Intrastromal Laser Research Articles

Mechanisms of corneal intrastromal laser dissection for refractive surgery: ultra-high-speed photographic investigation at up to 50 million frames per second.

Every year, more than a million refractive eye surgeries using femtosecond lasers are performed but the intrastromal cutting process remains an area of development. We investigated the mechanisms of laser dissection in cornea by ultra-high-speed photography. We found that the intrastromal bubble forms multiple lobes along the elongated laser plasma and the overlying lobes expand along the corneal lamellae. Videography demonstrated that the cutting process relies on crack propagation in the stroma along the bubble lobes with the crack originating from the pre-existing bubble layer. These insights are important for further improvement of the cutting mechanisms in refractive surgery.

Intraocular pressure rises during laser in situ keratomileusis: Comparison of 3 femtosecond laser platforms

To measure intraocular pressure (IOP) elevations in porcine eyes during laser insitu keratomileusis (LASIK) performed using 3femtosecond laser platforms. Clínica Novovisión, Madrid, Spain. Experimental study. Three femtosecond devices, the iFS 150kHz, which is the newest-generation IntraLase with a flat interface, and the Victus and LenSx, which are both dual femtosecond lasers with curved interfaces, were used to create lamellar corneal flaps in freshly enucleated porcine eyes. The IOP was recorded during placement of the suction ring on the eye (suctioning phase) and during the intrastromal laser application for flap creation (cutting phase) using a manometric technique with direct cannulation to the anterior chamber. Twenty-one eyes were analyzed (7 per group). The mean IOP increase during suctioning was significantly higher with the iFS system (78.14mm Hg±23.6 [SD]) than with the Victus system (20.28±6.7mm Hg) (P=.0001). The LenSx system performed the suctioning and applanation phases simultaneously, making it impossible to obtain the results of the suctioning phase alone. The mean IOP elevation during the cutting phase was significantly lower with the LenSx system (20±5.3mm Hg) than with the iFS (108.1±17.0mm Hg) and Victus (96.4±16.8mm Hg) systems (P=.0001). The total surgical time was significantly lower with the LenSx system (17.21±0.7seconds) than with the iFS (25.10±4.3seconds) and Victus (33.40±0.7seconds) systems (P=.0001). The preliminary results suggest that the iFS and Victus systems induced higher IOP increases and required longer surgical times to cut a LASIK flap than the LenSx system.

Historical Overview of the Clinical Development of the Small Incision Lenticule Extraction Surgery (SMILE)

The clinical use of femtosecond lasers has led to significant progress in the quality of refractive surgery. SMILE femtosecond laser surgery (SMILE: Small Incision Lenticule Extraction) permits the first one step intrastromal laser procedure without a flap. This article describes the gradual development of this surgery during the last ten years.

Structure of intracorneal femtosecond laser pulse effects in conical incision profiles

As the applicative potential of femtosecond lasers is to be extended from LASIK-flap creation into intrastromal ablation uses, the interdependency of influencing factors has to be understood. We therefore evaluated the relationship between focus depth, energy level, spatial distribution and morphology of fs-Laser pulse effects at a given repetition rate in corneal tissue. The experimental study included five porcine corneae obtained from slaughterhouse pigs. Using a prototype of a femtosecond laser (FEMTEC; 20/10 Perfect Vision AG, Heidelberg, Germany), a conical circular cut was performed in posterior-anterior direction through the entire corneal profile. The laser energy applied ranged from 4.0 to 8.5 microJ. Histological sections (n = 337) of a thickness of 7 microm were obtained, stained with hematoxylin/eosin, and morphometrically evaluated. The intrastromal femtosecond laser effects were aligned throughout the corneal stroma in a line that followed the dissection line programmed for the laser. The lesions were mostly of roughly elliptic shape with a fine dense lining at the inner wall, without evidence of a collateral damage beyond the disruption cavity. The mean maximal diameter of the intrastromal laser effects was 34.2 +/- 18.6 microm (range: 9-120 microm), and the mean maximal lesion diameter was 60.8 +/- 42.6 microm. In multivariate analysis, the lesion type (single shot cavity, partly confluent lesions, and fully confluent lesions) was significantly associated with the laser energy applied (P = 0.027) and the lesion diameter (P = 0.01). At higher laser energies, the intrastromal laser lesions were larger and more confluent, suggesting that, with the prototype of femtosecond laser used, a higher laser energy may lead to more confluent intrastromal laser effects. It may facilitate the complete cutting of the corneal tissue with the laser. Neither discernable debris nor stainable collateral damage were detected, suggesting a purely mechanical action of the laser.

Multiphoton microscopy for monitoring intratissue femtosecond laser surgery effects

Multiphoton microscopy/tomography has been used as a novel diagnostic method for corneal imaging with subcellular resolution. Here, we used this technique to monitor femtosecond laser intratissue surgery effects. Multiphoton microscopy/tomography on rabbits based on intense 90 MHz femtosecond Ti: sapphire laser was realized at intensities of MW-GW/cm(2), whereas the surgical procedures were performed with the same system at a higher light intensity on the order of TW/cm(2). Multiphoton microscopy/tomography proved capable of determining the target of interest, and of visualizing and optically evaluating the in vivo intrastromal laser surgical outcomes with high efficiency. More interesting, using this technique, activated intrastromal keratocytes (myofibroblasts) were detected in vivo 24 hours after intrastromal surgery. Multiphoton microscopy/tomography is an efficient and convenient non-invasive imaging method which can be used not only to assess intrastromal microsurgical performance but also to perform in vivo follow-up observations on wound repair.

Porcine Model to Compare Real-Time Intraocular Pressure during LASIK with a Mechanical Microkeratome and Femtosecond Laser

To compare real-time intraocular pressure (IOP) during laser in situ keratomileusis (LASIK) in porcine eyes using two types of microkeratomes. An interventional, prospective study of two microkeratomes: a Moria 2 (Moria group) and an IntraLase femtosecond laser (IntraLase Corp., Irvine, CA; IntraLase group). These devices were used to create lamellar corneal flaps in freshly enucleated porcine eyes. The IOP changes induced by the procedures were recorded with a reusable blood pressure transducer connected to the anterior chamber by direct cannulation. Seven porcine eyes were studied in each group. The IOP increased during the suctioning phase, reaching a mean of 122.52 +/- 30.40 and 160.52 +/- 22.73 mm Hg during the cutting phase in the Moria group (the total time in this group was 36.42 +/- 7.48 seconds; suctioning required 21.42 +/- 7.48 seconds and the cutting phase, 15 +/- 2.88 seconds). In the IntraLase group, the IOP reached 89.24 +/- 24.26 mm Hg during the suctioning phase and 119.33 +/- 15.88 mm Hg during the intrastromal laser application (the total time was 92.85 +/- 13.49 seconds; suctioning required 40.00 +/- 9.57 seconds and the cutting phase 52.85 +/- 5.66 seconds). Both IOPs during both phases differed significantly between the two groups (P = 0.01 for all comparisons). Real-time IOP can be measured during LASIK using a transducer connected to the anterior chamber. The results showed a significant increase in IOP during the procedure in both groups, although with the IntraLase the IOP seemed to increase to a lesser extent than with the conventional mechanical microkeratome.

Corneal multiphoton microscopy and intratissue optical nanosurgery by nanojoule femtosecond near-infrared pulsed lasers

Multiphoton microscopy including multiphoton autofluorescence imaging (MAI) and second-harmonic generation (SHG) is being used as a novel diagnostic tool to perform tissue nonlinear optical tomography with submicron resolution. The three-dimensional corneal ultrastructure of whole depth has been viewed without any staining or mechanical slicing. Compared with photodisruptive surgical effects occurring at TW/cm2 light intensity, multiphoton imaging can be induced at MW-GW/ cm2 photon intensity. The intratissue surgical effect including nanojoule (nJ) femtosecond laser ablation and flap generation was induced through multiphoton nonlinear absorption at a wavelength of 800 nm and ascertained by the histological outcomes. More interesting, the multiphoton microscopy based on nonlinear absorption of femtosecond laser pulses at the wavelength of 715-930 nm emitted from solid-state Ti:sapphire system is acting as a precise non-invasive monitoring tool to determine the interest of region, to visualize and verify the outcomes in in vivo intrastromal laser nanosurgery. Overall, these data suggest that multiphoton microscopy is a highly sensitive and promising technique for studying the morphometric and biomechanical properties of biological tissues and that the nJ ultrashort Lasers can be used as a ultra-precise nanoscalpel for performing intratissue surgery.

Intrastromal refractive surgery with ultrashort laser pulses: in vivo study on the rabbit eye.

Femtosecond (fs) laser pulses may offer new possibilities in the field of refractive surgery, especially when using the laser as a microkeratome. By induction of nonlinear absorption processes the laser can be used to perform intrastromal cuts. The conventional microkeratome, associated with numerous potential side effects, can possibly be replaced. Furthermore, refractive lenticules can be prepared within the stroma and removed in a single-step operation. In 10 rabbits, cuts were made to create both a lamellar flap and an intrastromal refractive lenticule. The flap was lifted, the lenticule was extracted and, finally, the flap was repositioned (intrastromal laser keratomileusis, ILK). The corneal samples were collected up to 120 days after treatment and processed for histopathological analysis. All flaps could be opened and prepared lenticules could be extracted in one piece by the surgeon. The treated corneas developed a mild wound healing reaction, comparable to that known from excimer laser in situ keratomileusis (LASIK) studies. The wound healing was restricted to the flap-stroma interface, most pronounced at the periphery of the flaps. The use of the fs-laser offers new possibilities in preparation of corneal flaps, possibly providing advantages over conventional microkeratomes. Furthermore, the fs-laser has the potential to create intrastromal refractive lenticules for complete refractive procedures (ILK).

Myopic picosecond laser keratomileusis with the neodymium—yttrium lithium fluoride laser in the cat cornea

Objective: The study aimed to evaluate the effects of myopic picosecond laser keratomileusis (PLK) in the feline model with follow-up of up to 6 months. Design: The study design was a case-controlled, feline animal model. Participants: The procedure was completed in 1 eye each of 12 cats divided into 3 groups (group 1, sham operation; group 2, 100- μ m lenticle thickness; and group 3, 150- μ m lenticle thickness). The second eye of each cat was used as a control. Intervention: Picosecond laser keratomileusis, a new intrastromal laser technique with the neodymium-yttrium lithium fluoride picosecond laser, was presented. The procedure, analogous to laser keratomileusis in situ, consists of two lamellar ring cuts and one vertical ring-shape cut that define a 4-mm—diameter intrastromal lenticle. Main Outcome Measures: Corneal pachymetry, topography, tonometry, and biomicroscopic examination were performed before and after surgery at scheduled intervals for 6 months. Results: The mean (±standard deviation) diopter change for group 2 was 5.4 ± 3.2 diopters at 1 month and remained stable during the 6-month period. For group 3, the change was 8.1 ± 0.22 diopters at 1 month and 6.8 ± 1.5 diopters at 6 months. Group 1 (sham operation) did not show significant diopter change compared with that of control eyes at any timepoint. Pachymetry results for group 1 showed no significant difference in the thickness of the cornea at any timepoint ( P >0.05). For groups 2 and 3, the corneal thickness was reduced significantly by 1 month ( P Conclusion: Myopic intrastromal PLK produces a refractive effect on the cornea that depends on the thickness of the lenticle removed and persists after 6 months with minimal stromal haze and no surgical complications. The authors' results, although encouraging, indicate the need for further studies to confirm the efficacy of PLK as a valid refractive procedure.