Purchase this article with an account.
Zheng Sun, Hong Fu; Retinal Safety Analysis for a Novel Ultrashort Femtosecond Laser. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5290.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We are exploring a novel ultrashort femtosecond laser for refractive vision correction related corneal incisions. This novel technology uses short laser pulsewidth, small focus spot size, and an ultrafast scanning system. The purpose of this poster is to analyze the laser exposure at retina based on the eye safety guidelines provided by IEC 60825-1: 2007.
The analysis consists of three steps. Step-1, determine the maximum permissible exposures (MPE) at the cornea from the IEC guidelines. Step-2, convert the MPE at cornea to MPE at retina. Step-3, use Zemax optical design software to simulate the novel laser beam delivery technology on a standard optical eye model. The analysis is for the worst case: the laser beam is at a fixed location throughout the procedure, and the input laser power is 100% deposited onto the retina. Under nominal conditions, the laser beam is being scanned, and over 50% of laser pulse energy is converted into plasma and does not reach retina. The actual exposure at a given location at retina is estimated to be less than 40% of the worst case scenario.
The IEC guidelines require three MPEs to be met simultaneously for a pulsed laser: the single pulse MPE, the grouped pulse MPE, and the average pulse MPE. In our case, the latter two are equal and more restrictive, MPE = 9.33t- 0.25 W/cm2 at retina, where t is the exposure time in seconds. Applying actual parameters, and using Zemax to simulate various cutting conditions, we obtain that the MPE at retina corresponds to a maximum pulse energy EMAX = 418t-0.25nJ/pulse. We considered two cases. Case-1: create a 9mm diameter flap in 8.7s on pig eyes. In this case, EMAX = 418x8.7-0.25 nJ/pulse = 243nJ/pulse; the actual pulse energy were: 70nJ/pulse, 7s for bed cut, 110nJ/pulse, 1.7s for side cut. The total exposure is 32% of MPE. Case-2: perform a 6mm diameter corneal lenticule procedure in 15s on pig eyes. In this case, EMAX = 418x15-0.25nJ/pulse = 212nJ/pulse; the actual pulse energy were: 70nJ/pulse for the two lenticular surfaces, 70nJ/pulse for the internal side cut and the entry cut, the total exposure is 33% of MPE.
Based on the IEC guidelines for MPE at retina, the maximum allowed pulse energy is given by EMAX ≤ 418t-0.25nJ/pulse. The retinal exposure in flap and lenticule incision procedures is ≤ 40% of MPE in the worst case scenario, i.e., it has a ≥ 60% safety margin.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only