The human optic system is a imperfect system. The difference between real image quality focused on the retina and ideal image quality is called wavefront ablation. Lower order aberrations could be easily corrected by spectacles or lasik laser surgery, But higher order aberrations are not able to be corrected freely. If we could do this, our vision acuity will reach to 2.0 or better.

There are some basic knowledge about it as follows:
1. We usually use RMS(the root mean square) and Zernike coefficients(7 steps 35 coefficients) to express aberrations.
2. Z, C, and (0,1,2,3,4,5,6, stands for 7steps)
see below

3. HOA, LOA
HOA: higher order aberrations
LOA: lower order aberrations
4. some basic nouns
spheric, coma, trefoil, tilting, astigmatism and so on
5. Myopia, hyperopia and astigmatism we usually meet in common life are lower order aberraitons, and could be corrected easily by spectacles.