Ex-vivo study on the surface quality of corneal lenticule and stroma after low energy femtosecond laser lenticule extraction

Evaluation of Higher-Order Aberrations After the Smooth Incision Lenticular Keratomileusis (SILKTM) Procedure Using the ELITATM Femtosecond Platform for Correction of Myopic and Astigmatic Refractive Errors

Purpose

To evaluate the changes of higher-order wavefront aberrations following the Smooth Incision Lenticular Keratomileusis (SILKTM) procedure for correction of myopic refractive errors with and without astigmatism, using the ELITATM Femtosecond Platform.

Methods

This prospective study included 24 eyes that underwent SILK procedure using one ELITA femtosecond laser system for the correction of myopic refractive errors with and without astigmatism. Preoperative and postoperative 1-day, 1-week, 1-month, 3-month, and 9-month eye exams were measured with a commercial wavefront aberrometer (iDESIGN ® Refractive Studio, Johnson & Johnson Surgical Vision, Inc). Wavefront aberrations up to the 6th order Zernike coefficients, including coma Z(3, -1) and Z(3, 1), spherical aberration Z(4, 1), and the wavefront error of all higher-order aberrations (HOAs RMS), were evaluated across a 6 mm pupil.

Results

The mean manifest refractive spherical equivalent changed from the preoperative refractions -3.82 ± 1.26 D (range -6.00 to -2.25 D) to the postoperative refractions -0.20 ± 0.15 D (range -0.50 to 0.00 D) at the 9-month follow-up. Compared to baseline preoperative HOAs, the mean postoperative HOAs were significantly increased at the 1-day follow-up. On average, at the 9-month postoperative assessment the vertical coma Z(3, -1) was -0.054 ±0.186 µm, horizontal coma Z(3, 1) was 0.016 ± 0.124 µm, spherical aberration Z(4, 0) was 0.046 ± 0.163 µm, and HOAs RMS was 0.363 ± 0.115 µm across a 6 mm pupil. There is no significant difference in the mean HOAs starting at 1-week follow-up for the horizontal coma (P = 0.346) and spherical aberration (P = 0.095).

Conclusions

The visual outcomes demonstrated that the SILK procedure for refractive lenticule extraction using ELITA femtosecond laser system is effective and predictable for the correction of myopic refractive errors with and without astigmatism. The ELITA femtosecond laser system induced minimal HOAs in surgical eyes following the SILK procedures. These results demonstrate fast corneal recovery starting at 1-week follow-up, and spherical aberration was not induced.

Assessment of Changes in Cap and Residual Stromal Thickness Values during a 6-Month Observation after Refractive Lenticule Extraction Small Incision Lenticule Extraction

Background: In this study, the changes in corneal cap and residual stromal thickness (RST) values during a 180-day observation period after refractive lenticule extraction small incision lenticule extraction (ReLEx SMILE) were assessed. Methods: Fifty patients underwent ReLEx SMILE using the VisuMax 500 femtosecond laser, with corneal imaging conducted pre and post procedure via anterior segment optical coherence tomography (AS-OCT). Cap thickness in the center and 1.5 mm from the center in four meridians was measured at various intervals. Results: The results showed a significant decrease in cap thickness 180 days post procedure compared to earlier intervals (p < 0.05). Similarly, RST decreased gradually and significantly post procedure (p < 0.05). Notably, changes in cap thickness within the central 1.5 mm area were more dynamic than RST changes during the 6-month observation period following SMILE. Conclusions: The corneal cap thickness measured with swept-source AS-OCT within the central 1.5 mm area underwent more dynamic changes than the residual stromal thickness during the 6-month observation following SMILE.

Incisional surface quality of electron-beam irradiated cornea-extracted lenticule for stromal keratophakia: high nJ-energy vs. low nJ-energy femtosecond laser

Introduction

Corneal lenticules can be utilized as an additive material for stromal keratophakia. However, following extraction, they must be reimplanted almost immediately or cryopreserved in lenticule banks. Electron-beam (E-beam) irradiated corneas permit room-temperature storage for up to 2 years, enabling keratophakia to be performed on demand. This study aims to compare the performance of high nano Joule (nJ)-energy (VisuMax) and low nJ-energy (FEMTO LDV) femtosecond laser systems on the thickness consistency and surface quality and collagen morphology of lenticules produced from fresh and E-beamed corneas.

Methods

A total of 24 lenticules with -6.00 dioptre power were cut in fresh human donor corneas and E-beamed corneas with VisuMax and FEMTO LDV. Before extraction, the thickness of the lenticules was measured with anterior segment-optical coherence tomography (AS-OCT). The incisional surface roughness of extracted lenticules was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Multiphoton microscopy was then used to assess the surface collagen morphometry.

Results

The E-beamed lenticules that were cut using FEMTO LDV were significantly thicker than the fresh specimens as opposed to those created with VisuMax, which had a similar thickness as the fresh lenticules. On the vertex, they were ∼11% thicker than the fresh lenticules. The surface roughness (Rq) of E-beamed lenticules incised with FEMTO LDV did not differ significantly from the fresh lenticules. This contrasted with the VisuMax-fashioned lenticules, which showed notably smoother surfaces (∼36 and ∼20% lower Rq on anterior and posterior surfaces, respectively) on the E-beamed than the fresh lenticules. The FEMTO LDV induced less cumulative changes to the collagen morphology on the surfaces of both fresh and E-beamed lenticules than the VisuMax.

Conclusion

It has been previously demonstrated that the low nJ-energy FEMTO LDV produced a smoother cutting surface compared to high nJ-energy VisuMax in fresh lenticules. Here, we showed that this effect was also seen in the E-beamed lenticules. In addition, lower laser energy conferred fewer changes to the lenticular surface collagen morphology. The smaller disparity in surface cutting quality and collagen disturbances on the E-beamed lenticules could be beneficial for the early visual recovery of patients who undergo stromal keratophakia.