Abstract: Objective  To identify the diagnostic criteria used for the terms subclinical keratoconus in published articles. Methods  This was a systematic review of all research on the use of the keyword "subclinical keratoconus" in PubMed, Cochrane Library, Embase database, CNKI, Wanfang Data Knowledge Service Platform and China Science and Technology Journal Database from January 2000 to March 2022. Two independent reviewers analyzed the data. The inclusion criteria for articles included that a sample size of subclinical keratoconus eyes was greater than 20 eyes, they contained the definition of subclinical keratoconus, and Newcastle-Ottawa Scale(NOS) was used to evaluate the quality of literature. Inclusion criteria for definition and examination technology used of the selected articles were then analyzed. Results  A total of 263 studies were included, of which 207 were excluded. Definitions for subclinical keratoconus included that the criteria of having keratoconus in the fellow eye was in 66.07% (37 of 56) of the articles. Lacking of any keratoconus-related findings/signs in the slit-lamp biomicroscopy was in 35.71% (20 of 56). Normal-appearing corneal on slit-lamp biomicroscopy, or keratometry, or retinoscopy, or ophthalmoscopy was in 33.93% (19 of 56). Conclusions  This review demonstrates the lack of unified criteria to define subclinical keratoconus. According to the literature review, the most common subclinical keratoconus definition used refers to an eye with keratoconus in the fellow eye and normal-appearing corneal on slit-lamp biomicroscopy.(Int Rev Ophthalmol, 2023, 47: 97-103)

Key words: subclinical keratoconus, diagnostic criteria, systematic review