ORIGINAL PAPER Repeatability of corneal and ocular aberration measurements and changes in aberrations over one week Clin Exp Optom 2009; 92: 3: 253–266 DOI:10.1111/j.1444-0938.2009.00364.x Marco A Miranda MSc Clare O’Donnell PhD MCOptom FAAO Hema Radhakrishnan PhD MCOptom Faculty of Life Sciences, The University of Manchester, United Kingdom E-mail: marco.miranda@postgrad. manchester.ac.uk Background: Both Shack-Hartmann aberrometry (IRX3, Imagine Eyes, Orsay, France) and Scheimpflug photography (Oculus Pentacam, Oculus Inc Wetzlar, Germany) are known to provide repeatable measurements. The variability in measurements of corneal and ocular aberrations obtained with these instruments over one week had not been assessed. The aim was to study the variability in corneal and ocular aberrations in the human eye over one week and to determine the impact of age on corneal and crystalline lens aberrations and on the variability of these measurements. Methods: Monochromatic ocular aberrations were measured with the IRX3 and mono- chromatic corneal aberrations were measured using Scheimpflug photography on one eye of 23 normal subjects at periods of a few seconds, one hour and one week after the initial measurement. Results: No significant differences were found between the initial aberrations and aber- rations measured at 59  24 seconds, 1.10  0.24 hours and 7.11 0.31 days later. Analysis with Bland and Altman plots showed that measurements with both instruments were highly repeatable over the times studied. There was no relationship between age and the variance of corneal and ocular aberrations (higher order, spherical and coma aberrations). Corneal spherical aberration did not show a significant correlation with age, whereas the lens aberrations changed from being negative in the younger age groups to positive in the older age group, however, these differences failed to reach statistical significance (p > 0.05). Conclusion: The variability found in all the measurements was small and not clinically significant and could be attributable to instrument noise, changes in the tear film and to small fixational eye movements. Submitted: 30 August 2008 Revised: 23 December 2008 Accepted for publication: 5 February 2009 Key words: corneal aberrations, crystalline lens aberrations, ocular aberrations, Oculus Pentacam, Scheimpflug imaging, Shack- Hartmann aberrometer Aberrations are usually the main factors, beyond diffraction, that degrade image quality in the human eye, 1–3 however, aber- rations can be desirable to minimise pos- sible aliasing as a result of mismatches between optical and neural performance of the visual system. 3 Of all available techniques to determine the wavefront aberrations of an eye, Shack- Hartmann aberrometry is probably the most commonly used. 4,5 Shack-Hartmann wavefront sensors consist of an array of microlenses associated with sensors that provide directional information about rays of light generated from a small infra-red laser spot imaged on the retina. The shape of the wavefront in the pupil is derived by analysing the position of the image pro- duced by each of these rays. Subsequently, various systems of analysis can be used to describe the shape of the wavefront and CLINICAL AND EXPERIMENTAL OPTOMETRY © 2009 The Authors Clinical and Experimental Optometry 92.3 May 2009 Journal compilation © 2009 Optometrists Association Australia 253