Intra-Corneal Lens Inlays by Richard L. Lindstrom MD Corneal inlay treatment is still experimental as of early 2007, but clinical studies are progressing and seem encouraging. This method treats presbyopia by inserting a very tiny lens into the central cornea, using instruments similar to those employed for LASIK. This method of treatment is slightly less invasive (and carries slightly lower risks) than lens-based surgery including cataract removal and/or clear lens insertion. The potential market for a really good presbyopia treatment is enormous. There are about 62 million presbyopes in the US today who do not wear prescriptive correction for distance. This includes roughly 44 million naturally occurring; 6 million that have had LASIK, and 12 million that have had lens implant type care. It goes without saying that, as the population ages, with longer life expectancies, the ranks of emmetropic presbyopes will grow. Effective treatment for presbyopia? Small diameter intracorneal inlays are implants designed to correct presbyopia without intraocular surgery. This treatment has been shown to improve reading vision without significant detriment to distance vision, making it an exciting treatment option for emmetropic presbyopes. Emerging results from clinical trials at both international and US sites are promising. There are four products currently in development: AcuFocus/Bausch & Lomb ACI 7000®, AcuFocus/Bausch & Lomb Hydrogel lens®, ReVision Optics PresbyLens® and Biovision's Invue Intracorneal Microlens system. Intracorneal inlays are good news for both surgeons and patients. These implants offer new opportunities to expand the LASIK market because inlays are appropriate for both presbyopic patients undergoing LASIK, and also existing LASIK patients who may be experiencing recent onset presbyopia. Many surgeons believe this may be an optimal solution for correcting the emmetropic presbyope. Procedures for all four implants are fast, without a steep learning curve and offer relatively easy explantation for those patients who might wish to exchange the implant to compensate for presbyopic progression that may occur later. Bausch & Lomb/AcuFocus Hydrogel Lens . This meniscus lens is constructed of 45 percent Hydrogel: Hefilcon–A, with a diopter range of +1.50 to +3.50. The lens thickness ranges from 0.03 to 0.006mm, and its diameter is 1.80 to 2.20mm, with a resolution of ≥3/4 AFTR. Near vision improvement is achieved when a multi-focal cornea is created by utilizing the different refractive indices of the hydrogel lens and the cornea. In one study, eight patients were implanted monocularly with the lens in a modified monovision approach, and examined five years later. Their typical vision was 20/25 at distance and near, with reading distance ranges from 7”-16”, averaging about 14” comfortably. The loss of distance with best corrected vision, versus the other eye, is one letter to one line. This lens also works in phakic and pseudophakic patients. 
A CI Centered Inlay
At five years the pocket incision was still visible. The surgical technique is straightforward. Explantation is possible with no permanent loss of vision or adverse reaction. The lens material was well-tolerated by patients with few pigment deposits detected. Every patient was satisfied with their results, and 75 percent were spectacle-free. Only one patient noticed “ghosts” and no one complained of halos. Biovision Invue™ Intracorneal Microlens System : Biovision’s intracorneal microlens is a made of water-permeable, biocompatible hydrogel, 20 µm thick and 3 mm in diameter. This Invue system positions the lens in a tunnel, 200 µm to 400 µm deep, in the center of the cornea in a patient’s non-dominant eye. The system offers implantation within minutes and stable centration of the lens, giving steady and permanent near visual acuity/improvement. If required, lens removal is easily accomplished without loss of tissue. Biovision’s Visitome 20-10 microkeratome and blade cartridges are used to cut a precise corneal tunnel, and an inserter is used to position the lens precisely in the center of the eye. This lens is for the emmetropic presbyope whose cornea is the proper power for distance with no astigmatism. By adding plus power to the cornea with a hydrogel material that has a higher refractive index than the cornea, an emmetropic cornea is transformed into a multifocal cornea. The lens is also appropriate for patients who are emmetropic as a result of refractive or cataract surgery. A multifocal cornea significantly improves a patient’s ability to read. Potential drawbacks include a small loss of contrast sensitivity and an induction of mild night-vision symptoms; primarily halo, as occurs with other multifocal optics. However, the lens is monocularly implanted, and it is the extremely rare patient who is bothered significantly by optical aberration problems. In clinical trials presbyopia was corrected in nearly all cases that received an implant. The material was well-tolerated and, after surgery, patients rapidly gained their near vision, resulting in a high degree of patient satisfaction. In a preliminary clinical evaluation 13 patients had a mean vision of 20/40 at distance without correction. Preoperatively, four patients had 20/100 uncorrected near vision. At one month postop, two patients were at 20/25; the other two were at 20/20. Side effects have included loss of distance acuity, halo, decentration and mild interface haze. Bausch & Lomb/AcuFocus ACI 7000™ Inlay : The ACI is an ultra-thin, 10 µm disc made of Kynar®, an opaque biocompatible polymer with a small aperture in the center, like a camera’s pinhole, where the peripheral rays are obscured and the central rays pass unaffected. Both preoperative preparation and postoperative care are handled in the same way as a standard LASIK procedure. A corneal flap is cut using a mechanical microkeratome or IntraLase. The ACI 7000 is then placed on the stromal bed over the pupil of the non-dominant eye, increasing the eye’s depth of focus by reducing the circle of blur. The flap is then replaced. Appropriate post-surgical care is consistent with that for standard LASIK. The ACI 7000 has been used to treat up to 2 D of presbyopia, and significantly improves near visual acuity with minimal loss of distance visual acuity. Patients also have good intermediate visual acuity. Clinical results for mean visual acuity indicate that 59 pre-operative patients had 20/20 UCDVA, with UCNVA at J-9. Three months later, 51 patients maintained a MVA of 20/20. UCDVA, UCIVA and UCNVA was J-2. ReVision Optics PresbyLens®: The PresbyLens, developed by ReVision Optics (formerly IntraLens), is a promising new treatment for presbyopia that has also been extensively studied for hyperopia correction. Made from a proprietary micro-porous hydrogel material called Nutrapore®, the PresbyLens is composed of 78 percent water, with the same refractive index as the human cornea. It is also the first bio-engineered intracorneal implant to be used for keratophakia. This lens is used to change the anterior curvature of the cornea when placed under a LASIK flap. One and one-half millimeters in diameter, the PresbyLens is an intracorneal implant designed to provide a central near add zone and a paracentral intermediate zone, which allows the remaining cornea to be used for distance vision. The lens is placed in the patient's nondominant eye, and can be combined with LASIK, with bilateral plano vision as the objective. Currently ReVision Optics is operating clinical trials at several international sites to evaluate PresbyLens for presbyopia correction. Clinical trials are also underway in the US to determine this lens’ efficacy in hyperopia up to +6 D. Conclusion Intracorneal inlays are potentially safe, simple and minimally invasive procedures that present a new solution for presbyopes in all ranges – including the emmetropic patient. Research data continues to suggest that inlay technology offers promising results and high patient satisfaction, by preserving distance vision and enhancing near vision. |