Nomogram Development for Femtosecond Laser Arcuate Incisions in Refractive Laser-Assisted Cataract Surgery
Narrative Responses:
Purpose
To develop a femtosecond laser-specific nomogram using an image-guided femtosecond laser by investigating the effect of anterior penetrating laser arcuate incisions.
Methods
This retrospective study evaluated 49 eyes treated using anterior penetrating arcuate incisions with the Catalys precision laser system (Optimedica, Sunnyvale). All arcuate incision parameters were standardized: 9mm Optical Zone, 80% corneal incision depth (by OCT); incision length based on 70% of the Donnenfeld LRI nomogram. Preop auto-keratometry and corneal topography were used to determine magnitude and axis of corneal astigmatism. Post-op k-values and refractive astigmatism were recorded at 1-2 months. Results were analyzed using ASSORT astigmatism analysis software for vector analysis and calculations to compare keratometric change and preop keratometry versus postoperative refractive astigmatism.
Results
Astigmatism reduced from a mean preop corneal astigmatism value of 1.05 +/- 0.57 D (range 0.5 to 4.0 D; only 13 eyes had an attempted correction of > 1 D) to mean postop refractive astigmatism of 0.63 + 0.44 D (range 0 to 1.6 D) (p < 0.001). Postop refractive astigmatism was < 1 D in 92%, < 0.75D in 71%, < 0.5 D in 51% and < 0.25 D in 27% of eyes. Vector analysis disclosed a correction index (CI) of 0.82, indicating a mean under correction of 18% versus the intended outcome.
Conclusion
Anterior penetrating corneal arcuate incisions using an image guided FS laser with a liquid immersion interface are both safe and effective. Using this data set, increasing the correction factor from 70% to 83% of the Donnenfeld nomogram should yield an average CI of 1, or 100%. Further analysis of a larger series of eye would be useful to determine whether the effect of this adjustment would be comparable for higher corrections.