Abstract
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...