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To the Editor.
—In ophthalmic laser surgery, contact lenses are employed to allow the visualization of internal features of the eye and their exposure to carefully controlled laser irradiation. The contact lenses are modifications of designs that were originally developed for slit-lamp biomicroscopy. The danger of portions of the laser beam being reflected back from a contact lens has been well recognized, and antireflection coats are used on the first surface of all laser-treatment lenses.Despite the presence of front surface coatings, uncomfortable "flashback" reflections of bright aiming beams occur when portions of the beam return to enter the viewing microscope. On other occasions, significant portions of light are observed to be reflected back into the room. These bright reflections occur most noticeably in lenses that have two or more mirrors. The design of four-mirrored lenses appears to allow the greatest chance of flashback reflections of substantial portions of the