paradox
- Giovanzana, Stefano, Evans, Tanya, Pierscionek, Barbara
- Authors: Giovanzana, Stefano , Evans, Tanya , Pierscionek, Barbara
- Date: 2017
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/245913 , uj:25480 , Citation: Giovanzana, S. & Evans, T. 2017. Lens internal curvature effects on age-related eye model and lens paradox.
- Description: Abstract: The gradient index (GRIN) model is the most accurate way to represent the eye lens which, because of its growth mode, is a lamellar, shell-like structure. The GRIN is thought to provide optical properties that counteract age-related changes in curvature that would otherwise create an increasingly myopic eye: the so-called lens paradox. This article investigates how fine-tuning the refractive index and the internal curvatures of the lenticular indicial contours may prevent the ageing eye from becoming myopic. A system matrix approach is applied for analysis of a shell model with 200 shells to obtain the paraxial characteristics of the eye model.
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- Authors: Giovanzana, Stefano , Evans, Tanya , Pierscionek, Barbara
- Date: 2017
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/245913 , uj:25480 , Citation: Giovanzana, S. & Evans, T. 2017. Lens internal curvature effects on age-related eye model and lens paradox.
- Description: Abstract: The gradient index (GRIN) model is the most accurate way to represent the eye lens which, because of its growth mode, is a lamellar, shell-like structure. The GRIN is thought to provide optical properties that counteract age-related changes in curvature that would otherwise create an increasingly myopic eye: the so-called lens paradox. This article investigates how fine-tuning the refractive index and the internal curvatures of the lenticular indicial contours may prevent the ageing eye from becoming myopic. A system matrix approach is applied for analysis of a shell model with 200 shells to obtain the paraxial characteristics of the eye model.
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Chromatic properties of astigmatic eyes
- Evans, Tanya, Harris, William F.
- Authors: Evans, Tanya , Harris, William F.
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/273659 , uj:29156 , Citation: Evans, T. & Harris, W.F. 2018. Chromatic properties of astigmatic eyes. African Vision and Eye Health, 77(1), a435. https://doi. org/10.4102/aveh.v77i1.435 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: Chromatic differences in power, refractive compensation, position and magnification have been described in the literature for Gaussian eyes. Aim: This article explores these definitions and defines chromatic properties for eyes that have astigmatic and decentred or tilted elements. Setting: Linear optics. Methods: The optical model is linear optics and makes use of the ray transference T. Results: Results are presented as either 2 × 2 matrices or 2 × 1 vectors. The dependence of the chromatic properties on the position of an object and the limiting aperture is explored and results are presented as independent of, or dependent on, object and aperture position. Apertures undergo both longitudinal and transverse shifts in position. The results are general and apertures may include pupils or pinholes, either surgically inserted inside the eye or held in front of the eye. Numerical examples are provided for Le Grand’s four-surface eye and an arbitrary astigmatic heterocentric four-surface eye.
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- Authors: Evans, Tanya , Harris, William F.
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/273659 , uj:29156 , Citation: Evans, T. & Harris, W.F. 2018. Chromatic properties of astigmatic eyes. African Vision and Eye Health, 77(1), a435. https://doi. org/10.4102/aveh.v77i1.435 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: Chromatic differences in power, refractive compensation, position and magnification have been described in the literature for Gaussian eyes. Aim: This article explores these definitions and defines chromatic properties for eyes that have astigmatic and decentred or tilted elements. Setting: Linear optics. Methods: The optical model is linear optics and makes use of the ray transference T. Results: Results are presented as either 2 × 2 matrices or 2 × 1 vectors. The dependence of the chromatic properties on the position of an object and the limiting aperture is explored and results are presented as independent of, or dependent on, object and aperture position. Apertures undergo both longitudinal and transverse shifts in position. The results are general and apertures may include pupils or pinholes, either surgically inserted inside the eye or held in front of the eye. Numerical examples are provided for Le Grand’s four-surface eye and an arbitrary astigmatic heterocentric four-surface eye.
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Linear optics of eyes with pinhole apertures
- Authors: Evans, Tanya
- Date: 2018
- Subjects: Intraocular lenses , Physiological optics , Ophthalmology
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/399815 , uj:33340
- Description: Abstract : , D.Phil. (Optometry)
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- Authors: Evans, Tanya
- Date: 2018
- Subjects: Intraocular lenses , Physiological optics , Ophthalmology
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/399815 , uj:33340
- Description: Abstract : , D.Phil. (Optometry)
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