Temperature increase in human cadaver retina during direct illumination by femtosecond laser pulses.

PURPOSE

Femtosecond lasers have been approved by the US Food and Drug Administration for ophthalmic surgery, including use in creating corneal flaps in LASIK surgery. During normal operation, approximately 50% to 60% of laser energy may pass beyond the cornea, with potential effects on the retina. As a model for retinal laser exposure during femtosecond corneal surgery, we measured the temperature rise in human cadaver retinas during direct illumination by the laser.

METHODS

The temperature increase induced by a 150-kHz iFS Advanced Femtosecond Laser (Abbott Medical Optics) in human cadaver retinas was measured in situ using an infrared thermal imaging camera. To model the geometry of the eye during the surgery, an approximate 11x11-mm excised section of human cadaver retina was placed 17 mm behind the focus of the laser beam. The temperature field was observed in 10 cadaver retina samples at energy levels ranging from 0.4 to 1.6 microJ (corresponding approximately to surgical energies of 0.8 to 3.2 microJ per pulse).

RESULTS

Maximal temperature increases up to 1.15 degrees C (corresponding to 3.2 microJ and 52-second illumination) were observed in the cadaver retina sections with little variation in temperature profiles between specimens for the same laser energy illumination.

CONCLUSIONS

The commercial iFS Advanced Femtosecond Laser operating with pulse energies at approximately the lower limit of the range evaluated in this study would be expected to result in a 0.2 degrees C temperature increase and do not therefore present a safety hazard to the retina.