Astigmatism is actually an optical defect in which the person’s vision is blurred due to the inability of the eye optics to focus an object into a sharp focused image on the back of their retina. The term Astigmatism comes from Greek (a-) meaning “without” and (stigma) “a mark, spot, puncture”.
Astigmatism frequently is present with other vision conditions such as myopia and hyperopia and the specific cause of astigmatism is unknown. It is usually present from birth but can decrease or worsen over time as child grows. Astigmatism is a very common vision defect and most people have some element of astigmatism. But since slight amounts of astigmatism don’t affect vision, they don’t require treatment.
There are two common types of astigmatism (irregular & regular). The first irregular astigmatism is often caused by a scattering in the the crystalline leans or a corneal scar which cannot be corrected by average spectacle lenses but can be contact lenses. The second type is regular astigmatism and occurs from either the cornea or crystalline lens but can be corrected by a toric lens. The surface of a toric lens resembles a football which gives raised optical shape.
The difference in degree of curvature refraction of the 2 diferent focal points in different plans relates to degree of refractive error experienced. In a patentient affected by astigmatism an image may appear focused in the vertical(tangential) plane but not the horizontal(sagittal) plane. Astigmatism typically causes patients difficulties in seeing fine detail and in some cases vertical lines such as walls may appear to be tilted.
The astigmatism can often by corrected by:
- hard contact lenses
- compensating optic contact lenses
- cylindrical lenses
- refractive surgery
Higher amounts of astigmatism can cause other symptons such as squinting, fatigue, headaches, blurry vision, asthenopia.
There are a range of tests used by optometrists and ophthalmologists during eye exams which can determine the presence of astigmatism and to assess the axis and amount of astigmatism. During an eye exam to measure the curvature of the flattest and steepest meridians on the cornea’s top surfer a keratometer maybe used. But to obtain a more accurate representation Corneal topography may also be used by the doctor.
Where the patient has a very high degree of astigmatism, or suffers from irregular astigmatism a refraction technique involving a stenopaic slit maybe used to determine specific meridians.
Astigmatism can be corrected by a surgeon reshaping the cornea using a highly focused laser beam of light. Two of the most commonly used treatment procedures are photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
What is the Cornea?
- if the cornea is too flat
- if the corena is irregular in shape
- if the cornea is too step