The axial length in patients with unilateral congenital ptosis was prospectively examined in this study and lengths compared to fellow eyes. Thirty-seven patients included 24 male and 13 females with mean age of 17.8 ±16.3 years. Right ptosis was present in 15 and left ptosis in 22 cases. There was no significant difference in mean axial lengths between ptotic and fellow eyes. Only two patients (both adults) showed axial length differences of >0.67mm.Mean cylinder power was larger on the ptosis side than fellow eye but there was no significant difference for spherical power. The authors conclude that congenital ptosis may have little impact on axial length and the risk of axial myopia induced anisometropic amblyopia is low in unilateral congenital ptosis.