Author: Irene Sisó Fuertes, University of Manchester

Accommodation is the capability of the human eye to change focus in order to maintain a clear image of an object as its distance varies. Despite the fact that nowadays the lens is established to be the ocular structure that suffers the principal anatomical changes during accommodation, the cornea is known to be a very malleable entity whose changes whilst accommodating still remain unsure. This is the reason why a study was conducted to assess whether corneal parameters and aberrations are affected by accommodation. A dual Scheimpflug photography device was used to obtain data on anterior and posterior axial curvature, total corneal power and corneal pachymetry from three different corneal zones including a more peripheral corneal area (7-10 mm) than in previous studies due to the usage of the latest technology of Galilei G4. Twelve young emmetropic eyes in unaccommodated and four accommodated states were evaluated. Second, third and four-order aberrations as well as the root mean square were also collected for the entire cornea at the same accommodative demands. Results showed no significant (p > 0.05) changes in any of the measured parameters during accommodation for any of the corneal zones. However, statistically significant differences (p<0.01) were found in the various corneal zones when assuming they are constant with accommodation. A stable lineal trend with accommodation was also found for corneal aberrations, although individual variations exist because of the high standard deviation values. All these results suggest that different parameters in various zones of the cornea as well as corneal aberrations are stable during accommodation and will be published in the Journal of Cataract & Refractive Surgery.

Figure 1: Function of Galilei G4. Thanks to its duality, Galilei captures slit images from opposite sides of the illuminated slit, and averages the elevation data obtained from corresponding opposite slit images. This reduces possible decentration errors caused by ocular movements.

Figure 2: Schematic drawing that demonstrates the changes occurring during accommodation.