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. Author manuscript; available in PMC: 2018 Nov 15.
Published in final edited form as: Prog Retin Eye Res. 2018 Jul 13;67:150–167. doi: 10.1016/j.preteyeres.2018.05.002

Table 2.

Keratoconus Severity Score. Instructions for use: (**higher-order first corneal surface wave front root mean square error). For grades 0–1, all of the parameters in a category must be met. For all grades, the required features must be met. The worst of the additional features is then assessed, with the “worst” of the features carrying the greater weight (as long as the required features are met).

Grade Stage Corneal scarring consistent with KC Slit-lamp signs consistent with KC Axial Pattern Other Features
0 Normal topography None None Typical Average corneal power (ACP) ≤ 47.75 D, Higher-order RMS error** ≤ 0.65
1 Atypical Topography None None Atypical:
  • -

    Irregular

  • -

    Asymmetric superior bowtie

  • -

    Asymmetric inferior bowtie

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    Inferior or superior steepening no more than 3.00 D steeper than ACP

 ACP ≤ 48.00 D Higher-order RMS error ≤ 1.00
2 Suspect Topography None None Isolated area of steepening:
  • -

    Inferior steep pattern

  • -

    Superior steep pattern

  • -

    Central steep pattern

 Additional features: ACP ≤ 49.00 D or Higher-order RMS error > 1.00, ≤ 1.50
3 Mild disease None Possible Consistent with KC Additional features: ACP ≤ 52.00 D or Higher-order RMS error > 1.50, ≤ 3.50
4 Moderate disease Add features: Corneal scarring and overall CLEK grade up to 3.0 Must have Consistent with KC Additional features: ACP > 52.00 D, ≤ 56.00 D or Higher-order RMS error > 3.50, ≤ 5.75
5 Severe disease Add features: Corneal scarring CLEK grade 3.5 or greater overall Must have Consistent with KC Additional features: ACP > 56.00 D or Higher-order RMS error > 5.75″