A protective, but inconsistent association between myopia and a decreased risk of diabetic retinopathy (DR) has been suggested in several studies. However, it is unclear whether the structural, or the refractive components of myopia; or both, is the main contributor to this protective relationship. This paper provides a comprehensive review of existing evidence on the association between myopia, and its structural (axial length [AL], anterior chamber depth [ACD]) and refractive (lens biometry and corneal curvature [CC]) components, with DR. 11 studies consisting of 7230 subjects from 1960 to April 2012, were reviewed. A longer AL was the only variable associated with a lower risk and severity of DR. Therefore, the available evidence suggests that AL is the main contributor to the protective influence of myopia on DR observed in earlier studies. Further investigations are now needed to determine the mechanisms by which AL protects against DR.