Making sense out of wavefront sensing

The presence of optical aberrations that blur retinal images were the subject of popular lectures by Helmholtz in the 1860s, and led him to state: "Now, it is not too much to say that if an optician wanted to sell me an instrument which had all these defects, I should think myself justified in blaming his carelessness in the strongest terms and giving him back his instrument."1 Recently, the availability of wavefront aberrometers in the clinical setting and wavefront-guided vision correction has rekindled an intense interest in the optical aberrations of the eye and in particular those aberrations that cannot be corrected with traditional sphero-cylindrical lenses.