Surfaces of constant visual acuity in symmetric dioptric power space
- Authors: Rubin, Alan
- Date: 2012-08-28
- Subjects: Visual acuity , Eye -- Accommodation and refraction , Multivariate analysis , Refraction
- Type: Thesis
- Identifier: uj:3290 , http://hdl.handle.net/10210/6695
- Description: D.Phil. , Visual acuity and refractive state probably are the two most basic or fundamental quantities that concern optometry, ophthalmology and vision science. Both of these variables are complicated and their mathematical and statistical use in research and other activities has been poorly understood. During particularly the last decade, modern statistical multivariate methods have become available to optometry and ophthalmology and this has assisted with the understanding of concepts such as refractive state (and its underlying nature, namely, dioptric power). It is now possible to transform measurements of refractive state from the conventional notation that is commonly used in the fields of optometry and ophthalmology to an orthodox mathematical form that can be understood by scientists and mathematicians. With this matrix form of refractive state it then is possible to use appropriate methods of linear algebra and multivariate statistics. Other theoretical approaches and analytical procedures or methods also have become accessible or have been developed recently as a consequence of this significant shift in thought as regards the fundamental nature of dioptric power. On the other hand, the scientific understanding of visual acuity (that is, the measurement of the resolving ability of the eye) perhaps has been somewhat neglected. Certainly there has been an abundance of research involving visual acuity and there also has been discussion concerning some of the difficulties that become apparent when measuring or attempting to interpret results from studies involving visual acuity. Visual acuity, unlike refractive state, can be represented by means of a single number and thus univariate, rather than multivariate, statistical methods are appropriate. And, of course, univariate statistics is less complicated than the multivariate form. But there are various difficulties with the understanding and researching of visual acuity. Some of these difficulties are relatively simple and thus can be solved more easily. For example, visual acuity measurements can be obtained from charts designed according to a logarithmic scale, or measurements from other charts can be transformed to a logarithmic scale. And thereby the ordinal nature of the basic or more common visual acuity scale is avoided and certain statistical methods become available that otherwise would not be possible. But more fundamentally visual acuity probably cannot truly be considered without the subject from which the measurement is obtained and, more particularly, the refractive state of the eye concerned. So the visual acuity and refractive state of an eye, perhaps, should be more appropriately regarded as a unitary concept that ideally should not be separated into two distinct parts. Thus to truly understand the relationship between visual acuity and refractive state we need to understand the 4-dimensional (mathematical) nature of the particular relationship involved. It follows then that the relationship between visual acuity and refractive state is a multivariate problem and that multivariate methods are best suited to its consideration. If we then begin to take into account other variables such as age or the ocular health, or say, iris aperture diameter of the eye then the complicated multivariate nature of the situation becomes even more obvious. In this dissertation an attempt is made to consider the possibilities of a modern multivariate approach to studies involving visual acuity, refractive state and other variables. The methodology used in this dissertation differs from those used in previous studies involving visual acuity and refractive state and other related variables. For example, here Jackson crossed cylinders are used extensively to produce dioptric blur or defocus in experimental subjects (positive and negative spheres also are used to a more limited extent). In previous published studies spherical or, less commonly, cylindrical lenses were used instead. Another difference between this dissertation and previous research studies is that the visual stimulus that the subjects observed, generally but not always, was a meridionally-independent or non-directional letter 0. The reasons for this choice is explained in the dissertation but in other research an enormous variety of visual stimuli have been used depending upon the interests of the researchers. But even more essentially this dissertation differs significantly from that of previous studies in terms of the manner in which the various experimental and other results (for instance, that from earlier researchers such as HB Peters) are presented. Entirely new, and largely unpublished, methods are used in many parts of this dissertation that probably represent a paradigmatic transition in understanding of visual acuity and its relation to refractive state. New terms such as decompensation and accompensation surfaces of constant visual acuity and antistigmatic ellipses are defined herein. (Briefly, one imagines starting from a state of compensation (of the refractive state of, say, an eye viewing a stimulus).
- Full Text:
- Authors: Rubin, Alan
- Date: 2012-08-28
- Subjects: Visual acuity , Eye -- Accommodation and refraction , Multivariate analysis , Refraction
- Type: Thesis
- Identifier: uj:3290 , http://hdl.handle.net/10210/6695
- Description: D.Phil. , Visual acuity and refractive state probably are the two most basic or fundamental quantities that concern optometry, ophthalmology and vision science. Both of these variables are complicated and their mathematical and statistical use in research and other activities has been poorly understood. During particularly the last decade, modern statistical multivariate methods have become available to optometry and ophthalmology and this has assisted with the understanding of concepts such as refractive state (and its underlying nature, namely, dioptric power). It is now possible to transform measurements of refractive state from the conventional notation that is commonly used in the fields of optometry and ophthalmology to an orthodox mathematical form that can be understood by scientists and mathematicians. With this matrix form of refractive state it then is possible to use appropriate methods of linear algebra and multivariate statistics. Other theoretical approaches and analytical procedures or methods also have become accessible or have been developed recently as a consequence of this significant shift in thought as regards the fundamental nature of dioptric power. On the other hand, the scientific understanding of visual acuity (that is, the measurement of the resolving ability of the eye) perhaps has been somewhat neglected. Certainly there has been an abundance of research involving visual acuity and there also has been discussion concerning some of the difficulties that become apparent when measuring or attempting to interpret results from studies involving visual acuity. Visual acuity, unlike refractive state, can be represented by means of a single number and thus univariate, rather than multivariate, statistical methods are appropriate. And, of course, univariate statistics is less complicated than the multivariate form. But there are various difficulties with the understanding and researching of visual acuity. Some of these difficulties are relatively simple and thus can be solved more easily. For example, visual acuity measurements can be obtained from charts designed according to a logarithmic scale, or measurements from other charts can be transformed to a logarithmic scale. And thereby the ordinal nature of the basic or more common visual acuity scale is avoided and certain statistical methods become available that otherwise would not be possible. But more fundamentally visual acuity probably cannot truly be considered without the subject from which the measurement is obtained and, more particularly, the refractive state of the eye concerned. So the visual acuity and refractive state of an eye, perhaps, should be more appropriately regarded as a unitary concept that ideally should not be separated into two distinct parts. Thus to truly understand the relationship between visual acuity and refractive state we need to understand the 4-dimensional (mathematical) nature of the particular relationship involved. It follows then that the relationship between visual acuity and refractive state is a multivariate problem and that multivariate methods are best suited to its consideration. If we then begin to take into account other variables such as age or the ocular health, or say, iris aperture diameter of the eye then the complicated multivariate nature of the situation becomes even more obvious. In this dissertation an attempt is made to consider the possibilities of a modern multivariate approach to studies involving visual acuity, refractive state and other variables. The methodology used in this dissertation differs from those used in previous studies involving visual acuity and refractive state and other related variables. For example, here Jackson crossed cylinders are used extensively to produce dioptric blur or defocus in experimental subjects (positive and negative spheres also are used to a more limited extent). In previous published studies spherical or, less commonly, cylindrical lenses were used instead. Another difference between this dissertation and previous research studies is that the visual stimulus that the subjects observed, generally but not always, was a meridionally-independent or non-directional letter 0. The reasons for this choice is explained in the dissertation but in other research an enormous variety of visual stimuli have been used depending upon the interests of the researchers. But even more essentially this dissertation differs significantly from that of previous studies in terms of the manner in which the various experimental and other results (for instance, that from earlier researchers such as HB Peters) are presented. Entirely new, and largely unpublished, methods are used in many parts of this dissertation that probably represent a paradigmatic transition in understanding of visual acuity and its relation to refractive state. New terms such as decompensation and accompensation surfaces of constant visual acuity and antistigmatic ellipses are defined herein. (Briefly, one imagines starting from a state of compensation (of the refractive state of, say, an eye viewing a stimulus).
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Short-term variation of refractive behaviour in human eyes
- Authors: Rubin, Alan
- Date: 2014-04-14
- Subjects: Eye - Accommodation and refraction , Optical properties
- Type: Thesis
- Identifier: uj:10593 , http://hdl.handle.net/10210/10117
- Description: M.Phil. (Optometry) , An investigation of the nature of variability or variation of refractive behaviour (in a sample of universi ty students studying optometry) is described. Measurements of refractive behaviour were obtained by means of autorefraction. This study was based upon multivariate methods of statistical analysis which have only recently become available in optometric science. Variation is examined using both quali tative and quanti tative methods including stereo-pair scatter plots, confidence and distribution ellipsoids, trajectories of change of dioptric power, meridional profiles, testing of hypotheses on means and variance-covariance, and graphs which represent the type of uniform variation in a 2-dimensional plane known as the i)-plane. These methods are of great assistance in developing an understanding of the nature of the variation shown, as well as, in developing an awareness of the distribution or spread of the population from which the sample was drawn. Analyses of variability of refractive behaviour on both an artificial, or test eye, and on several individual human eyes are also described. The significance of some important aspects of variabili ty of refractive behaviour involving normality and departures therefrom (such as results from outliers) are discussed and illustrated by means of examples. Distributions were found in which more than one mode was present (polymodal or multimodal behaviour). Distributions were also observed to vary from having an almost spherical spread of measurements (of refractive behaviour) to having a spindle or rod-like spread of measurements instead...
- Full Text:
- Authors: Rubin, Alan
- Date: 2014-04-14
- Subjects: Eye - Accommodation and refraction , Optical properties
- Type: Thesis
- Identifier: uj:10593 , http://hdl.handle.net/10210/10117
- Description: M.Phil. (Optometry) , An investigation of the nature of variability or variation of refractive behaviour (in a sample of universi ty students studying optometry) is described. Measurements of refractive behaviour were obtained by means of autorefraction. This study was based upon multivariate methods of statistical analysis which have only recently become available in optometric science. Variation is examined using both quali tative and quanti tative methods including stereo-pair scatter plots, confidence and distribution ellipsoids, trajectories of change of dioptric power, meridional profiles, testing of hypotheses on means and variance-covariance, and graphs which represent the type of uniform variation in a 2-dimensional plane known as the i)-plane. These methods are of great assistance in developing an understanding of the nature of the variation shown, as well as, in developing an awareness of the distribution or spread of the population from which the sample was drawn. Analyses of variability of refractive behaviour on both an artificial, or test eye, and on several individual human eyes are also described. The significance of some important aspects of variabili ty of refractive behaviour involving normality and departures therefrom (such as results from outliers) are discussed and illustrated by means of examples. Distributions were found in which more than one mode was present (polymodal or multimodal behaviour). Distributions were also observed to vary from having an almost spherical spread of measurements (of refractive behaviour) to having a spindle or rod-like spread of measurements instead...
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Ocular aberrations and wavefront aberrometry : a review
- Unterhorst, Holly A., Rubin, Alan
- Authors: Unterhorst, Holly A. , Rubin, Alan
- Date: 2016
- Subjects: Aberrometry
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/92205 , uj:20200 , Citation: Unterhorst, H.A & Rubin, A. 2015. Ocular aberrations and wavefront aberrometry: a review. African Vision Eye Health, 74(1), 6 pages. http://dx.doi. org/10.4102/aveh.v74i1.21
- Description: Abstract: Refer to full text to view abstract
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- Authors: Unterhorst, Holly A. , Rubin, Alan
- Date: 2016
- Subjects: Aberrometry
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/92205 , uj:20200 , Citation: Unterhorst, H.A & Rubin, A. 2015. Ocular aberrations and wavefront aberrometry: a review. African Vision Eye Health, 74(1), 6 pages. http://dx.doi. org/10.4102/aveh.v74i1.21
- Description: Abstract: Refer to full text to view abstract
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Oscillatory thresholds and foveal and macular thickness using coherence tomography
- Authors: Humphreys, Amy , Rubin, Alan
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/281215 , uj:30256 , Citation: Humphreys A, Rubin A. Oscillatory thresholds and foveal and macular thickness using coherence tomography. Afr Vision Eye Health. 2018;77(1), a448. https://doi. org/10.4102/aveh.v77i1.448 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: Technology is evolving and advancing rapidly as is evident in the ophthalmic and optometric fields with the development of new equipment and software programs that assist in the examination of patients and diagnoses of ocular diseases. The new vision psychophysical software for measurements of oscillatory sensitivity (OS) is a recently developed program that can be used to assess visual ability at the fovea by establishing oscillatory thresholds (OT) and it is therefore necessary to assess the reliability and repeatability of this new software...
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- Authors: Humphreys, Amy , Rubin, Alan
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/281215 , uj:30256 , Citation: Humphreys A, Rubin A. Oscillatory thresholds and foveal and macular thickness using coherence tomography. Afr Vision Eye Health. 2018;77(1), a448. https://doi. org/10.4102/aveh.v77i1.448 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: Technology is evolving and advancing rapidly as is evident in the ophthalmic and optometric fields with the development of new equipment and software programs that assist in the examination of patients and diagnoses of ocular diseases. The new vision psychophysical software for measurements of oscillatory sensitivity (OS) is a recently developed program that can be used to assess visual ability at the fovea by establishing oscillatory thresholds (OT) and it is therefore necessary to assess the reliability and repeatability of this new software...
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A review of higher order aberrations of the human eye
- Suliman, Ayesha, Rubin, Alan
- Authors: Suliman, Ayesha , Rubin, Alan
- Date: 2019
- Subjects: Higher order aberrations , Lower order aberrations , Aberrometry
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/403807 , uj:33852 , Citation: Suliman A, Rubin A. A review of higher order aberrations of the human eye. Afr Vision Eye Health. 2019;78(1), a501. https://doi. , ISSN: (Online) 2410-1516
- Description: Abstract: Background: This literature review is part of a research study for aberration-correcting soft contact lenses, where wavefront aberrometry was utilised. Aim: This study was conducted as part of a postgraduate research degree by the first author with particular relevance to spherical aberrations in relation to myopia and soft contact lenses, both aberration control and non-control types. Setting: This study reports on a literature review of higher order aberrations. Methods: A comprehensive review of various databases was performed, including PubMed and Google Scholar in terms of aberration control contact lenses and particular customised contact lenses for compensation of spherical aberration in myopia, was performed. Results: Wavefront sensing and Zernike polynomials are increasingly used in optometry and ophthalmology to quantify the wavefronts for an optical system such as the eye, using either lower order (LOA) or higher order aberrations (HOA). Although other mathematical methods are available, zero, 1st and 2nd orders of the Zernike polynomial expansion are LOA. Defocus ( 2 Z0 ) and astigmatism ( − and 2 2 2 Z Z2 ) are 2nd-order modes that usually can be corrected by clinicians using ordinary sphero-cylindrical compensations such as spectacle lenses. Until recently, only LOA were easily correctable by clinicians in optometry and ophthalmology. Higher order aberrations are those modes in the third radial order, n = 3 and higher, which in the past were not correctable. However, HOA contribute to only about 7% of retinal image quality and often go unnoticed by individuals, although in some instances, for example, with keratoconus or after refractive surgery, such aberrations can become more problematic. Today, new treatments are available via specially designed or customised (to an individual) rigid or soft contact lenses that are claimed to reduce or eliminate HOA such as spherical aberration ( 4 Z0 ). Conclusion: Although such specially designed or customised contact lenses have some effect on HOA, there are conflicting reports and so further investigation of this intriguing aspect remains necessary.
- Full Text:
- Authors: Suliman, Ayesha , Rubin, Alan
- Date: 2019
- Subjects: Higher order aberrations , Lower order aberrations , Aberrometry
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/403807 , uj:33852 , Citation: Suliman A, Rubin A. A review of higher order aberrations of the human eye. Afr Vision Eye Health. 2019;78(1), a501. https://doi. , ISSN: (Online) 2410-1516
- Description: Abstract: Background: This literature review is part of a research study for aberration-correcting soft contact lenses, where wavefront aberrometry was utilised. Aim: This study was conducted as part of a postgraduate research degree by the first author with particular relevance to spherical aberrations in relation to myopia and soft contact lenses, both aberration control and non-control types. Setting: This study reports on a literature review of higher order aberrations. Methods: A comprehensive review of various databases was performed, including PubMed and Google Scholar in terms of aberration control contact lenses and particular customised contact lenses for compensation of spherical aberration in myopia, was performed. Results: Wavefront sensing and Zernike polynomials are increasingly used in optometry and ophthalmology to quantify the wavefronts for an optical system such as the eye, using either lower order (LOA) or higher order aberrations (HOA). Although other mathematical methods are available, zero, 1st and 2nd orders of the Zernike polynomial expansion are LOA. Defocus ( 2 Z0 ) and astigmatism ( − and 2 2 2 Z Z2 ) are 2nd-order modes that usually can be corrected by clinicians using ordinary sphero-cylindrical compensations such as spectacle lenses. Until recently, only LOA were easily correctable by clinicians in optometry and ophthalmology. Higher order aberrations are those modes in the third radial order, n = 3 and higher, which in the past were not correctable. However, HOA contribute to only about 7% of retinal image quality and often go unnoticed by individuals, although in some instances, for example, with keratoconus or after refractive surgery, such aberrations can become more problematic. Today, new treatments are available via specially designed or customised (to an individual) rigid or soft contact lenses that are claimed to reduce or eliminate HOA such as spherical aberration ( 4 Z0 ). Conclusion: Although such specially designed or customised contact lenses have some effect on HOA, there are conflicting reports and so further investigation of this intriguing aspect remains necessary.
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Preliminary demographics for patients with keratoconus attending a university-based clinic in Johannesburg, South Africa
- Chetty, Elizabeth, Rubin, Alan
- Authors: Chetty, Elizabeth , Rubin, Alan
- Date: 2019
- Subjects: South Africa , Keratoconus , Demographics
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/399451 , uj:33293 , Citation: Chetty E, Rubin A. Preliminary demographics for patients with keratoconus attending a university-based clinic in Johannesburg, South Africa. Afr Vision Eye Health. 2019;78(1), a472. https://doi.org/10.4102/ aveh.v78i1.472
- Description: Abstract: Keratoconus (KC) is a visually debilitating disease if left undiagnosed and untreated. Early intervention is necessary to ensure a good quality of life for those afflicted by the disease. Although much research has been done in other parts of the world, there is a paucity in the literature that describes the disease from a South African perspective. Aim: The aim of this study was to provide the demographics of KC patients attending a university-based contact lens clinic between January 2007 and December 2017...
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- Authors: Chetty, Elizabeth , Rubin, Alan
- Date: 2019
- Subjects: South Africa , Keratoconus , Demographics
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/399451 , uj:33293 , Citation: Chetty E, Rubin A. Preliminary demographics for patients with keratoconus attending a university-based clinic in Johannesburg, South Africa. Afr Vision Eye Health. 2019;78(1), a472. https://doi.org/10.4102/ aveh.v78i1.472
- Description: Abstract: Keratoconus (KC) is a visually debilitating disease if left undiagnosed and untreated. Early intervention is necessary to ensure a good quality of life for those afflicted by the disease. Although much research has been done in other parts of the world, there is a paucity in the literature that describes the disease from a South African perspective. Aim: The aim of this study was to provide the demographics of KC patients attending a university-based contact lens clinic between January 2007 and December 2017...
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The Cambridge Colour Test: Reliability of discrimination trivectors in colour space
- Hasrod, Nabeela, Rubin, Alan
- Authors: Hasrod, Nabeela , Rubin, Alan
- Date: 2019
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/398903 , uj:33229 , Citation: Hasrod N. & Rubin A. 2019. The Cambridge Colour Test: Reliability of discrimination trivectors in colour space. Afr Vision Eye Health. 2019;78(1), a451. https://doi.org/10.4102/ aveh.v78i1.451 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: The reliable assessment of colour discrimination has become increasingly important as some ophthalmic diseases and systemic conditions manifest themselves via acquired impairments of colour vision. The Cambridge Colour Test (CCT) is a computerised procedure, developed using the basic principles of traditional pseudoisochromatic plates to evaluate colour function or discrimination. Aim: The study investigated reliability of the CCT, with emphasis on the Trivector subtest, which measures thresholds along the three protan, deutan and tritan confusion lines to probe the sensitivity of the long, medium and short wavelength cones...
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- Authors: Hasrod, Nabeela , Rubin, Alan
- Date: 2019
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/398903 , uj:33229 , Citation: Hasrod N. & Rubin A. 2019. The Cambridge Colour Test: Reliability of discrimination trivectors in colour space. Afr Vision Eye Health. 2019;78(1), a451. https://doi.org/10.4102/ aveh.v78i1.451 , ISSN: 2410-1516 (Online) , ISSN: 2413-3183 (Print)
- Description: Abstract: The reliable assessment of colour discrimination has become increasingly important as some ophthalmic diseases and systemic conditions manifest themselves via acquired impairments of colour vision. The Cambridge Colour Test (CCT) is a computerised procedure, developed using the basic principles of traditional pseudoisochromatic plates to evaluate colour function or discrimination. Aim: The study investigated reliability of the CCT, with emphasis on the Trivector subtest, which measures thresholds along the three protan, deutan and tritan confusion lines to probe the sensitivity of the long, medium and short wavelength cones...
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A comparison of anterior and posterior central corneal powers in eyes with and without keratoconus
- Chetty, Elizabeth, Rubin, Alan
- Authors: Chetty, Elizabeth , Rubin, Alan
- Date: 2020
- Subjects: Keratoconus , Cornea , Multivariate analysis of dioptric power
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/460647 , uj:40999 , Citation: Chetty E, Rubin A. A comparison of anterior and posterior central corneal powers in eyes with and without keratoconus. Afr Vision Eye Health. 2020;79(1), a607. https:// , ISSN: (Online) 2410-1516
- Description: Abstract: Background: Keratoconus affects the anterior segment of the eye, which directly affects the refractive state of the eye. There are three components for the measurement of a corneal curvature or central corneal power (CCP) of the eye, namely, the power along the flat meridian, the power along the steep meridian and the axis of the flat meridian. Traditionally, CCP is analysed using univariate methods that processes each component separately; however, because of the trivariate nature of CCP, the use of multivariate methods and statistics may be beneficial. Aim: The aim of this study was to compare the short-term variation of the anterior and posterior CCP in eyes with and without keratoconus using multivariate methods of analysis. Setting: Data were extracted from a doctoral study by the first author. The group with keratoconus (KC) was obtained from patients attending a university-based contact lens clinic in Johannesburg, South Africa. Methods: A total of 28 eyes with KC and 28 eyes of 28 healthy control eyes without KC were included in this prospective quantitative study. Measurements were taken with the Oculus Pentacam (Wetzlar, Germany) and data related to the anterior and posterior CCP were analysed using multivariate methods and analysis. Results: For both KC and control groups, short-term variation of CCP of the anterior corneal surfaces was significantly greater than that for the posterior corneal surfaces. Whilst shortterm variation was similar for both corneal surfaces in the KC group, variation of the posterior corneal surfaces was significantly different from that of the anterior corneal surfaces for the control group. Conclusion: Multivariate analysis of short-term variation of CCP of both surfaces of the cornea in eyes with or without KC contributed towards a more complete understanding of the disease.
- Full Text:
- Authors: Chetty, Elizabeth , Rubin, Alan
- Date: 2020
- Subjects: Keratoconus , Cornea , Multivariate analysis of dioptric power
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/460647 , uj:40999 , Citation: Chetty E, Rubin A. A comparison of anterior and posterior central corneal powers in eyes with and without keratoconus. Afr Vision Eye Health. 2020;79(1), a607. https:// , ISSN: (Online) 2410-1516
- Description: Abstract: Background: Keratoconus affects the anterior segment of the eye, which directly affects the refractive state of the eye. There are three components for the measurement of a corneal curvature or central corneal power (CCP) of the eye, namely, the power along the flat meridian, the power along the steep meridian and the axis of the flat meridian. Traditionally, CCP is analysed using univariate methods that processes each component separately; however, because of the trivariate nature of CCP, the use of multivariate methods and statistics may be beneficial. Aim: The aim of this study was to compare the short-term variation of the anterior and posterior CCP in eyes with and without keratoconus using multivariate methods of analysis. Setting: Data were extracted from a doctoral study by the first author. The group with keratoconus (KC) was obtained from patients attending a university-based contact lens clinic in Johannesburg, South Africa. Methods: A total of 28 eyes with KC and 28 eyes of 28 healthy control eyes without KC were included in this prospective quantitative study. Measurements were taken with the Oculus Pentacam (Wetzlar, Germany) and data related to the anterior and posterior CCP were analysed using multivariate methods and analysis. Results: For both KC and control groups, short-term variation of CCP of the anterior corneal surfaces was significantly greater than that for the posterior corneal surfaces. Whilst shortterm variation was similar for both corneal surfaces in the KC group, variation of the posterior corneal surfaces was significantly different from that of the anterior corneal surfaces for the control group. Conclusion: Multivariate analysis of short-term variation of CCP of both surfaces of the cornea in eyes with or without KC contributed towards a more complete understanding of the disease.
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