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Perspective
Astigmatism and the analysis of its surgical correction
  1. NIGEL MORLET
  1. Moorfields Eye Hospital, London, UK and Eye Surgery Foundation, Perth, Western Australia
  2. International Centre for Eye Health, Institute of Ophthalmology, London, UK
  3. Moorfields Eye Hospital, London, UK
  1. DARWIN MINASSIAN
  1. Moorfields Eye Hospital, London, UK and Eye Surgery Foundation, Perth, Western Australia
  2. International Centre for Eye Health, Institute of Ophthalmology, London, UK
  3. Moorfields Eye Hospital, London, UK
  1. JOHN DART
  1. Moorfields Eye Hospital, London, UK and Eye Surgery Foundation, Perth, Western Australia
  2. International Centre for Eye Health, Institute of Ophthalmology, London, UK
  3. Moorfields Eye Hospital, London, UK
  1. Nigel Morlet, 592 Stirling Highway, Mosman Park, WA, 6012, Australia

https://doi.org/10.1136/bjo.85.9.1127

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    Modern cataract and refractive surgery aims not only to improve vision but to provide a good unaided visual acuity. Correcting astigmatic errors and control of surgically induced astigmatism are now an integral part of such operative procedures. Technological innovations and surgical developments in recent times have provided new methods for correction of astigmatism. However, evaluating the outcome of surgery for astigmatism presents particular difficulties, especially with the statistical comparison of different treatment groups.

    In this review we will discuss the nature of astigmatism and its various refractive effects and how this relates to cataract and refractive surgical outcomes. The use and limitations of vectors and other methods for the analysis of change in astigmatism after surgery will be discussed along with appropriate statistical methods and suggestions for data presentation.

    Ocular astigmatism

    Astigmatism occurs when toricity of any of the refractive surfaces of the optical system produces two principal foci delimiting an area of intermediate focus called the conoid of Sturm. Thomas Young in 1801 was the first to describe ocular astigmatism, discovering that his own astigmatism was predominantly lenticular.1 However, it was some years later before Airy (1827) corrected astigmatism with a cylindrical lens.2 Corneal astigmatism was characterised by Knapp and also Donders in 1862 after the invention of the ophthalmometer by Helmholtz.34 In the same year Donders5 also described the astigmatism due to cataract surgery and soon after Snellen (1869) suggested that placing the incision on the steep axis would reduce the corneal astigmatism.6 Surgery to specifically treat astigmatism was suggested by Bates7 who described corneal wedge resection in 1894, but it was the work of Lans8 that provided most of the early theoretical basis for refractive corneal surgery. Little further work was published until that of Sato in the 1940s and 1950s. …

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