A laser’s effect on tissue is defined by three key parameters: (1) wavelength, ranging from short (UV light) to long (infrared); (2) energy density, defined as fluence or irradiance; and (3) pulse duration/exposure time. These parameters determine the type of treatment effect achieved (Table).
Excimer Laser Fundamentals
The excimer laser’s mechanism of action involves a reaction between a noble gas and a halogen gas. Under strong electrical discharge, the atoms are excited and form an unstable molecule called excited dimer (hence excimer). As the photons return to their original state, energy is released. The wavelength of this energy depends on the noble gas used.
Excimer lasers emit a short wavelength in the UV light range. A powerful energy release is emitted, particularly in pulsed mode, and because the pulse duration is short, little to no heat is generated.
Whereas corneal excimer lasers use argon as a noble gas, the ELIOS laser uses xenon. Thus, the ELIOS laser’s wavelength is longer than that used in corneal refractive surgery (308 nm vs 193 nm), and the ELIOS laser energy can be transmitted through optical fibers.
Trabeculostomy Versus Trabeculoplasty
With ELIOS, the excimer laser uses a photoablative effect to create trabecular microperforations that allow aqueous humor bypass with direct passage into the canal. The effect on the tissue is permanent. In contrast, argon and selective laser trabeculoplasty (ALT and SLT) use a photothermal or photochemical effect, respectively, to enable extracellular matrix renewal. This effect is transient, as it triggers a cellular and biochemical cascade within the TM during transmission.
