Another recent follow-up study again had identified four novel loci for corneal astigmatism, with two also being novel loci for astigmatism: ZC3H11B (associated with axial length), NPLOC4 (associated with myopia), LINC00340 (associated with spherical equivalent refractive error) and HERC2 (associated with eye color). Acquired
Astigmatism may also occur following a cataract surgery or a corneal injury. Contraction of the scar due to wound or cataract extraction causes astigmatism due to flattening of the cornea in one direction. In keratoconus, progressive thinning and steepening of the cornea cause irregular astigmatism. Pathophysiology
Axis of the principal meridian
Regular astigmatism – principal meridians are perpendicular. (The steepest and flattest meridians of the eye are called principal meridians.) With-the-rule astigmatism – the vertical meridian is steepest (a rugby ball or American football lying on its side). Against-the-rule astigmatism – the horizontal meridian is steepest (a rugby ball or American football standing on its end). Oblique astigmatism – the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees. Irregular astigmatism – principal meridians are not perpendicular.In with-the-rule astigmatism, the eye has too much "plus" cylinder in the horizontal axis relative to the vertical axis (i.e., the eye is too "steep" along the vertical meridian relative to the horizontal meridian). Vertical beams of light focus in front (anterior) to horizontal beams of light, in the eye. This problem may be corrected using spectacles which have a "minus" cylinder placed on this horizontal axis.
Astigmatism is a type of refractive error due to rotational asymmetry in the eyes refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at night. Astigmatism often occurs at birth and can change or develop later in life. If it occurs in early life and is left untreated, it may result in amblyopia.The cause of astigmatism is unclear; however, it is believed to be partly related to genetic factors. The underlying mechanism involves an irregular curvature of the cornea or abnormalities in the lens of the eye. Diagnosis is by an eye examination, through objective and subjective refraction.Three treatment options are available: glasses, contact lenses, and surgery. Glasses are the simplest. Contact lenses can provide a wider field of vision. Refractive surgery permanently changes the shape of the eye.In Europe and Asia, astigmatism affects between 30 and 60% of adults. People of all ages can be affected by astigmatism. Astigmatism was first reported by Thomas Young in 1801. Signs and symptoms
Although astigmatism may be asymptomatic, higher degrees of astigmatism may cause symptoms such as blurred vision, double vision, squinting, eye strain, fatigue, or headaches. Some research has pointed to the link between astigmatism and higher prevalence of migraine headaches. Causes
Congenital
The cause of congenital astigmatism is unclear, however it is believed to be partly related to genetic factors.