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.
- Full Text:
Short-term keratometric variation in the human eye
- Authors: Cronje- Dunn, Sonja
- Date: 2014-02-10
- Subjects: Eye - Accommodation and refraction - Statistical methods
- Type: Thesis
- Identifier: uj:3726 , http://hdl.handle.net/10210/9106
- Description: M.Phil. (Optometry) , Previous studies of corneal and keratometric variation used incomplete or incorrect statistical methods. For the first time, proper multivariate statistical methods are applied to evaluate short-term keratometric variation in human eyes. Keratometric variation is represented graphically by means of stereo-pair scatter plots, trajectories of change in dioptric power, ellipsoidal confidence regions for mean dioptric power, as well as meridional profiles. Quantitative expressions of variation are given in terms of mean values, variance-covariance matrices and volumes of 95% distribution ellipsoids. Manual and automatic keratometry is compared, both on a steel ball and on an eye. It appears that the automatic keratometer exhibits less variation than the manual keratometer....
- Full Text:
- Authors: Cronje- Dunn, Sonja
- Date: 2014-02-10
- Subjects: Eye - Accommodation and refraction - Statistical methods
- Type: Thesis
- Identifier: uj:3726 , http://hdl.handle.net/10210/9106
- Description: M.Phil. (Optometry) , Previous studies of corneal and keratometric variation used incomplete or incorrect statistical methods. For the first time, proper multivariate statistical methods are applied to evaluate short-term keratometric variation in human eyes. Keratometric variation is represented graphically by means of stereo-pair scatter plots, trajectories of change in dioptric power, ellipsoidal confidence regions for mean dioptric power, as well as meridional profiles. Quantitative expressions of variation are given in terms of mean values, variance-covariance matrices and volumes of 95% distribution ellipsoids. Manual and automatic keratometry is compared, both on a steel ball and on an eye. It appears that the automatic keratometer exhibits less variation than the manual keratometer....
- Full Text:
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