Ocular axial length and its associations: A systematic review

Background: Axial length is a key factor in determining the underlying cause of refractive errors, including myopia. It is essential for assessing myopic progression or risk in patients. Aim: To systematically evaluate associations between ocular axial length and various ocular biometric, demographic and anthropometric parameters. Method: A systematic review was conducted on studies highlighting the significance of axial length and its associations with anthropometric factors including height and body mass index; ocular biometry factors including refractive error; corneal thickness and radius; crystalline lens; anterior chamber depth; vitreous chamber depth; retinal, choroidal and scleral thicknesses and demographic factors including age, ethnicity, race and gender. The review includes studies demonstrating the impact of axial length changes on the eye’s refractive status. Results: Axial length is associated with anthropometric, ocular biometric and demographic metrics, suggesting a complex interplay of factors. Increased axial length is linked to increased anterior chamber depth, vitreous chamber depth, body height and myopia. Axial length is negatively associated with spherical equivalent refractive error, lens and choroidal thickness. Conclusion: The interplay of age, gender, ethnicity and environmental factors complicates the generalisation of axial length measurements. The strength and direction of these associations vary across studies, indicating complex relationships between factors. Tailored axial length norms based on individual characteristics are necessary, highlighting the need for populationbased studies to minimise the generalisation of ocular biometry in clinical practice. Contribution: This review emphasises the need for population-specifi norms in ocular biometry, considering factors like age, gender, ethnicity and stature to enhance the precision and applicability of axial length measurements in clinical practice. The scarcity of instruments to measure axial length in primary and community eye care settings may hinder myopia control treatments.