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Research Papers: Therapeutic

Improving the therapeutic window of retinal photocoagulation by spatial and temporal modulation of the laser beam

[+] Author Affiliations
Christopher Sramek

Stanford University, Hansen Experimental Physics Laboratory, 452 Lomita Mall, Stanford, California 94305

Loh-Shan Leung

Stanford University, Department of Ophthalmology, 452 Lomita Mall, Stanford, California 94305

Theodore Leng, Yannis M. Paulus

Eye Institute at Stanford, 2452 Watson Court, Palo Alto, California 94303

Jefferson Brown

Stanford University, Department of Physics, Stanford, California

Georg Schuele

OptiMedica Corp., 3130 Coronado Drive, Santa Clara, California 95054

Daniel Palanker

Stanford University, Hansen Experimental Physics Laboratory, 452 Lomita Mall, Stanford, California 94305

Stanford University, Department of Ophthalmology, 452 Lomita Mall, Stanford, California 94305

J. Biomed. Opt. 16(2), 028004 (February 24, 2011). doi:10.1117/1.3542045
History: Received April 22, 2010; Revised December 21, 2010; Accepted December 27, 2010; Published February 24, 2011; Online February 24, 2011
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Decreasing the pulse duration helps confine damage, shorten treatment time, and minimize pain during retinal photocoagulation. However, the safe therapeutic window (TW), the ratio of threshold powers for thermomechanical rupture of Bruch's membrane and mild coagulation, also decreases with shorter exposures. Two potential approaches toward increasing TW are investigated: (a) decreasing the central irradiance of the laser beam and (b) temporally modulating the pulse. An annular beam with adjustable central irradiance was created by coupling a 532-nm laser into a 200-μm core multimode optical fiber at a 4–7 deg angle to normal incidence. Pulse shapes were optimized using a computational model, and a waveform generator was used to drive a PASCAL photocoagulator (532 nm), producing modulated laser pulses. Acute thresholds for mild coagulation and rupture were measured in Dutch-Belted rabbit in vivo with an annular beam (154–163 μm retinal diameter) and modulated pulse (132 μm, uniform irradiance “flat-top” beam) with 2–50 ms pulse durations. Thresholds with conventional constant-power pulse and a flat-top beam were also determined. Both annular beam and modulated pulse provided a 28% increase in TW at 10-ms duration, affording the same TW as 20-ms pulses with conventional parameters.

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© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Christopher Sramek ; Loh-Shan Leung ; Theodore Leng ; Jefferson Brown ; Yannis M. Paulus, et al.
"Improving the therapeutic window of retinal photocoagulation by spatial and temporal modulation of the laser beam", J. Biomed. Opt. 16(2), 028004 (February 24, 2011). ; http://dx.doi.org/10.1117/1.3542045


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