Optical Pachometry in the Measurement of Anterior Corneal Disease: An Evaluative Tool for Phototherapeutic Keratectomy

To the Editor. —The 193-nm excimer laser offers a potentially beneficial therapeutic technique for the precise removal of diseased or opaque anterior corneal lamellar tissue, leaving a smooth surface that provides for reepithelialization, a clear cornea, and an appropriate refractive surface. The therapeutic potential of the excimer laser in lamellar ablative keratectomy depends on an accurate means for measuring the depth of the anterior corneal disease. We have found the modified Haag-Streit optical pachometer1useful in the preoperative evaluation of patients considered for such laser treatment. Since its introduction, the optical pachometer has been used for the determination of full corneal thickness by measuring the apparent thickness of an optical section of the cornea viewed from a fixed angle.1Using accurate alignment of the slit lamp and the microscope in relation to the corneal surface, one obtains typical precision values2of between 0.007 and 0.013 mm, with