Analysis of Femtosecond Laser LRI Depth Using AS-OCT and Factors Affecting Surgically Induced Astigmatism Correction
To evaluate the depth of the femtosecond laser limbal relaxing incisions (LRI) compared to pre-operative target using anterior segment optical coherence tomography (AS-OCT). We also looked at additional factors affecting the surgically induced astigmatism correction (SIAC) of these incisions.
Retrospective chart review of eyes undergoing femtosecond laser assisted cataract surgery with LRIs between 2012 and 2014 at the University of Colorado Eye Center, Aurora, CO. Post operative Visante OCT (Zeiss) images were analyzed to determine the true depth of incisions. This was compared to the targeted depth inputted into the femtosecond laser. Post operative keratometric data was compared to pre operative values. The main outcomes measured include arcuate incision depth error, pre and post operative keratometric values, pre and post operative best corrected visual acuity and pre- and postoperative manifest refraction.
Preliminary data has shown that error in depth of incisions measured by AS-OCT is 7.8% (3.0%-13.3%). All but one incision was shallower than targeted depth. Error in astigmatism correction ranged from 30.1% to 119.6%. The error in depth is not correlated to error in astigmatism correction; more data needs to be collected to confirm any mathematical relationship. Despite the error in astigmatism correction, all patients had post-operative uncorrected visual acuity of 20/40 or better with high patient satisfaction. Femtosecond laser main incisions without LRIs was also shown to induce 0.71D (SD± 0.46) of astigmatism averaged 103 degrees from the incision.
In our practice, despite high patient satisfaction and good post operative uncorrected visual acuity, femtosecond laser LRI depth and astigmatism correction appears to be unpredictable. Further evaluation of post operative keratometric data is needed to fully characterize these incisions and improve their surgically induced astigmatism correction.