Kojima 2020.

Study characteristics
Patient Sampling	Multicentre (Japan), retrospective, case‐control study which included 329 eyes (healthy controls and people with keratoconus).
Patient characteristics and setting	People with keratoconus were aged < 50 years, visited 1 of the facilities between January 2015 and December 2018, were diagnosed with keratoconus, Amsler‐Krumeich classification stage 1 (average K value < 48 D and corneal astigmatism < 5 D), had no ocular diseases other than keratoconus and refractive error, and had no history of ocular surgery. Healthy subjects were people aged < 50 years who had undergone an ophthalmic screening.
Index tests	Multivariate logistic regression analysis to create an equation that predicts early keratoconus (keratometer keratoconus index) using auto‐keratometer parameters.
Target condition and reference standard(s)	Keratoconus diagnosis was based on corneal topography or tomography results (corneal steepening and asymmetric astigmatism, protrusion of the posterior cornea, and thinning of the cornea at the area of protrusion) and slit‐lamp findings. 2 corneal specialists classified the cases before inclusion.
Flow and timing	All cases were included in the reference standard and index test. All data were included in a 2 × 2 table.
Comparative	Not applicable
Notes	This research did not receive any specific grant from funding agencies in the public, commercial, or not‐for‐profit sectors.
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	No
Was a case‐control design avoided?	No
Did the study avoid inappropriate exclusions?	Yes
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			High
DOMAIN 2: Index test (All tests)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
If a threshold was used, was it pre‐specified?	No
Was the model designed in an appropriate manner?	No
Could the conduct or interpretation of the index test have introduced bias?		High risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Yes
Could the patient flow have introduced bias?		Low risk
DOMAIN 5: Comparative