13 New Innovative Applications of Femtosecond Laser Technology
Summary
Over the last years femtosecond laser assisted surgery have widely spread among ophthalmic surgeons. Due to the high versatility, precision and safety of the femtosecond laser assisted procedures corneal tissue has become one of the target for excellence where to perform such type of procedures. From the many interventions that can be accomplish in the cornea, in the present chapter we report the use of femtosecond laser technology in order to precisely remove part of the corneal tissue that is affected by a leucoma, a procedure known as lamellar keratectomy. Additionally, we aim to report how femtosecond laser may assist both functional and cosmetic keratopigmentation procedures.
Keywords: Femtosecond assisted surgery, lamellar keratectomy, keratopigmentation, corneal tattooing
13.1 Femtosecond-Assisted Lamellar Keratectomy for the Treatment of Corneal Leukomas
13.1.1 Introduction
Corneal leukomas are one of the main causes of keratoplasty procedures due to the visual impairment that they may induce mainly when their presence is advocated to the central cornea in the visual axis. Conventionally, penetrating keratoplasty is considered the therapeutic approach when severe corneal scaring is present. Nevertheless, when corneal opacities do not induce significant alterations in the corneal endothelium, deep anterior lamellar keratoplasty (DALK) procedure is the best choice of treatment. The latest has the well-known advantages of almost zero risk of rejection when compared to full grafting techniques. However, it is a surgical procedure with a steep learning curve, long recovery process, and high amount of induced postoperative astigmatism, which partially restored the visual function of the patient. 1, 2 Another way to treat such corneal scarring is by manual superficial keratectomy, which is a less invasive method. Nevertheless, it induces several alterations and irregularities in the corneal surface, which lead to poor visual rehabilitation after the procedure. 3 In order to avoid performing such complex surgical interventions as keratoplasty procedures, some authors have reported different approaches to remove the damaged tissue without the need of lamellar or full corneal grafting. Alió et al proposed one of these approaches by exciding the pathological tissue using masked excimer laser ablation showing a significant improvement of the visual function of the patients that underwent this type of surgical intervention. 4 Other authors have also demonstrated the efficacy of treating corneal opacities using microkeratomes to remove the area of the cornea affected by the leukoma. 5, 6
In the recent years, with the advent of femtosecond laser technology, more precise dissection can be performed in the ocular tissues, which have enhanced the different therapeutic approaches that we use to treat corneal diseases. Moreover, femtosecond lasers offer many advantages in comparison with the manual dissections and microkeratomes in terms of quality of vision, reproducibility, and reduced incidence of complications. 7
In this chapter, we describe one of these therapeutic choices aiming to treat superficial corneal leukomas, thus avoiding the need of keratoplasty procedures, using femtosecond laser–assisted superficial keratectomy together with excimer laser ablation.
13.1.2 Indications
The main indication for femtosecond-assisted lamellar keratectomy is superficial corneal opacities (▶ Fig. 13.1). We have to bear in mind that corneal leukomas should not be accompanied by new vessels to avoid limitations in the dissection of the cornea when using the femtosecond laser. In a case series conducted by the authors, 8 it was observed that the main causes of corneal scaring treated with femtosecond-assisted lamellar keratectomy were as follows: complications due to previous corneal refractive surgery, pterygium surgery, corneal dystrophy, and infectious keratitis (should not be active).
Another relevant factor to take into account when planning this type of procedure is the depth of the corneal leukoma. By general rule, the calculated postoperative pachymetry should be more than 300 μm. In the study mentioned earlier, 8 the mean depth of the corneal leukoma was 171.55 μm with a mean degree of haze opacity of 3.67 over 4 (all cases grades 3 and 4) based on the haze degree system described by Fantes et al. 9
13.1.3 Ophthalmological Assessment
A complete ophthalmological examination should be performed in every case including uncorrected and corrected visual acuity measure under cycloplegic conditions; biomicroscopy, having special attention in the degree of haze; and fundus evaluation to make sure that there isn’t an underlying ophthalmic pathology that could potentially limit the degree of visual acuity after the procedure.
The complementary evaluation should include the following:
Corneal pachymetry.
Corneal topography, including corneal aberrometry.
Anterior segment optical coherence tomography (OCT) to assess both the depth and the length of the corneal leukoma.
Corneal confocal microscopy, which will help accurately measure the depth of the corneal opacity.
The patient should be informed that a significant refractive error will be induced after the procedure due to the important amount of tissue that will be removed. This refractive error can be further corrected with contact lens, spectacle correction, or a refractive surgical technique such as phakic intraocular lens (pIOL) implantation.
13.1.4 Surgical Technique
Lamellar keratectomy assisted by femtosecond laser is a surgical procedure that is performed in two steps.
Step 1: Under topical anesthesia, a free corneal cap is created using the femtosecond laser. The parameters used in this step should double the amount of energy that is conventionally done when performing the corneal flap for refractive procedures in order to achieve a proper dissection passing through the corneal opacity. As a routine, the power for the stromal dissection is 1.5 μJ and the energy for the side cut varies between 1.5 and 2 μJ. Additionally, a superior hinge of 4 mm is created, which is further dissected by hand using a crescent knife. The thickness of the corneal cap is selected according to the thickness of the leukoma that was previously measured.
Step 2: The second step consists in a sodium hyaluronate masked excimer laser ablation using the phototherapeutic keratectomy (PTK) mode as previously described by the authors. 10 The complete procedure is performed in the following manner: once the free cap created with the femtosecond laser is removed, a drop of sodium hyaluronate 0.25% is applied over the corneal stroma, which is followed by a PTK ablation. As a standard, a 30- to 50-μm ablation is performed over a 6-mm corneal diameter area. Afterward, a drop of fluorescein is instilled in order to confirm the complete disappearance of the hyaluronate masking agent. Finally, mitomycin C 0.02% is applied during 1 minute, and then the corneal is copiously irrigated with balanced saline solution and a bandage contact lens is placed over the cornea.
During the postoperative period, cycloplegic agent and a combination of antibiotic/steroids are prescribed. The patient should be examined at 24 hours and then after a week to confirm that the corneal epithelium has been completely restored and remove the contact lens.
13.1.5 Clinical Outcomes
Recently, our research group published an investigation work that assessed the clinical results of 12 cases of patients affected by different degrees of corneal opacities and that were treated by means of femtosecond laser–assisted lamellar keratectomy. 8 In that study, the mean corrected visual acuity change from a preoperative level of 0.26 in the decimal scale to a postoperative is 0.58 (▶ Table 13.1).
UCVA | CDVA | |
Preoperative | 0.11 ± 0.09 | 0.26 ± 0.18 |
1 mo | 0.16 ± 0.18 | 0.42 ± 0.25 |
6 mo | 0.33 ± 0.25 | 0.56 ± 0.28 |
1 y | 0.34 ± 0.20 | 0.58 ± 0.31 |
In the aforementioned study, changes in keratometric readings and anterior corneal aberrometry coefficient were also analyzed. A trend toward less aberrated tissue was observed after the procedure although these changes were not statistically significant. These findings clearly demonstrate that the improvement observed in the visual acuity after the surgery is due to the removal of the corneal opacity and enhancement of the corneal transparency. Moreover, it also confirms the stability of the surgical technique throughout the follow-up period (▶ Table 13.2).
Preoperative | Postoperative | |
K1 | 39.59 ± 6.36 | 39.13 ± 5.35 |
K2 | 43.15 ± 4.29 | 42.20 ± 6.57 |
Total aberrations | 7.81 ± 4.73 | 5.15 ± 1.40 |
RMS astigmatism | 3.28 ± 3.88 | 2.38±1.56 |
RMS HOA | 4.54 ± 3.08 | 4.33 ± 4.79 |
Spherical-like | 0.84 ± 0.47 | 0.95 ± 0.65 |
Coma-like | 1.95 ± 0.98 | 1.48 ± 0.78 |
Abbreviations: HOA: higher order aberration; K: keratometry; RMS: root mean square. | ||
During the 12 months of follow-up that covered the entire study period, none of the cases developed any type of complications. Nevertheless, it should be borne in mind that patients that underwent femtosecond lamellar keratectomy should be closely followed because the amount of tissue removed during the procedure could lead to long-term biomechanical alterations that potentially may affect the refractive stability of the cornea.
13.1.6 Clinical Case
The following case corresponds to a 36-year-old male patient, who came to our office complaining about decreased vision with his right eye (RE). The patient refers that he was under treatment 1 year ago because of infectious keratitis and since then lost a significant amount of vision.
Ophthalmological examination showed the following findings:
Uncorrected visual acuity (decimal scale):
RE: 0.150.
Left eye (LE): 0.300.
Best corrected visual acuity (decimal scale):
RE: 0.400.
LE: 1.000.
Manifest refraction:
RE: sphere –1.00 cylinder (cyl) – 3.00 × 160 degrees.
LE: sphere –1.50 cyl – 0.75 × 80 degrees.
Biomicroscopy: RE—superficial central leukoma with mild irregularity of the surface of the cornea (▶ Fig. 13.2). LE—normal.
Fundus evaluation: Normal in both eyes.
Corneal pachymetry: RE—540 μm.
OCT: RE—High-resolution corneal mode shows a corneal opacity that extends 214 μm in depth (▶ Fig. 13.3). This finding was also confirmed by confocal microscopy evaluation.
Fig. 13.2 Left eye: normal.
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