EVLA Mechanism of Action

EVLA  works  by  means  of  thermal  destruction  of venous tissues. Laser energy is delivered to the desired incompetent  segment  inside  the

vein  through  a  bare laser fber that has been passed through a sheath to thedesired location.

Several wavelengths have been proposed: 810, 940, 980, 1,064, and 1,320 nm, with 810, 940,  and  980  being  the most commonly  used. More recently,  use  of  a  1,470-  to  1,500-nm  diode  laser  has been  proposed. Wavelengths  of  1,470–1,500  nm  are preferentially absorbed by water.

When using laser light, heat is generated within the zone  of  optical  penetration  by  direct  absorption  of laser  energy.  Absorption  is  the

primary  event  that allows a  laser or other  light source  to cause a poten-tially  therapeutic  (or  damaging)  effect  on  a  tissue. Without absorption,  there  is no energy  transfer  to  the tissue  and  the  tissue  is  left  unaffected  by  the  light. Scattering  of  light  occurs  in  all  

biological  tissues: blood, vessel walls, and perivenous tissue. Due to fuc-tuations  in  the  refractive  index  of  these  media,  the propagation of light into the tissue is modifed and the scattering  affects  “where”  the  absorption will  occur, usually reducing the penetration of light into the tissue. 

Heating decreases with tissue depth as absorption and scattering  attenuate  the  incident  beam. Based  on  the absorption and effective scattering coeffcients of  the biological  tissue,  the  optical  extinction  (µeff)  can  be determined.