Energy fluctuations in an excimer laser during photorefractive keratectomy

We performed an experiment with the MEL 60 excimer laser (Aesculap Meditec Technology) to demonstrate the variations of energy of the laser beam that could happen during a refractive surgical procedure. In order to quantify such variations, we measured the whitening of a photographic paper after a series of exposures to the laser beam with the X rite 400 B/W reflection densitometer. The energy fluctuations noted between two series of pulses averaged 11.02% (minimum 0; maximum 46). These fluctuations tended to decrease progressively during the procedure. The energy of the laser beam decreased with time. At the end of the experiment, the total loss of energy was 45.16%. These results suggest that clinically meaningful energy variations could happen during the photorefractive keratectomy and reduce refractive predictability.