Limitations in existing studies of the epidemiological aspects of refraction are attributed to both technical and statistical procedures. Early influences of ocular parameters on refraction are identified accordingly as prematurity and may or may not be involved. Attention is paid to familial and genetic influences, and infants and toddlers are examined as a group separate from schoolchildren and teenagers, who are likely to have experienced significant periods of near work. The effects of sex and geographical distribution are considered both for younger and older age ranges. Special attention is paid to anisometropia, which is shown-apparently for the first time-to increase appreciably among presbyopes. The connection between refractive errors and ocular pathologies is reviewed, and possible means of preventing early onset myopia are examined. Presbyopia is addressed with reference to its geographical distribution and hypothetical links to accommodation insufficiency.