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Antonio Guirao, Jaime Tejedor, María Gómez-Valcárcel; Corneal Aberrations after Astigmatism Correction by Limbal Relaxing Incisions. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5751.
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To evaluate topographical changes and corneal aberrations following limbal relaxing (LRI) incisions for astigmatism correction.
We studied 4 eyes of 4 astigmatic patients (mean age: 57 years; 38 to 71 years) treated with LRI. Mean preoperative subjective refraction was +2.9 D (1.5 to 4.5 D) for sphere and -3.9 D (-3.25 to -4.75 D) for cylinder. Paired incisions were made by a diamond micrometer knife (Katena Inc.) on the steepest meridians with length according to the patient’s age and astigmatism (Hays-Thornton nomogram) and to 90% depth of the corneal thickness at the limbus, as measured by pachymetry. We obtained corneal topography (Pentacam, Oculus Inc.) preoperatively, 3 months, 6 months and 1 year after surgery. Aberrations of the anterior and posterior corneal surfaces were calculated by ray-tracing for a 6-mm pupil and up to 4th order. Pre and postoperative corneal shape and aberrations were compared during the 1 year follow-up.
All corneas experienced flattening of the steepest meridian (mean radius: 7.64 mm, pre; 7.78 mm, 1 year post) and steepening of the orthogonal meridian (8.17 mm, pre; 8.09 mm, 1 year post). Surgery reduced astigmatism by 75% across patients, but there was a small regression from 1 month to 1 year after surgery. The average corneal curvature remained almost constant in each patient (radius: 7.89 mm, pre; 7.89, 7.89 and 7.93 mm, at 3 months, 6 months and 1 year post). High-order aberrations increased after surgery (RMS: 0.7 microns, pre; 1.1 microns, 1 year post). Spherical aberration changed to more negative values (-0.42 microns, pre; -0.55 microns, 1 year post). Coma-like aberrations did not increase much on average (0.36 to 0.51 microns), although there were important changes of the axis. The posterior corneal surface did not change with surgery and continued stable later (RMS: 0.19 microns pre or post).
LRI induce a great change in the corneal anterior shape, and leave the posterior surface intact. The major changes occur just after surgery and continue moderately at least one year. Flattening/steepening processes reduce astigmatism but increase high-order aberrations, particularly spherical. LRI is effective up to some degree, since the correction is only partially predictable. Biomechanics may help to better understand the evolution of the postoperative astigmatism and to improve nomograms, for example for the reduction of pre-existing corneal astigmatism at the time of cataract surgery.
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