Corneal ectasias such as keratoconus (KC) are typically conceptualised as an anterior segment disorder, characterised by progressive corneal thinning and irregularity. The recent systematic review and meta-analysis by Bayat et al. and co-authored by ELZA’s CMO, Prof. Farhad Hafezi, MD, PhD, FARVO, aimed to determine whether structural changes in the retina, choroid, and optic nerve head occur in patients with keratoconus, using optical coherence tomography (OCT) to synthesise the available evidence.
The authors systematically searched PubMed, EMBASE, and Web of Science (through 28 Nov 2024, updated 1 Sep 2025) and identified 38 studies involving 4,584 eyes; 26 studies (3,124 eyes) were included in the meta-analysis.
Their key findings were:
- Significant reductions in macular thickness measurements: average macular thickness, temporal para-foveal thickness (inner ring), and temporal & superior perifoveal (outer ring) thickness.
- Peripapillary and optic nerve head changes: decreased lamina cribrosa thickness, decreased average retinal nerve fibre layer (RNFL) thickness, and RNFL in superior, temporal, and inferior quadrants.
- Conversely, sub-foveal choroidal thickness was significantly increased in KC patients compared with controls.
- Optic nerve head parameters (cup area, cup volume) were larger in KC patients.
- Interestingly, the differences across disease severity were modest: for instance, moderate KC patients had greater superotemporal RNFL thickness than severe disease. The posterior segment changes were found across mild to advanced stages.
From a clinical and research perspective, these findings challenge the long-held notion that keratoconus is confined to the cornea. The demonstration of posterior segment structural alterations implies that the disease may involve more widespread ocular tissue changes, or that biomechanical/structural consequences of ectasia extend beyond the anterior segment.
This meta-analysis extends the conceptual framework of management. While CXL remains focused on halting anterior stromal progression, the recognition of retinal and choroidal changes may prompt discussion of comprehensive monitoring in KC patients, particularly those with advanced disease or co-morbidities.
However, several limitations must be acknowledged: heterogeneity across OCT devices and protocols, retrospective and cross-sectional nature of many included studies, and the inability to determine causality (i.e., whether posterior changes are secondary to corneal biomechanics, axial elongation, altered optical media, or entirely independent).
In summary, this meta-analysis provides robust evidence that keratoconus involves more than corneal shape and stromal architecture – it may also influence retinal thickness, choroidal structure, and optic nerve head morphology. Future longitudinal studies will be necessary to elucidate the temporal relationship, clinical significance (e.g., effect on visual function), and potential implications for screening, monitoring, and treatment of KC.
