Teresa S. Ignacio

Advances in refractive surgery: microkeratome and femtosecond laser flap creation in relation to safety, efficacy, predictability, and biomechanical stability.

Purpose of review Methods of flap creation have changed over the years from the evolution of the mechanical microkeratome to the introduction of the IntraLase femtosecond laser keratome, both of which have different mechanisms of action to create corneal resections. Previous studies report the advantages and disadvantages of the mechanical microkeratome and the IntraLase femtosecond laser. The critical components in laser in-situ keratomileusis surgery remain the same, however: safety, efficiency, predictability, and biomechanical stability. Recent findings Keratoectasia and flap efficiency remain a constant safety concern in laser in-situ keratomileusis surgery. Unexpectedly thick flaps as well as variable thickness continue to be a concern with safety in relation to microkeratome technology. Epithelial preservation, flap complications, and newer issues such as Transient Light Sensitivity Syndrome are safety concerns of flap creation. Improved outcomes with regards to vision, induced astigmatism, induced higher-order aberrations, and enhancement rates are seen to favor predictability of femtosecond technologies over the microkeratome. Recent biomechanical studies show improved healing with femtosecond laser flap creation compared with blade-assisted flap creation. Summary The aim of this review is to summarize the key components for both the microkeratome and the femtosecond laser and to update on the recent advances reported on these topics.

Femtosecond laser-assisted cataract incisions: Architectural stability and reproducibility

There is considerable interest in the potential relationship between postoperative endophthalmitis and clear corneal tunnel incisions for cataract surgery. Earlier work from Ernest et al. clearly demonstrated that incisions that are square in surface architecture are significantly more resistant to deformation and leakage than those that are rectangular. The purpose of this preliminary investigation was to determine whether corneal tunnel incisions could be constructed with femtosecond laser technology and in a manner that would preclude deformation and leakage at any intraocular pressure (IOP).

Comparative study of stromal bed quality by using mechanical, IntraLase femtosecond laser 15- and 30-kHz microkeratomes.

Purpose: To evaluate corneal stromal bed quality of lamellar keratectomy in laser in situ keratomileusis (LASIK) procedures by using mechanical and femtosecond laser microkeratomes. Methods: LASIK corneal flaps were created in 9 fresh human globes not suitable for transplantation. We grouped the samples into 3 different groups of 3 globes each. Group 1 was the control group, in which the flaps were created using a Hansatome microkeratome with a 160-μm head. Groups 2 and 3 consisted of flaps created at the 110-μm flap thickness setting using the IntraLase 15- and 30-kHz femtosecond laser, respectively. All the flaps were removed, and the corneal stromal beds were prepared for scanning electron microscopy (SEM). Qualitative surface roughness (QlSR) of the SEM images was graded using a roughness grading scale from 1 to 5 by 3 masked observers. Quantitative surface roughness (QnSR) of the SEM images was also assessed using software designed for roughness analysis. Mann-Whitney nonparametric statistical analysis was performed to compare groups. Results: There was no statistically significant difference in QlSR and QnSR scores between group 2 and group 1 (brand-new blade only). Group 3 30-kHz IntraLase samples showed a smoother stromal bed compared with group 1 and 2 samples. This was a statistically significant difference for QlSR (QlSR = 1.1 ± 0.17, P < 0.001) and showed borderline significance for QnSR (QnSR = 24.4 ± 0.96, P = 0.05). Conclusions: The IntraLase 15-kHz femtosecond laser 110-μm flaps and the Hansatome 160-μm head using a new blade both produced smooth, good-quality, compact stromal beds as assessed qualitatively by masked observers and quantitatively by image analysis software. The 30-kHz femotsecond laser permits a tighter spot/line separation and lower energy per pulse, which creates smoother corneal stromal beds.

Transient light sensitivity after femtosecond laser flap creation: Clinical findings and management

PURPOSE: To describe the constellation of subjective and objective findings associated with unusual occurrences of photosensitivity after laser in situ keratomileusis (LASIK) with femtosecond flap creation and identify optimal management strategies. METHODS: Demographic data, laser settings, subjective complaints, clinical findings, treatment, and response to treatment were recorded for suspected cases of transient postoperative photosensitivity from 3 surgeons operating at 3 different sites. All cases were estimated for the period covering the suspected cases at each site to assess incidence. Additional cases were solicited from IntraLase users via a survey. RESULTS: For the 3 sites, 63 eyes from 33 patients were reported of a total estimated case log of 5667 (incidence, 1.1%). Average age was 41 years, and 51.7% of patients were women. Onset of symptoms ranged from 2 to 6 weeks after uneventful LASIK. All patients were treated with prednisolone acetate drops, whereas 1 surgeon also used Restasis (cyclosporine ophthalmic solution 0.05%). Patients noted improvement of symptoms within 1 week of treatment. When the raster and side‐cut energy settings were lowered (by an average of 24% and 33%, respectively), significant reductions in incidence were noted. Similar findings were reported by 3 additional surgeons reporting 17 cases in the survey of IntraLase users. CONCLUSIONS: This report describes a new complication of LASIK performed with a femtosecond laser keratome that may be related to the pulse energy used for flap creation. Although there is no loss of uncorrected visual acuity, symptoms can be prolonged, especially without prompt steroid therapy. Technical advances that reduced pulse energies appear to decrease the incidence.

Femtosecond laser posterior lamellar keratoplasty: a laboratory model.

Purpose To evaluate feasibility of femtosecond laser application in posterior lamellar keratoplasty. Methods To evaluate the lasers effectiveness through opaque corneas, anterior corneal caps were resected from opaque corneas induced with 80% acetone solution. To evaluate the femtosecond laser posterior lamellar keratoplasty surgical procedure, human corneoscleral rims were mounted on an artificial anterior chamber. After corneal pachymetry, the femtosecond laser was used to create a 6-mm-diameter, 200-μm-thick endostromal lenticule. Access to the lenticule was provided by a small perilimbal surface opening, also created by the laser. The lenticule was removed using a pair of corneal forceps. A donor lenticule of similar dimensions was created, its endothelial surface coated with viscoelastic, inserted, and positioned on the recipient bed. Two sutures were placed to seal the small surface opening. Results The femtosecond laser produced an effective and smooth dissection through opaque corneas even at deeper settings. Graft transplantation was fairly simple and effective. Conclusion Femtosecond laser posterior lamellar keratoplasty is a procedure that may provide an alternative to penetrating keratoplasty or the technically challenging manual posterior lamellar keratoplasty.

A 60 kHz IntraLase Femtosecond Laser Creates a Smoother LASIK Stromal Bed Surface Compared to a Zyoptix XP Mechanical Microkeratome in Human Donor Eyes

PURPOSE To compare the stromal surfaces created by the latest mechanical microkeratome and femtosecond, laser technologies. METHODS Laser in situ keratomileusis (LASIK) flaps were created in six fresh human globes unsuitable for transplantation. The eyes were placed in one of two groups of three globes each. One group had LASIK flaps created with a Zyoptix XP microkeratome using a 120-microm head and a fresh blade for each eye. Another group had flaps created at an attempted 100-microm thickness using the 60 kHz IntraLase femtosecond laser. Immediately following flap creation, the stromal beds were prepared for scanning electron microscopy (SEM). Qualitative roughness of the SEM images was graded by masked observers. Quantitative roughness of the SEM images was assessed using computerized software designed for roughness analysis. Mann-Whitney non-parametric statistical analysis was performed to compare groups. RESULTS A statistically significant difference was noted in bed smoothness as measured by qualitative roughness and quantitative roughness scores. The IntraLase samples showed smoother stromal beds compared to the Zyoptix group (qualitative roughness = 2.0 +/- 0.7 pm vs 3.6 +/- 1.6 pm, P = .03; quantitative roughness = 20238 +/- 1869 pm vs 26368 +/- 8133 pm, P = .03). CONCLUSIONS The 60 kHz IntraLase femtosecond laser and the Zyoptix XP 120-microm head using a new blade produced smooth, good quality, compact stromal beds qualitatively and quantitatively. Because the 60 kHz femtosecond laser permits a tight spot/line separation using low energy, it creates a smoother corneal stromal bed compared to previous femtosecond laser engines.

In vivo femtosecond laser-assisted posterior lamellar keratoplasty in rabbits

Purpose: To develop a rabbit model for femtosecond laser-assisted posterior lamellar keratoplasty. Methods: The femtosecond laser was used to make the posterior corneal lamellar interface and trephine (side) cut in 12 eyes of 11 rabbits. Laser parameters were energy 6.0 to 8.7 (lamellar cut) and 6.0 to 8.8 μJ (trephination cut), spot size 2.4 μm, firing rate 15 kHz, and trephination diameter 6.0 to 7.0 mm. In all eyes, the posterior corneal disc was removed from the eye after laser treatment through a blade incision in the peripheral cornea. The same excised corneal disc was repositioned into the posterior stromal bed to simulate posterior lamellar transplantation. Four eyes of 3 rabbits were enucleated immediately after surgery, and 8 eyes of 8 rabbits were enucleated after a mean follow-up of 17.9 ± 6.5 weeks. The corneal cut surfaces were examined by light microscopy and scanning electron microscopy. Results: The femtosecond laser was successful in producing posterior lamellar and trephination cuts in rabbit eyes. The thickness of the posterior corneal discs was 204.3 ± 21 μm (56.9% of central corneal thickness), and postoperative keratometry was 49.1 ± 5.8 D. Clinical appearance consistent with corneal ectasia was noted in 3 eyes. Conclusion: The femtosecond laser can make nonmechanical cuts for posterior lamellar keratoplasty with relative ease and reliability in rabbit eyes. A minimum residual anterior corneal thickness may need to be maintained to prevent ectasia.

Characterization of submicrojoule femtosecond laser corneal tissue dissection

PURPOSE: To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created using an IntraLase femtosecond laser (IntraLase, Inc.) with a 60 kHz engine. SETTING: Laser suite in a clinical practice. METHODS: A LASIK flap was created in 4 human eye‐bank eyes using the 60 kHz IntraLase femtosecond laser with the following settings: 110 μm flap thickness, 9.0 mm flap diameter, 60‐degree hinge length, 65‐degree side cut, 0.4 μJ or 0.7 μJ raster energy, 7 μm × 7 μm or 9 μm × 9 μm spot/line separation, and 1 μJ side‐cut energy. Immediately after the laser pass and without the flap being lifted, the globes were placed in fixative and subsequently processed for light and transmission electron microscopy. RESULTS: All 4 procedures were completed without complications or the appearance of an opaque bubble layer. The flaps were of uniform thickness and equaled the attempted thickness. Some areas had a complete dissection; other areas had scattered, incomplete tissue bridges. The adjacent corneal stroma and keratocytes were uninjured. When the epithelium was removed, the stromal component of the flap was measured as the attempted thickness; when the epithelium was present, the total flap thickness approximated the attempted flap thickness. CONCLUSIONS: Laser in situ keratomileusis flaps were safely created using raster energies and laser spot separations below those being used clinically. This technique may allow creation of flaps that are reproducibly thinner than those currently being performed and thus confer the benefits of surface ablation and LASIK.

Femtosecond laser-assisted intracorneal keratoprosthesis implantation: a laboratory model.

Purpose: To demonstrate femtosecond laser-assisted intracorneal keratoprosthesis implantation and determine the mechanical stability as a function of intraocular pressure. Methods: Eight human corneoscleral rims were mounted on an artificial anterior chamber. The femtosecond laser microkeratome was used to create a 2.5-mm diameter posterior corneal cap. A 7.2-mm-diameter lamellar stromal pocket was then created at mid-corneal depth. Finally, a 6-mm arc opening to the corneal surface was created at the periphery of the lamellar cut. The posterior lenticule was removed using corneal forceps and a 7.0-mm biopolymer keratoprosthesis was inserted into the stromal pocket. The surface wound was sealed using two 10-0 nylon sutures. A 3.0-mm anterior corneal opening was trephined to expose the keratoprosthesis. Intrachamber pressure was raised until wound leak was observed. Results: Seven of the 8 implants withstood pressures of at least 135 mm Hg without implant extrusion. Conclusion: Femtosecond laser corneal dissection provides an alternative to more challenging manual dissection methods for keratoprosthesis implantation. Use of the femtosecond laser microkeratome will further refine keratoprosthesis surgical technique and may allow rapid and easy execution of the surgery.

Accommodating intraocular lens implantation in an epikeratophakia patient

We report a case of implantation of the Crystalens AT-45SE and AT-52SE intraocular lenses in a highly myopic patient who had bilateral epikeratophakia surgery 15 years previously. Lessons learned from the first eye were taken into consideration when selecting the dioptric power for the fellow eye. With secondary interventions and meticulous lens calculations, the final outcomes were excellent and equivalent, allowing the patient to achieve uncorrected distance and intermediate visual acuities of 20/25 and near visual acuity of 20/50 in both eyes. To our knowledge, this is the first reported case of accommodating lens implantation in an epikeratophakic eye.