Changes in axial length in adult eyes

Purpose It is generally assumed that axial length remains constant in adults, although there have been reports of gradual axial length decreases with age. These findings are often considered with scepticism by the authors themselves, however. This work investigates the cause for this apparent decrease and looks into any other factors that may influence axial length measurements. Methods The analysis reviews the literature on non‐myopic axial length changes with age in adults and correlates these changes against year of birth and average level of education obtained from United Nations reports. Furthermore a series of calculations were performed to assess how optical biometry methods respond to the thickening of the crystalline lens, while its equivalent refractive index decreases, as well as how they respond to refractive index increases due to cataract. Results The literature analysis shows that axial length does not significantly decrease with age (linear regression, p = 0.071 for the linear term). Axial length does increase with the year of birth, especially in Western countries that all saw similar economic developments during the 20th Century. In non‐Western countries, where the economic development was more diverse, the changes were less pronounced. The correlation of the axial length increase with the increasing education level that occurred in all countries on the other hand was very high ( r² = 0.681; p < 0.001 ). Optical axial length measurements appear to increase by 0.07 mm between 20‐80 years of age due to internal media changes, even if the actual length remains constant. Apparent increases due to cataract are of the same order of magnitude. Conclusions The reported axial length decrease with age is an artefact caused by the gradual myopization of the population. Optical artefacts due to changes in the optical media have very little effect.