Such a refractive error as astigmatism gives blurred image as well, however no longer due to irregular ray focusing, but due to the structure of the cornea or the crystalline lens. Normally, both the cornea and the crystalline lens should have the form of a sphere. Should any irregularities exist on their surface - this is considered to be the anomaly. Irregular refracting surface gives rise to the condition when light rays going through it, deflect in different ways, and the image of the object is focused not in one but in several points on the retina. As a result a distorted and blurred image of the object is obtained.
Astigmatism mostly is inheritable.
For adequate definition of the degree of astigmatism and its axes in particular, meticulous computer examination is required, since tiniest little error may lead to complete glasses/ lenses intolerance and visual deterioration.
Astigmatism treatment includes the following methods:
- laser biostimulation (treatment of astigmatism-related amblyopia)
- spectacles and contact lens vision correction - currently this is the main treatment of astigmatism.
Surgical laser treatment of astigmatism also exists.
From the ophthalmologist's manual:
Astigmatism is one of the forms of refractive error, when in different meridians of the same eye there are different types of refraction or different degrees of the same refraction.
Astigmatism mostly depends on imperfection in the curvature of the corneal center. The anterior surface of the cornea does not represent spherical surface where all radii are equal, but the segment of a turning ellipsoid, where each radius has its own length. Therefore each meridian has its specific deflection, different from the adjacent meridian.
Astigmatism may also depend on unequal curvature of the surface of the crystalline lens.
Low degree of astigmatism is inherent in almost all eyes; if it has no affects on the vision acuity, it is considered a physiological condition and does not require correction. Otherwise astigmatism reduces vision, complicates work at a short distance, therefore requires correction. Astigmatism is treated by the use of cylindrical lenses. Preventive treatment of astigmatism and progressive keratikonus is provided using contact lenses (soft and rigid).