Abstract
M.Phil.
Using newly developed statistical analysis methods for refractive error this study examines
the difference between autorefraction and subjective refraction and how it is related to
age. The term autorefractive excess refers to the amount obtained by subtracting the
subjective refraction from the autorefraction. The clinical sample consisted of five groups of fifty subjects each. The subjects in group 1 ranged in age from 1 to 10 years, group 2 from 11 to 20 years, group 3 from 21 to 30 years, group 4 from 31 to 40 years and group 5 from 41 years and older. Only one examiner (the author) and one autorefractor (Allergan-Humphrey 580) were used. The study found that there was a difference between the mean autorefractive excesses for the different age groups and that the difference between autorefraction and subjective refraction was statistically significant in both the left and the right eyes of all age groups. Left and right eyes exhibited similar behavior. The autorefractive excess for both the left and the right eyes together of group 1 was approximately -0.25/-0.18 x180 in conventional and (-0.25 0.00 -0.43)' in h-notation. The autorefractive excess increases by approximately (0.10 0.00 0.10)' per decade. There is an astigmatic component of approximately -0.18 x180 in both eyes of all age groups. Approximately 60% of the subjects had sphere-equivalent strengths of autorefractive excesses of under 0.50 D. Therefore 60% of subjects might be content with a prescription given from the autorefractor reading. Approximately 50% of subjects had cylinderequivalent strengths of autorefractive excesses of under 0.50 D.