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Chapter-15 Regular and Irregular Astigmatism

BOOK TITLE: Atlas and Text of Corneal Pathology and Surgery

Author
1. Cigales Melania
2. Hoyos Jairo E
3. Iradier Maria T
ISBN
9789962678335
DOI
10.5005/jp/books/11349_15
Edition
1/e
Publishing Year
2011
Pages
20
Author Affiliations
1. Instituto Oftalmológico Hoyos, Sabadell-Barcelona – Spain, Instituto Oftalmológico Hoyos, Sabadell—Barcelona—Spain, the Instituto Oftalmológico Hoyos, Sabadell, Barcelona, Spain, Sabadell - Barcelona, Spain, Instituto Oftalmologico De Sabadell, Barcelon, Spain, Instituto Oftalmologico De, Sabadell, Barcelona, Spain, Instituto Oftalmologico De Sabadell, Barcelona, Spain, Instituto Oftalmológico Hoyos, Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 1º, 08201 Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos Barcelona, Spain, Instituto Oftalmologico Hoyos, Sabadell (Barcelona), Spain, Instituto Oftalmologico Hoyos, Sabadell (Barcelona) Spain
2. Ophthalmology of the Instituto Oftalmológico Hoyos KM Study Group; Sabadell Barcelona, Spain, Instituto Oftalmológico Hoyos, KM Study Group President, Sabadell - Barcelona – Spain, Instituto Oftalmologico De, Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 10, 08201 Sabadell, Barcelona (Spain), Instituto Oftalmologico De Sabadell, Barcelona, Spain, Instituto Oftalmológico Hoyos, KM Study Group President, Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 1, 08201 Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 1°, 08201 Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 1°, 8201 Sabadell, Barcelona, Spain, Instituto Oftalmologico Hoyos, Rambla de Sabadell 62 10, 08201 Sabadell, Barcelona, Spain, Instituto Oftalmológico Hoyos, KM Study Group President, Sabadell-Ba
3. Clinica Moreno Alguacil, San Pascual 47, Aranjuez 28300, Spain, Medical Staff at San Carlos University Hospital Medical Director, Iradier Eye Clinical Madrid, Spain, San Pascual 47, Aranjuez 28300, Spain, Clinica Moreno Alguacil, San Pascual 47, Aranjuez 283 00, Spain, Clinica Moreno Alguacil, San Pascual 47, Aranjuez, Spain, San Carlos University Hospital, Madrid, Spain, Clinica Moreno Alguacil San Pascual 47, Aranjuez, Spain
Chapter keywords

Abstract

Astigmatism is a refractive error that occurs when the optical system does not have the same refractive power at all its meridians. Astigmatism is chiefly determined by the anterior curvature of the cornea. Corneal astigmatism occurs when the curvatures of the principal meridians of the cornea at right angles to each other are different. Astigmatism is described as with-the-rule when the vertical Regular and Irregular Astigmatism meridian is the steepest and against-the-rule when the meridian showing most curvature is the horizontal meridian. Astigmatism with axes more than 30º from the horizontal or vertical meridians is referred to as oblique astigmatism. Astigmatism is usually regular, which means that the principal meridians are perpendicular to each other. Irregular astigmatism occurs when the principal meridians are not perpendicular to each other or when there are other asymmetries that are not correctable with conventional lenses or refractive surgery. This may occur in corneal pathologies such as keratoconus or pellucid marginal degeneration. Regular astigmatism is generally congenital and hereditary, developing at an early age and not usually advancing thereafter. When confronted with a late-onset progressive astigmatism, we should consider the possibility of a corneal degeneration such as keratoconus or pellucid marginal degeneration. A form of acquiring astigmatism not degenerative is post-surgery astigmatism, especially associated with extracapsular cataract surgery and keratoplasty. Surgical treatment of regular and irregular astigmatism is different and in this chapter they will studied in two different parts.

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