Dynamics of retinal photocoagulation and rupture.
In laser retinal photocoagulation, short (<20 ms) pulses have been found to reduce thermal damage to the inner retina, decrease treatment time, and minimize pain. However, the safe therapeutic window (defined as the ratio of power for producing a rupture to that of mild coagulation) decreases with shorter exposures. To quantify the extent of retinal heating and maximize the therapeutic window, a computational model of millisecond retinal photocoagulation and rupture was developed. Optical attenuation of 532-nm laser light in ocular tissues was measured, including retinal pigment epithelial (RPE) pigmentation and cell-size variability. Threshold powers for vaporization and RPE damage were measured with pulse durations ranging from 1 to 200 ms. A finite element model of retinal heating inferred that vaporization (rupture) takes place at 180-190 degrees C. RPE damage was accurately described by the Arrhenius model with activation energy of 340 kJ/mol. Computed photocoagulation lesion width increased logarithmically with pulse duration, in agreement with histological findings. The model will allow for the optimization of beam parameters to increase the width of the therapeutic window for short exposures.
Sramek
Christopher
C
Stanford University, Department of Applied Physics, 452 Lomita Mall, Room 140, Stanford, California 94305, USA. csramek@stanford.edu
Paulus
Yannis
Y
Nomoto
Hiroyuki
H
Huie
Phil
P
Brown
Jefferson
J
Palanker
Daniel
D
D000818:Animals; D002470:Cell Survival; D003198:Computer Simulation; D020342:Finite Element Analysis; D006358:Hot Temperature; D017075:Laser Coagulation / Q000009:adverse effects / Q000379:methods*; D053685:Laser Therapy; D008954:Models, Biological; D011817:Rabbits; D012160:Retina / Q000000981:diagnostic imaging* / Q000293:injuries; D012164:Retinal Diseases / Q000601:surgery*; D055213:Retinal Pigment Epithelium / Q000293:injuries / Q000473:pathology; D013552:Swine; D013816:Thermodynamics; D014463:Ultrasonography