New technologies are targeting emmetropic presbyopia

Three companies with U.S. operations are investigating the use of corneal inlays to treat the presbyopic patient who sees well at a distance. John A. Hovanesian, MD, FACS, interviewed PCON Editorial Board member Richard L. Lindstrom, MD, on this prospect.

Richard L. Lindstrom

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 distance but has a deficit at near. Today, other than monovision, we do not have a good procedure for this patient, and the corneal inlay looks promising.

Dr. Hovanesian: Tell us about the different implants in development and their results, as well as your impressions.

Three approaches being studied

Dr. Lindstrom: There are three current approaches being used. AcuFocus, based in California, is using small-diameter aperture optics, or pinhole optics, to increase depth of focus. In the nondominant 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. So, one can basically treat presbyopia for a patient in the 45- to 65-year-old range with this approach.

The good news is the minimal loss of quality of vision at distance. There is a little reduction of night vision, and there can be some halos at night. Basically, this approach gives increased and improved near vision 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 with a higher refractive index than the cornea is implanted into the cornea. 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.

John A. Hovanesian

With this approach, you can improve near vision of any amount desired. 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 contrast, as well as night vision halos, as you would see with a bifocal IOL or a bifocal contact lens.

The third approach is being done by ReVision Optics, a California company that is using a small hydrogel implant and placing it under a flap. Rather than using a refractive index change, it changes the shape of the cornea by causing central steepening in a blended fashion when the flap drapes over the implant. 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 somewhat of a multifocal corneal shape, so while near vision can be significantly improved, there is some loss of distance and contrast sensitivity, again, the same as a multifocal contact lens.

All three approaches are in some stage of human clinical trials.

Dr. Hovanesian: Do all three have the intent of implantation only in the nondominant eye?

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

Technologies are reversible

Dr. Hovanesian: Presumably, the advantage of these technologies is that not only are they reversible, but 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 promising technologies targeted at presbyopia? For example, there is talk about femtosecond procedures treating the crystalline lens of the eye.

Reshaping the cornea

Dr. Lindstrom: 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, 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, where he is actually doing an intrastromal ablation with the femtosecond laser, which also is being used to reshape the cornea.

In each of these cases, you are creating some form of multifocality of the cornea itself rather than trying to use the various optical methods I described with the corneal inlays. The laser approaches are somewhat similar to the ReVision Optics approach, 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 do a laser treatment to undo what you originally did with the laser, although this can be done. Some patients have been treated with an excimer laser in an attempt to create a multifocal cornea, 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 type of impact would you anticipate in the near future on the many emmetropic presbyopic patients?

Dr. Lindstrom: There are actually as many emmetropic presbyopes as there are myopes, 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. 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 to reduce their visual handicap.

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, it could be as big an opportunity as LASIK for myopia has been.

For more information:

• 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, is a member of the Primary Care Optometry News Editorial Board and chief medical editor of PCON sister publication Ocular Surgery News. He is also a professor of ophthalmology at the University of Minnesota and in private practice at Minnesota Eye Consultants. Dr. Lindstrom 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: rlindstrom@mneye.com.