(1) by reason categories: 1) corneal astigmatism: corneal front surface due to the different curvature of the meridian, the most common level of vertical curvature than those larger (and often pressure on the eyelid), and therefore also its fake oakley sunglasses refractive power was stronger than the horizontal meridian , a difference of about 0.25D value about, is physiological, a living rational astigmatism. Astigmatism can be acquired due to corneal disease (such as keratoconus, keratitis, etc.) or service caused by surgery, mostly for irregular astigmatism. 2) residual astigmatism: refractive other factors may be caused by abnormalities such as bending the lens, tilted position, causing inconsistent ministries refractive index. 3) Full astigmatism: corneal astigmatism and residual astigmatism above sum.

 (2) whether the vertical meridian by the strength of the main fake oakleys intersection (corrective lenses available) Classification: 1) irregular laser: a different refractive power of the meridian, no certain rules, even if the distortion is not correct because the same meridian, the refractive index of not one, its refractive power is also different. It is such degree of astigmatism can not be quantitative. Multiple lesions caused by the cornea, the lens can not be corrected. 2) rule astigmatism: two main meridian (ie, the refractive power of the largest and smallest refractive power meridian) orthogonal to each other, the astigmatism correction lenses available, called the rule astigmatism. Strong rule astigmatism to follow the main radial cheap oakley sunglasses direction is divided into: patients with astigmatism cis (cis-rule astigmatism, astigmatism cis-law): strong in the vertical direction by the main meridian. Counter-examples astigmatism (against the rule astigmatism, astigmatism against the law): strong in the horizontal direction by the main meridian. Oblique astigmatism: strong in the oblique direction of the main meridian person.