Abstract
Abstract: :
The introduction of digital photography in fluorescein angiography has enabled ophthalmologists to routinely perform angiograms and, within minutes, carry out retinal laser photocoagulation in the presence of residual fluorescein in the eye. During these treatments, we have noticed flashes of bright yellow light coming back to the surgeon. When excited by any wavelength of light, fluorescein characteristically emits light with a peak at 520 nanometers (range, 450 to 700 nm). The fixed laser delivery systems such as the slit lamp microscope or indirect ophthalmoscope, contain filters designed to block the laser light reflected from the retina, but may not block light emitted from fluorescein retained in vitreous or aqueous fluid. Purpose: We studied the absorption characteristics of krypton laser light at wavelengths commonly encountered in clinical settings (488nm, 518nm, 568nm, 647nm) using serial dilutions of sodium fluorescein dye to determine if there might be unblocked light emission from fluorescein reaching the treating ophthalmologist. Methods:A Unicam p500 series II ultraviolet and visible spectrophotometer was used to measure fluorescein absorption at serial dilutions ranging from 100,000,000 Ng/ml to 100 Ng/ml for laser emissions at 488nm, 518nm, 568nm, and 647nm. Distilled water was used as control. Results: Absorption of laser light decreased as the concentration of fluorescein decreased. Absorption also decreased as the wavelength of light increased from 488nm to 647nm. Specifically, blue light (488nm) had the highest absorption and showed absorption at all dilutions of fluorescein. Similarly, green light (518nm) also absorbed at all dilutions. Yellow light (568nm) did not show any significant absorption below a concentration of 100,000 Ng/ml and red light (647nm) did not absorb below a dilution of 3,000,000 Ng/ml. Discussion: Fluorescein dye is known to remain in vitreous and aqueous fluid for up to 24 hours following intravenous administration. Incoming laser light is absorbed by fluorescein that might still be present in significant concentration in vitreous and aqueous fluid. We have demonstrated absorption of all wavelengths of incoming laser light by dilutions of fluorescein with 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. This effect may be aggravated by the presence of diseases that produce breakdown of the blood–retinal barrier and lead to elevated fluorescein concentrations. Whether or not this unblocked light emission might be harmful to the treating surgeon remains to be demonstrated.
Keywords: laser • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina