Primary objective of this study was to evaluate the diagnostic capability of keratoconus match index (KMI) and keratoconus match probability (KMP) indexes in forme fruste keratoconus (FFK), and their association with a series of Pentacam-derived keratconus (KC) indexes. KMI and KMP parameters are KC-specifc indexes that are measured by Ocular Response Analyzer (ORA), based on the distinct ORA-derived waveform characteristics of KC eyes.

Study participants were recruited from the Cornea Outpatient service in a consecutive if eligible basis. Two study groups were formed: a) FFK group (FFKG) that included patients diagnosed with FFK, and, b) Control group (CG) was formed by refractive surgery candidates.

All ORA (Reichert Ophthalmic Instrument, Buffalo, NY, USA, software version: 3.01)and Pentacam (Pentacam HR, Oculus Optikgerate GmbH, Heidelberg, Germany)measurements were performed by the same experienced operator in a consistent way

Inclusion Criteria:

• diagnosis of keratoconus KC in the fellow eye according to the Amsler-Krumleich criteria (FFKG)
• KISA index between 60 and 100% in the FFK eye (FFKG)
• lack of any KC-related findings / signs in the slit-lamp biomicroscopy (FFKG)
• uneventful ophthalmologic history (CG)
• no indications of corneal pathology in slit-lamp biomicroscopy and Placido disk-based videokeratography (CG)
• KISA index value less than 60% (CG)

Exclusion Criteria:

for both study groups:

• previous incisional eye surgery
• corneal scars and opacities
• history of herpetic keratitis, severe eye dryness
• pregnancy or nursing
• current corneal infection
• glaucoma
• suspicion for glaucoma
• IOP lowering treatment
• underlying autoimmune disease

All participants were recruited from the Outpatients Cornea service, in a consecutive if eligible basis