State of the art: New technologies target emmetropic presbyopia

Richard L. Lindstrom, MD, discusses corneal inlays and their use in the growing baby boomer population.

John A. Hovanesian

John A. Hovanesian, MD, FACS: Today we are joined by Ocular Surgery News Chief Medical Editor Richard L. Lindstrom, MD, who is a professor of ophthalmology at the University of Minnesota and in private practice at Minnesota Eye Consultants. Dr. Lindstrom, thanks for joining us.

Richard L. Lindstrom, MD: You’re welcome.

Dr. Hovanesian: Tell us why corneal inlays may be a useful technology in the future.

Dr. Lindstrom: The corneal inlay opportunity relates to the emmetropic presbyope, which is the presbyopic patient who sees well at the distance but has a deficit at near. Today, other than monovision, we do not have a good procedure for the emmetropic presbyope, and the corneal inlay looks promising in this category of refractive error.

Dr. Hovanesian: Tell us about the different implants that are in development and maybe some results, as well as your impressions.

Richard L. Lindstrom

Dr. Lindstrom: There are three current approaches being utilized, and each of these companies has a significant base in the United States. The first and largest company at this time is AcuFocus, based in California, and it is using what is called small-diameter aperture optics, or pinhole optics, to increase depth of focus. Basically, in the non-dominant eye, an opaque corneal inlay 3.8 mm in diameter with a central small aperture of 1.6 mm diameter is placed in the cornea. Much like reducing the f-stop on a camera, this increases the depth of focus, and it has been possible to increase the depth of focus equivalent to an add of about 2 D to 2.5 D, and so one can basically treat presbyopia for a patient in the 45- to 65-year-old range with this approach.

The good news about this approach is there is minimal loss of quality of vision at distance. There is a little reduction of night vision, but there can be some halos at night. Basically, this approach gives increased and improved near with no meaningful loss of distance.

The second approach is being pursued by a company called BioVision, which has a base in the United States and also in Switzerland. A small lens, made of a hydrogel material, is implanted into the cornea, and this particular approach utilizes a lens that has a higher refractive index than the cornea. Basically, through bending of light from the corneal refractive index to the material refractive index, one can create an add-in the cornea. This makes the cornea much like a center near surround distance multifocal/ bifocal contact lens.

With this approach, you can definitely improve near vision any amount that you want. You can create a 2 D or a 2.5 D or a 3 D add, but there is a small loss of quality of distance vision and small loss of contrast and certainly night vision halos, much the same as you would see with a bifocal IOL or a bifocal contact lens.

The third approach is being done by ReVision Optics. ReVision Optics is a California company, and it is using a small hydrogel implant and placing it under a flap. Rather than utilizing a refractive index change, it is basically changing the shape of the cornea. It causes some central steepening of the cornea, and this is done in a blended fashion when the flap drapes over the implant, steepening the cornea centrally. So a 1.5-mm implant manufactured out of a hydrogel material of the same refractive index as the cornea is used as a shaper to add power centrally and, therefore, increase the near vision. This creates a shape to the cornea that is somewhat of a multifocal corneal shape, and so while near vision can be significantly improved, there is some loss of distance and some loss of contrast sensitivity, again, the same as a multifocal contact lens.

So the three primary approaches out there are all in some stage of clinical trial in human patients.

Dr. Hovanesian: Do all three have the intent of implantation just in the non-dominant eye?

Dr. Lindstrom: Yes, all three are intended to be unilateral. It is possible that you could imagine in the future patients who are so happy with their outcome that they would want the device implanted in their second eye, but they all today use one eye only, which I define as modified monovision. That is, the dominant eye would be untouched so it would have good distance vision and useful, depending on the patient’s age, intermediate vision. And then the non-dominant eye would have the increased depth of focus and would be used for reading.

Dr. Hovanesian: Presumably the advantage of these technologies is that not only are they reversible, but that they have better distance vision in the treated eye than we achieve with monovision. Is that correct?

Dr. Lindstrom: That is correct. It is reversible, which is a plus. In addition, even though there is some loss of distance vision, there is significantly better distance vision than with monovision. So using monovision to induce, for example, –2 D of myopia in an eye, you can anticipate a distance vision of 20/100 to 20/200 achieving J1 or J2 near. With these implants, you can achieve a J1 or J2 near with, in the case of AcuFocus, almost no measurable loss of vision, and with the other two perhaps as little as one to two lines loss of distance acuity, so they might be 20/30 and J1 rather than 20/200 and J1.

Dr. Hovanesian: Shifting gears, are there other technologies that are purely targeted at presbyopia that are showing promise? For example, there is talk about femtosecond procedures treating the crystalline lens of the eye.

Dr. Lindstrom: Well, the idea of doing a synthetic keratophakia, if you will, or implanting a corneal inlay in the cornea, is one approach. One can also reshape the cornea itself, and so there are various approaches utilizing excimer and femtosecond lasers to reshape the cornea. There is conductive keratoplasty to reshape the cornea, and more recently there has been a report by Luis Ruiz, MD, of an approach where he is actually doing an intrastromal ablation with the femtosecond laser, which also is being utilized to reshape the cornea.

In each of these cases, you are creating some form of multifocality of the cornea itself rather than trying to utilize the various optical methods that I have described with the corneal inlays. The laser approaches are somewhat similar to what is being utilized by ReVision Optics, where they are reshaping the surface curvature of the cornea, but the laser approaches are less reversible, although it is possible to reverse them with either a wavefront-guided or topographic-guided enhancement procedure.

Dr. Hovanesian: Either way you would be removing tissue and then removing more tissue to reverse the optic.

Dr. Lindstrom: That would be correct. You would have to basically do a laser treatment to undo of what you did with the laser, although this can be done. There have been patients treated in the world with excimer laser in particular to try to create a multifocal cornea who had unsatisfactory outcomes and have been undone with the excimer laser as well, but it can be a pretty complex laser ablation to achieve that goal and it does require more tissue removal.

Dr. Hovanesian: What sort of impact would you anticipate in the not-too-distant future will this have on the general ophthalmologist who has many emmetropic presbyopic patients?

Dr. Lindstrom: I will try to put the opportunity in perspective. I think there are actually as many emmetropic presbyopes as there are myopes in the population, and so the opportunity arguably is the same size as the myopia-treatment opportunity. Over the past 10 years, since the approval of the first excimer laser, we have all gained some insight into the size of the myopia treatment opportunity.

One would have to put in perspective whether or not people consider presbyopia as big a handicap as low to moderate myopia, and being a presbyope, I think it is in the same ballpark. In addition, the 45- to 65-year-old presbyope, who is a baby boomer, is part of a more affluent group than the younger patients, who usually seek LASIK for myopia. So arguably, we have a large group of emmetropic presbyopes who can probably afford to have a safe and effective procedure applied to reduce their visual handicap of presbyopia. So if we get a high-quality procedure that can enhance near vision in a safe way, with minimal loss of distance vision and minimal unwanted visual disturbances, I think it arguably could be as big an opportunity as LASIK for myopia has been.

Dr. Hovanesian: Dr. Lindstrom, thanks very much for joining us.

Dr. Lindstrom: You are welcome, John.

• John A. Hovanesian, MD, FACS, can be reached at Harvard Eye Associates, 24401 Calle De La Louisa, Suite 300, Laguna Hills, CA 92653; 949-951-2020; fax: 949-380-7856; e-mail: drhovanesian@harvardeye.com.
• Richard L. Lindstrom, MD, can be reached at Minnesota Eye Consultants, 9801 DuPont Ave. S, Suite 200, Bloomington, MN 55431; 952-888-5800; fax: 952-567-6182; e-mail: rllindstrom@mneye.com.