Keratometric variation during pregnancy and postpartum
- Klaassen, Donald Gregory Istvan
- Authors: Klaassen, Donald Gregory Istvan
- Date: 2012-08-27
- Subjects: Eye - Accommodation and refraction , Eye - Accommodation and refraction - Statistical methods , Eye - Accommodation and refraction - Data processing , Pregnancy
- Type: Thesis
- Identifier: uj:3234 , http://hdl.handle.net/10210/6644
- Description: M.Phil. , Keratometric readings on three subjects were taken both during pregnancy and postpartum. One subject was visually non-compensated and did not require refractive correction, one was a contact lens wearer and one had undergone radial keratotomy. Twenty readings were taken by means of an automatic keratometer on each eye, morning and afternoon, every fortnight. The recent matrix method of optometric statistical analysis was employed and the results graphically compared and analysed. Findings indicate diurnal variations including variation in corneal curvature and variance through the course of normal pregnancy. Most evident was an increase in keratometric variation in all three subjects at the time of birth and a substantial decrease in corneal refractive power in the subject who had before undergone radial keratotomy. This result may have far-reaching implications on the long term prognosis of refractive surgery especially for females of child bearing age. Outliers representing transient increases in curvature were most common in the vertical meridian (indicating possible lid interaction), while the presence of bimodal distributions suggests a sensitivity of the automatic keratometer to changes in head posture.
- Full Text:
- Authors: Klaassen, Donald Gregory Istvan
- Date: 2012-08-27
- Subjects: Eye - Accommodation and refraction , Eye - Accommodation and refraction - Statistical methods , Eye - Accommodation and refraction - Data processing , Pregnancy
- Type: Thesis
- Identifier: uj:3234 , http://hdl.handle.net/10210/6644
- Description: M.Phil. , Keratometric readings on three subjects were taken both during pregnancy and postpartum. One subject was visually non-compensated and did not require refractive correction, one was a contact lens wearer and one had undergone radial keratotomy. Twenty readings were taken by means of an automatic keratometer on each eye, morning and afternoon, every fortnight. The recent matrix method of optometric statistical analysis was employed and the results graphically compared and analysed. Findings indicate diurnal variations including variation in corneal curvature and variance through the course of normal pregnancy. Most evident was an increase in keratometric variation in all three subjects at the time of birth and a substantial decrease in corneal refractive power in the subject who had before undergone radial keratotomy. This result may have far-reaching implications on the long term prognosis of refractive surgery especially for females of child bearing age. Outliers representing transient increases in curvature were most common in the vertical meridian (indicating possible lid interaction), while the presence of bimodal distributions suggests a sensitivity of the automatic keratometer to changes in head posture.
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Refractive and keratometric measurements: departures from and transformations towards normality.
- Authors: Blackie, Caroline Adrienne
- Date: 2014-02-11
- Subjects: Eye - Accommodation and refraction - Data processing , Optometry - Data processing
- Type: Thesis
- Identifier: uj:3864 , http://hdl.handle.net/10210/9231
- Description: M.Phil. (Optometry) , Different representations of dioptric power and their relative coordinate systems are summarised. The transition matrices required to switch from one coordinate system to another are provided. Three sets of data are analysed; a sample of 205 refractions, a sample of 205 keratometric readings and a sample of 790 autorefractive excesses of 790 autorefractions over 790 subjective refractions. Brief mention is made of emmetropisation. In the event that such a driving force exists, the possible effects on the distributional characteristics of refractive error are noted. Normality and the assessment thereof are discussed qualitatively and quantitatively. The univariate marginal and multivariate joint distributions .of the samples are examined using the coordinate system introduced by Deal and Toop (1993): their vector is represented by d=(d 1 d 2 d3)~ Departure from normality is determined in three ways; assessment of the linearity of the chi-square probability plots, measures of skewness and measures of kurtosis. Marginal normal probability plots are included for completeness. The statistical procedures and some of the theory involved in the implementation of these techniques are described briefly to assist in the interpretation of the distribution analysis. Marginal transformations are employed to improve the normality of the marginal distributions in an attempt to reduce the multivariate departure from normality. Power transformations and shifted power transformations are described and applied to the data.
- Full Text:
- Authors: Blackie, Caroline Adrienne
- Date: 2014-02-11
- Subjects: Eye - Accommodation and refraction - Data processing , Optometry - Data processing
- Type: Thesis
- Identifier: uj:3864 , http://hdl.handle.net/10210/9231
- Description: M.Phil. (Optometry) , Different representations of dioptric power and their relative coordinate systems are summarised. The transition matrices required to switch from one coordinate system to another are provided. Three sets of data are analysed; a sample of 205 refractions, a sample of 205 keratometric readings and a sample of 790 autorefractive excesses of 790 autorefractions over 790 subjective refractions. Brief mention is made of emmetropisation. In the event that such a driving force exists, the possible effects on the distributional characteristics of refractive error are noted. Normality and the assessment thereof are discussed qualitatively and quantitatively. The univariate marginal and multivariate joint distributions .of the samples are examined using the coordinate system introduced by Deal and Toop (1993): their vector is represented by d=(d 1 d 2 d3)~ Departure from normality is determined in three ways; assessment of the linearity of the chi-square probability plots, measures of skewness and measures of kurtosis. Marginal normal probability plots are included for completeness. The statistical procedures and some of the theory involved in the implementation of these techniques are described briefly to assist in the interpretation of the distribution analysis. Marginal transformations are employed to improve the normality of the marginal distributions in an attempt to reduce the multivariate departure from normality. Power transformations and shifted power transformations are described and applied to the data.
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The excess of objective automatic refraction over subjective clinical refraction : methods of analysis and results
- Authors: Malan, Dawid Johannes
- Date: 2014-03-18
- Subjects: Eye - Accommodation and refraction - Data processing , Optical properties , Optometric practice
- Type: Thesis
- Identifier: uj:4407 , http://hdl.handle.net/10210/9753
- Description: M.Sc. (Optometry) , The difference between objective automatic and subjective clinical refraction is studied using new statistical techniques. The question, by how much the two refraction techniques differ, is investigated by subtracting the subjective refraction finding from the auto refractory finding and then examining the distribution of the difference or excess as it will be called here. Computerized procedures were developed to automate mathematical and statistical methods of analysis. The methods were applied to two different samples: one of patients visiting an ordinary optometric practice (the clinical sample) and the other of children refracted in a screening program (the sample of school children) . The clinical sample, consisting of mainly older patients, is examined first. The difference between the autorefractor and subjective findings is studied and described. This difference could be used to compare different types of auto refractors assuming that the subjective refraction is correct. For the purpose of this study, however, the results of eight autorefractors are grouped together, combining left and right eyes, to serve as basis for studying the older population. The study shows that on the average there is no clinically significant excess. This means that there is on average no clinically significant difference between the automatic and clinical refraction for this population.
- Full Text:
- Authors: Malan, Dawid Johannes
- Date: 2014-03-18
- Subjects: Eye - Accommodation and refraction - Data processing , Optical properties , Optometric practice
- Type: Thesis
- Identifier: uj:4407 , http://hdl.handle.net/10210/9753
- Description: M.Sc. (Optometry) , The difference between objective automatic and subjective clinical refraction is studied using new statistical techniques. The question, by how much the two refraction techniques differ, is investigated by subtracting the subjective refraction finding from the auto refractory finding and then examining the distribution of the difference or excess as it will be called here. Computerized procedures were developed to automate mathematical and statistical methods of analysis. The methods were applied to two different samples: one of patients visiting an ordinary optometric practice (the clinical sample) and the other of children refracted in a screening program (the sample of school children) . The clinical sample, consisting of mainly older patients, is examined first. The difference between the autorefractor and subjective findings is studied and described. This difference could be used to compare different types of auto refractors assuming that the subjective refraction is correct. For the purpose of this study, however, the results of eight autorefractors are grouped together, combining left and right eyes, to serve as basis for studying the older population. The study shows that on the average there is no clinically significant excess. This means that there is on average no clinically significant difference between the automatic and clinical refraction for this population.
- Full Text:
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