A transilluminator marker is used for retinal detachment surgery. The light, conducted by a fiber optics bundle to the tip of the applicator, is brightly visible in the fundus even when the light of the indirect ophthalmoscope is at maximum illumination. The scleral mark at the selected spot is made by releasing a diathermy current of short duration, controlled by an electronic timer. The scleral mark, which affects only the external layers of this tissue, is visible as a small gray ring or a gray spot.
deGuillebon H, Schepens CL. A Transilluminator Scleral Marker. Arch Ophthalmol. 1971;86(3):298-300. doi:10.1001/archopht.1971.01000010300012