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Julie M. Schallhorn, Jan Venter, Steven C. Schallhorn; Preliminary Results of Intrastromal Femtosecond Astigmatic Keratotomy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1504.
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© ARVO (1962-2015); The Authors (2016-present)
To describe a new technique for the treatment of astigmatism using the femtosecond laser to perform intrastromal astigmatic keratotomy.
110 eyes of 93 patients with astigmatism post cataract surgery had intrastromal femtosecond astigmatic keratotomy (IFAK) performed to improve their uncorrected visual acuity. Arcuate intrastromal incisions were made with a 150KHz femtosecond laser from 60 microns below the anterior surface to 80% corneal depth. The initial nomogram varied the arc length of the incision according to the amount of attempted cylinder correction. Patients were examined and refracted at 1 week, 1 month, and 3 months postoperative.
The preoperative mean manifest spherical equivalent (MSE) of -0.06D +/- 0.42 (range -1.50 to +0.88) did not change after surgery, with a 3 month postoperative mean MSE of -0.02D +/- 0.44(range -1.38 to +1.25). The mean preoperative astigmatism of -1.28D +/- 0.59 (range -3.50 to -0.50) was reduced to -0.60D +/- 0.53 (range -2.75 to 0.00) at 3 months postoperative. Sixty percent of eyes had <= 0.50D of cylinder at 3 months postoperative, as compared to 6% before surgery. The uncorrected distance visual acuity was 20/20 or better in 53% of eyes at 3 months as compared to 17% before surgery. The vector analyzed correction ratio (surgically induced refractive correction (SIRC) divided by the intended refractive change (IRC)) was 0.78, indicating an overall under-correction. The cylindrical refraction was stable from 1 week to 3 months postop with a mean cylinder of -0.62 and -0.63D at the 1 week and 3 month examination, respectively.
Intrastromal femtosecond astigmatic keratotomy can safely and effectively reduce moderate amounts of astigmatism and improve uncorrected distance acuity. Undercorrection of astigmatism indicates a need for nomogram refinement.
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