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Multifocal LASIK offers multitude of options for treating prebyopia
RESEARCHERS are increasingly optimistic about the potential of multifocal LASIK as a treatment for presbyopia. This method is being investigated using a variety of treatment paradigms and lasers.
Those clinical observations led the VISX laser company to pursue the treatment of presbyopia as a major research and development program. Dr. Jackson has been an investigator in the clinical studies that began about two years ago with the VISX laser. Based on rigorous analysis of the hyperopic eyes that benefited with near vision gains and extensive modelling, VISX researchers developed a patented ablation profile that steepens the cornea centrally to allow near vision, targeting an add of about 1.5 D, and treats the peripheral cornea for distance. The first trial enrolled both myopes and hyperopes, but the best results were achieved in the latter. Of six hyperopes who were treated bilaterally, five have been followed for up to one year. They have all achieved 20/25 uncorrected distance vision and 50% can read J1 without glasses. The other 50% of the eyes are 20/40 for distance and J3 for near and none lost more than one line of BSCVA.
"We still have only early follow-up data, but the continued improvement in these few eyes is more striking than in our first group, and that is very encouraging. Considering our results, I would discuss enrolment in this multifocal ablation study for any presbyopic hyperope who came into our centre seeking laser vision correction," Dr. Jackson said. VISX has also gone back to treating myopes using a wavefront-guided treatment. Initial data are now in and are being analysed.
Another approach being studied is the Presbyopic Avalos Rozakis Method (PARM).It involves treating the periphery for near and the central cornea for distance vision. That pattern replicates the design of contact lenses used for the treatment of presbyopia and was developed by Guillermo Avalos MD, Guadalajara , Mexico . In PARM, a hyperopic ablation is performed first with an optical zone of 6.0 mm, and then a smaller area of the central cornea, at a 4.0 mm optical zone, is treated with a myopic ablation, Dr Avalos told EuroTimes. Dr. Avalos performs PARM in presbyopes who are plano or with low amounts of myopia or hyperopia, and includes eyes with up to 2.5 D of astigmatism, treating the astigmatic error as a positive cylinder. However, he notes the best results are achieved in the plano eyes and that keratometry is a critical consideration for patient selection. "If the final cornea curvature exceeds 48.0 D, quality of vision will be poor. Therefore, considering that the K value increases by 0.89 D for each dioptre of hyperopia corrected, it is preferable to treat only patients with K values no higher than 42.0 or 43.0 D," said Dr. Avalos. He began performing this procedure in 1998 using a laser with an expanding aperture device. Over time he switched to a broad-beam laser and then to one with a flying spot, but his ablation approach has remained basically the same. So far, he has treated more than 300 patients, and in that series he reports 82% have achieved distance UCVA of 20/20 to 20/25 and 76% are able to read J1 to J3 near, uncorrected."Some patients treated with LASIK for hyperopia will attain good reading vision, especially in the less than ideal situation where the treatment is decentred inferiorly. However, the PARM technique creates a bifocal cornea, which is the goal for correcting presbyopia. I believe it is a very good approach because it is simple and allows for enhancement over time or even reversibility," Dr. Avalos said. In Chennai , India , Amar Agarwal MD, and colleagues have adopted Dr. Avalos' technique and are performing the treatment with a Bausch and Lomb laser under an 8.5- to 9.5-mm flap that is large enough to accommodate the ablation. Given the importance of the K value in patient selection, Dr. Agarwal advises evaluating corneal steepness on a topographic map and not with a manual keratometer. He also observes that the treatment can induce 0.5 to 0.75 D of astigmatism, which can result in a decrease of one or two lines in uncorrected visual acuity. W Bruce Jackson MD, FRCSC Amar Agarwal MD Guillermo Avalos MD |
The concept first attracted interest when some presbyopic hyperopic patients reported both improved near and distance vision after undergoing LASIK. Careful corneal analysis of those cases led to the appreciation that it might be possible to use the excimer laser to intentionally create a multifocal cornea."Although there has been interest in using the excimer laser to treat presbyopia since the early 1990s, it really became something to strive for several years later when older hyperopic patients achieved reading vision post-LASIK that far exceeded any expectations," said W. Bruce Jackson, MD, professor and chairman, University of Ottawa, Ontario, Canada. 
"This pilot study showed the multifocal ablation procedure was very safe, because we were able to provide reasonable reading vision without compromising distance outcomes. Moreover, the patients are quite happy, and many have described how the ability to function without glasses as a result of this surgery has improved their daily life," noted Dr. Jackson. The myopes benefited with improved distance vision, but their reading vision was not what had been hoped for. "Myopes will be a very difficult group to satisfy because they knew what good near vision was like without glasses and now will want to have that back along with really clear distance vision. While the ablation profile in the VISX studies makes good sense and seems to work very well for hyperopes, perhaps another approach is needed for myopes," Dr. Jackson said. 
That initial experience led VISX to concentrate on refining the treatment for hyperopic patients. Accordingly, a revised ablation plan was developed taking into account pupil diameter with the goal of further improving the near vision outcomes. Eight eyes were initially treated with the modified algorithm and subsequently 10 eyes were treated using a wavefront-guided hyperopic treatment with the Star S4 laser. Of those 18 eyes, all have been seen at one week, and 14 were evaluated at one month. The results from those early visits are almost identical to those achieved at one year in the first cohort of patients treated. At one month, UCVA is 20/20 or better in 86% of eyes and 50% achieved J1 and 86% J3. A few patients have reached the three-month mark, and their results suggest that near vision improves with time. Data are not available yet to determine whether the wavefront-guided treatment enhances the outcome. 
Alternative techniques