Objective To clarify the optical etiology of anisometropia by analyzing the difference in the optical components between the two eyes in anisometropia. Methods Ninety-one anisometropes with a spherical equivalent difference of ＞2.00 D were studied. Two groups were created based on the type of anisometropia: a hyperopic anisometropia group and a myopic anisometropia group. All eyes were examined for refraction and corneal curvature (CC) with a Topcon KR.8800 autor refractor (Japan). Anterior chamber depth (ACD), lens thickness (LT), vitreous chamber length (VCL) and axial length (AL) were measured by A-scan ultrasound (French Quantel 0459). Self-control analysis, multiple linear regression and partial correlation analysis were used to describe the optical differences in anisometropia. Results Only vitreous chamber length and axial length differed between the two eyes in anisometropia (tVCD=9.506, 3.654, P＜0.01; tAL=12.334, 3.447,P＜0.01). Multiple linear regression analysis found that corneal curvature and anterior chamber depth were not correlated with age (tcc=0.0491, P＞0.05; tACD=0.449, P＞0.05). The keratometry and anterior chamber depth of myopic anisometropia were greater than that of hyperopic (tK=4.600, P＜0.01; tACD=2.894, P＜0.01), while there was no difference in the thickness of the lens between the two groups (t=0.936, P＞0.05). The keratometry and anterior chamber depth of the two groups were not correlated with axial length (rCC=-0.177, -0.110, P＞0.05; rACD=-0.080, -0.041, P＞0.05), while lens thickness was correlated with axial length for the two groups (r=0.358, 0.296, P＜0.01). Vitreous chamber length was correlated with both refraction and axial length (r=0.975, 0.979, P＜0.01). Conclusion A change in vitreous chamber length is an underlying cause of anisometropia.