April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
Application of Multiple Diagnostic Modalities to Differentiate Between Corneal Ectasia Types
Author Affiliations & Notes
  • G. Patel
    Pepose Vision Institute, Chesterfield, Missouri
  • M. A. Qazi
    Pepose Vision Institute, Chesterfield, Missouri
  • A. M. Mahmoud
    Ohio State University, Columbus, Ohio
  • P. S. Kollbaum
    Indiana University, Bloomington, Indiana
  • M. M. Merchea
    Bauch & Lomb, Rochester, New York
  • C. J. Roberts
    Ohio State University, Columbus, Ohio
  • J. S. Pepose
    Pepose Vision Institute, Chesterfield, Missouri
  • Footnotes
    Commercial Relationships  G. Patel, None; M.A. Qazi, None; A.M. Mahmoud, None; P.S. Kollbaum, None; M.M. Merchea, Bauch & Lomb, E; C.J. Roberts, None; J.S. Pepose, Bauch & Lomb, C.
  • Footnotes
    Support  None.
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 5097. doi:
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      G. Patel, M. A. Qazi, A. M. Mahmoud, P. S. Kollbaum, M. M. Merchea, C. J. Roberts, J. S. Pepose; Application of Multiple Diagnostic Modalities to Differentiate Between Corneal Ectasia Types. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5097.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : To demonstrate how scanning slit videokeratography (Orbscan II, Bausch & Lomb) and wavefront aberrometry (Zywave IIz, Bausch & Lomb) may be used for clinical discrimination of corneal ectasias, such as keratoconus (KCN) and pellucid marginalis (PMD).

Methods: : A retrospective review identified patients with a clinical diagnosis of KCN or PMD, and a control group of non-ectatic preoperative refractive surgery eyes. Orbscan exams from these eyes (n=72 KCN, 26 PMD, 105 controls) were analyzed to obtain corneal aberrations and topographical and pachymetric characteristics. Shack-Hartmann whole eye aberrations were also evaluated (5 mm).

Results: : Minimum optical pachymetry was lower in KCN (473 +/-88 µm) than PMD (548 +/-74) eyes; the thinnest pachymetry point in PMD (-1.27 +/-1.07 mm) was more inferiorly displaced than KCN (-0.71 +/-0.47, p<0.001), with both groups differing from normals (-0.26 +/-0.39, p<0.001). While the 3 mm zone irregularity index was higher in KCN than PMD (p=0.002), there was no difference for the 5 mm zone. There was no difference in the maximum value above the anterior elevation best fit sphere (BFS) between PMD and KCN (p=1.0); the maximum value of the posterior elevation BFS was higher for KCN (0.116 +/-0.05 mm) than for PMD (0.088 +/-0.07, p=0.02). The cone location magnitude index (CLMI), derived from mean curvature maps, was greater for both KCN and PMD relative to controls (p<0.001), with greater radial displacement of the steepest region from the ordinate center in PMD than KCN (p<0.001). Whole eye trefoil was greater in PMD than KCN (p=0.04), while vertical coma was higher in KCN than PMD (p<0.02).

Conclusions: : The measured magnitude and location of the ectasia appear to be key differentiators of KCN and PMD. These differences are highlighted by both Orbscan and whole-eye aberrometry measurements. Metrics attained from videokeratography and wavefront aberrometry offer a framework to differentiate between ectasia types, allowing clinicians to provide improved treatment plans.

Keywords: refractive surgery: corneal topography • keratoconus • refractive surgery 

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