Determination of pulse profile characteristics of multi spot retinal photocoagulation lasers

A system is described for determination of discrete pulse train characteristics of multi spot laser delivery systems for retinal photocoagulation. While photodiodes provide an ideal detection mechanism, measurement artifacts can potentially be introduced by the spatial pattern of the delivered beam relative to a discrete photodiode element. This problem was overcome by use of an integrating sphere to produce a uniform light field at the site of the photodiode detector. A basic current driven photodiode detection circuit incorporating an operational amplifier was used to generate a signal captured by a commercially available USB interface device at a rate of 10 kHz. Studies were undertaken of a Topcon Pascal Streamline laser system with output at a wavelength of 577 nm (yellow). This laser features the proprietary feature of 'Endpoint Management' ™ where pulses can be delivered as 100% of set energy levels with visible reaction on the retina and also at a reduced energy level to create potentially non visible but clinically effective lesions. Using the pulse train measurement device it was identified that the 'Endpoint Management' ™ delivery mode of pulses of lower energy was achieved by reducing the pulse duration of pulses for non-visible effect pulses while maintaining consistent beam power levels within the delivered pulse profile. The effect of eye geometry in determining safety and effectiveness of multi spot laser delivery for retinal photocoagulation is discussed.