Abstract
Abstract: :
Purpose: To quantify the reflected laser light incident on an operator’s eye during argon laser photocoagulation using the slit lamp (SL) and indirect ophthalmoscope (IO) delivery systems with standard protective filters and to identify factors that influence these irradiance levels. Methods: Reflected laser energy incident on the operator’s eye was measured using a spectacle mounted photodiode connected to a laser power meter (PD300/Nova, Ophir Optronics). This system was interfaced with StarCom v3.03 software (Ophir Optronics) for real time data logging. A 60 diopter model eye with an internal optical trap was used for argon laser (526nm) photocoagulation with the Novus Omni console and the SL and IO delivery system. For the SL measurements an area centralis lens and 500 micron spot size was used while for the IO a 28 D lens was used in different settings: simulating a patient in the supine and sitting positions; operator with and without a white coat; and with and without additional laser safety glasses between the operator eye and the IO optics. Reflected laser irradiance was measured for a total of 100 pulses for each setting using identical treatment parameters (240 mW, 0.10 seconds). All other confounding wavelengths were eliminated from the measurements. Results:With the SL delivery average irradiance was 7.89 nW (SD 0.805) per laser pulse, while with the IO delivery average irradiance was 59.3 nW (SD 136) per laser pulse in the supine and 73.3 nW (SD 39) in the sitting position. Removing the operator’s white coat reduced the IO irradiance to an average of 27.8 nW (SD 39) per pulse and laser protective glasses further reduced the levels to only 1.83 nW (SD 1.19). With the IO system, large fluctuations in irradiance were noted with the patient in the supine position, the maximal flashback measured was 789 nW. Conclusions: Compared to the SL, IO delivery shows a seven–fold increase in laser irradiance from treatment beam reflections and therefore has a higher potential for cumulative retinal photochemical damage. With the IO delivery system, patients are best treated in the supine position (lower average irradiance to the operator eye). Since the effects of such exposure are as yet unknown, measures such as removing the white coat during treatment and using safety devices to bridge the gap between the IO optics and the operator’s eye are recommended.
Keywords: retina • laser • clinical laboratory testing