Post PRK corneal scatter measurements with a scanning confocal slit photon counter

摘要

Increased corneal light scatter or "haze" has been associated with excimer laser photorefractive surgery of the cornea. The increased scatter can affect visual performance; however, topical steroid treatment post surgery substantially reduces the post PRK scatter. For the treatment and monitoring of the scattering characteristics of the cornea, various methods have been developed to objectively measure the magnitude of the scatter. These methods generally can measure scatter associated with clinically observable levels of haze. For patients with moderate to low PRK corrections receiving steroid treatment, measurement becomes fairly difficult as the haze clinical rating is non observable. The goal of this development was to realize an objective, non-invasive physical measruemdent that could produce a significant reading for any level including the background present in a normal cornea. As back-scatter is the only readily accessible observable, the instrument is based on this measuremnet. To achieve this end required the use of a confocal method to bias ot the background light that would normally confound conventional methods. A number of subjects with nominal refractive errors in an Air Force study have undergone PRK surgery. A measurable increase in corneal scatter has been observed in these subjects whereas clinical ratings of the haze were noted as level zero. Other favorable aspects of this bakc-scatter based instrument include an optical capability to perform what is equivalent to an optical A-scan of the anterior chamber. Lens scatter can also be measured.