Decentered Ablation Zones Resulting from Photorefractive Keratectomy with an Erodible Mask

Four patients underwent photorefractive keratectomy for compound myopic astigmatism using the erodible mask. All achieved improvements in unaided visual acuities despite manifesting varying levels of decentration of the ablated zones. However, one patient had significant monocular diplopia because of the severity of the decentration. The problems with the present system include the use of a NON coaxial microscope; difficulty with obtaining and maintaining proper alignment of the excimer laser beam to the erodible mask and the central corneal zone; the inability to interrupt and restart the procedure due to the ablation of the reference marks on the mask; and patient discomfort. We suggest installation of the PMMA mask at the laser aperture in order to alleviate the above difficulties. In the meantime, use of a coaxial microscope, a limbal suction device for fixation, permanent reference marks on the mask and peribulbar anaesthesia may be helpful.