Advertisement

Corneal Ectasia

  • Melanie Corbett
  • Nicholas Maycock
  • Emanuel Rosen
  • David O’Brart
Chapter

Abstract

In primary corneal ectasias, noninflammatory stromal thinning causes the cornea to progressively protrude forwards. Secondary ectasia occurs as a result of thinning due to corneal surgery or inflammatory stromal melt. In both types, in the early stages, the classical clinical signs may be absent, so the diagnosis relies upon topographic findings alone.

In keratoconus the cornea has an exaggerated prolate shape with paracentral corneal steepening, which most commonly occurs inferiorly, with corneal flattening in the opposite hemisphere. This causes corneal irregularity which can only be improved by glasses in the earliest stages. Keratoconus can be classified according to the severity, location and shape of the cone.

In pellucid marginal degeneration, the thinning is further inferiorly, creating a “droopy bow tie” area of corneal steepening, associated with high orders of regular astigmatism. With further progression, the “bows” of the “tie” may meet in the inferior periphery, producing a pattern resembling a more inferior keratoconus. Keratoglobus has a more even thinning affecting the whole cornea, which expands more symmetrically, with relatively little effect on the refraction.

Topographic indices have been developed to detect very early stages of ectasia and quantify progression. These include the asymmetry and regularity indices, inferior-superior value, difference in central power, keratoconus predictability index, enhanced ectasia display and, in certain devices, neural networks. The differential diagnosis includes artefact, contact lens-induced corneal warpage and various types of corneal disease and surgery.

Keywords

Corneal topography Corneal ectasia Corneal thinning Keratoconus Keratoglobus Pellucid marginal degeneration Prolate Bow tie Corneal asymmetry index Corneal irregularity index Inferior-superior value Keratoconus predictability index Enhanced ectasia display Subclinical keratoconus 

References

*References Particularly Worth Reading

  1. 1.
    Rabinowitz YS, Maumenee IH, Lundergan MK. Molecular genetic analysis in autosomal dominant keratoconus. Cornea. 1992;11:302–8.CrossRefGoogle Scholar
  2. 2.
    Rabinowitz YS, Garbus J, McDonnell PJ. Computer-assisted corneal topography in family members of patients with keratoconus. Arch Ophthalmol. 1990;108:365–71.CrossRefGoogle Scholar
  3. 3.
    Gonzalez V, McDonnell PJ. Computer-assisted corneal topography in parents of patients with keratoconus. Arch Ophthalmol. 1992;110:1412–4.CrossRefGoogle Scholar
  4. 4.
    *Rabinowitz YS, Nesburn AB, McDonnell PJ. Videokeratography of the fellow eye in unilateral keratoconus. Ophthalmology. 1993;100:181–186.CrossRefGoogle Scholar
  5. 5.
    Behrens-Baumann W. Detection of keratoconus before refractive surgery [letter]. Ophthalmology. 1994;101:794–5.CrossRefGoogle Scholar
  6. 6.
    Hustead JD. Detection of keratoconus before keratorefractive surgery [letter]. Ophthalmology. 1993;100:975.CrossRefGoogle Scholar
  7. 7.
    *Holland DR, Maeda N, Hannush SB, Riveroll LH, Green MT, Klyce SD, Wilson SE. Unilateral keratoconus. Ophthalmology. 1997;104:1409–1413.CrossRefGoogle Scholar
  8. 8.
    Eran P, Almogit A, David Z, et al. The D144E substitution in the VSX1 gene: a non-pathogenic variant or a disease causing mutation? Ophthalmic Genet. 2008;29:53–9.CrossRefGoogle Scholar
  9. 9.
    Sherwin T, Brookes NH, Loh IP, et al. Cellular incursion into Bowman’s membrane in the peripheral cone of the keratoconic cornea. Exp Eye Res. 2002;74(4):473–82.CrossRefGoogle Scholar
  10. 10.
    Mas-Tur V, MacGregor C, Jayaswal R, et al. A review of keratoconus: diagnosis, pathophysiology and genetics. Surv Ophthalmol. 2017;62(6):770–83.CrossRefGoogle Scholar
  11. 11.
    Tuft SJ, Moodaley LC, Gregory WM, Davison CR, Buckley RJ. Prognostic factors for the progression of keratoconus. Ophthalmology. 1994;101:439–47.CrossRefGoogle Scholar
  12. 12.
    Karolak JA, Kulinska K, Nowak DM, et al. Sequence variants in COL4A1 and COL4A2 genes in Ecuadorian families with keratoconus. Mol Vis. 2011;17:827–43.PubMedPubMedCentralGoogle Scholar
  13. 13.
    Mintz-Hittner HA, Semina EV, Frishman LJ, et al. VSX1 (RINX) mutation with craniofacial anomalies, empty sella, corneal endothelial changes and abnormal retinal and auditory bipolar cells. Ophthalmology. 2004;111:828–36.CrossRefGoogle Scholar
  14. 14.
    Godefrooij DA, Ardine de Wit G, Uiterwaal CS, et al. Age-specific incidence and prevalence of keratoconus: a nationwide registration study. Am J Ophthalmol. 2017;175:169–72.CrossRefGoogle Scholar
  15. 15.
    *Rabinowitz YS, McDonnell PJ. Computer-assisted corneal topography in keratoconus. Refract Corneal Surg. 1989;5:400–408.Google Scholar
  16. 16.
    *Wilson SE, Lin DTC, Klyce SD. Corneal topography of keratoconus. Cornea. 1991;10:2–8.CrossRefGoogle Scholar
  17. 17.
    de Cunha DA, Woodward EG. Measurement of corneal topography in keratoconus. Ophthal Physiol Opt. 1993;13:377–82.CrossRefGoogle Scholar
  18. 18.
    Corbett MC, O’Brart DPS, Stultiens BAT, Jongsma FHM, Marshall J. Corneal topography using a new moiré image-based system. Eur J Implant Ref Surg. 1995;7:353–70.CrossRefGoogle Scholar
  19. 19.
    Mok JW, Baek SJ, Joo CK, et al. VSX1 gene variants are associated with keratoconus in unrelated Korean patients. J Hum Genet. 2008;53:842–9.CrossRefGoogle Scholar
  20. 20.
    Reinstein DZ, Archer TJ, Gobbe M. Corneal epithelial thickness profile in the diagnosis of keratoconus. J Refract Surg. 2009;25(7):604–10.CrossRefGoogle Scholar
  21. 21.
    Maguire LJ, Bourne MW. Corneal topography of early keratoconus (reply). Am J Ophthalmol. 1989;108:747–8.CrossRefGoogle Scholar
  22. 22.
    Belin MW, Khachikian SS. An introduction to understanding elevation based topography: how elevation data are displayed – a review. Clin Exp Ophthalmol. 2009;37:14–29.CrossRefGoogle Scholar
  23. 23.
    Li X, Bykhovskaya Y, Canedo AL, et al. Genetic association of COL5A1 variants in keratoconus patients suggests a complex connection between corneal thinning and keratoconus. IOVS. 2013;54(4):2696–704.Google Scholar
  24. 24.
    Sharma A, Tovey JC, Ghosh A, et al. AAV serotype influences gene transfer in corneal stroma in vivo. Exp Eye Res. 2010;3:440–8.CrossRefGoogle Scholar
  25. 25.
    Manuolio TA. Genome-wide association studies and assessment of the risk of disease. N Engl J Med. 2010;2:166–76.CrossRefGoogle Scholar
  26. 26.
    *Madea N, Klyce SD, Smolek MK, Thompson HW. Automated keratoconus screening with corneal topography analysis. Invest Ophthalmol Vis Sci. 1994;35:2749–2757.Google Scholar
  27. 27.
    Smolek MK, Klyce SD, Maeda N. Keratoconus and contact lens-induced corneal warpage analysis using the keratomorphic diagram. Invest Ophthalmol Vis Sci. 1994;35:4192–203.PubMedGoogle Scholar
  28. 28.
    Maeda N, Klyce SD, Smolek MK. Comparison of methods for detecting keratoconus using videokeratoscopy. Arch Ophthalmol. 1995;113:870–4.CrossRefGoogle Scholar
  29. 29.
    Goren MB. Comparison of methods for detecting keratoconus using videokeratography [letter]. Arch Ophthalmol. 1996;114:631.CrossRefGoogle Scholar
  30. 30.
    Klyce SD, Smolek MK, Maeda N. Comparison of methods for detecting keratoconus using videokeratography [reply]. Arch Ophthalmol. 1996;114:631–2.CrossRefGoogle Scholar
  31. 31.
    *Smolek MK, Klyce SD. Current keratoconus detection methods compared with a neural network approach. Invest Ophthalmol Vis Sci. 1997;38:2290–2299.PubMedGoogle Scholar
  32. 32.
    Ambrosio R Jr, Alonson RS, Luz A, et al. Corneal thickness spatial profile and corneal volume distribution: tomographic indices to detect keratoconus. J Cat Refract Surg. 2006;32(11):1851–9.CrossRefGoogle Scholar
  33. 33.
    Abad JC, Rubinfeld RS, Del Valle M, et al. Vertical D: a novel topographic pattern in some keratoconus suspects. Ophthalmology. 2007;114(5):1020–6.CrossRefGoogle Scholar
  34. 34.
    Khachikian SS, Belin MW. Posterior elevation in keratoconus. Ophthalmology. 2009;116(4):816e1.CrossRefGoogle Scholar
  35. 35.
    Arce C. Qualitative and quantitative analysis of aspheric symmetry and asymmetry on corneal surfaces. ASCRS (American Society of Cataract and Refractive Surgeons) Conference: Boston; 2010.Google Scholar
  36. 36.
    Smadja D, Touboul D, Cohen A, et al. Detection of subclinical keratoconus using an automated decision tree classification. Am J Ophthalmol. 2013;156(2):237–246e1.CrossRefGoogle Scholar
  37. 37.
    Maeda N, Klyce SD, Smolek MK, et al. Automated keratoconus screening with corneal topography analysis. IOVS. 1994;35(6):2749–57.Google Scholar
  38. 38.
    Dingeldein SA, Klyce SD, Wilson SE. Quantitative descriptors of corneal shape derived from the computer-assisted analysis of photokeratographs. Refract Corneal Surg. 1989;5:372–8.CrossRefGoogle Scholar
  39. 39.
    Wilson SE, Klyce SD. Quantitative descriptors of corneal topography. A clinical study. Arch Ophthalmol. 1991;109:349–53.CrossRefGoogle Scholar
  40. 40.
    Maeda M, Klyce SD, Smolek MK. Neural network classification of corneal topography. Invest Ophthalmol Vis Sci. 1995;36:1327–35.PubMedGoogle Scholar
  41. 41.
    Amsler M. Le keratocone fruste au javal. Ophthalmologica. 1938;96:77–83.CrossRefGoogle Scholar
  42. 42.
    Amsler M. Keratocone classique et keratocone fruste, arguments unitaire. Ophthalmologica. 1946;111:96–101.CrossRefGoogle Scholar
  43. 43.
    Belin MW, Duncan J, Ambrosio R Jr, et al. A new tomographic method of grading keratoconus: the ABCD Grading system. Int J Kerat Ect Cor Dis. 2015;4(3):85–93.Google Scholar
  44. 44.
    *Wilson SE, Klyce SD. Screening for corneal topographic abnormalities before refractive surgery. Ophthalmology. 1994;101:147–152.CrossRefGoogle Scholar
  45. 45.
    Nesburn AB, Bahri S, Salz J, Rabinowitz YS, Maguen E, Hofbauer J, Belin M, Macy JI. Keratoconus detected by videokeratography in candidates for photorefractive keratectomy. J Refract Surg. 1995;11:194–201.PubMedGoogle Scholar
  46. 46.
    Bowman CB, Thompson KP, Stulting RD. Refractive keratotomy in keratoconus suspects. J Refract Surg. 1995;11:202–6.PubMedGoogle Scholar
  47. 47.
    Doyle SJ, Hynes E, Naroo S, Shah S. PRK in patients with a keratoconic topography picture. The concept of a physiological ‘displaced apex syndrome’. Br J Ophthalmol. 1996;80:25–8.CrossRefGoogle Scholar
  48. 48.
    Colin J, Cochener B, Bobo C, Malet F, Gallinaro C, Le Floch G. Myopic photorefractive keratectomy in eyes with atypical inferior corneal steepening. J Cat Refract Surg. 1996;22:1423–6.CrossRefGoogle Scholar
  49. 49.
    O’Brart DPS, Saunders DC, Corbett MC, Rosen ES. The corneal topography of keratoconus. Eur J Implant Ref Surg. 1995;7(1):20–30.CrossRefGoogle Scholar
  50. 50.
    Eiferman RA, Lane L, Law M, Fields Y. Superior keratoconus [letter]. Refract Corneal Surg. 1993;9:394–5.PubMedGoogle Scholar
  51. 51.
    *McMahon TT, Robin JB, Scarpulla KM, Putz JL. The spectrum of corneal topography found in keratoconus. CLAO J. 1991;17:198–204.PubMedGoogle Scholar
  52. 52.
    *Hubbe RE, Foulks GN. The effect of poor fixation on computer-assisted topographic corneal analysis. Ophthalmology. 1994;101:1745–1748.CrossRefGoogle Scholar
  53. 53.
    Silverman CM. Misalignment of videokeratoscope produces pseudo-keratoconus suspect. J Cat Refract Surg. 1994;10:468.Google Scholar
  54. 54.
    *Karabatsas CH, Cook SD. Topographic analysis in pellucid marginal degeneration and keratoglobus. Eye. 1996;10:451–455.CrossRefGoogle Scholar
  55. 55.
    *Rabinowitz YS, Garbus JJ, Garbus C, McDonnell PJ. Contact lens selection for keratoconus using a computer assisted videokeratoscope. CLAO J. 1991;17:88–93.PubMedGoogle Scholar
  56. 56.
    Khong AM, Mannis MJ, Plotnik RD, Johnson CA. Computerised topographic analysis of the healing graft after penetrating keratoplasty for keratoconus. Am J Ophthalmol. 1993;115:209–15.CrossRefGoogle Scholar
  57. 57.
    Kremer I, Eagle RC, Rapuano CJ, Laibson PR. Histological evidence of recurrent keratoconus seven years after keratoplasty. Am J Ophthalmol. 1995;199:511–2.CrossRefGoogle Scholar
  58. 58.
    Bechrakis N, Blom ML, Stark WJ, Green WR. Recurrent keratoconus. Cornea. 1994;13:73–7.CrossRefGoogle Scholar
  59. 59.
    Serdarevic ON, Renard GJ, Pouliquen Y. Penetrating keratoplasty for keratoconus: role of videokeratoscopy and trephine sizing. J Cataract Refract Surg. 1996;22:1165–74.CrossRefGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Melanie Corbett
    • 1
  • Nicholas Maycock
    • 2
  • Emanuel Rosen
    • 3
  • David O’Brart
    • 4
  1. 1.Imperial College Healthcare NHS TrustLondonUK
  2. 2.University Hospital Coventry and WarwickshireCoventryUK
  3. 3.ManchesterUK
  4. 4.Department of OphthalmologySt. Thomas HospitalLondonUK

Personalised recommendations