Table 1.

Previously suggested parameters used to determine progression of ectatic disease

Suggested Parameter	Value Representing Progression	Validated
Spherical power, and higher order irregular astigmatism [32, 35]	Positive Rate of Change per Year	No
Spherical component, regular astigmatism, decentration component, and higher order irregularity [37]	Positive Rate of Change per Year	No
Kmax (steepest K) [27, 38]	≥ 1.00 D increase	No
Kmax – Kmin [38]	≥ 1.00 D increase	No
Kmean (average of Kmax and Kmin)	≥ 0.75 D increase	No
Pachymetry [38]	≥ 2 % decrease in central thickness	No
Back optic zone radius of the best fitting contact lens [27]	0.1 mm or more decrease	No
Increase in the central K power [25]	≥ 1.50 D increase from baseline	No
Manifest cylinder [38]	Increase of ≥ 1.00 D in 24 months	No
Manifest refraction spherical equivalent change (MRSE) [27, 38]	≥ 0.50 D	No
ISV [22]	Specific values for each KCN stage	No
IHA [22]	Specific values for each KCN stage	No

ISV = index of surface variance, IHA = index of height asymmetry, KCN = keratoconus