Traditional refraction still serves as the basis for eyeglass lens prescriptions. This is the result of a two-part process:
Objective refraction: The refractive errors of the eye are first estimated objectively using retinoscopy or autorefraction followed by
Subjective refraction: A prescription is subjectively refined by an eye doctor, allowing the patient to compare their vision through trial lenses, using either a refractor head or trial frame.
Subjective refraction uses different eyeglass lens powers to correct refractive errors (such as myopia, hyperopia or astigmatism) in the eye, which are called low order aberrations (LOAs).
However, due to variations in pupil size with varying light conditions, other types of aberrations occur, affecting the quality of vision. These affect the final quality of vision experienced by the wearer. This is referred to as high order aberrations, HOAs (e.g. coma, trefoil, and spherical aberration).