| Abstract: | Because the growth of the eys is considered to be complex by the age of 13 of 14 years, many vision scientists and practitioners have believed that myopia having its onset in the lated teen or early adult years is due to refractive component changes other than axial elongation. During the past several years, five studies of the refrative components in early adult-onset myopia, as compared to those in emmetropia and youth-onset myopia, have been reported. Three of these studies include only cross-sectional data, whereas two have provided longitudinal data. The results of these studies, taken together, leave no doubt that early adult-onset mypoia occurs, as does youth-onset myopia, as a result of an uncompensated increase in vitreous chamber depth. Many studies, including two to the five studies reviewed here, have provided evidence that corneal steepening occurs prior to or consequent with the development of mypoia. The role of corneal steeping is particularly well illustrated by evidence that an increase in the ration between axial length and corneal radius (the axial length/corneal radius ration) appears to be a risk factor for the developement of myopia. None of the studies cited here supplies evidence for a form of myopia that is caused by an increase in corneal power or lens power in the absence of vitreous chameber elongation. |
