A Brazilian study published in 2005 found that 34% of the students in one city were astigmatic. Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatism.A Polish study published in 2005 revealed "with-the-rule astigmatism" may lead to the onset of myopia.A number of studies have found the prevalence of astigmatism increases with age. History
As a student, Thomas Young discovered that he had problems with one eye in 1793. In the following years he did research on his vision problems. He presented his findings in a Bakerian Lecture in 1801.Independent from Young, George Biddell Airy discovered the phenomenon of astigmatism on his own eye. Airy presented his observations on his own eye in February 1825 at the Cambridge Philosophical Society. Airy produced lenses to correct his vision problems by 1825, while other sources put this into 1827 when Airy obtained cylindrical lenses from an optician from Ipswich. The name for the condition was given by William Whewell.By the 1860s astigmatism was a well established concept in ophthalmology, and chapters in books described the discovery of astigmatism.In 1849, Irish English physicist and mathematician George Stokes invented Stokes lens to detect astigmatism. In 1887 American ophthalmologist Edward Jackson revised the Stokes lens concept and made a cross cylinder lens to refine power and axis of astigmatism. In 1907 Jackson described determination of the axis of a correcting cylinder in astigmatism using a cross cylinder.
Irregular astigmatism is quantified by a vector calculation called topographic disparity. Focus of the principal meridian
With accommodation relaxed:

Simple astigmatism
Simple hyperopic astigmatism – first focal line is on the retina, while the second is located behind the retina. Simple myopic astigmatism – first focal line is in front of the retina, while the second is on the retina. Compound astigmatism
Compound hyperopic astigmatism – both focal lines are located behind the retina. Compound myopic astigmatism – both focal lines are located in front of the retina. Mixed astigmatism – focal lines are on both sides of the retina (straddling the retina). Throughout the eye
Astigmatism, whether it is regular or irregular, is caused by some combination of external (corneal surface) and internal (posterior corneal surface, human lens, fluids, retina, and eye-brain interface) optical properties. In some people, the external optics may have the greater influence, and in other people, the internal optics may predominate. Importantly, the axes and magnitudes of external and internal astigmatism do not necessarily coincide, but it is the combination of the two that by definition determines the overall optics of the eye. The overall optics of the eye are typically expressed by a persons refraction; the contribution of the external (anterior corneal) astigmatism is measured through the use of techniques such as keratometry and corneal topography. One method analyzes vectors for planning refractive surgery such that the surgery is apportioned optimally between both the refractive and topographic components.