A keratoscope is a standard device for measuring the shape or me cornea. unfortunately, it cannot take measurements from diffuse corneal surfaces after photorefractive keratectomy (PRK), when such measurements are needed. A tradeoff in keratoscope principles is involved: whether to make the pinhole as small as possible to maintain the operative principles of the device or to emphasize maximum measurement precision. In answer to the National Institutes of Health's request for new methods of measuring the optical properties of the cornea, Physical Optics Corporation (POC) proposes a nonscanning speckle interferometer (NSI) that will measure corneal shape and radius during and immediately following photorefractive keratectomy (PRK). The NSI, based on a well-known principle for optical testing of rough surfaces, incorporates important improvements, including an acousto-optic deflector for creating a beam rake with frequency shift for nonscanning measuring, fiber optic wavelength division-multiplexing technology, and principles of absolute distance interferometry developed by implementing the Chinese remainders theorem. The NSI is flexible, allowing measurement of the corneal shape in diffuse surface zones after PRK; smooth zones are also accessible because of the special position of the exit pupil in the focusing lens. Shape measuring precision is about 0.1 microm, and is defined mostly by surface roughness.
The nonscanning speckle interferometer will permit surgeons to safely monitor the shape of a cornea during surgery. The device will be useful following surgery for mapping the corneal surface. Commercial market demand for such an instrument already exists in clinics and doctors' offices.
