On the ocular refractive components: the Reykjavik Eye Study.

PURPOSE To study the correlation between ocular refraction and the refractive components (corneal power, lens power and axial length) in a population-based sample of normal subjects. METHODS We analysed the refractive and biometric findings for 723 right eyes (325 males and 398 females) comprising a population-based random sample of citizens 55 years and older participating in the Reykjavik Eye Study. Measurements of refraction, corneal curvature (by keratometry), anterior chamber depth, lens thickness and axial length (all by ultrasound biometry) were used to calculate crystalline lens power. The correlation and regression between refraction and ocular refractive components (corneal power, anterior chamber depth, lens power and axial length) were studied by distributional statistical methods. RESULTS Refraction (spherical equivalent) showed a significant negative correlation with axial length (r = -0.59, P < 0.0001), lens power (r = -0.26, P < 0.0001) and corneal power (r = -0.16, P < 0.0001). There were significant negative correlations between axial length and corneal power (r = -0.44, P < 0.0001) and between axial length and lens power (r = -0.44, P < 0.0001). Based on multiple linear regression analysis, refraction could be correlated with corneal power, lens power and axial length in combination with a correlation coefficient of 0.98 (P < 0.0001). CONCLUSION This study confirms that ocular refraction is statistically significantly correlated with not only axial length but also lens power and (to a lesser extent) corneal power. The variation and correlations of crystalline lens power were considerable -- possibly indicating this component's modulatory effect on ocular refraction during growth. We conclude the refractive error of the eye to be a multifactorial condition involving a complex interplay between the cornea, the lens and the length of the eye.