For an image to be seen clearly, the horizontal and vertical rays of light that reach the eye's optical system must form a focal point on the retina.
Astigmatism is a refractive defect whereby the horizontal and vertical rays of light have different points of focus on the retina. It can be associated with both myopia and hypermetropia.
Causes of astigmatism
In the majority of cases, it is due to a lack of symmetry (toricity) in the cornea which gives it an oval or elliptical shape that impedes proper focus on objects.
The cause of this irregularity is usually genetically determined, although it can also arise as a consequence of trauma, after an eye operation like cataract surgery, due to cornea ulcers or dislocation of intraocular lenses, etc.
An eye with astigmatism sees distorted images given that it cannot focus properly neither far nor near. Objects may appear much longer or wider, sometimes letters and numbers get confused and, on occasions, shadows may even appear.
The most common signs and symptoms of astigmatism are:
Interesting fact: It is believed that the Italian painter Amedeo Modigliani may have suffered from astigmatism due to the distorted images in his works.
Astigmatism cannot be prevented by can be detected with a full eye exam.
In childhood, an uncorrected astigatism may cause lazy eye (amblyopia). This situation can be avoided by correcting it with glasses before the age of 8. For this reason, it is essential to have an eye check-up, even in the absence of any symptoms.
A symptom of astigmatism is blurred vision both in both farsight and nearsight.
A high astigmatism that develops over time in association with myopia in particular may indicate the presence of a pathological change in the cornea like keratoconus.
The current treatment options for correcting astigmatism are:
Frequently asked questions
A dioptre is a unit of lens power and its positive or negative power expresses the refractive power of a lens. The positive sign corresponds to the converging lens and the negative power corresponds to the diverging power. Converging lenses are perfect way of correcting hypermetropia, prebyopia and other astigmatisms.
Diverging lenses are demarcated by two surfaces, one of them being concave. They have the ability to separate the rays that pass through them and make them "diverge". They are used in refraction to make up for the myopia errors and some types of astigmatism.