High axial length/corneal radius ratio as a risk factor in the development of myopia.

Results of refractive component measurements have shown that eyes of Melanesian schoolchildren living in Vanuatu, almost all of whom are emmetropic, have relatively short axial lengths and relatively flat corneas in comparison to emmetropic eyes of children examined in England. Evidence is presented to suggest that the relation between the axial length of the eye and corneal radius--the axial length/corneal radius (AL/CR) ratio--may be a useful predictor of future refractive state. Mean axial length/corneal radius ratios for 6- to 19-year-old Melanesian school children were found to be 2.88 for boys and 2.86 for girls, as compared to mean AL/CR ratios for 6- to 19-year-old British schoolchildren of 3.05 for boys and 3.04 for girls. It is proposed that an eye having a high AL/CR ratio is at risk for the development of myopia, and that such an eye has maintained its state of emmetropia by virtue of a compensatory flattening of the crystalline lens. In order to test the proposition that an increase in axial length occurs as a precursor to the development of myopia, a prospective longitudinal study of a group of 6- to 7-year-old schoolchildren is proposed.