Influence of accommodation on the anterior and posterior cornea.

PURPOSE: To evaluate whether significant change occurs in the topography of the anterior or posterior cornea or in corneal thickness with accommodation.
SETTING: Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia.
METHODS: Corneal data were acquired for 12 young, healthy emmetropic subjects under 2 accommodation levels (relaxed and approximately 5.0 diopters) using a rotating Scheimpflug camera. Anterior and posterior corneal elevation and sagittal curvature data as well as pachymetry data were analyzed to evaluate changes associated with accommodation. Corneal elevation data were also analyzed using a recentering procedure designed to minimize the effect of ocular micromovements between measurements.
RESULTS: Changes in corneal parameters resulting from accommodation were small and generally insignificant. The mean change in pachymetry was 0.49 microm +/- 2.62 (SD) across an 8.0 mm pachymetry map. No significant change was found in the best-fit corneal spherocylinder (anterior and posterior cornea) (P>.05). Small changes were found in the corneal cylinder axis, indicative of small cyclotorsional eye movements accompanying accommodation. The mean changes in corneal elevation were 0.09 +/- 0.41 microm (anterior cornea) and 0.17 +/- 0.65 microm (posterior cornea). Only 0.50% (anterior cornea) and 0.27% (posterior cornea) of corneal elevation data points exhibited a statistically significant change with accommodation. Recentering the corneal elevation data led to a reduction in the magnitude of change in corneal elevation with accommodation.
CONCLUSIONS: Small cyclotorsional eye movements occurred with accommodation. When these eye movements were accounted for in data analysis, no consistent significant change in the topography of the cornea was found with accommodation across an 8.0 to 9.0 mm corneal diameter.