Skip to main content
SpringerLink
Log in

Introduction to Astigmatism and Corneal Irregularities

  • Chapter
  • First Online:
Customized Laser Vision Correction

Abstract

A good knowledge of the geometry of the human eye in general and the cornea, is important for customized laser vision correction (CLVC). The difference between optical, visual, pupillary, and achromatic axes, in addition to line of sight, angles kappa, alpha and lambda, is important for understanding the basics of CLVC. The same can be said about corneal dimensions, zones, shape and power.

CLVC aims at improving both quality and quantity of vision by correcting the lower order aberrations (refractive errors) and the higher order aberrations (HOAs). The HOAs are induced by irregularity and asymmetry in the optical system of the eye. To understand the HOAs and their role in the management, definitions, classifications, and etiology of astigmatism, particularly the irregular type, should be understood.

Irregular astigmatism is evaluated subjectively and objectively. The evaluation starts from suspicion and goes through subjective refraction before it ends with ancillary tests, the most important being corneal topography/tomography and aberrometry. The former is essential to confirm the diagnosis, study the tomographic patterns of corneal maps and define ectatic corneal diseases (ECDs).

Objective corneal dioptric power (ODP) is a new concept. It measures the potential power of the cornea in reference to an average K reading of the normal population. This concept is based on understanding the factors affecting corneal power measurement and the types of corneal power maps. Calculating the ODP helps in understanding how the laser ablation profile works.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

Log in via an institution
Chapter
USD 29.95
Price excludes VAT (USA)
  • Available as PDF
  • Read on any device
  • Instant download
  • Own it forever
eBook
USD 69.99
Price excludes VAT (USA)
  • Available as EPUB and PDF
  • Read on any device
  • Instant download
  • Own it forever
Softcover Book
USD 99.99
Price excludes VAT (USA)
  • Compact, lightweight edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info
Hardcover Book
USD 119.99
Price excludes VAT (USA)
  • Durable hardcover edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

References

  1. Mosquera SA, Verma S, McAlinden C. Centration axis in refractive surgery. Eye Vis. 2015;2:4. https://doi.org/10.1186/s40662-015-0014-6.

    Article  Google Scholar 

  2. Miller D, Gurland JE, Isby EK, et al. Human eye as an optical system. In:American Academy of Ophthalmology Basic and Clinical Sciences Course. San Francisco: American Academy of Ophthalmology; 1988-1990. p. 108–9.

    Google Scholar 

  3. Ferris J. Gross structure. In:Basic sciences in ophthalmology: a self assessment text. 2nd ed. London: BMJ Publishing Group; 1999. p. 18.

    Google Scholar 

  4. Harvey EM, Dobson V, Miller JM. Prevalence of high astigmatism, eyeglass wear, and poor visual acuity among native American grade school children. Optom Vis Sci. 2006;83:206–12.

    Article  PubMed  Google Scholar 

  5. Srivannaboon S, Chotikavanich S. Corneal characteristics in myopic patients. J Med Assoc Thail. 2005;88:1222–7.

    Google Scholar 

  6. Gudmundsdottir E, Arnarsson A, Jonasson F. Five-year refractive changes in an adult population: Reykjavik eye study. Ophthalmology. 2005;112:672–7.

    Article  PubMed  Google Scholar 

  7. American Academy of Ophthalmology. Corneal zones. https://www.aao.org/bcscsnippetdetail.aspx?id=65c7bff9-4f1e-4717-8585-40318390fc7c.

  8. Gatinel D, Haouat M, Hoang-Xuan T. A review of mathematical descriptors of corneal asphericity. J Fr Ophtalmol. 2002;25:81–90.

    PubMed  CAS  Google Scholar 

  9. Boxer W, Huynh VN, El-Shiaty AF, et al. Evaluation of corneal functional optical zone after laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:948–53.

    Article  Google Scholar 

  10. Holladay JT, Janes JA. Topographic changes in corneal asphericity and effective optical zone after laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:942–7.

    Article  PubMed  Google Scholar 

  11. Gatinel D, Malet J, Hoang-Xuan T, et al. Analysis of customized corneal ablations: theoretical limitations of increasing negative asphericity. Invest Ophthalmol Vis Sci. 2002;43:941–8.

    PubMed  Google Scholar 

  12. Haouat M, Gatinel D, Duong MH, et al. Corneal asphericity in myopes. J Fr Ophtalmol. 2002;25:488–92.

    PubMed  CAS  Google Scholar 

  13. Gatinel D, Malet J, Hoang-Xuan T, et al. Corneal asphericity change after excimer laser hyperopic surgery: theoretical effects on corneal profiles and corresponding Zernike expansions. Invest Ophthalmol Vis Sci. 2004;45:1349–59.

    Article  PubMed  Google Scholar 

  14. Jimenez JR, Anera RG, Diaz JA, et al. Corneal asphericity after refractive surgery when the Munnerlyn formula is applied. J Opt Soc Am A Opt Image Sci Vis. 2004;21:98–103.

    Article  PubMed  Google Scholar 

  15. Holladay JT. Detecting Forme Fruste keratoconus with the Pentacam. Supplement to CRST. 2008;11:12.

    Google Scholar 

  16. Benes P, Synek S, Petrova S. Corneal shape and eccentricity in population. Coll Antropol. 2013;1:117–20.

    Google Scholar 

  17. GH B, Haigis W, Steinmueller A, et al. Distribution of corneal spherical aberration in a comprehensive ophthalmology practice and whether keratometry can predict aberration values. J Cataract Refract Surg. 2007;33(5):848–58.

    Article  Google Scholar 

  18. Holladay JT. Effect of corneal asphericity and spherical aberration on intraocular lens power calculations. J Cataract Refract Surg. 2015;41(7):1553–4.

    Article  PubMed  Google Scholar 

  19. Saleh-Mabed I, Saad A, Gattine D. Topography of the corneal epithelium and Bowman layer in low to moderately myopic eyes. J Cataract Refract Surg. 2016;42:1190–7.

    Article  Google Scholar 

  20. Guilbert E, Saad A, Grise-Dulac A, et al. Corneal thickness, curvature, and elevation readings in normal corneas: combined Placido–Scheimpflug system versus combined Placido–scanning-slit system. J Cataract Refract Surg. 2012;38(7):1198–206.

    Article  PubMed  Google Scholar 

  21. Huang J, Savini G, Hu L, et al. Precision of a new Scheimpflug and Placido-disk analyzer in measuring corneal thickness and agreement with ultrasound pachymetry. J Cataract Refract Surg. 2013;39(2):219–24.

    Article  PubMed  Google Scholar 

  22. Feizi S, Jafarinasab MR, Karimian F, et al. Central and peripheral corneal thickness measurement in normal and Keratoconic eyes using three corneal Pachymeters. J Ophthal Vis Res. 2014;9(3):296–304. https://doi.org/10.4103/2008-322X.143356.

    Article  Google Scholar 

  23. Feng MT, Kim JT, Ambrósio R Jr, et al. International values of central Pachymetry in normal subjects by rotating Scheimpflug camera. Asia Pac J Ophthalmol (Phila). 2012;1(1):13–8. https://doi.org/10.1097/APO.0b013e31823e58da.

    Article  Google Scholar 

  24. Rabinowitz YS, Rasheed K. KISA% index: a quantitative videokeratography algorithm embodying minimal topographic criteria for diagnosing keratoconus. J Cataract Refract Surg. 1999;25:1327–35.

    Article  CAS  PubMed  Google Scholar 

  25. Rabinowitz YS, Nesburn AB, McDonnell PJ. Videokeratography of the fellow eye in unilateral keratoconus. Ophthalmology. 1993;100:181–6.

    Article  CAS  PubMed  Google Scholar 

  26. Li X, Yang H, Rabinowitz YS. Keratoconus: classification scheme based on Videokeratography and clinical signs. J Cataract Refract Surg. 2009;35(9):1597–603.

    Article  PubMed  PubMed Central  Google Scholar 

  27. Rabinowitz YS. Videokeratographic indices to aid in screening for keratoconus. J Refract Surg. 1995;11(5):371–9.

    PubMed  CAS  Google Scholar 

  28. Park CY, Oh SY, Chuck RS. Measurement of angle kappa and centration in refractive surgery. Curr Opin Ophthalmol. 2012;23:269–75.

    Article  PubMed  Google Scholar 

  29. Basmak H, Sahin A, Yildirim N, et al. Measurement of angle kappa with synoptophore and Orbscan II in a normal population. J Refract Surg. 2007;23:456–60.

    PubMed  Google Scholar 

  30. Pande M, Hillman JS. Optical zone centration in keratorefractive surgery. Entrance pupil center, visual axis, coaxially sighted corneal reflex, or geometric corneal center? Ophthalmology. 1993;100:1230–7.

    Article  CAS  PubMed  Google Scholar 

  31. Prakash G, Prakash DR, Agarwal A, et al. Predictive factor and kappa angle analysis for visual satisfactions in patients with multifocal IOL implantation. Eye (Lond). 2011;25:1187–93.

    Article  CAS  Google Scholar 

  32. Hayashi K, Hayashi H, Nakao F, et al. Correlation between pupillary size and intraocular lens decentration and visual acuity of a zonal-progressive multifocal lens and a monofocal lens. Ophthalmology. 2001;108:2011–7.

    Article  CAS  PubMed  Google Scholar 

  33. Karhanová M, Marešová K, Pluhácek F, et al. The importance of angle kappa for centration of multifocal intraocular lenses. Cesk Slov Oftalmol. 2013;69(2):64–8.

    PubMed  Google Scholar 

  34. Hashemi H, Khabazkhoob M, Yazdani K, et al. Distribution of angle kappa measurements with Orbscan II in a population-based survey. J Refract Surg. 2010;26:966–71.

    Article  PubMed  Google Scholar 

  35. Gharaee H, Shafiee M, Hoseini R, et al. Angle kappa measurements: normal values in healthy Iranian population obtained with the Orbscan II. Iran Red Crescent Med J. 2015;17(1):e17873. https://doi.org/10.5812/ircmj.17873.

    Article  PubMed  Google Scholar 

  36. Basmak H, Sahin A, Yildirim N, et al. The angle kappa in strabismic individuals. Strabismus. 2007;15:193–6.

    Article  PubMed  Google Scholar 

  37. Kermani O, Schmeidt K, Oberheide U, et al. Hyperopic laser in situ keratomileusis with 5.5-, 6.5-, and 7.0-mm optical zones. J Refract Surg. 2005;21:52–8.

    PubMed  Google Scholar 

  38. Choi SR, Kim US. The correlation between angle kappa and ocular biometry in Koreans. Korean J Ophthalmol. 2013;27(6):421–4.

    Article  PubMed  PubMed Central  Google Scholar 

  39. Read SA, Collins MJ, Carney LG. A review of astigmatism and its possible genesis. Clin Exp Optom. 2007;90(1):5–19. https://doi.org/10.1111/j.1444-0938.2007.00112.x.

    Article  PubMed  Google Scholar 

  40. Schwartz SH. Image formation: point sources. In:Geometrical and visual optics: a clinical introduction. 2nd ed. New York: McGraw-Hill Education; 2013. p. 143.

    Google Scholar 

  41. Wilson SE, Klyce SD, Husseini ZM. Standardized color-coded maps for corneal topography. Ophthalmology. 1993;100:1723–7.

    Article  CAS  PubMed  Google Scholar 

  42. Smolek MK, Klyce SD, Hovis JK. The universal standard scale: proposed improvements to the American National Standard Institute (ANSI) scale for corneal topography. Ophthalmology. 2002;109:361–9.

    Article  PubMed  Google Scholar 

  43. Belin MW, Khachikian SS, Ambrosio R Jr. Suggested set-up and screening guidelines. In: Belin MW, Khachikian SS, Ambrosio Jr R, editors. Elevation based corneal tomography. 2nd ed. Panama City: Jaypee-Highlights Medical Publisher Inc; 2012. p. 57–69.

    Chapter  Google Scholar 

  44. Ziemer Ophthalmic Systems AG. ZIEMER® GALILEI™ software version 5.2 upgrade information package. Ziemer Ophthalmic Systems AG; 2010.

    Google Scholar 

  45. Sinjab MM. A 12-point algorithm to master corneal tomography. CRSTEurope; 2017.

    Google Scholar 

  46. Bogan SJ, Waring GO III, Ibrahim O, et al. Classification of normal corneal topography based on computer-assisted videokeratography. Arch Ophthalmol. 1990;108(7):945–9.

    Article  CAS  PubMed  Google Scholar 

  47. Dingeldein SA, Klyce SD. The topography of normal corneas. Arch Ophthalmol. 1989;107:512–8.

    Article  CAS  PubMed  Google Scholar 

  48. Rabinowitz YS, Yang H, Brickman Y, et al. Videokeratography database of normal human corneas. Br J Ophthalmol. 1996;80(7):610–6.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  49. Litoff D, Belin MW, Winn SS, et al. PAR technology corneal topography system. Inv Ophthalmol Vis Sci. 1991;32:922.

    Google Scholar 

  50. Belin MW, Litoff D, Strods SJ, et al. The PAR technology corneal topography system. Refract Corneal Surg. 1992;8:88–96.

    PubMed  CAS  Google Scholar 

  51. Khachikian SS, Belin MW, Ambrosio R Jr. Normative data for the Oculus Pentacam. In: Belin MW, Khachikian SS, Ambrosio Jr R, editors. Elevation based corneal tomography. 2nd ed. Panama City: Jaypee-Highlights Medical Publisher Inc; 2012. p. 71–9.

    Chapter  Google Scholar 

  52. Belin MW, Khachikian SS, Ambrosio R Jr. Understanding elevation based topography: how elevation data is displayed. In: Belin MW, Khachikian SS, Ambrosio Jr R, editors. Elevation based corneal tomography. 2nd ed. Panama City: Jaypee-Highlights Medical Publisher Inc; 2012. p. 25–45.

    Chapter  Google Scholar 

  53. Sinjab MM. Classifications and patterns of keratoconus and keratectasia. In:Quick guide to the management of keratoconus. Heidelberg: Springer; 2012. p. 13–57.

    Chapter  Google Scholar 

  54. Ambrosio R Jr, de Oliveira Ramos IC, Luz A, et al. Comprehensive Pachymetric evaluation. In: Belin MW, Khachikian SS, Ambrosio Jr R, editors. Elevation based corneal tomography. 2nd ed. Panama City: Jaypee-Highlights Medical Publisher Inc; 2012. p. 25–45.

    Google Scholar 

  55. Galletti JD, Ruiseñor Vázquez PR, Minguez N, et al. Corneal asymmetry analysis by Pentacam Scheimpflug tomography for keratoconus diagnosis. J Refract Surg. 2015;31(2):116–23.

    Article  PubMed  Google Scholar 

  56. Sinjab MM. Displaced Apex syndrome. In:Corneal topography in clinical practice (Pentacam System): basics and clinical interpretationh. 2nd ed. New Delhi: Jaypee Brothers Medical Publishers; 2012. p. 159–64.

    Chapter  Google Scholar 

  57. Hick S, Laliberté JF, Meunier J, et al. Effects of misalignment during corneal topography. J Cataract Refract Surg. 2007;33(9):1522–9.

    Article  PubMed  Google Scholar 

  58. Saad A, Gilbert E, Gatinel D. Corneal enantiomorphism in normal and keratoconic eyes. J Refract Surg. 2014;30(8):542–7.

    Article  PubMed  Google Scholar 

  59. Gomes JAP, Tan D, Rapuano CJ, et al. Global consensus on keratoconus and ectatic disease. Cornea. 2015;34(4):359–69.

    Article  PubMed  Google Scholar 

  60. Berti T, Ghanem V, Ghanem R, et al. Moderate keratoconus with thick corneas. J Refract Surg. 2013;29:430–5. https://doi.org/10.3928/1081597X-20130515-05.

    Article  PubMed  Google Scholar 

  61. Sinjab MM, Youssef LN. Pellucid-like keratoconus. www.ncbi.nlm.nih.gov/pmc/articles/PMC3752625.

  62. Lee BW, Jurkunas UV, Harissi-Dagher M, et al. Ectatic disorders associated with a claw-shaped pattern on corneal topography. Am J Ophthalmol. 2007;144:154–6.

    Article  PubMed  Google Scholar 

  63. Baillif S, Garweg JG, Grange JD, et al. Keratoglobus: review of the literature. J Fr Ophthalmol. 2005;28:1145–9.

    Article  CAS  Google Scholar 

  64. Wallang BS, Das S. Keratoglobus. Eye. 2013;27(9):1004–12.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  65. Belin MW, Kim JT, Zloty P, et al. Simplified nomenclature for describing keratoconus. Int J Keratoco Ectatic Corneal Dis. 2012;1(1):31–5.

    Article  Google Scholar 

  66. Klyce SD. Chasing the suspect: keratoconus. Br J Ophthalmol. 2009;93(7):845.

    Article  PubMed  Google Scholar 

  67. Butler TH. Two rare corneal conditions: I. Acute conical cornea II. Keratoconus Posticus Circumscriptus. Br J Ophthalmol. 1932;16(1):30–5.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  68. Williams R. Acquired posterior keratoconus. Br J Ophthalmol. 1987 Jan;71(1):16–7.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  69. Skuta GL, Cantor LB, Weiss JS. Refractive surgery. In:American Academy of Ophthalmology Basic and Clinical Sciences Course. San Francisco: American Academy of Ophthalmology; 2011-2012. p. 45–6.

    Google Scholar 

  70. Randleman JB. Etiology and clinical presentations of irregular astigmatism after Keratorefractive surgery. In: Wang M, editor. Irregular astigmatism: diagnosis and treatment. Thorofare, NJ: Slack; 2008. p. 73–84.

    Google Scholar 

  71. Alio JL. Corneal irregularity. In: Alio J, Azar D, editors. Management of complications in refractive surgery. Berlin: Springer; 2008. p. 143–6.

    Chapter  Google Scholar 

  72. Murta J, Rosa AM. Measurement and topography guided treatment of irregular astigmatism. In: Goggin M, editor. Astigmatism—optics, physiology and management. Rijeka, Croatia: InTech; 2012. https://doi.org/10.5772/23613.

    Chapter  Google Scholar 

  73. Seitz B. Astigmatism after keratoplasty: prophylaxis and therapy. Ocular surgery news U.S. edition, September 15, 2000.

    Google Scholar 

  74. Stuphin JE. External diseases and cornea. In: American Academy of Ophthalmology Basic and Clinical Sciences Course. San Francisco: American Academy of Ophthalmology; 2006–2007. ISBN: 1-56055-612-9.

    Google Scholar 

  75. Swartz T, Duplessie M, Munir W, et al. Non ectatic corneal problems causing irregular astigmatism. In: Wang M, editor. Irregular astigmatism: diagnosis and treatment. Thorofare, NJ: Slack; 2008. p. 145–73.

    Google Scholar 

  76. Liu Z, Pflugfelder SC. The effects of long-term contact lens wear on corneal thickness, curvature and surface regularity. Ophthalmology. 2000;107:105–11.

    Article  CAS  PubMed  Google Scholar 

  77. Holden BA, Sweeney DF, Vannas A, et al. Effect of long-term extended contact lens wear on the human cornea. Invest Ophthalmol Vis Sci. 1985;26:1489–−1501.

    PubMed  CAS  Google Scholar 

  78. Wang X, McCulley JP, Bowman RW, et al. Time to resolution of contact lens-induced corneal warpage prior to refractive surgery. CLAO J. 2002;28(4):169–−71.

    PubMed  CAS  Google Scholar 

  79. Hansen A, Norn M. Astigmatism and surface phenomena in pterygium. Acta Ophthalmol. 1980;58:174–81.

    Article  CAS  Google Scholar 

  80. Oldenburg JB, Garbus J, McDonnell JM, et al. Conjunctival pterygia: mechanism of corneal topographic changes. Cornea. 1990;9:200–4.

    Article  CAS  PubMed  Google Scholar 

  81. Ozdemir M, Cinal A. Early and late effects of pterygium surgery on corneal topography. Ophthalmic Surg Lasers Imaging. 2005;36:451–6.

    PubMed  Google Scholar 

  82. Walland MJ, Stevens JD, Steele AD. The effect of recurrent pterygium on corneal topography. Cornea. 1994;13:463–4.

    Article  CAS  PubMed  Google Scholar 

  83. Gridley MJ, Perlman EM. A form of variable astigmatism induced by pseudo pterygium. Ophthalmic Surg. 1986;17:794–5.

    PubMed  CAS  Google Scholar 

  84. Tomidokoro A, Oshika T, Amano S, et al. Quuantitative analysis of regular and irregular astigmatism induced by pterygium. Cornea. 1999;18:412–5.

    Article  CAS  PubMed  Google Scholar 

  85. Oner FH, Kaderli B, Durak I, et al. Analysis of the pterygium size inducing marked refractive astigmatism. Eur J Ophthalmol. 2000;10:212–4.

    Article  CAS  PubMed  Google Scholar 

  86. Sinjab MM. Diagnosis of keratoconus. In:Quick guide to the management of keratoconus. Heidelberg: Springer; 2012. p. 1–11.

    Chapter  Google Scholar 

  87. Harvey W, Gilmartin B. Paediatric optometry. Edinburg: Butterworth-Heinemann; 2004. p. 47.

    Google Scholar 

  88. Belin MW, Khachikian SS. Introduction and overview. In: Belin MW, Khachikian SS, Ambrosio Jr R, editors. Elevation based corneal tomography. 2nd ed. Panama City: Jaypee-Highlights Medical Publisher Inc; 2012. p. 2.

    Chapter  Google Scholar 

  89. OCULUS website. https://www.pentacam.com/int/technology/topography-maps.html.

  90. Holladay JT, Hill WE, Steinmueller A. Corneal power measurements using Scheimpflug imaging in eyes with prior corneal refractive surgery. J Refract Surg. 2009;25:863–8.

    Article  Google Scholar 

  91. Alpins N, Ong JKY, Stamatelatos G. Corneal topographic astigmatism (CorT) to quantify Total corneal astigmatism. J Refract Surg. 2015;31(3):182–6.

    Article  PubMed  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Damascus University, Damascus, Syria

    Mazen M. Sinjab

Authors
  1. Mazen M. Sinjab
    View author publications

    You can also search for this author in PubMed Google Scholar

Editor information

Editors and Affiliations

  1. Damascus University, Damascus, Syrian Arab Republic

    Mazen M. Sinjab

  2. Wellington Eye Clinic, Dublin, Ireland

    Arthur B. Cummings

Rights and permissions

Reprints and permissions

Copyright information

© 2018 Springer International Publishing AG, part of Springer Nature

About this chapter

Check for updates. Verify currency and authenticity via CrossMark

Cite this chapter

Sinjab, M.M. (2018). Introduction to Astigmatism and Corneal Irregularities. In: Sinjab, M., Cummings, A. (eds) Customized Laser Vision Correction. Springer, Cham. https://doi.org/10.1007/978-3-319-72263-4_1

Download citation

  • DOI: https://doi.org/10.1007/978-3-319-72263-4_1

  • Published:

  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-319-72262-7

  • Online ISBN: 978-3-319-72263-4

  • eBook Packages: MedicineMedicine (R0)

Publish with us

Policies and ethics

Search

Navigation