Purpose: To assess whether low concentrations of a fluorescent dye such as Rhodamine 6G would help the unaided human eye visualize the vitreous and ILM under standard halogen illumination.
Material/methods: The UV/Vis absorption (E) and fluorescence (I) spectra of Rhodamine 6G in water was measured and compared to ICG. Surgery was performed in two rhesus monkeys and consisted of standard pars plana vitrectomy with halogen light source used for illumination. Rhodamine 6G was diluted in BSS. A few drops of the dye in a concentration of 0.2% (307 mOsm) were applied over the posterior pole in the air filled globe and washed out by irrigation after one minute. Immediately after surgery, the globes were enucleated, fixated and prepared for histological evaluation.
Results: In contrast to ICG, both the maximum of the absorption and emission of Rhodamin 6G are very well within the spectral sensitivity of the human eye. The Rhodamine 6G-BSS solution itself appears red in color. Using a dye concentration of 0.1% there was no visible red-staining of the ILM as such. As the dye was irrigated out with BSS, a marked green fluorescence of the fluid within the vitreous cavity was noted. With halogen illumination through a standard 20ga light pipe, the dye provided a sufficient green fluorescence to identify and safely remove the ILM and to clearly differentiate areas of peeled from non-peeled ILM. During light microscopy eyes revealed a peeled ILM demarcation with no signs of acute retinal toxicity.
Conclusion: Our findings indicate that a fluorescent dye can be used for ILM peeling. Assuming that the fluorophore provides a high enough fluorescence quantum yield after adsorption to the ILM, much lower dye concentrations could be used compared to absorbent dyes thereby minimizing toxic effects.