Early Detection of Keratoconus: Diagnostic Advances and Their Impact on Visual Outcomes: A Systematic Review

<i>Background and Objectives</i>: Keratoconus is a progressive corneal ectatic disorder and a leading cause of corneal transplantation in developed countries. Early detection is critical for initiating timely interventions such as corneal cross-linking, which can halt disease progression and preserve long-term visual function. This review aims to synthesize current diagnostic approaches for early keratoconus detection and assess their clinical impact on visual outcomes. <i>Materials and Methods</i>: A comprehensive literature search was conducted across PubMed/MEDLINE, Web of Science, Google Scholar, Scopus and the Cochrane Library through September 2025. Search terms included "early keratoconus," "subclinical keratoconus," "forme fruste keratoconus," "keratoconus detection," "corneal topography," "corneal tomography," "anterior segment optical coherence tomography (AS-OCT)," "corneal biomechanics," "artificial intelligence," "genetic risk, "environmental factors", and "machine learning." Two independent reviewers analyzed the data. Studies were included if they investigated diagnostic modalities for early-stage keratoconus and discussed their relevance to visual outcomes. <i>Results</i>: One hundred and seven studies were included in the final review. Four diagnostic modalities demonstrated consistent clinical value: 1. corneal topography for assessing anterior surface irregularities; 2. corneal tomography, currently regarded as the gold standard due to its ability to detect early posterior elevation and pachymetric changes; 3. AS-OCT for epithelial and stromal profiling; and 4. biomechanical assessments, which evaluate corneal tissue stability prior to structural alterations. Artificial intelligence, when integrated with imaging data, enhances diagnostic sensitivity and standardizes interpretation across clinical settings. <i>Conclusions</i>: Early keratoconus detection is crucial for preserving vision; and integrating multimodal, AI-supported diagnostics into routine care-especially for high-risk groups-enhances accuracy, improves outcomes, and reduces progression rates of disease.