By Roibeard O'hEineachain

CANNES-A new procedure called conductive keratoplasty, which involves inducing a selective shrinkage of stromal tissue by delivering radio frequency energy directly to the stromal cornea, appears to bring about a highly stable and predictable correction of mild-to-moderate hyperopia, according to Josep L. Guell, MD, Ph.D., who will be presenting his findings here at the Fifth Winter Refractive Meeting of the ESCRS.

In 21 eyes of 13 patients who underwent conductive keratoplasty with The ViewPointTM CK System to correct hyperopia ranging from 0.5 D to 3.0 D, 42% were within 0.5 D and 70% were with in 1.0 D of emmetropia after a mean follow-up of six months (range 2-12 months). Furthermore, mean un-corrected visual acuity improved from a pre-operative value of 20/40 to 20/30 and mean best-corrected visual acuity remained unchanged. Three patients lost one or more lines during the first two months after surgery said Dr. Guell, Institute of Ocular Microsurgery, Autonomous University of Barcelona, Barcelona, Spain told EuroTimes in an interview.

The ViewPointTM CK system delivers controlled-release radio frequency energy via a 90 µm-wide KeratoplastTM tip. Impedance in the flow of energy through collagen fibrils increases the tissue temperature and theoretically induces a stable collagen shrinkage, affording a predictable and stable correction of hyperopia with little regression. The KeratoplastTM provides a uniform column of treatment (~100 µm wide x 500 µm deep) which reaches 80% of stromal depth. Collagen fibrils theoretically reach a precise 65°C, the optimal temperature for permanent collagen shrinkage, Dr. Guell explained, adding:

"The concept of conductive keratoplasty is that you are increasing temperature enough to contract the collagen fibres without destroying them. Because if you only contract the collagen fibres, theoretically it will remain in this situation forever, whereas if you destroy collagen fibres you will have a substitution of scar tissue which will return the eye to its pre-operative refraction.

"Furthermore, conductive keratoplasty distributes the energy equally like cylinder more deeply into the collagen, instead of using probes that work from the top like the holmium or erbium laser where you produce a conic burn which diminishes in proportion to its distance from the surface. Therefore, again theoretically, it does not depend so much on the surface of the cornea which varies more between individuals, so theoretically you increase the predictability with this approach."

The Barcelona investigators commence the procedure by first applying a topical anaesthetic, and then stabilising the eyelid with a special speculum which also serves as the return path for energy. They then mark the centre of the cornea and make eight radial marks, and three concentric ring-markings 6 mm, 7mm, and 8mm in diametre. The points of intersection between the radial marks and the rings identify the placement points for the Keratoplast tip. Each eye receives from eight to 32 "shots" from the View point device, depending on the amount of hyperopia to be corrected.

"The idea is that you are working on more effective area without going inside the 6mm optical zone where you are increasing the risk of irregular astigmatism and not going further than the 8 mm optical zone where you are increasing the risk of no effect or reverse effect."

The average age of patients in the study was 42 years (range 31-56) and most were 40 years or over, he said. Hyperopic patients in that age group tend to be less concerned with regression have a better subjective response to the treatment, he noted. During the first few weeks after treatment, eyes tend to be slightly myopic before they achieve their final refraction. So far there have been no major complications, he added.

Dr. Guell noted that in addition to the theoretical advantages conductive keratoplasty has over other collagen shrinkage procedures in terms of predictability and stability, the technique conceptually, also has several safety advantages over LASIK in the treatment of hyperopia.

"Conductive keratoplasty offers the surgeon much greater control than LASIK does because you are the one who is touching the cornea where you want the effect. You are also not doing any lamellar cut and the worst refractive complication you can have is regression and induced regular astigmatism, whereas with LASIK you run the risk of inducing irreversible irregular astigmatism."

Trials with the Viewpoint CK system are much further advanced in the United States, where a phase III seven-centre study has recently been completed although the device still has only investigational status, he noted. The Barcelona centre is one of three in the world which are currently seeking to determine the nomograms for using the conductive keratoplasty in the treatment of hyperopic astigmatism, he said adding:

"Theoretically what you will achieve with conductive keratoplasty is the best effect with the least regression, and while longer follow-up is needed, so far the results seem to show a correlation with the clinical results and the theory because in my experience to date stability is much better than with any of the other lasers I have been using in hyperopia. On the other hand, we cannot accept the procedure as a standard treatment until a minimum 18-24 months of follow up is available and more patients are recruited."

Dr. Guell's co-authors were Mercedes Vasquez, MD, Chris P. Lohman, MD, Ph.D, and Francois Malecaze, MD.