Scanning laser tomography is an objective non-invasive method for the three-dimensional imaging of the eye in-vivo. It has become a valuable tool in the diagnosis and monitoring of changes to the fundus and optic nerve head in diseases such as glaucoma. Optical errors should be eliminated where possible to improve accuracy and maximise the potential for the detection of subtle change due to disease progression. Alterations in the keratometry reading cause scaling changes in the (x, y) plane. This study demonstrated the importance of the keratometry value on retinal measurements. Accurate fundus measurements require input of the appropriate keratometry value for each subject, while for the detection of subtle change over time in longitudinal study, the keratometry reading should not be altered from baseline.