Optical Axial Length Research Articles

Optic disc oval ness, refractive error and axial length of Hong Kong Chinese

Myopic crescent, refractive error and axial length were previously investigated in Hong Kong Chinese subjects. The myopic crescent was found to correlate with axial length and myopic refraction. In this study, three groups of Hong Kong Chinese with different degrees of myopia were assessed for optic disc ovalness, refractive error and axial length. The axial length was significantly correlated with the degree of myopia, indicating that the myopia was axial in nature. The regression line shows that 0.44 mm of axial elongation would give about one dioptre of increase in myopia. The elliptical ratio of the optic disc was defined as the maximal disc diameter divided by the minimal disc diameter. All three groups showed an oval disc with vertical axis greater and an increased ovalness for the high myopic group with an elliptical ratio from 1.11 in low myopia to 1.29 in high myopia. There is a small amount (about four degrees) of temporal rotation of this vertical oval orientation, which is independent of the amount of myopia. This result shows an association between axial elongation of the globe and optic disc ovalness, in addition to the previously described temporal myopic crescent. Therefore, in myopic subjects, a vertically oval disc may be associated with a myopic refraction rather than glaucoma.

Relationship between morphometric optic disc parameters, sex and axial length.

Optic disc correlations were evaluated in normal eyes by means of computer-aided morphometry. Two hundred and thirty-five subjects (144 women and 91 men) entered the study. One eye per patient was randomly chosen for statistical analysis. Disc area (P < 0.05) and axial length (P < 0.0001) were statistically different between sexes. There was a correlation between axial length and both disc area (r for females = 0.55, P < 0.00001; r for males = 0.35, P < 0.0007) and refraction (r for females = 0.40, P < 0.00001; r for males = 0.50, P < 0.00001). The main findings of this investigation were that disc area is greater in male than in female eyes (thus clinically confirming the Ishi's and Quigley's previous observations of autopsy eyes) on the basis of axial length difference between the two sexes, and that disc size correlated with axial length. Disagreements in disc measurements reported in previous studies may be caused by differences in the male/female ratios of their samples.