The use of autorefractors using the image-size principle in determining on-axis and off-axis refraction. Part 1: Analysis of optical principles of autorefractors.

For image-size principle autorefractors, simple equations describe the dependence of measured refraction on the height and angle of the instrument beam as it enters the eye and the angle of the light, reflected back from the retina, after it exits the eye. Further work will investigate the validity of such instruments for determining peripheral refraction.