Table 1. Trial characteristics. Among the 23 trials included, 4 were RCTs, 11 were prospective controlled studies, and 8 were retrospective studies.

A. Prospective and retrospective studies
Source	Year of Publication	Study Quality(NOS)	Country of Origin	No. of Patients	No. of Eyes	Mean Age (years)	Main Results	Mean follow up
Stojanovic	2012	3	Norway	53	61	32 ± 10	27.4% of the eyes gained 2 or more lines	12
Anders Ivarsen	2013	4	Denmark	22	28	22	14 eyes showed a Kmax decrease of more than 2.0D	22
Cosimo Mazzotta	2012	5	Italy	44	44	10–40	Corneal micro-morphological changes observed with in vivo confocal microscopy related with function	12
Dalal Asri	2011	4	France	142	142	24.12 ± 7.58	Keratoconus progression had stopped in 42 eyes (68.8%)	12
Deepa Viswanathan	2013	7	Australia	35	51	24.25 ± 8.08	Kmax decreased 0.96 ± 2.23D	14.38 ± 9.36
Eberhand Spoerl	2011	7	Germany	46	50	29.4 ± 9.3	CH and CRF did not change significantly after CXL	12
Efekan Coskunseven	2009	5	Switzerland	19	19	22 ± 5	Kmax decreased 1.57 ± 1.14D	9 ± 2
Frea Sloot	2013	5	Netherlands	42	53	21.5	Progression was halted in 48 eyes (91%)	12
Frederik Raiskup-Wolf	2008	4	Germany	272	480	30.04 ± 10.46	Kmax decreased 2.68D in the first year; 53% of 142 improved BCVA more than 1 line	26.7 ± 16.2
Hassan Hashemi	2013	6	Iran	32	40	22.45 ± 5.48	CXL could stop disease progression, based on 5-year studies	60
Kinga Kranitz	2012	7	Germany	22	40	29.92	Posterior elevation is a sensitive parameter for monitoring corneal remodelling after CXL	12
Ladan Saffarian	2010	4	Iran	53	92	21.5 ± 3.4	CXL halted the progression of keratoconus in Iranian patients	12
Maria A. Henriquez	2011	5	CA, USA	10	10	29.7	Eight (80%) and 6 (60%) of 10 eyes showed a decrease in the anterior and posterior elevation values, respectively	12
Maria Clara Arbelaez	2009	3	Oman	19	20	24.4	BCVA increased 1.65 lines, and Kave decreased 1.36D	6
Paolo Vinciguerra	2009	6	Italy	28	28	18–60	AK reduced from 58.94D to 55.18D	12
Ritu Arora	2013	6	India	15	15	21.73 ± 9.5	Progression was halted in 11 of 15 patients	16
Tamer M. EL-Raggal	2009	3	Egypt	9	15		No progression within 6 months follow-up	6
Tobias Koller	2009	4	Italy	99	117	27–40	In 39 (37.1%) eyes, Kmax decreased more than 1D	12
Yakov Goldich	2012	5	Israel	14	14	28.2 ± 5.9	Two years after CXL, improved BCVA and reduced Kmax were observed	24