Pan-retinal photocoagulation in patients with diabetic retinopathy typically involves application of more than
1000 laser spots; often resulting in physician fatigue and patient discomfort. We present a semi-automated patterned
scanning laser photocoagulator that rapidly applies predetermined patterns of lesions; thus, greatly improving the
comfort, efficiency and precision of the treatment.
Patterns selected from a graphical user interface are displayed on the retina with an aiming beam, and
treatment can be initiated and interrupted by depressing a foot pedal. To deliver a significant number of burns during
the eye's fixation time, each pulse should be considerably shorter than conventional 100ms pulse duration. We
measured coagulation thresholds and studied clinical and histological outcomes of the application of laser pulses in the
range of 1-200ms in pigmented rabbits.
Laser power required for producing ophthalmoscopically visible lesions with a laser spot of 132&mgr;m decreased
from 360 to 37mW with pulse durations increasing from 1 to 100ms. In the range of 10-100ms clinically and
histologically equivalent light burns could be produced. The safe therapeutic range of coagulation (ratio of the laser
power required to produce a rupture to that for a light burn) decreased with decreasing pulse duration: from 3.8 at 100ms, to 3.0 at 20ms, to 2.5 at 10ms, and to 1.1 at 1ms. Histology demonstrated increased confinement of the thermal damage with shorter pulses, with coagulation zone limited to the photoreceptor layer at pulses shorter than 10ms. Durations of 10-20ms appear to be a good compromise between the speed and safety of retinal coagulation. Rapid application of multiple lesions greatly improves the speed, precision, and reduces pain in retinal photocoagulation.