Impact Of Keratoconus On Ocular Surface Parameters: A Systematic Review And Meta-Analysis.

Keratoconus (KC) is a progressive ectatic disease that may lead to severe vision loss. Although its etiology is not fully understood, there is growing evidence that suggests a pivotal role of ocular surface and tear film abnormalities leading to an inflammatory state in the pathogenesis and progression of KC. We aimed to systematically review and critically assess the most updated evidence on ocular surface parameter changes in patients with keratoconus.

Instituto Universitario Fernández-Vega, Oviedo, Spain.

Systematic review of studies comparing ocular surface parameters between patients with and without KC. The Protocol was prospectively registered in PROSPERO database (CRD42023456694). Medline/PubMed, Web of Science, and Scopus databases were searched without time or language restrictions on January 1st, 2024. An additional hand-searching was performed. Selection of studies and data extraction was peer-reviewed. A pairwise meta-analysis was performed. Outcomes were ocular surface index (OSDI), ocular surface staining, break-up time (BUT), Schirmer test, conjunctival impression cytology (CIC), meibomian gland dysfunction (MGD) and corneal nerve assessment. Newcastle-Ottawa Scale (NOS) for quality assessment of evidence.

24 studies were included (2843 eyes from 2120 patients), of which 13 were meta-analyzed. Most studies were performed in Turkey (7,29%). All were observational and had a NOS≥7. KC subjects had higher values of OSDI (Mean difference [MD]=17.95 [95%CI 13.25–22.65], 9 studies, 1348 subjects), shorter BUT (MD= -3.56 [95%CI -4.84– -2.27], 9 studies, 1149 subjects), less tear production by Schirmer test (Standardized mean difference= -1.23 [95%CI -1.86– -0.59], 7 studies, 922 subjects), higher grade of conjunctival squamous metaplasia (MD=1.21 [95%CI 1.04– 1.39], 3 studies, 191 subjects) and higher levels of MGD (MD=0.24 [95%CI 0.24– 0.36], 2 studies, 600 subjects), higher staining scores and nerve alterations compared to healthy volunteers.  

The findings suggest that patients with KC have significant alterations on ocular surface parameters, showing more severe symptoms and greater impact on ocular surface damage, tear film stability and production than do healthy subjects without KC. This underscores the importance of integrating ocular surface and tear film assessment and management into a comprehensive care of KC patients, extending beyond the corneal ectasia.