Longitudinal measures of pupil barycenter and estimation of angle kappa in young children.

PURPOSE: The angle between the visual axis and the pupillary axis (angle kappa), and its approximation (angle lambda-between the line of sight and the pupillary axis), are reported to be larger in shorter eyes. However, there is only one previous study of these angles in children, and no longitudinal studies. This study evaluated angle kappa in young children over a 3-year period.

METHODS

Pupil barycenter measures (pupil centre relative to the corneal apex) were taken with an optical biometer and used to estimate angle kappa using the Pythagorean theorem. Both eyes of young children (6 to ≤8 years at baseline) with functional emmetropia were measured biannually for 3 years (seven visits) following complete cycloplegia.

RESULTS

The pupil barycenter was located inferior nasal to the corneal apex in most eyes, with a median absolute angle kappa of 5.01° ± 2.54° (0.33 ± 0.15 mm). There was no significant interocular difference in this angle. Correlations of angle kappa with axial length (AXL) and refractive error at baseline were not significant (both p > 0.05), with a trend of a smaller angle kappa in longer eyes. The rate of decrease of angle kappa (slope) was significant for the right eye, as the rate of increase in AXL increased (r = 0.33, p < 0.01), but not in the left eye. The rate of change in AXL and refractive error did not show a significant correlation with the rate of change in angle kappa (p > 0.05).

CONCLUSIONS

Angle kappa appears to be independent of AXL or refractive error in these young children with a limited range of eye sizes. However, angle kappa may decrease at a higher rate in eyes with a greater rate of increase in AXL over the course of 3 years.