Table 1.

Progression definitions among literature

Study	Criteria for progression
Dresden protocol (Raiskup-Wolf et al,31 2008)	Any of the following three:
	• Increase in Kmax ≥1.00 diopter (D)
	• Patient’s self-report of deteriorating of visual acuity
	• Need for new contact lens fitting more than once in 2 years
Wittig-Silva et al,17 2008	One or more of the following:
	• Increase of ≥1.00 D in the steepest simulated keratometry reading (Kmax)
	• Increase of ≥1.00 D in manifest refraction’s astigmatism
	• Increase of ≥0.50 D in manifest refraction SE
	• Decrease of ≥0.1 mm in back optic zone radius of the best fitting contact lens
Vinciguerra et al,80 2009	Any of the following three:
	• Change in myopia and/or astigmatism of ≥3.00 D in the previous 6 months
	• Mean central K-reading change of ≥1.50 D in 3 consecutive topographies during the previous 6 months
	• Mean central corneal thickness decrease of ≥5% in 3 consecutive tomographies performed in the previous 6 months
O’Brart et al,16 2011	Any of the following two criteria met over the previous 18 months:
	• Reduced UCDVA or CDVA by more than one line
	• Increase of refractive or corneal astigmatism, keratometry, or cone apex power by 0.75 D
Hersh et al,18 2011	One or more of the following changes over a period of 24 months:
	• Increase of ≥1.00 D in the steepest K measurement
	• Increase of ≥1.00 D in manifest cylinder
	• Increase of ≥0.50 D in manifest refraction SE
Chatzis and Hafezi,73 2012	• Increase of ≥1.00 D in Kmax over a maximum of 12 months
Hashemi et al,38 2013	Any of the following criteria met during the previous 12 months:
	• Increase in Kmax, manifest cylinder error, or manifest refraction SE ≥1.00 D
	• Loss of ≥2 lines of CDVA attributable just to keratoconus progression
Mazzotta et al,60 2014	Variation of at least three of the following parameters (one clinical plus two instrumental) during a period of 4 months for patients under 18 years and 6 months for adults:a
	• Worsening of UCDVA/CDVA >0.50 Snellen lines
	• Increase of SPH/CYL >0.50 D
	• Increase of topographic symmetry index SAI/SI >1.00 D
	• Increase of mean K reading >1.00 D
	• Reduction of the thinnest point at corneal optical coherence tomography pachymetry ≥10 μm
Stojanovic et al,50 2014	During a period of 12 months:
	• Increase of astigmatism or myopia ≥1.00 D or increase in average Sim K by 1.50 D
Shetty et al,54 2015	• Increase in Kmax, corresponding change in the subjective refraction ≥ 1.0 D or ≥5% decrease in the thinnest pachymetry in the preceding 6 months
Poli et al,36 2015	• Deterioration of uncorrected (UDVA) and/or corrected (CDVA) distance visual acuities >1 Snellen line, SE refraction >0.75 D, cone apex keratometry >0.75 D, and/or reduction in corneal thickness (thinnest point) >10 microns lasting more than 6 months
Gomes et al,89 2015	Consistent change in at least two of the following parameters:
	• Progressive steepening of the anterior corneal surface
	• Progressive steepening of the posterior corneal surface
	• Progressive thinning and/or an increase in the rate of corneal thickness change from the periphery to the thinnest point
	• No specific values were given because the panel considered them to be specific for each device
	• In addition, the panelists also indicated that CXL could be indicated for the treatment of KCN with a perceived risk of progression even if it had not been documented
Godefrooij et al,110 2016	• Increase of ≥1.00 D in the steepest K measurement within 6–12 months

Note:

^aThe follow-up period was obtained from personal communication from the authors (Mazzotta et al, unpublished data, January 2, 2017).

Abbreviations: K_max, maximum keratometry; SE, spherical equivalent; UCDVA, uncorrected distance visual acuity; CDVA, corrected distance visual acuity; SAI, surface asymmetry index; SI, superior-inferior symmetry index.