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Femtosecond astigmatic keratotomy before LASIK can be beneficial
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Early in my years as a refractive surgeon performing incisional corneal refractive surgery, I learned that I could achieve the maximal effect of corneal incisions when they were made at 90° to the corneal plane. With the advent of femtosecond laser technology, surgeons now have the ability to create precise incisions anywhere from 30° to 150° relative to the corneal plane. This has allowed for a new means of titrating the effect because angulated femtosecond laser incisions are greater in length, provide an increased corneal healing interface and thus have less effect.
When I first started performing femtosecond astigmatic keratotomy (AK) in virgin eyes with astigmatism, I used maximal settings consisting of an 8-mm optical zone, paired 80° arc length incisions on the steep corneal meridian, a consistent depth of 75% of the thinnest pachymetry readings in the optical zone of treatment and an incision angle of 90°. This approach corrected astigmatism ranging from 2.3 D to 3.5 D (average of 2.8 D), but there were instances of poor predictability and occasional overcorrection.
Martin L. Fox
The iFS advanced femtosecond laser (Abbott Medical Optics) has taken my initial AK procedure to new levels of predictability and safety due to the incisional options it affords. There are four parameters we consider for each patient: optical zone, depth of the incision, arc length of the incisions (either single or paired) and angle of incision (30° to 120°). I have developed a femtosecond AK nomogram using these parameters to allow for greater precision and predictability.
Click here to read the full publication exclusive, Surgical Maneuvers, by Martin L. Fox, MD.