Femtosecond Laser Arcuate Incisions

Using a femtosecond laser to perform customised arcuate incisions at the time of cataract surgery holds promise â€” especially if the same laser can be used for LASIKÂ

About 25 per cent of cataract patients have significant astigmatism, so there is a substantial market for the correction of astigmatism at the time of cataract surgery. Many eye surgeons already are buying femtosecond lasers, which means these devices probably will be part of standard treatment in cataract surgery in two or three years. Our early experiences with femtosecond laser incisions demonstrate that the ability to perform both refractive and cataract surgery applications with the same laser system is highly desirable. The advantages include more frequent use of the machine, more efficient use of space and reduced maintenance costs. Toward that end, we have been studying intrastromal arcuate incisions for astigmatism correction using our current femtosecond laser (AMO IntraLase). To date, we have treated about 25 eyes with up to one year of follow-up. Subjects have included both cataract patients and those patients who simply require a refractive astigmatism correction. At this time, we limit treatment to patients with astigmatism of 0.75 D to 2.50 D.

Planning the incisions

To determine the depth of the incision and appropriate treatment pattern, we obtain central pachymetry measurements in all four quadrants at the time of surgery. The thinnest quadrant â€“ often the lower temporal quadrant â€“ is selected. We identify an optical zone that is large enough for the procedure, approximately 6.0mm, and then set the laser for the appropriate depth. We use a surgical topography system (Keratron Scout, Optikon) to precisely determine the axis of astigmatism at the time of surgery. The arcuate cuts are made on the steep axis, with the procedure lasting nine to 12 seconds. Treatment is confined strictly within the stroma, eliminating danger of infection, wound gape or epithelial ingrowth because one doesnâ€™t cut through Bowmanâ€™s. We can customise results for each patient by producing different treatment patterns based on optical zone diameter, incision depth and the angle of the cuts (Figure 1). Four angled incision patterns between 30Â° and 150Â° were identified for study. We selected patterns for individual patients based on factors such as amount of astigmatism, corneal thickness, age and pupil diameter. The larger the optical zone diameter and inclination angle with a given anterior diameter, the smaller the correcting effect.

Study results

So far, our femtosecond laser arcuate incisions for correction of low astigmatism have produced very safe, precise and predictable results. During initial treatments, we identified an optimal treatment pattern with a constant arc length, inclination angle and changes in incision depth that were based on corneal thickness. This pattern was applied to 10 eyes, followed for three to six months (mean of 4.9 months), upon which we base our early results: n Mean UCVA improved from 20/50 pre-op to 20/32 post-op; n 81.8 per cent of subjects gained at least one line of UCVA, 19.2 per cent were stable, and no one lost a Snellen line of UCVA; n Average reduction of keratometric astigmatism was 58.7 per cent (Figure 2). In the study, all incisions were on target and no perforations occurred. In one case, suction was lost during surgery, but the procedure was completed successfully. Patient satisfaction also has been high because the procedure can be done quickly and with minimal discomfort. Compared to bladed incisions, intrastromal laser incisions appear to be safer, enabling us to preserve the corneal surface, including Bowmanâ€™s membrane and the epithelium. We look forward to acquiring more data with the recent initiation of a larger trial involving about 125 eyes at our centre and three others in Europe. As the numbers of patients undergoing these treatments increase, we anticipate development of more accurate nomograms that incorporate new incision patterns and additional factors such as age and gender to improve results. We would also like to explore the addition of concentric incisions to increase effect for higher degrees of astigmatism. Prof Grabner is professor of ophthalmology and chairman of the University Eye Clinic at Paracelsus Medical University in Salzburg, Austria. Contact him at: G.Grabner@salk.atÂ