Measurement of the temperature increase in the porcine cadaver iris during direct illumination by femtosecond laser pulses

Abstract

Multiple femtosecond lasers have now been cleared for use for ophthalmic surgery, including for creation of corneal flaps in LASIK surgery. Preliminary measurements indicated that during typical surgical use, 50-60% of laser energy may pass beyond the cornea with potential effects on the iris. To further evaluate iris laser exposure during femtosecond corneal surgery, we measured the temperature increase in porcine cadaver iris in situ during direct illumination by the iFS Advanced Femtoosecond Laser (AMO Inc. Santa Ana, CA) with an infrared thermal imaging camera. To replicate the illumination geometry of the eye during the surgery, an excised porcine cadaver iris was placed 1.5 mm from the flat glass contact lens. The temperature field was observed in twenty cadaver iris at laser pulse energy levels ranging from 1 to 2 μJ (corresponding approximately to surgical energies of 2 to 4 μJ per pulse). Temperature increases up to 2.3 °C (corresponding to 2 μJ per pulse and 24 second procedure time) were observed in the cadaver iris with little variation in temperature profiles between specimens for the same laser energy illumination. For laser pulse energy and procedure time characteristic to the iFS Advanced Femtoosecond Laser the temperature increase was measured to be 1.2 °C. Our studies suggest that the magnitude of iris heating that occurs during such femtosecond laser corneal surgery is small and does not present a safety hazard to the iris.