Theoretical model and design of a device to reduce the influence of environmental factors on refractive surgery outcomes

Recently many different groups show that environmental temperature and relative humidity affect the outcomes of refractive surgery performed by excimer lasers in an unpredictable fashion. A theoretical model of the water vapor absorption at 193 nm wavelength is presented and discussed in order to quantitatively assess the influence of environmental parameters on the laser energy that actually reaches the corneal surface. Model simulations show that laser energy absorption (up to 7% of the available energy) occurs along the path of laser beam, into the existent space between the laser beam source and the patient's eye, and is caused by environmental temperature and relative humidity (respectively 35°C and 95%). Our findings suggest that this energy loss reduces the ablation rate, producing a significant undercorrection of the treated corneas. A cost effective device which keeps thermo hygrometric parameters constant along the laser beam path, is also provided.