Cross-cylinder technique

Historical Significance: The booklet describes the author as a technical adviser to the London Optical Co Ltd of Gray's Inn Road London. It was written, acording to the author, because there is little information about the technique in standard text books in the hope that it might be useful to older practitioners, who may not be as versed in the technique as recent graduates. The Cross cylinder technique for determination of the power and axis of astigmatism was devised by Gabriel Stokes, an Irish mathematician of Cambridge in 1849 and known as Stokes' lens. It was used ophthalmologically by Javal, Snellen and others in the second half of the 19thC but was popularised by Edward Jackson. Jackson (1856 - 1942) was Professor of Diseases of the Eye in the Philadelpia Polyclinic and the College for Graduates in Medicine and was a surgeon at the Wills Eye Hospital. He popularized retinoscopy in the United States and the cross cylinder technique.