It is the situation where a single focus cannot be formed as a result of different refraction of light in different meridians due to irregularities in the curvature of the optical system of the eye. Simple, combined and mixed types are available.
1- Regular astigmatism:
It is astigmatism in which the dioptric power difference between the meridians is uniform and regular.
2- Irregular astigmatism:
If the difference between the meridians is different in every part of the optic zone, it is called irregular (irregular) astigmatism. It is a type of astigmatism that manifests itself with thinning and steepening of the cornea. It is not possible to correct irregular astigmatism with glasses and hard contact lenses must be used. (Example: Keratoconus)
Treatment
In regular astigmatism; cylindrical lenses or soft contact lenses
In irregular astigmatism; rigid contact lenses, refractive surgery and keratoplasty.
Soft contact lenses can be tried in mild cases of keratoconus and in those who cannot tolerate hard contact lenses in the early stages.