Untold secrets - effective presbyopia correction in the cornea

Günther Grabner MD Years of experience using numerous technologies have revealed a number of “secrets” regarding the treatment of presbyopia in the cornea, according to Günther Grabner MD, University Eye Clinic, Paracelsus Medical University, Salzburg, Austria. “The first secret that I would like to share with you is that no technique for presbyopia is perfect and it’s always going to involve a compromise, but you know that,” Dr Grabner told the 20th ESCRS Winter Meeting in Athens, Greece. He noted that in some cases the compromises necessary are excessive. As an example, he cited INTRACOR, a treatment introduced in 2010 which involves the use of a femtosecond laser to create circular concentric sections in the cornea, allowing the central cornea to bulge forward in response to intraocular pressure. The treatment is quite unpredictable in its effects, is basically irreversible, severs all of the central corneal nerves, and 20 per cent of patients are dissatisfied, he said. “This technique has been taken off the market and it’s really not working too nicely. That is the second secret I'm going to share with you,” he said.

GREAT PROMISE

Another of the secrets learned is that using heat to reshape the cornea has no lasting effect. Both holmium laser thermal keratoplasty, introduced in the late 1980s, and conductive keratoplasty, introduced in the late 1990s, showed great promise initially. However, Dr Grabner noted that with all of the techniques corneas regressed to their preoperative values within a few years, usually one to two years. There are a number of corneal ablative techniques which are designed to afford a range of pseudo-accommodation, either through inducing corneal multifocality or by extending the eye’s depth-of-focus. Dr Grabner noted that the global optimum approach, based on the achievement of the optimum Q value of the cornea’s asphericity, is promising and leaves open the option of improvement of near vision with reading glasses. The central steep island approach is also promising, but has the disadvantages of being highly dependent on accurate centration and being difficult to reverse. In addition, it does not provide very good near vision and frequently reduces best corrected visual acuity by two or more lines.

BETTER DISTANCE VISION

Peripheral presbyLASIK, which involves the creation of a steep annulus on the peripheral cornea, results in better distance vision than that achieved with central presbyLASIK, but it is less effective for near vision. Another LASIK-based treatment that is showing promise is non-linear aspheric micro monovision, developed by Dr Dan Reinstein, UK. The technique has the advantages of being able to correct pure presbyopia while leaving distance vision nearly unchanged and also simultaneously correcting astigmatism. In studies published so far, this laser-blended vision technique was able to provide 99 per cent of emmetropic and myopic eyes with a uncorrected distance visual acuity of 20/25, and 95 per cent and 96 per cent of the two groups, respectively, with an uncorrected near visual acuity of J3 or better. Hyperopes fared nearly as well, with 93 per cent 20/20 or better, and 81 per cent J3 or better. Furthermore, Dr Reinstein has reported that his patients have had minimal loss of contrast sensitivity and night-time vision problems and have maintained their functional stereoacuity. Corneal inlays is another approach that has been gaining some ground in the treatment of presbyopia in recent years, Dr Grabner said. The implants are in general designed for implantation in the non-dominant eye. There are currently two types of corneal inlays in clinical use. They are those based on the intracorneal micro-lens principle, such as the Raindrop® Near Vision Inlay (ReVision Optics) and the Presbia Flexivue Microlens™ (Presbia), and the small aperture, pinhole lens principle as in the KAMRA inlay (AcuFocus). By design, the micro-lens approach alters the cornea’s focus to favour near vision. A consequence of that is a loss of uncorrected distance visual acuity in the eye receiving the lens, Dr Grabner explained. For example, in a study involving 20 emmetropic patients implanted with the Raindrop Inlay, over 80 per cent of eyes with the implant had an improvement of three to five lines in uncorrected near visual acuity. However, distance visual acuity, which was 0.1 logMAR preoperatively, was 20/30 or worse in half of patients at one year postoperatively. Similarly, results with the Presbia Flexivue Microlens published to date showed that 75 per cent of eyes with the implant achieved an uncorrected near visual acuity of 20/30 or better. But mean uncorrected average distance visual acuity in the treated eye was reduced from 20/20 to 20/50. In contrast, studies involving series totalling over 7,000 patients implanted with the KAMRA inlay show that on average patients achieve an uncorrected near visual acuity of J2 and a decimal uncorrected visual acuity distance of 0.8 to 1.0. Summing up, Dr Grabner noted that patient selection and expectation management are crucial. In addition, it is important to have an exit strategy, he said. Günther Grabner: g.grabner@grabner-augen.at