Light flashbacks during retinal laser photocoagulation following fluorescein angiography

BACKGROUND AND OBJECTIVE: Yellow light flashbacks can often be seen In cases of laser photocoagulation performed shortly after fluorescein angiography. To determine whether unblocked secondary emission from retained aqueous and vitreous fluorescein may be reaching the treating ophthalmologist, the absorption characteristics of serial dilutions of sodium fluorescein were studied at wavelengths similar to the output of the krypton laser. MATERIALS AND METHODS: A Unicam sp500 series II visible spectrophotometer (Pye Unicam Ltd., Cambridge, UK) was used to measure fluorescein absorption at serial dilutions ranging from 100,000,000 to 100 ng/mL at 488, 518, 568, and 647 nm. RESULTS: Absorption decreased with progressive dilution of fluorescein concentration and with increased wavelength. Blue (488 nm) and green (518 nm) light absorbed at all dilutions of fluorescein. Yellow light (568 nm) did not show any significant absorption below a concentration of 100,000 ng/mL and red light (647 nm) absorbed little below a concentration of 3,000,000 ng/mL. CONCLUSIONS: Dilutions of fluorescein absorbed all commonly used laser wavelengths. There is concern that fluorescein absorption results in emission of light at 520 nm (range: 450 to 700 nm), which may not be blocked by the filters currently placed in fixed laser delivery systems.