Table 3 Definitions and significance of indices based on vertical thickness profiles of the corneal epithelium, Bowman’s layer and stroma.

From: Value of corneal epithelial and Bowman’s layer vertical thickness profiles generated by UHR-OCT for sub-clinical keratoconus diagnosis

Indices

Definitions

Significance

EEI, BEI, SEI

Minimum thickness in the inferior half divided by the average thickness in the superior half multiplied by 100

Localized thinning in the vertical meridian

EEI-MAX, BEI-MAX, SEI-MAX

Minimum thickness in the inferior half divided by the maximum thickness in the superior half multiplied by 100

Maximum localized thinning in the vertical meridian

EPV, BPV, SPV

Root mean square between zonal thicknesses and profile average within one subject

Variation of thickness profile within each individual

EPSD, BPSD, SPSD

Root mean square of the zonal thicknesses of individual profiles and zonal thicknesses of pattern average

Standard deviation of thickness profile between individual and normal pattern

  1. EEI, epithelium ectasia index; BEI, Bowman’s layer ectasia index; SEI, stroma ectasia index; EEI-MAX, maximum epithelium ectasia index; BEI-MAX, maximum Bowman’s layer ectasia index; SEI-MAX, maximum stroma ectasia index; EPV, epithelium profile variation; BPV, Bowman’s layer profile variation; SPV, stroma profile variation; EPSD, epithelium profile standard deviation; BPSD, Bowman’s layer profile standard deviation; SPSD, stroma profile standard deviation.
  2. Zonal thickness, the averaged thickness of 100 A-scans (0.42-mm chord distance) of each zone on the UHR-OCT B-scan image.
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