Femtosecond Laser Arcuate Incisions

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 – often the lower temporal quadrant – 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 doesn’t cut through Bowman’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 30° and 150° 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.