Association between axial length and corneal refractive power in the two-continent population-based studies project

To examine associations between corneal refractive power (CRP) and axial length (AL) in various populations of different ethnicities and age.

Using biometry, we measured AL and CRP in population-based studies (Ural Eye and Medical Study (UEMS), Ural Very Old Study (UVOS), Beijing Eye Study (BES), Central India Eye and Medical Study (CIEMS), and Kailuan Eye Study (KES), all examining adults, and the Ural Children Eye Study (UCES), Shandong Children Eye Study (SCES) and Hinggan Children Eye Study (HCES), all examining schoolchildren).

In all studies examining adults, CRP significantly and linearly decreased with longer AL for the AL range from 21.0 mm to 24.0 mm (UEMS and UVOS) or 24.5 mm (BES, CIEMS and KES). For an AL > 24.0-24.5 mm, CRP was statistically independent of AL (UEMS:P = 0.38; UVOS:P = 0.10), or increased with longer AL (BES:P = 0.02; CIEMS:P < 0.001). In the KES, CRP plateaued for an AL from 24.0 mm to 26.5 mm, and showed a decrease for an AL of 26.5 + mm. In all studies on schoolchildren, CRP continuously decreased with longer AL across the whole range of AL, spanning from 21.0 mm to 26.5 + mm, with a steeper decrease for an AL between 21.0 mm and 24.0 mm than for an AL of 24.0 + mm. For an AL of 24.0 + mm, the CRP values were significantly (P > 0.001) lower in all three schoolchildren studies than in the studies including adults.

Myopia varies between schoolchildren and adults in the relationship between AL and CRP, potentially pointing to a difference between entities.

What is known Corneal refractive power (CRP) is correlated with axial length. What is new In adults, CRP significantly and linearly decreased with longer axial length for the axial length range from 21.0mm to approximately 24.5mm, while for an axial length of >24.5mm, the CRP was statistically independent of axial length or increased with longer axial length. In schoolchildren, the CRP continuously decreased with longer axial length across the whole range of axial length, including the highly myopic part, with a steeper decrease in CRP for an axial length between 21.0mm and 24.0mm than for an axial length of 24.0+mm. These differences between myopia in schoolchildren and myopia in adults may give a hint that today´s schoolchildren myopia may partially differ from the myopia of adults.