Objective changes in astigmatism during accommodation.

Purpose: Previous studies have shown small but clinically significant changes in the power and axis of astigmatism when the eye accommodates. Monocular objective measurements of the eye during accommodation, when the object approaches the eye without convergence, also reveal small astigmatic changes. Moreover, it is known that the eye exhibits ocular cyclotorsion at different gaze angles.

Optical factors influencing the amplitude of accommodation.

The purpose of this work was to find plausible predictors among optical parameters that may explain the inter-individual differences in subjective amplitude of accommodation not explained by age. An exploratory multivariable regression analysis was carried out retrospectively on a dataset with 180 eyes from 97 subjects (ages ranged from 20 to 58years). Subjective amplitudes of accommodation were recorded with the use of a custom-made Badal system.

Changes in the objective amplitude of accommodation with pupil size.

Purpose: We evaluate the effect of pupil size on objectively measured amplitude of accommodation (AA).

Methods: Pupil diameter and wavefront aberrometry were obtained in 15 eyes when stimulus swept across the range of clear vision in steps of 0.5 diopters.

Refractive status in eyes with inhomogeneous or irregular pupils.

Purpose: In some eyes, aberrometric measurements of the refractive error can differ by more than 1 diopter from standard subjective refraction. We aim to understand the reasons for these discrepancies and to study the role of both amplitude (irregular or inhomogeneous pupil transmission) and phase (aberrations) of the wavefront.

Methods: The spherical equivalent was measured by different subjective, objective, and aberrometric methods in a population of 177 eyes.

The change of spherical aberration during accommodation and its effect on the accommodation response.

Theoretical and ray-tracing calculations on an accommodative eye model based on published anatomical data, together with wave-front experimental results on 15 eyes, are computed to study the change of spherical aberration during accommodation and its influence on the accommodation response. The three methodologies show that primary spherical aberration should decrease during accommodation, while secondary spherical aberration should increase. The hyperbolic shape of the lens' surfaces is the main factor responsible for the change of those aberrations during accommodation.

Limitations of the ocular wavefront correction with contact lenses.

We analyze theoretically, by means of both computer simulations and laboratory experiments, the limitations of correcting aberrations with ideal customized contact lenses. Four experiments are presented: In the first one, we have analyzed the limitations of a static correction on the dynamic wavefront. In the second one, we studied the rotations of a contact lens on the eye using an optical method.

Comparison of partial coherence interferometry and ultrasound for anterior segment biometry.

Purpose: To assess the performance of a partial coherence interferometry (PCI)-based device for the determination of anterior segment biometry.

Setting: Clinica Centrofama, Cartagena, Murcia, Spain.

Methods: Central corneal thickness (CCT), anterior chamber depth (ACD), and lens thickness (LT) were measured with the ACMaster PCI anterior segment biometer and an Echoscan US-1800 ultrasound (US) biometer/pachymeter with and without cycloplegia.

Effect of 3rd-order aberrations on human vision.

Purpose: To investigate the effect of 3rd-order aberrations on human vision.

Setting: Grupo de Ciencias de la Visión, University of Murcia, Murcia, Spain.

Methods: The 3rd-order aberrations coma and trefoil were induced with purpose-designed soft contact lenses, 3 inducing coma (low [0.

Accommodation-related changes in monochromatic aberrations of the human eye as a function of age.

Purpose: To investigate the relationship between accommodation and the optical aberrations of the whole human eye, as a function of age.

Methods: Sixty healthy subjects with spherical ametropia in the range +/-3 D, astigmatism less than 1 D, corrected visual acuity of 20/18 or better, and normal findings in an ophthalmic examination were enrolled. Subjects were divided into four groups, with age ranges of 19 to 29, 30 to 39, 40 to 49, and 50 to 60 years.