Refractive surgeons continue to search for new presbyopia-correction procedures that are less invasive than the previous technique. For the first time worldwide, I performed an intrastromal correction of presbyopia with the Femtec femtosecond laser (20/10 Perfect Vision, Heidelberg, Germany). This noninvasive technique combines an intrastromal ablation that reshapes the cornea with the redistribution of biomechanical forces to produce the desired presbyopia correction.
Most people over 51 years of age have presbyopia; more than 26 million people in the United States alone are affected by the condition.1,2 Until now, I treated presbyopic patients with LASIK. I found it difficult for patients to have 20/20 distance vision and J1 reading because of poor contrast sensitivity. With an intrastromal ablation, however, patients achieving 20/15, J1, and better contrast sensitivity are common.
A refractive laser correction performed completely intrastromally is desirable because it does not impact the epithelium, maintains the structural integrity of the cornea, has a low risk of infection, and promotes wound healing.
Intrastromal correction of presbyopia does not produce any flap- or surface-related complications, does not induce dry eye, and provides a faster visual recovery. What this procedure aims to do is change the biomechanics of the cornea by working completely in the stroma. In turn, the epithelium, Bowman's membrane, and Descemet's endothelium are preserved. Alternatively, Bowman's membrane is cut during flap creation and destroyed during PRK and surface ablation. The only thing the laser touches during an intrastromal correction is the stromal tissue, and therefore has added protection compared with these other techniques.
Previous intrastromal approaches were not predictable; however, during our ongoing pilot study, I have so far found that intrastromal correction with the Femtec laser is predictable and safe. This procedure is neither ConformitiÈ-EuropÈenne (CE)- nor US Food and Drug Administration (FDA)-approved and should not, at this time, be used on patients with irregular corneas, keratoconus, thin corneas, or patients who previously underwent a corneal transplant.
HOW IT WORKS
The finite element modeling (FEM) software for presbyopia correction, which uses a spatial 3D grid adapted to the individual corneal curvature, predicts the impact of the intrastromal ablation on the biomechanical response. For this process to adequately predict the correction, the patient's cornea must be as stress-free as possible during the treatment to allow precise, 3D positioning of the laser pulses. We maintain a specific distance between the laser ablation and the corneal surface and endothelium to prevent an anterior or posterior surface incision and reduce the risk of poor healing.
After calculating the patient's refractive, geometric, and biometric properties of the cornea, we created a customized pattern for each eye. We docked the patient's eye to the Femtec laser (Figure 1) and performed the intrastromal ablation, which lasted between 18 and 30 seconds.
Our ongoing clinical study started in October 2007, and to date, we have treated 89 eyes with intrastromal correction for myopia, hyperopia, astigmatism, or presbyopia. All eyes were operated on at the Centro Oftalmológico Colombiano in Bogotá, Columbia, with the Femtec femtosecond laser.
At 2-month analysis, data was available for 59 patients who were followed and examined on day 1 and at 1 week, 1 month, and 2 months. We have previously reported on the outcomes for presbyopia.3 At 2 months, patients' (age range, 41–66 years) near visual acuity were calculated with Jaeger charts under consistent photopic conditions. Distance visual acuity was also calculated using Snellen charts under the same conditions, and biomechanic properties of the cornea were evaluated.
Results showed a huge potential to instantly improve near visual acuity by several lines. The near UCVA and distance UCVA are depicted in decimal units in Figures 2 and 3. The average gain in near UCVA after 1 month was 5.9 ±2.7 Jaeger lines and 0.6 ±2.1 Snellen lines for distance UVCA. We found that the laser induced a biomechanical response on the cornea, which positively effects visual acuity. In most patients, this occurs in minutes to a few hours postoperatively. We found a high stability in longer observation periods.
Intrastromal ablation for the correction of presbyopia is not only easy to perform but also a fast procedure that provides patients with instant results. Further multicenter studies are necessary; however, our preliminary results are promising and have motivated us to continue research at our institution.
Parallel to the success of intrastromal corrections for presbyopia, investigations into the correction of myopia, hyperopia, and astigmatism are currently ongoing. We continue to refine the FEM model with the goal of calculating an ideal intrastromal pattern for each ametropia subset.
In my 30 years of practicing ophthalmology, I have developed astigmatic keratotomy, created a patent for topography surface ablation, helped develop LASIK, and designed my own microkeratome. But that excitement does not compare with my hope for this technique. I believe that the intrastromal correction of ametropia, including presbyopia, is on the horizon.
Luis Antonio Ruiz, MD, is the Scientific Director at the Centro Oftalmológico Colombiano, Bogotá, Columbia. Dr. Ruiz did not provide financial disclosure information. He may be reached at +57 236 00 00; luisantonio.ruiz@gmail.com.
