Abstract
M.Phil.(Optometry)
The concept of contact lenses was conceived over 500 years ago and has now
evolved into a fundamental component of optometric practice. Soft contact lenses
have become a convenient, aesthetically pleasing and comfortable alternative to
spectacles that are becoming increasingly popular. The use of rigid contact lenses is
imperative in the management of conditions such as keratoconus due to spectacles
being insufficient in providing adequate vision.
Placing a contact lens onto the cornea is an invasive procedure. The contact
lens is a foreign body to the eye hence it is expected that the eye would react to that
foreign body. Literature has revealed that the general reactions of the eye to contact
lens wear are initial tearing, alteration of the tear layer and oedema due to reduced
oxygen transmission but these are just a few of the known consequences amongst the
multitude of the unknown consequences. What exactly goes on under a contact lens
remains an enigma which contact lens researchers have strived to uncover over the
past century. The consequence of contact lens wear is a vast area of research and can
best be investigated by focusing on one aspect at a time.
The aim of this study was to use dioptric power matrices and multivariate
statistics to explore the effects of both gas permeable and gas non-permeable rigid
contact lenses on corneal curvature. This study involves auto-keratometric
measurements of the corneal curvature before and after lens wear to establish if there
are any curvature changes induced by the contact lens. Keratometric data was
collected with an automated keratometer (Nidek ARK-700) and was analysed
correctly and completely using multivariate statistics.
This thesis presents the findings of a study done in an effort to establish the
short-term effects of rigid contact lens wear on keratometric behaviour by using
complete methods of multivariate statistical analysis. Twenty four subjects were
equally divided into three groups. One group wore polymethyl methacrylate (PMMA)
rigid lenses, another group wore rigid gas permeable (RGP) contact lenses and the
third group served as the control. The control group was included in the study to
establish a reference for normal diurnal changes in keratometric behaviour. Fifty autoii
keratometric measurements were taken before and immediately after three hours of
rigid contact lens wear for the experimental groups and 50 auto-keratometric
measurements were taken before and immediately after three hours of no lens wear
for the control group. Data collected was analysed using multivariate statistical
methods that in the past have been used infrequently in this area of research.