World Record In Low Dose Laser Induced Optical Breakdown For Keratorefractive Lenticule Extraction (Klex) Procedure On Schwind Atos Femto Second Device - 354 Mj/Cm2

Laser induced optical breakdown is a major but mostly unexplored factor in KLEx. Most surgeons still struggle with differences in dose and energy per pulse when thinking about the changes femtosecond lasers make in the cornea. By standard definition most doctors accept that under 1000 mJ/cm2 as low dose. Most Visumax 500 users are at doses of 800 to 900 mJ/cm2, but David Donate and David Kang attempted to reach what they call Ultra Low Dose - sub 500 mJ/cm2 to achieve better visual outcomes. This work was our guide as we wanted to explore sub 500 mJ/cm2 range in KLEx on Schwind ATOS and what this means for lenticule extraction time ,difficulty and patient visual recovery - namely UCVA and sine wave contrast sensitivity. 

Eye Clinic Svjetlost Zagreb, Croatia

We treated over 150 eyes using sub 500 mJ/cm2 and using a stairstep approach reached the lowest dose so far of 354 mj/cm2 at which lenticule dissection was possible but approaching very difficult. Our start point was 750 mJ/cm2 power level with mild asymmetric settings. We then proceeded to lower the dose in increments of 25 mJ/cm2 with keeping the track-to-track distance fixed at 2.7 microns. Each setting was validated in 6 eyes for dissection parameters and compared to UCVA and contrast sensitivity to previous settings, if the new ones were better or the same, we proceeded to lower the dose further.   

From 750 mJ/cm2 to about 550 mJ/cm2 the results were very comparable, next day UCVA was on average 0.1 logMAR with contrast sensitivity recovering between week 3 and week 6 to baseline values. As we reached 494 mJ/cm2 there still no difficulty in dissection so as the standing confirmed world record was broken, we decided to explore this extreme low dose environment to better understand the effects of this dose range on the cornea. When we reached doses of 460 mJ/cm2 we started to get next day UCVA od 0.0 or better in all eyes with contrast recovering to bassline levels on day 1 for low to moderate myopia and week one for high myopia and astigmatic corrections. 

The lowest dose of 354 was reached during this exploration but a sweet spot of 420 mJ/cm2 was found to offer the best ratio of ease of dissection, lenticule extraction time, next day UCVA and contrast sensitivity.  

We hope to encourage other surgeons and laser companies to explore this extreme (or just lower) dose regiment for their KLEx procedures as by lowering the dose and increasing surgeon work in dissection KLEx patients can achieve next day visual outcomes comparable to Femto LASIK.