Relationships between the Aberrations and the Morphology of Ocular Anterior Segment during Accommodation

Abstract

Purpose: : To investigate the relationships between the morphometric dimensions of ocular anterior segment and the ocular aberrations during accommodation.

Methods: : Thirty-five eyes of 35 healthy subjects (21 women and 14 men, mean ± SD age: 25.6 ± 3.1 years) were enrolled. The mean spherical ametropia of the text eye was -0.44 ± 0.64 D (range: +0.50D to -2.00D), with astigmatism less than 0.75D. A custom-built Hartmann-Shack aberrometer and a custom-built ultra-long scan depth spectral domain optical coherence tomography (UL-OCT) were combined. They were used to measure the monochromatic optical aberrations and obtain the full range of ocular anterior segment simultaneously. Each subject was asked to fix the target with the left eye while the right eye was measured by the aberrometer and UL-OCT under the conditions of non-accommodation and 3.0D-accommodative stimuli. The Root-Mean-Square of high-order aberrations (HO-RMS) were calculated up through seventh order for fixed pupil size of 3.0 mm. Custom software was developed to obtain the morphometric dimensions, including anterior chamber depth (ACD), pupil diameter (PD), lens thickness (LT), anterior (ASC) and posterior (PSC) surfaces curvatures of the lens. The relationships of the between the dimensional parameters and wavefront aberrations during accommodation were investigated.

Results: : Compared to the non-accommodative condition, the ACD, PD, and the radii of ASC and PSC decreased significantly, while the LT and HO-RMS increased under 3.00D-accommodative stimuli (Paired t-test, P < 0.01). For both non-accommodative and accommodative conditions, HO-RMS was negatively correlated with the PD (R = -0.532 and -0.801, respectively, P < 0.01). Negatively correlation between the change of ASC and HO-RMS was found (R = -0.348, P = 0.022).

Conclusions: : Both the morphometric dimensions of ocular anterior segment and high-order aberrations changed significantly during accommodation. It appeared that high-order aberrations increased mainly due to the increased convexity of the lens anterior surface during accommodation. The variance of pupil size between subjects may indicate the presence of autoregulatory mechanism in ocular high-order aberrations that maintain good retinal image.

Keywords: accommodation • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • aberrations