Abstract: The eye astigmatism mainly includes corneal astigmatism and intraocular astigmatism (i.e., the lens astigmatism). Both the anterior and posterior corneal surfaces contribute to the total corneal astigmatism.In most eyes, the posterior corneal steep meridian is aligned vertically and approximately has   0.3D astigmatism. The asphericity of the posterior corneal surface decreas significantly with age and is not purely governed by that of the anterior surface. With aging, the anterior surface astigmatism shows a significant trend toward against-the-rule while the posterior corneal astigmatism shows toward with the rule, but the change of posterior astigmatism is smaller. The ratio of the anterior-to-posterior corneal radius also has a negative correlation with age. The compensating effects of the posterior corneal surface on anterior corneal astigmatism decreased with  age. Therefore the posterior corneal astigmatism often leads to partially decrease of total corneal astigmatism in young adults while often adds to total corneal astigmatism in older individuals. Omission of the posterior corneal astigmatism may lead to significant inaccuracies in estimating  the total corneal astigmatism. There is a clear clinical need to measure the posterior corneal surface for calculating the total corneal astigmatismin in cataract refractive surgery.   (Int Rev Ophthalmol, 2015, 39：170-174)