Presbyopia is a multifactorial physiologic aging mechanism that leads to the progressive loss of functional near vision. Scleral expansion surgery;1 corneal laser surgery with multifocal patterns or monovision approaches;2 conductive keratoplasty (CK);3 and clear lens extraction or cataract surgery using multifocal, accommodating, or monovision monofocal IOLs4,5 are among the techniques that have been used for the treatment of presbyopia. Corneal laser surgery and CK are minimally invasive methods, but they provoke irreversible changes in corneal anatomy, whereas scleral surgery and clear lens extraction are more invasive techniques.
The desire to develop a minimally invasive, reversible, stable, and safe surgical technique with an easy learning curve for patients between the ages of 45 and 60 years—patients who could be considered too old for presbyopia corneal surgery and too young for lens extraction—led to the development of a new approach based on the use of refractive corneal inlays. These devices are placed inside a tunnel created in the corneal stroma.
The Flexivue Micro-Lens corneal inlay (Presbia Coöperatief UA, Amsterdam, Netherlands) is a refractive hydrophilic polymer lens intended for insertion inside a corneal stromal tunnel in the nondominant eye. The lens' central zone is free of refractive power, and the peripheral zone has a standard positive refractive power. The diameter of the Flexivue is 3 mm, and the thickness is less than 20 µm.
The Flexivue inlay provides the operated (nondominant) eye with two focal points, one for far vision and one for near
Far vision. The rays passing through the central zone of the implant (ie, neutral zone without refractive power) and the free peripheral corneal tissue are focused sharply on the retina. Alternatively, the rays passing through the refractive peripheral zone are focused in front of the retina.
Near vision. The rays passing through the peripheral refractive zone are focused on the retina, and the rays passing through the central zone of the inlay are out of focus (ie,focused behind the retina). The pupil blocks the rays passing through the peripheral clear cornea.
Using a femtosecond laser (IntraLase; Abbott Medical Optics Inc., Santa Ana, California) and a special mask, a tunnel is created inside the corneal stroma, from the temporal periphery to the mid-nasal periphery, passing through the center of the cornea. Using the centration device of the Allegretto excimer laser (WaveLight Laser Technologie, AG, Erlangen, Germany), the center of the visual axis is marked on the cornea. The stroma is then separated with a spatula, and the lens is implanted using a special inserter (Figure 1). With the spatula, the lens is positioned at the marked center of the visual axis (Figure 2).
Presbyopic patients with emmetropia who are between the ages of 45 and 60 years are a particular target group for corneal inlays because they have healthy eyes, usually with excellent distance visual acuity. Many surgeons consider these individuals too old for corneal laser surgery and too young for cataract surgery. Furthermore, these patients are dissatisfied with procedures that leave even minimal damage to their far binocular visual acuity and quality of vision.
In our clinic, we started performing corneal inlay implantation in 2007 with the InVue system (BioVision AG, Brüggs, Switzerland), which used a mechanical microkeratome for tunnel creation.6 Mean near UCVA improved to 20/25 the first week after surgery and remained stable at 1-year follow-up. Binocular far vision remained 20/20; however, in the operated eye far vision decreased to 20/32.
Implantation of corneal inlays is differentiated from simple monovision procedures with laser correction or cataract surgery not just in the procedure's reversibility but also in its dependence on pupil size.
Measuring wavefront refraction, there was a noticeable effect of the Flexivue inlay only when we analyzed the central 3-mm zone (corresponding to the diameter of the inlay). When we analyzed the central 6-mm zone, the effect decreased. Therefore, the maximal inlay effect occurs during near vision when the pupil becomes smaller, and it decreases during far vision when the pupil is larger. We called this phenomenon smart monovision.
The Flexivue Micro-Lens is just one available corneal inlay on the market. Its unique mechanism of action is the smart monovision that we just described; other inlays have different mechanisms of action, including increasing depth of focus (AcuFocus; AcuFocus, Inc., Irvine, California), and reshaping of corneal curvature (PresbyLens; ReVision Optics, Inc., Lake Forest, California). See Available Corneal Inlays for further description of these inlay technologies.
We are studying the visual outcomes and safety of the Flexivue corneal inlay in the treatment of presbyopia using a femtosecond laser for tunnel creation. Our initial reaction is that this combination maximizes precision and customization. Ease of implantation and reversibility are the main advantages of the procedure. Additionally, the transparent lens is aesthetically acceptable and does not interfere with ophthalmologic examinations. We believe that surgeons should consider corneal inlays as a treatment option for emmetropic presbyopes 45 to 60 years old. Further followup and a larger series of surgeries are needed to demonstrate the safety and efficacy of this promising surgical method.
Dimitrios I. Bouzoukis, MD, practices in the Department of Ophthalmology and the Institute of Vision and Optics, University of Crete, Greece. Dr. Bouzoukis states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +30 2810 371800; fax: +30 2810 394653; e-mail: Dbouzoukis@hotmail.com.
Alice Limnopoulou, MD, practices at the University of Crete Medical School, Greece. Dr. Limnopoulous states that she has no financial interest in the products or companies mentioned. She may be reached at e-mail: email@example.com.
Ioannis G. Pallikaris, MD, PhD, is a Professor of Ophthalmology at the University of Crete, and Director of the Institute of Vision and Optics, Heraklion, Greece. Professor Pallikaris states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: firstname.lastname@example.org.
Sophia I. Panagopoulou, PhD, practices at the University of Crete Medical School, Greece. Dr. Panagopoulou states that she has no financial interest in the products or companies mentioned. She may be reached at email@example.com.