Extending the range of the surgical keratometer

Interest in optical precision in ocular surgery has been increasing recently. The surgical keratometer is central to the practice of ocular surgery, and research is needed to increase the precision of surgical keratometry techniques. Animal corneas used for these purposes may be outside the range of the surgical keratometer. Extension of the lower range of the Terry keratometer is achieved by substituting a 200- or 250-mm-focal-length objective lens for the standard 175-mm lens on the Zeiss operating microscope. Conversion equations and graphs are presented that allow conversion of the values obtained with these lenses.